sailboat power consumption calculator

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Boat Electrics: The Demands of the Domestic System

The subject of boat electrics is a complex one, but the bottom line is that the current draw, battery bank capacity and charging regime must all be matched for the 12volt system to function satisfactorily.

Here we deal with the first part of that equation; calculating the current draw of your of the domestic circuit of the boat electrics over a typical 24 hour period.

Once this is known it's straightforward to assess the required size of the domestic battery bank.

And with that knowledge we can readily calculate the battery charging regime necessary to prevent undue strain on the batteries and keep the whole electrical system ticking over.

Boat Electrics ~ Assessing the Daily Current Draw

To calculate our daily domestic electrical requirement we must first make a list of all electrical equipment on board, and apply a current rating to each item.

If you've got a battery monitor installed in the system and capable of being switched to read amps - like the one shown here - you'll be able, by turning on one item at a time, to read the actual current draw for each item - otherwise you'll have to use a multimeter, or work it out.

Ratings can usually be found on equipment nameplates or in their manuals, and will be expressed in terms of power (measured in watts) or current draw (measured in amps). The relationship between power and current is expressed as: Power (W) = Current (A) x System Voltage (V) To derive amps from watts, simply transpose this equation and divide the wattage by the system voltage.

For example, a 6 watt navigation light bulb in a 12 volt system will draw 0.5 amps - which, if it's switched for ten hour each day when underway will have consumed 5 amp-hours (Ah).

Continuing in this vein for each item of equipment will produce a table much like that shown below, which incidentally, is the one I did for my boat Alacazam.

This calculation though, remains an estimate. For example:

• in cold weather the fridge will draw less power than in hot weather;
• in rough weather the autopilot would use more power than when it's calm;
• hours of darkness will vary with latitude and time of year, affecting current draw for navigation and domestic lighting;
• you'll use the watermaker more when you've got guests aboard etc, etc;
• plus there are start-up currents and other losses that have been ignored.

So it's approximate, but indicates that you'll need to replace around 325Ah each day when you're sailing and 211Ah when you're at anchor.

The underway current consumption clearly presents the worst case scenario, with more power being consumed during the night than during the day. In this example the domestic battery bank will be drawn down by 175Ah during the hour night-time hours - an average discharge of around 14.6A over 12 hours.

So what's the difference between amps (A) and amp-hours (Ah)?

The best way to explain it is by example...

If an appliance drawing 5A was to run for 1 hour, its consumption would amount to 5Ah.

This would be the same as an appliance drawing 1A running for 5 hours - again the consumption would be 5Ah.

So amp-hours are simply the (average) amperage drawn multiplied by the time in hours.

Boat Electrics ~ Power Conservation

In our example there're several things that could be done to reduce the daily consumption:

• LED (light emitting diode) lights. These draw a fraction of the current taken by a standard incandescent light and have an exceptionally long service life. I reckon if the anchor light, tricolour, cockpit light and cabin lights were replaced with LED's then at least 15amps could be shaved off the underway consumption and a similar amount off when at anchor. A further benefit of a combined anchor/tricolour LED light is that you won't have to scoot up the mast to change a blown bulb - a prospect I view with increasing dismay these days.
• The autopilot. If you had windvane self-steering it wouldn't use any power at all, reducing the daily drawdown by a whopping 31%.
• The freshwater pump. Turn it off on passage and use the hand pumps.

You might like to take a look at these...

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Controlled Marine Battery Charging for Reliable Onboard Electrics

Here's how to ensure that your marine battery charging regime properly matches the capacity of your boat's battery banks and keeps pace with the daily current draw down.

Which Deep Cycle Marine Battery Best Fits Your 12V Power Requirement?

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How To Calculate Amp Usage Aboard a Boat

Almost every cruising boat, including us, seems to underestimate the amount of electricity we use per day when planning alternative energy – for us solar panels and wind generator.  Very frustrating when your goal is to live by the sun and wind and not have to run the diesel or generator daily!

DISCLAIMER:   I am NOT an electronics guru – I don’t really understand much of this stuff other than basic principles.  What I DO know is that our alternative energy has NEVER kept up with our electrical consumption and this analysis shows why!    🙂     Keep in mind the power usage figures I’m using is what we’ve determined by using our Link 10 and turning things on & off to isolate individual items – not necessarily what’s quoted by the manufacturer. Hopefully, unlike us, you’ll figure out your alternative energy needs BEFORE you spend six years cruising frustrated every morning by the morning ritual of “how can we POSSIBLY be down that many amps!!!”   🙂

Before you can start to plan for a cruising vessel’s alternative energy plan, you need to know how many amp hours of electricity you use each day.  Do you need to replace 100 amp hours … or 150 …. or 200 ???   Unfortunately there’s no shortcut easy way to calculate this information — I can’t tell you because it’s vastly different for every cruising boat.  Even individual systems, such as radar, can consume vastly different amounts of juice based on how old they are (ours are ancient) and a variety of other factors, so there’s no one size fits all equation.

When we started outfitting Winterlude, we had a 55 amp alternator with our 30 hp diesel engine and that was it.  No alternative energy at all.  We didn’t pay as much attention as we should have to our alternative energy plan, and as a result, on an average we only replace about half of our daily usage via alternative energy.    Entirely preventable if you plan correctly.

THE INVERTER FACTOR

HOWEVER,  it’s not this simple — of course not!   There’s nothing worse than running the noisy Honda 2000 generator before I even get my first cup of coffee!  So, we use the inverter .  Ours is modified sine wave and we’re lucky we’ve never had anything electronic break – a better choice for us would be pure sine wave, but it still works, so se la vie.  Problem is, all inverters are different but ALL inverters waste power – it gets really really complicated to calculate how much wasted power there is in converting DC to AC so we use a “wasted” ratio of 2 to 1 — i.e. it takes twice as many DC amps to power that AC through the inverter.  So for items powered via the inverter, I double the amps usage.  I know this is not scientific, but it seems to come pretty close for our alternative energy calculations – if you’re more technical than I, feel free to jump in and let us know a better way to do this by leaving a comment below!

Here’s our at anchor list as a starting point, note that you need to know amps per hour AND an estimate of how many hours you use the item to calculate daily amp usage.

LED Anchor Light .25/hour X 10 hours = 2.5 amps/night

Adler Barber Cold Plate – Refrigerator & Freezer    6 amps/hour X 24 hours = 144 amps/day (theoretically it cycles on & off, which it does, but it still seems to take between 120 – 150 amps a day)

Bilge Pump:  3 amps/hour X 5 minutes + .25/day

Sensibulb LED Interior Lights:  avg 3 lights on for 3 hours each = .20 amps/hour X 9 = 2 amps/day

VHF Radio:  6 amps transmit/ .5 amps receive – 12 hours = 6 amps + 10 minutes talk time = 1 amp = 7 amps total

SSB Radio:  1 hour receive @ 3 amps/10 minutes talk time @ 30 amps = 8 amps total

(NOTE:  Both radios are different based on whether we’re using low power or high power, these are just guesstimate averages)

Coffee Pot:  6 cups of coffee – 3 amps each (including the inverter) = 18 amps

Cabin Fans:  2 amps/hour X 2 hours each or 4 hours = 8 amps (obviously if it’s hot and we run the pullman berth fan all night we use 20 amps, we probably need to replace these fans with more energy efficient fans, but they move SO much air!!)

Laptop Computer:  2 hours/day 5 amps/hour = 10 amps

Printer:  10 minutes/day at .35/hour

Charging Stuff (from phones to drills to handheld VHF’s etc):  5 amps/day average

So you can see with just the basic daily “stuff” we run, we average over 200 amps a day.  Unfortunately, we only have 4 55 watt solar panels and a KISS Wind Generator.  Figuring 14.5 amp hours from our solar (my simplified rule of thumb is 1 amp per every 15 watts) – and there are maybe 4 total hours when we generate max amps – so 14 amps X 4 hours = 56 amps, plus less  for the remaining 5 hours or another 25 amps – total solar on a good day is 81 amps.  Significantly short of our 200 amps/day usage.  YIKES!  Add wind — if it’s blowing 12 knots, we get maybe 3-4 amps/hour for a total of 72 amps a day – and rarely do we ever see this many amps in a day from the wind generator. Under perfect conditions, with our alternative energy choices, we would add 153 amps — and we’re using over 200.   Bottom line is we can go about 3 days without having to use either our Honda 2000 portable generator or the diesel to recharge our 6 Trojan T105 wet cell batteries.

We didn’t do our homework well enough when equipping the boat for alternative energy!  If we did it over again, we’d have at least 450 watts of solar – or 30 amps/hour from 450 watts or 120 amps from peak hours and another 55 from off peak hours = 174 amps on a good day for solar, plus the 72 from the wind generator for a total of 246 amp hours a day.  Unfortunately perfect days are rare, but with 450 watts of solar and the wind generator, we should be able to keep up with our 200 amp daily usage.

Other stuff:

Spectra Catalina 300 Watermaker:  15 amps/hour, 13 gallons/hour takes 3-4 hours to fill one tank or 52+ amps – we usually run the Honda 2000 or make water underway.  Technically we CAN make water using our alternative energy and sometimes do if the wind is blowing 15-18 and we’re generating significant wind amps as well as solar.

Don’t forget to calculate an under sail version of this same analysis – underway we run our navigation lights (since we’ve switched to LED, these are not a big draw, but before we switched they were HUGE – don’t leave them out of your analysis), our radar close to shipping lanes, our GPS – actually 2, a Garmin 541 at the helm and our laptop consistently for the Nobeltec electronic charts plus our Tridata Depth, Wind & Speed instruments. Update:  if we were to do the electronics over again, we’d include AIS, so that’s another energy draw underway … who knows, we may add one soon anyway! 🙂

If we’re sailing these add up – especially the laptop with it’s 5 amps an hour draw = 120 per 24 hour period, plus another 7 per hour below = 288 amp hours in 24 hours NOT including the daily stuff such as the refrigerator…. YIKES!  We limit the amount of time we need the laptop and radar actually running since we have a Garmin at the help and the radar only needs to be on if we’re dodging either ships or thunderstorms.

One last point …. we don’t include our electric windlass, electric autopilot or other items that are only used when the diesel is running because the alternator is charging and we’re not draining our batteries.    If you use an electric autopilot underway when SAILING, not under power, then you’ll need to calculate the usage because they can be huge amp hogs & you don’t want to run your batteries down while enjoying your sail!

Please leave a comment and chime in to the discussion!  THANKS!  Jan

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19 comments.

Thank you very much for such an informative article, just at the right time for us. I was just about to post a question on this exact topic and this has given me enough to ponder over before I post a question.

My wife and I are currently selling up our home, motorhome and all our worldly possessions here in the UK in order to realise our dream of sailing the Caribbean and East Coast of the USA (Of course once we are more confident and proficient with the yacht we decide on and of course once we have plucked up the courage, we might do a “crossing of the pond”) lol.

Hi Len! I’m glad the post was helpful! Good luck with your lifestyle change — it’s amazing to be able to change your neighborhood and get involved with new cultures by merely raising the sails! Of course, you probably have somewhat of that with your motorhome, but we have no experience there! 🙂 Cheers! Jan

Jan – Thanks for taking the time and effort to put this information together. Extremely helpful! My wife and I were having our “alternative energy” conversation again last night. We will be interested to see the thoughts and input of others.

Len – We just finished eliminating all of our land-based life style “stuff” in July and are l Icing aboard full-time. The hassle is worth it. Good luck.

Thanks Dave! It’s such a complicated subject and I’m sure I don’t have all the details exact, BUT I do know every morning we grumble about not taking the time to determine we needed 450 amps of solar BEFORE we left the US! 🙂 Cheers! Jan

This is some really good information! Thanks for sharing your experiences. It’ll definitely come in handy when my wife and I start setting up our own boat.

Hi Jan, We are currently re-configuring our alternative energy sources and I found your article helpful! Quick question: How many charge controllers do you have on board? Do you have one for each solar panel?

Hi Michelle – we do not have a charge controller for each solar panel. They are configured together with a Solar Boost 2000E MPPT charge controller. It will take up to I think 350 watts and we currently have 225 in it. We’re seriously thinking about adding another 100 watts since we can configure them through the same controller. Good luck!

This site was… how do I say it? Relevant!! Finally I have found something which helped me. Thank you!

Keep this going please, great job!

There’s certainly a lot to know about this subject. I love all of the points you made.

Things are never as simple as they first seem. It looks like you’ve done a thorough job though. On the inverter, the manufacturer should be able to get you figures on expected output vs input. They don’t like to publish efficiencies probably because they would scare off customers. Going from lower voltage in to higher voltage out or from DC in to AC out will waste a lot of power. Sometimes you just have to do it though. The more power they waste, the hotter they run, just something to keep in mind.

Not sure if this thread is still active, but here goes;

Last month I was hit with this problem, fortunately it was only on an 100NM overnight trip (my 2nd ever, and mileage towards the next skipper level), but it got me thinking nonetheless. I’ve actually thought about it many times before, but only when I woke up just before dawn to no nav equipment or sailing lights, did I get the required motivation to investigate further. I run my yacht off a 12V system, so there is no inverter involved, but it also means that I have to run an extension lead whenever I plug into shore power and then connect a battery charger if I need to top up the batteries.

Hopefully I can get some further information, which may seem easy for you;

I have 2 battery banks, both made up from 12V 23Ah deep cycle batteries. The 1st is a single battery that I use to start the engine, the 2nd is 2 batteries in parallel which power the house. If I calculate the amp hour drain as you have described, how do I work out the life expectancy of my batteries? (I did notice that when I switched off the expensive nav light the drain dropped by about 4 amps on the meter!, then everything else just came back on).

The other thing is, how to I measure how much charge is coming from the alternative chargers, my solar panel for example?

This should be enough to get me started!

Thanks again for a very informative article, I also enjoyed the LED conversion article, I sound very much like David!

Hi Clive — if your batteries are 23 amp hours and there are 2 in parallel, it’s my understanding that you actually have a total of 46 amp hours in your house bank, but you can only effectively use 50%, so you’re back to 23 amp hours. If your nav light is pulling 4 amps, overnight for 8 hours, that’s 32 amp hours – exceeding your capacity. YIKES! We replaced our masthead nav light with an expensive LED. Like yours, ours pulled too much juice and it’s not something you can casually turn off during an overnight! Hope this helps. We can measure how much charge is coming in from our Solar Panels via the charge controller panel, but we have difficulty estimating how much is coming in from the wind generator since it’s just wired into the system. Our Link 10 doesn’t give us separate readings, so sometimes, we turn off EVERYTHING so there’s no charge coming out and look to see what the wind generator is putting in. Not science, but it gives us an idea. Not enough, I can tell you that! And keep in mind, solar is great, but there’s no solar charge offsetting anything overnight. 🙂 Cheers – Jan

Fantastic website. Just found it via wherethecoconutsgrow linked from a tiny house website. I’ve always been a water “rat” (windsurfing) and at some point in the future I want to downsize, take sailing lessons and buy a sailboat. Practical troubles for me are equipment storage (windsurf, paddle board, kayak, …) and power for electronics use; so your article sheds a little light on the puzzle, and that I better solar up big time 🙂

PS: you may need to curate some of the comments made that are very short & generic but have direct active (or now dead) links to commercial websites via the user name (url profile spam).

Thanks Frank! I try to catch all the spam comments, but sometimes a few slip through. My spam catcher catches over 2,500 a day so it’s not horrid, but it’s annoying just the same. I appreciate the input. And let me tell you, Peter & Jody on MaryChristine/Coconuts left with more toys that we have, which is amazing. Peter has several surfboard, their two Tower inflatable SUPS, fishing equipment, two large puppies and a dinghy. It’s possible … and FUN! Cheers! Jan

Hi Frank! Great post. I stumbled across this while trying to find energy consumption of our Garmin 541s.

Have been pondering the linklite battery monitor. Would you consider this essential, or just helpful?

Cheers, Don

Thanks for your sharing. Just bought a 36′ mainship, everything is new, lots of things to learn. Great help.

Congratulations Stephen! Friends of ours have a Mainship and are getting ready to “do the loop”. ENJOY! Jan

Calculating the Amp Usage Here are a few tips on how to count the amp usage on a boat, and you do not necessarily have to be an engineer or very adept in electronics to be able to do so. First, you have to know how many amps are being consumed daily. You have to be very alert and count all the amps that are being used on board. The computation for amps and voltage, if you are not aware, is Watts / voltage = AMPs. For example, you use 1425 watts in 120 volts, then it lookst like 1425 / 120 ~ approximately 12 AMPs. Make sure you are able to go through this in details with all electronics on board, such as the LED lights, on board and on the anchor, VHF radio, cold plates used in the refrigerator and freezer. Coffee pot, electronic fan, and so on. This will be in so much detail, but the more you work on it, the more accurate your computation will be.

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Calculating Daily Battery Use

• Thread starter Bad Obsession
• Start date Sep 12, 2014
• Forums for All Owners
• Ask All Sailors

Bad Obsession

I know that this is a subject that comes up from time to time but I am still trying to figure out the voodoo science to calculate my daily power needs on my boat. If I am typically cruising for 8 hours a day, on a good day I may run my outboard with a 6amp alternator for 1 hour (longer on days with no wind). My power consumption is the tiller pilot (I calculate between use and standby it will consume about 27 amps per day), the Garmin 441s (I calculate 5.76 amps per day), and the stereo (about 20 amps per day). This is running them for 8 hours. Total power consumption for these devices would be around 52.64 amps per day, according to my calculations. Does this sound right? According to my other calculations, I put about 1 amp back for the 5 watt solar panel and 6 amps for the hour of using the outboard. That would be only 7 amps replaced. If this is the case I am going to need a pretty large solar panel, eventually, to keep the batteries up if I am cruising . Are my calculations off a bit?  

Stu Jackson

Yes, because of battery acceptance. Fuller batteries can take less current. Battery Acceptance by Stu http://c34.org/bbs/index.php/topic,4787.0.html Why Going Into FLOAT is NOT Full http://c34.org/bbs/index.php/topic,8216.0.html  

On my boat, I have a 50w panel. I run the following: Wheel Auto Pilot (active) GPS on Wheel (active) VHF DSC (standby) GPS on VHF DCS (active) My panel runs those items while I am afloat. The remainder goes back into the battery. So, for the most part, my 50w panel (50w/17vdc = 2.9ah) runs my boat. I am sure that there are extenuating circumstances that I am not aware of, and, someone can shoot holes in my system calculations, however, the proof is that my indicators tells me the battery is in float while I am on the water and those 4 items are operating. I think the major difference between us is I am not running a plotter, just a GPS. I also have a tablet with charts but that is not in the system.  

Charlie Jones s/v Tehani

At normal sailboat speeds, you're NOT gonna get 6 amps out of the outboard. That output is at wide open throttle, and very few sailboat folks run them WOT. You'll do good to get 1 amp Also I think your Tiller pilot amperage may be too high. I use only a 32 watt panel, one grp27 battery and have had the tiller pilot going 24 seven for several days (offshore) And I'd find a more frugal stereo- like an Ipod driving a battery speaker, but NOT Blue tooth-THAT uses some power.  

Bad Obsession said: on a good day I may run my outboard with a 6amp alternator for 1 hour (longer on days with no wind). My power consumption is the tiller pilot (I calculate between use and standby it will consume about 27 amps per day), the Garmin 441s (I calculate 5.76 amps per day), and the stereo (about 20 amps per day). This is running them for 8 hours. Total power consumption for these devices would be around 52.64 amps per day, according to my calculations. Does this sound right? According to my other calculations, I put about 1 amp back for the 5 watt solar panel and 6 amps for the hour of using the outboard. That would be only 7 amps replaced. If this is the case I am going to need a pretty large solar panel, eventually, to keep the batteries up if I am cruising . Are my calculations off a bit? Click to expand

TSBB 2 said: At normal sailboat speeds, you're NOT gonna get 6 amps out of the outboard. That output is at wide open throttle, and very few sailboat folks run them WOT. You'll do good to get 1 amp Also I think your Tiller pilot amperage may be too high. I use only a 32 watt panel, one grp27 battery and have had the tiller pilot going 24 seven for several days (offshore) And I'd find a more frugal stereo- like an Ipod driving a battery speaker, but NOT Blue tooth-THAT uses some power. Click to expand

twalker H260

Over all your power consumption figures appear a bit high. Raymarine st4000+ standby power consumption spec - .72w or .06amps In auto 25% duty cycle -10w or .83amps You'll have to figure out how you use your autopilot but using auto at the 25% cycle for 8 hours you use 6.64 amps - 100% will get you to 26 amps in 8 hours. In 8 hours of sailing my auto will usually see less than 1 hour of use with the remainder in standby. Stereo 1-3amps depending on volume, system backlighting etc - make sure to have on a switch to avoid standby power draw. Your plotter manual indicates 15w or 1.25 amps maximum consumption. If you have a separate sonar unit you will need the consumption of that as well. Autopilot - 6.64amp/hrs Stereo- 8-12.5amp/hrs depending on system/ volume etc Plotter - Max 10 amp/hrs + sonar Total 24.6-29 amp/hrs total consumption.  

Thanks for the information guys. I can be lazy and let the TP-10 do a lot of steering. Needless to say the course corrections are very small. If I am running and the waves are there I have to steer to keep up with the waves. My stereo should be pretty efficient. I also have smaller speakers and I don't run it wide open. It is LED backlit. The iPod hooks into the stereo to play through it. No amp. I am not running sonar off of the 441 S. I have a small humminbird digital display for depth. My eventual goal is to have a bank of 2 group 27 batteries. Then add at least a 30 watt panel, possibly up to a 60 watt panel. Finally I would like to add a battery monitor. I am hoping that it will cover my needs. My anchor light uses only .110 amps (it is the Davis Instruments LED light). I have LED lights in the cabin too. I guess I will have to take a slip a few times during my trip and plug into shore power.  

As Centerline has already pointed out: you actually need 120 to 140w of solar. On a Catalina 250 I have 2 ea. 80w panels across the stern and 2 ea. size 24 batterys. This design is excellent for a similiar system to yours. Having a nice summer/fall in beautiful Bodega Bay Ca. on our S/V Compass Rose! Chief  

since you are carrying outboard fuel, a little generator like this: http://www.harborfreight.com/900-Pe...zIjoiOTkuOTkiLCJwcm9kdWN0X2lk IjoiOTA1NyJ9 which is "on sale" now for $99, can run your battery charger on the boat. Yes, it is kinda loud but ya don't have to run it long since it will power the same charger that you are using when in a slip. Would let ya have some peace of mind for not much money. When ya get the big panels installed, you can use it less.  

another opinion First thing.. get the battery monitor. I think you will find you use way less power than your original estimate - unless you need a fridge and then everything changes dramatically. Your two highest numbers in that estimate were the tiller pilot and the stereo. I don’t know about the tiller pilot (two people who have them said the power is way less than the estimate) and I have been using a car stereo with four bookshelf speakers for years, the current is more like 1.25 amps on average, maybe 1.5 when Im playing it somewhat loud. By 2 or 3 amps its distorting and terrible to listen to. I had to post this because I just really disagree that you will need anything more than 30 or 40 watts of solar for what you described. I have a similar setup - exchange the autopilot for a laptop - I’ve marina lived in the boat for a week with only a 10 watt solar panel and two golf cart batteries. I’ve added a 40 watt panel to the same setup for 50 watts total and can have to really work to end up down 30 amp hours after the week is over. I do have a battery monitor and have been watching this for years. Also, all the outboard charging systems are not equal. I have a 2010 Nissan 9.8 and if you look at the electrical system, it shows a rectifier/regulator vs. just a rectifier that you will see in the older outboards. This charging system actually does put out near its rated current over a fairly large rpm range. The only issue I have with it is that tie regulator cuts back current at about 13.6 volts so it only is charging deeper into the bulk mode phase. However, I think part of this is caused by my outboard being at the very back of the boat and the batteries being at the very front of the boat and this "tends" to cut back on charging a little too soon. The best place for solar is at the back of the boat and this may not be important to you (depends on if the RV mode or sailing mode is more important to you) but even though panels doesn’t weigh much, they do have considerable air drag and can even make it harder to tack in high winds. This may not matter at all for the larger sailboats but it can on these smaller ones. I think get the battery monitor first. If your batteries are fully charged all the time, you probably put too much charging capability on the boat. Some will like that, some wont like the tradeoff of having all that panel on a small boat.  

On the other hand... The battery monitor is a nice toy as it tells you current, amp hours, voltage. It will also estimate % battery remaining but this is only valid when the battery is new. As the battery ages and loses capacity, the monitor has no way of knowing this. I just never use the % capacity reading because of this, only watch amp hours. Anyhow, when batteries are new and with some charging capacity, you generally have some margin of excess battery capacity. For example, my batteries are 200 amp hours (when new) but I rarely get them down more than 25 amp hours. So I have 75 amp hours reserve that I normally don’t use. However, as my batteries age, the amp hour capacity drops (which I can tell with the battery monitor but its not a direct reading, you have to watch patterns). So as the batteries age, my reserve capacity gets smaller and smaller until at some point, I really notice this and figure out that I need new batteries. However, in the above case, I could now increase my charging capacity and still keep on using the same batteries. So in effect, having more charging capacity makes the batteries last longer simply because you can tolerate less capacity. It also may be that the smaller charging cycles afforded by excessive charging capability actually does make the batteries last longer because of shallower discharges.. Tradeoffs..  

See my short Youtube video on battery monitor.... http://youtu.be/JUJ0o3SO1y0?list=PLnA9GMvTHKtYwE2hLyiRCwpj9OcuzlRID Greg  

I had a battery monitor in my last boat. I liked it a lot and it was great peace of mind. I intend to add one sooner than later. My budget is shot for this season so my upgrades are minimal and cheap right now. I am saving up to do a big job of rewiring stuff, moving a water tank and upgrading to a larger flexible tank, moving the battery, adding a battery, and putting pressurized water into the boat with a cockpit cold shower. As you can tell, this will be a fairly expensive project and I anticipate and early spring start time on working on this. This will be a chunk of next year's budget. Once that is completed I want to do a solar panel and finally the battery monitor. All things in moderation and in due time. It is so hard to behave yourself when West Marine is a mile from your house and it is so easy to shop on line too. Right now I am trying to make do for a fall cruise starting on Tuesday. This will be a good test of the boat and the systems and I will adjust my plans based on what I find.  

Bad Obsession said: I had a battery monitor in my last boat. I liked it a lot and it was great peace of mind. I intend to add one sooner than later. My budget is shot for this season so my upgrades are minimal and cheap right now. I am saving up to do a big job of rewiring stuff, moving a water tank and upgrading to a larger flexible tank, moving the battery, adding a battery, and putting pressurized water into the boat with a cockpit cold shower. As you can tell, this will be a fairly expensive project and I anticipate and early spring start time on working on this. This will be a chunk of next year's budget. Once that is completed I want to do a solar panel and finally the battery monitor. All things in moderation and in due time. It is so hard to behave yourself when West Marine is a mile from your house and it is so easy to shop on line too. Right now I am trying to make do for a fall cruise starting on Tuesday. This will be a good test of the boat and the systems and I will adjust my plans based on what I find. Click to expand

See my short Youtube video on battery monitor.... http://youtu.be/JUJ0o3SO1y0?list=PLn...RCwpj9OcuzlRID Click to expand

walt said: "Im not living in a cave. When I want to turn on a light, I want to turn on a light" Best advice is that you better follow the boss's rules... made me laugh.. Click to expand

Your calculations seem very high. A stereo is not going to draw even 1 amp so 56 Ah/day seems way to high. Same, same for the rest. I built and excel spread sheet that calculated the loads and production and show how that interacts with the storage. The storage feature is "rocket science" stuff and is not accurate but gives you an idea of what is going on. email me for a copy. All you need to know to use it is what the unit draws in amps and how long you use it (if at all) each hour of the day.  

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Energy on your Boat

Details and tips for understanding energy on your boat.

Managing Energy on your boat is like managing water on your boat – there is a limited supply and you have to constantly top it up as you use it.

With the maturity of Lithium-Ion batteries and high capacity storage, people look for smarter and faster ways to generate more energy on your boat. While solar will always be a cheap and easily available source of energy, for today’s modern boat with all the desired creature comforts – such as the array of electronics, refrigeration, electric ovens, water heaters, water makers, air conditioning, and more – solar cannot keep up.

Power vs Energy on your Boat

The concept of energy is likened to water for the easiest understanding. A bucket of water holds a specific amount of water that is measured in a number of gallons or liters. It is finite: when it is all drained out, it is gone. To gain more, it must be replaced from a water source.

In the same manner, energy is measured in a quantity like gallons or liters are to water. Energy quantity is measured in joules .  The battery itself is likened to the bucket. The battery holds a certain amount of joules of energy and when it is all gone, it is gone. To gain more usable electricity on your boat, you must add more joules back into your battery.

The concept of power is likened to a quantity of water flowing out of the bucket over time. While draining the bucket of water, the water is flowing out at a certain rate. If a 10-liter bucket drains out in 1 minute, the flow rate out is 10 liters per minute or 600 liters per hour.

Power is the flow rate or usage of energy over time measured in joules of energy per second of time. One joule of energy used every second is one watt of power . Thus, electrical devices are rated in watts – the amount of energy per second the device uses while it is ‘on’. The longer you leave the device on, the greater amount of energy is consumed and drained from your limited resource energy-holding batteries.

To summarize the above: Energy is a quantity, and power is the rate of usage of that energy over time.

When you are on a sailboat on a sailing vacation or cruising, you are the energy manager. As such, you’re going to need to understand the mathematics of it all and constantly do energy audits. When sailing at home, this is rarely an issue because typically at the end of the day you go back home and plug into the shore power to recharge your batteries. When sailing abroad or on extended trips, plugging into shore power rarely happens every night.

To put this all in perspective, a fridge/freezer unit on a sailboat is typically rated at 60 watts. This means that every second it is on and cooling it uses 60 joules of energy. But like a fridge at home, the fridge is not always running. It cools down to the right temperature then the thermostat switches the fridge off. When heat enters in through the walls of the fridge and raises the temperature a few degrees, the fridge turns back on and starts consuming 60 watts of power or 60 joules of energy every second to cool the fridge back down to its thermostat setting – then is switches itself off again.

Let’s say you load the fridge up with warm beer. After 1 hour of full running the fridge would have used:

60 j/sec * 3600 sec/hr  * 1 hr = 216,000 joules.

But that number, 216,000 joules really doesn’t mean much. So engineers simplified the concept using watt-hours , which is also a measure of energy (1 watt-hr =  1 joule/sec * 3600 sec/hr = 3600 joules). Since power (the flow rate of energy) is measured in watts, it is more practically meaningful to list energy in watt-hrs instead of joules. i.e. if you use 1 joule per second for 3,600 seconds you would have used 3,600 joules. Since one joule per second is one watt and 3,600 seconds is one hour this is 1 watt.hour (watt.hr). This is not watts per hour – there is no such thing – rather watt.hrs is the flow rate of energy (watts) multiplied by time (hours) and is thus watt.hours – a specific amount of energy used. In water terms, this is like liters/hour (akin to watts) multiplied by time (hours) – which is the amount of liters used.

Tip: Engineers use watt-hrs as the meaningful unit of energy

In this case, the 60-watt fridge/freezer ran for 1 hour and used 60 watt.hrs of energy from the house battery bank. If the fridge/freezer ran on full cooling for 24 hours then it would use:

60 watts x 24 hours = 1440 watt-hours of energy (or 1.44. kilowatt-hrs)

In reality, the fridge does not run 100% of the time (unless loaded with warm stuff). The % of time it runs is called the duty cycle. Assuming the duty cycle is 50% then a full day of running the fridge and keeping the beer (and food) cold consumes 720 watt-hrs or 0.72 kilowatt-hrs of energy.

Battery Capacity Ratings

Unfortunately, someone decided to measure lead-acid battery energy capacity in Amp-hrs . In reality, there is no unit of measurement as an Amp.hr and it drives engineers crazy. Amps need to be multiplied by the voltage to put it into real terms. For example, a 200 Amp.hr battery at 12 volts contains half the amount of energy as a 200 Amp.hr battery at 24 volts. So, Amp.hrs is really a nonsensical measurement of energy.

A more practical energy capacity rating of batteries is in watt.hrs. This allows anyone to easily calculate how long a battery will last at a certain wattage drain rate as the example above with the refrigerator. With the advent of Lithium-Ion batteries, fortunately, the ratings have now been universally listed in watt.hrs – whew. This makes the calculation of amount of available energy easy for the mariner.

How much energy?

We added up all the energy draws on a typical 40-foot boat with modern amenities. The conclusion was, on average, the boat will use about 5000 watt.hrs of energy per day – this is excluding air conditioning. This makes the math really easy – the 3,500 watt.hr Lithium-Ion battery above fully charged would provide 3500/5000 = 70% of the daily requirement.

When you add in air conditioning, the numbers go crazy. NauticEd performed an experiment on a Beneteau 41 monohull in Caribbean type conditions – 80 o F water temperature and 78 o air temp at night. The air conditioning thermostat was set at 75 o F. It was found that with 4 people sleeping onboard, the amount of energy consumed was 1,400 watt.hrs per hour. For a 10 hour evening using air conditioning, this means that 14,000 watt.hrs of energy would be consumed just for air conditioning. That is a lot: 4 of the lithium-ion batteries above!

Sources of Energy

Solar: Solar panels are conveniently and properly rated in watts – Joules of energy converted from sun energy per second to electrical energy. And actually, they are really rated in watts per square meter. The best solar panels today can produce about 300 watts per square meter. A big catamaran might have space for an array of about 6 square meters of panels (2m x 3m). This array can produce 300 watts/m 2 x 6 m 2 = 1800 watts. As a general rule of thumb, on a sunny day, you can multiply this by about 5 hours per day to gain the amount of energy produced. Thus a large array on a catamaran could produce up to about 9000 watt.hrs of energy. A monohull has significantly less available area for mounting solar panels and so 2 square meters is more realistic. This means 300 watt/m 2 x 2 m 2 x 5 hrs = 3000 watt.hrs per day can be produced from solar.

Thus while solar is capable of taking a big dent out of the energy used per day, if you add in air conditioning, solar can not keep up. You have to get more energy from other sources.

Alternator: An alternator does not produce very much energy despite it being connected to the engine. This is mostly because of the limited “dumb” electronics in the alternator such as the diode. An alternator will produce about 800 watts of energy. For every hour of engine run time, you only generate 800 watt.hrs which is not enough even if running the engine for 3 hours (2400 watt.hrs).

Generator : A generator onboard your boat can be a major source of energy. A typical marine generator that will fit on a 45-foot monohull provides up to 8,000 watts. This can keep up with the peak load of all air conditioners running at full speed as well as all your electronics. Generators are heavy and expensive to buy and operational maintenance is also expensive. Essentially, a generator is just another diesel engine that has an electrical generating device attached to it. It has soundproofing around it to lessen the noise, but if you’re running air conditioning from your generator, you’re going to be listening to the thrumb all night (as well as your neighbors).

High Output Alternators: Some alternators have been designed to output a large amount of energy as much as 3000 watts. However, these alternators have developed a reputation for being unreliable and often the diodes blow from surges of energy when throttling the propulsion engine up and down as you maneuver in a marina.

Intelligent Alternators (Integrel): Several attempts at smart alternators have been done which draw power off the front pulley via a large belt with a very stiff tensioner. One such is the Integrel device which NauticEd originally endorsed due to its innovation. However, Integrel has proven to be not reliable over time because of belt wear and breakage, high loads on the alternator bracket leading it to bend, as well as fatigue loads on the bracket bolts. Additionally, constant issues with the complex software lead to many installation problems costing many thousands of dollars to the installer and further ongoing operational problems to the user. The issue with Integrel really comes down to trying to pull too much energy off the front pulley. Consequently, the engine manufacturers have denied warranty coverage. Integrel is made by Triskel Marine in the UK – a small start-up company that did have a great idea but failed to implement it properly. Our advice is to stay away from the Integrel – there are other more innovative devices coming like hybrid engine/generators. See this article on why Integrel did not work .

Hybrid Engine/Generators: These are going to be seen more and more on sailboats and powerboats and seemingly are the ultimate solution.

The parallel hybrid system makes use of the high power available from the drive shaft driven by the diesel propulsion engine. Between the engine and the propeller, a smart clutch/gearbox is inserted. The clutch can send mechanical power to the propeller as well as to an electric generator. The electric generator creates electricity and stores it in a 48-volt bank of batteries for later usage. What is clever about this system is that the electric generator can double as an electric motor, so now if the 48-volt bank of batteries are full and the mariner decides to run their boat propulsion on electricity, they can switch off the diesel engine and allow the electric motor to drive the propeller through the clutch/gearbox.

The design below is supplied by Hybrid Marine

For further understanding on this particular product from Hybrid Marine , although there are other manufacturers out there. NauticEd has no relationship with Hybrid Marine and can not speak regarding their exact technology but does recognize that two major boat manufacturers, Antares Catamarans and HH Catamarans, are using their technology.

The 48-volt bank of batteries charged from the motor/generator also doubles as a large storage of energy for use onboard for air conditioners, refrigerators, and boat electronics, etc.

The smart mariner then just makes decisions about his stored electrical energy and runs the diesel or electric motor as appropriate. When at anchor, if there is not enough energy in the 48-volt bank, electricity can easily be made from the main engine through the electric generator.

This hybrid system completely eliminates the traditional generator which is just another diesel engine onboard with associated weight and cost. 

Using the hybrid system will allow the mariner to generate a huge amount of electrical energy very quickly and store it in Lithium-ion batteries. For example, if a catamaran uses 20 kW.hrs of energy for its air conditioning on a night, this amount of energy could be generated in 2 hours of dual engine run time as opposed to running a generator all night long. Add solar and you can cut that in half. Electrical energy can also be generated while using the spare available energy from the propulsion engines even while maneuvering in gear.

Wind Turbines: Manufacturers rate their turbines for 28 knots of wind speed. But power output from wind turbines decreases by the 3rd mathematical power with wind speed. So if you half 28 knots to 14 knots, an impressive-sounding 400 watt rated wind turbine can only produce 50 watts.

Water flow generators: As water flows over the propeller while the boat is sailing which turns the propeller. This can be harnessed into electrical energy. Many hybrid systems as above have this capability built into their system. While this adds to your incoming energy, it relies on you sailing (a lot).

Inverters and Converters

An inverter is not really a source of energy on your boat. It changes electric stored energy in batteries into 110 vAC or 220 vAC (alternating current) energy. AC is what your larger appliances run on such as a microwave and is the same as you have in your house. Thus to run AC appliances from your batteries, you need an inverter. Inverters are rated in watts (the amount of watts should be greater than the appliances you want to connect).

You can get a large inverter that is permanently mounted into your boat for running such devices as microwaves or a smaller portable inverter that will create a small amount of 110v/220v current for charging laptops and the like.

Similarly but opposite, a converter converts AC electricity into DC electricity. An example is the battery charger which takes electricity from the shore power or from the generator and uses it to charge the batteries. Additionally, a converter can change one DC voltage to another DC voltage – e.g. 48vDC down to 12vDC.

And just for completeness, a transformer changes from one AC voltage to another – e.g. 220vAC down to 110vAC or 110vAC up to 220vAC. You find these on boats that are world cruisers moving between continents and countries.

Running out of energy on your boat sucks. It will mean warm drinks, food going off in the warm refrigerator, navigation equipment going down, and worse. The prudent captain will monitor and manage energy usage just like drinking water on the boat. Training your crew to be energy conservative is a good idea. Air conditioning is the biggest energy drain so try to use natural cooling like wind scoops.

Lithium-Ion batteries are a technology gift to the marina but efficient ways of topping up those batteries need to be considered such as solar and hybrid engine/generator systems.

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Simple Guide for Calculating Your Sailboat’s Energy Budget

A helpful approach to calculating your solar and battery systems for your sailboat or RV.

• Post author By Ryan
• Post date December 22, 2020
• 3 Comments on Simple Guide for Calculating Your Sailboat’s Energy Budget

After spending way too much time figuring out how to size the power system for our boat, I thought it would be good to create a simple guide to estimating your needs. It is an excel file you can download/modify with your own sailing or RV needs. I ran through this math with our teardrop trailer, and now with the more complicated sailboat. This whole file is set up for a 12-volt system, you may need to make some modifications to this file for different voltages.

Start at the top of the document and fill out the yellow boxes. The file The results will show up at the bottom.

Energy Calculator

Think of your system as the combination of three different calculations:

• Energy generation from solar, wind turbine, generator, and/or alternator
• Energy storage to/from the battery bank
• Energy draw to the system demands

Each system needs to be sized appropriately for your application, which starts with the demand you expect to have in your system. Start by listing all of the loads that will be on your system, and classify them in different ways: on anchor vs. on passage and define the minimum critical requirements. Then figure out how many amps and how many hours each draw will take on a given day – either on passage or at anchor. For example, we don’t need to run our autopilot while at anchor, and it’s one of the biggest amp draws we have on our boat.

Once you understand your overall system needs, you can play with sizing your solar panels and battery bank. This is the generation side of the equation. You want to make sure you’re accounting for usable sunlight, clouds, and a safety factor when making your assumptions. You also want to make sure you’ve got the ability to weather a few days of low (or zero) power generation. This all gets calculated at the bottom of the excel file where it shows the final calculations of how long you’d be able to last (theoretically) in each scenario, and what your excess/deficit would be.

What do you think? I’d love to get some feedback on the file/calculations.

• Tags amp draw sailboat , autopilot , Battle Born Batteries , Battle born lithium sailboat , current draw sailing autopilot , energy demands sailboat , sailboat energy budget , sailboat power calculator , sailboat solar , Sailing , sailing current draw , sizing battery bank sailboat , Sizing solar boat , solar power calculator , solar powered sailboat

3 replies on “Simple Guide for Calculating Your Sailboat’s Energy Budget”

Hey guys , lovely to read your blog regarding your ericson. I too own a 39b here in New Zealand and slowly going through a Refit. My understanding is only 19 to 20 of these were built. yours looks in great condition. regards Kyle

Thanks for the comment! Great to hear about other 39B’s out there! Overall it is in great condition, however we do have some wet spots we’re currently re-coring in the cockpit & foredeck. We’d like to hear more about your refit – we’re pretty active on Instagram @gerbersunderway if you want to message us there

Only just noticed your reply, sorry we don’t have Instagram but will try looking you up. regards Kyle

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--> The energetic balance and the electric needs of sailboat

Electrical needs on cruising sailboat.

The owners of cruising sailboat equip more and more their boat with a lot instruments in order to increase security and comfort on board (navigation instrument, communication, home appliance). The energy needs on sailboats are constantly increasing . The electrical production becomes therefore essential.

Energy balance of your sailboat

The energy balance is needed to dimension the batteries bank and to choose the needed equipments to produce the requiered electricity for daily on board consumption.

It is necessary to realise an inventory of electrical material, to check the operating power (Watt) for each device and to estimate the utilisation time for each equipment during 24 hours.

Example : for an equipment consuming 10 watt of power during 3 hours per day, the daily energy will be 30 Wh (10W x 3 hours).

Electricity consumption and navigation mode

The sailboat equipments and the necessary electricity vary according to the navigation mode.

The next tables show a synthesis of current equipments and their daily consumption depending of navigation mode.

Warning, these elements don’t replace a complete energy balance sheet of your sailboat . 

Daily navigation

For 10 hours of navigation, the average electricity comsumption is about 50 Ah, a daily need for 600 Wh with 12V batteries. Every evening the boat can be reload on dock power post at harbour.

Coastal navigation with anchorage

The energy on board can become a problem because there is not recharging means as in daily navigation. There is a need of electrical autonomy.

The average electrical consumption for this navigation mode is 93Ah per 24 hours, this is corresponding at a daily need about 1000Wh with 12V batteries.

Offshore navigation

This mode of navigation requieres more important energy resources and electrical autonomy.

The average consumption for this navigation mode is 245Ah per 24 hours, this is corresponding at a daily need about 3.000 Wh with 12V batteries.

 Source :  « cahier spécial l’énergie à bord », BLOC MARINE 2017 .

• The energetic balance and the electric needs of sailboat
• Produce electricity on cruising sailboat
• Electrical production solutions by type of navigation

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Power management : power consumption on board.

If you are going on a trip with your yacht, you should be familiar with your boat, the traffic rules, navigation and the weather. For sailors in particular, it is also essential to be familiar with the power consumption on board if the trip is to be a success.

Many charter skippers are not sufficiently aware of the fact that normally there is much less electricity available on board a yacht than at home or in general: on land. Especially when it is uncomfortably cold outside and the diesel auxiliary heater is running often and for a long time, a lot of additional electricity is consumed.

Especially on sailing yachts, this can quickly lead to problems – particularly if it is a longer trip, anchoring in a quiet bay or long night strokes are undertaken under sail, because: when sailing, navigation devices such as chart plotters and autopilots still require 100 to 150 watts (so 8 to 12 amps). If then in the darkness additionally the Navi lighting is switched on, 10 to 15 amperes come fast in addition.

Rule of thumb: motor at least five hours a day to charge the batteries

As a rule of thumb, if you motor for five hours or more a day at medium speed, you should – depending on the technical equipment of the yacht – have charged your batteries sufficiently (with about 250 amps, depending on the engine/alternator and batteries) to be able to use normal consumers on board for a while. In general, however, you should call at a port with a shore power connection every two to three days to fully charge the batteries again, unless the yacht is equipped with power generators.

But when are batteries actually “sufficiently” charged and what does “normal consumers” mean? Here it makes sense to deal with the concrete voltage / volt or consumption situation on board once before the start of the trip and to draw up a small “energy balance” (for example, in simple table form) – to prevent unpleasant surprises during the trip in time.

Only those who regularly check the voltage know their consumers on board

This could look like this: when the yacht is disconnected from shore power, after about ten to 15 minutes the voltage/volt of the consumer battery should be read and noted. Depending on the battery type, this voltage/volt may be between 12.2 to 14.4 volts – value of the “full charge” of the batteries.

After an hour of sailing or a swim stop, the voltage should be checked again to correctly estimate the voltage loss. This should become a routine on board, because only if the voltage is checked regularly, it is possible to estimate which consumers on board are loading the batteries.

The lion’s share of power consumption on a yacht is usually the refrigerator

By the way, the lion’s share of electricity consumption on the yacht is usually the refrigerator. The consumes on average about 100 watts (eight amps per hour), and often runs through on hot summer days. This means that this consumer alone draws up to 120 amps from the batteries. Small consolation: modern on-board refrigerators often switch off at about 11.8 volts, so as not to overload the batteries.

The number of crew/people on board should also be considered when looking at the energy balance on board. How often is the refrigerator opened, how often do the guests shower off with fresh water after swimming in the sea? On an average summer day, you should generally calculate with about 100 amps for basic needs plus about 40 amps per person. Based on that, for a yacht with a crew of four, the main engine with its alternator should be able to replenish consumption after about five hours at medium speed, or a 70-amp charger after about four hours of shore power (or via the power generator).

If the voltage is too low: full charge with shore power!

In the evening before going to bed should be fully charged again. Typically, the engine or power generator is then charged in the morning until the consumption of the previous night is compensated. If the voltage drops to such a low level that the refrigerator automatically shuts down, a 12-hour charge with shore power should be used to bring the batteries back to normal voltage.

Example energy balance could look as follows: if the yacht has a power of 280 amps, for lighting (5 hours x 16 amps) 80 amps are consumed, for the radio (3 hours x 6 amps) 18 amps, for the TV (3 hours x 5 amps) 15 amps and for the refrigerator (17 hours x 4 amps) 68 amps, a total of 181 amps are consumed in our example consumption period. So everything is in the “green zone”.

But what happens if, during the same period, the dishes are also washed (drinking water pump, water heater), the heating is switched on because it is uncomfortably cold and damp outside, the bilge pump is possibly used, and the electric toilet flush is also regularly used? In this case, the exemplary 280 amps are consumed very quickly – the batteries are empty.

Guide values for the power balance of individual consumers

Here are a few rough guide values for orientation:

• Refrigerator per day about 120 amps
• Pressurized water pump per person per 24 hours about ten amps
• Electric toilet per person and 24 hours about ten amps
• Light for the cabins per hour approximately 15 amps
• Radio or music system per hour approximately 7 amps
• Mobile phone charging via 12 volt plug approx. 5 amps
• Anchor light for the night (eight hours) approx. 20 amps
• Underwater lighting per hour about ten amps
• Who wants to use satellite TV on board, should consider that here can be consumed quickly about 40 amps – per hour!
• Also the diesel heating for cabin and hot water consumes a lot, namely about 20 amps, also per hour.

Saving electricity is the number one motto on board

For this reason, you should consider in advance whether (especially at night), for example, the heating is to be used – in some circumstances, it then makes sense to visit a port and use shore power. The general rule on the water is: Saving electricity is the top priority on board. There are many ways to do this: For example, only as much light should be switched on as is actually needed (no “fixed lighting”). Televisions and other technical devices should not be in standby mode, which also saves energy! It should also be ensured that the refrigerator door is always well closed. The heating should only be used briefly to warm up, etc.

Even those who have one or more generators on board will strive to run them as seldom as possible in order to save fuel and not cause unnecessary noise and exhaust emissions, especially at night or in a dreamy, natural anchorage. Here, too, therefore, the rule is to save electricity – if necessary in conjunction with alternative power generators such as solar panels on board. Some shipyards are already experimenting with fuel cells on board for power generation.

Saving LED lights on board can help reduce energy consumption

However, this will remain a thing of the future on charter yachts for a long time to come. Therefore, the following applies: Establish energy balance and save electricity can already help immensely in normal cases. Because the alternator of an engine supplies (in the ideal case) only about 55 Ah. By the way: A good on-board power supply also helps save electricity, as do cables laid on board that have a sufficient cross-section (higher resistance and voltage drop with cables that are too thin). And those who often go night cruising should think about replacing their conventional lanterns with modern and much more economical LED lamps ( Caution: subject to approval )!

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Battery consumption/charging calculator

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I'm in the process of trying to figure out what my power demands will be if we take off cruising. I got to messing around and created a online energy calculator of sorts. Sailing Adventure I don't know a whole lot of experience estimating what realistic energy consumption and charging will be and would be interested in what other folks have experienced. The big energy consumption items that pop to mind are refrigeration, electronics (maybe playing with a laptop a few hours a day, chart plotters, VHF radios, etc.), and autopilot (for sailing days -- which I expect to be much fewer than anchor days). Has anyone been able to get experimental data for how much each of these really use? What about on the charging side? How much energy do you really get out of your solar panel? wind generator?  

If you are going off cruising I would highly recommend investing in a true battery monitor. The Victron BMV-600 is under $185.00 and is perhaps one of the best investments a cruiser can make. it is well worth the expense. It will also tell you a LOT about your system that you might not have known like how fast your batteries actually accept a charge or how long it takes you to get from 50% state of charge back to 80% etc. etc.. They MUST however be programmed & used correctly in order to be even close to accurate.. No matter how much of an energy budget you do it will only be a ball park shot at best. Many items are variable draw and lights are on and off for varying times per day fridges draw more based on outside temps, new food, how many times per day you open it, autopilots also vary depending upon sail trim and sea state etc. etc.. It is very difficult to be accurate trying to count amps and turn them into Ah's... I would be very surprised to see your fridge run only 25% of the day. Most I've come across cycle between a low of about 35%-80% depending upon insulation. 25% would be a very,very well insulated ice box opened infrequently.  

I've been through the same exercise. I don't see that there is any precise way to end up with an accurate load calculation. You can only get a ballpark number. I believe a battery monitoring system is an absolute necessity if you take off cruising. In very basic terms wind or solar are very nice to have, but while away from shore power it's hard to beat a high output alternator for putting amp hours back into a battery bank at a rapid rate. I'd spend money on a monitoring system, good batteries, and a high output alternator. If you have more money left over add solar or wind power.  

I'd second the purchase of a battery monitor as one of the best investments you can make when it comes to your boat's electrical system.  

Putting $ aside, is there another brand which you have dealt with that you would reccomend Maine, or SD? In particular, i wish to monitor my consumption with the onboard computer.  

Blu, There are a number of monitors but the easiest and most widely accepted, at least here in the US, are the Xantrex Link series which is really made by made by TBS Electronics and the Victron. Blue Seas and BEP also make monitors as does Sterling Power. The best value is the Victron as it comes with all the wiring you need to hook it up and it is plug & play.. Don't know of any that will allow monitoring only through a computer as the computer would need to be on and powered up 24/7 and that can draw massive amounts of power and the Link or Victron are very,very low standby draw. The Link Pro and the older version called the XBM can be connected and communicate with a laptop, with the extra communications kit, but it's still a sand alone unit if you need it to. I own three Xantrex monitors a Link 10, XBM and a Link Pro. The older Link 10/20 units, made by Cruising Equpment Co., were very buggy in comparison to the TBS made units. The Xantrex XBM, Link Lite and Link Pro are all made by TBS and are very, very reliable. TBS used to also make the monitors for Victron but Victron is now making them elsewhere as TBS contracted with Xantrex to supply all thier monitors. I have installed a couple of Victron BMV-600's and they are excellent units and easier to hook up than the Xantrex models, and also less money.  

Your 'article' is excellent. Thank you for taking the time to lay it all out. But I have a slightly off-topic question regarding the siting of panels and wind-vanes. Do you, or any other subscriber here, have any data on the wind effect of solar panels sited near wind vanes....in my case a Narvik pendulum type... I don't have dinghy davits but I have extended the aft deck by 1.5M, using steel framing and slat flooring, so that I can get at the wind-vane which is mounted behind a transome-hung rudder. I guess a fair descritpion would be...I have created an extended pushpit. I could set a panel on each side, on the top rail of the pushpit, hinged so I can get to the vane when necessary, but I wonder about the turbulence effect of the panels on the vane, despite the fact that at most times I'll be reaching or running when using the vane. Opinions greatly welcomed.  

Nice article Sailingdog. I didn't know that was how some of the "smart" charge controllers work. That makes a lot of sense to have built in DC to DC converters. I was looking at the KISS site for their wind generator. They apparently don't use or even recommend a regulator at all, which I find interesting. Basically, their argument is that batteries can accept 2.5% charge of their capacity indefinitely. So a 400 amp-hr bank can be charged at 10 amps continually without any harm. So if I understand correctly, we could do the same thing with the solar panels. If we have a 400 amp-hr bank, we could probably pretty safely have a 80 Watt or even a 120 Watt panel without regulation. But we would be loosing out, especially in the situations where we end up with a shaded panel.  

While you could go without a charge controller, provided the panel was sized properly, you probably would regret it. First, as you said, in shaded situation or on cloudy days, the panel would be less effective than it would be with an MPPT type charge controller. Second, some panels will discharge at night, since they don't have a blocking diode. Adding the diode will cost you about .75 volts in output... using a charge controller, which will prevent the panels from self-discharging at night, will not require a blocking diode installed, and increase the overall output of the panel a bit.  

Thank you sirs. FWIW I believe that the Link 2000 has been discontinued.  

You will avoid many wasted hours of charging via the alternator if you follow the 80 - 50 rule (start charging at 50% and only try to go up to 80%). Don't just charge every day needed or not. You will probably save on diesel enough to pay for the monitoring system if you charge when needed as opposed to a daily schedule.  

I'd point out that you will want to charge the batteries up to 100% at least ocassionally. If you do not, they will start to sulfate.  

...good to mention that. Proper battery maintenance - equalization, float charging, etc. is another important topic net yet discussed here. Proper technique depends on the battery type selected, of course.  

You guys are definitely making me a believer in the battery monitors. I was thinking they make sense anyway. Looks like they are pretty easy to install and well worth it. I was looking at the manual for the Victron BMV. Interesting how the device works by just essentially monitoring current/voltage and using a sophisticated equation for capacity.  

Stu Jackson said: This is why people say the BEST investment for un-knowledgeable and knowledgeable skippers alike is to buy a battery monitor FIRST. Wish I did, because I'd been chronically UNDERCHARGING my house bank, even after all the spouting I do here and on other forums! Click to expand...

dawg - one round, (3) 130 ah wet cells - yet to be purchased, I'm limping along but sorry that I have to run my engine the way they did in the olden daze, every morning! That really s*cks.  

If using wet cells plan on max acceptance of about 25% of Ah rating so. Most recommend an alt of 20-40% of bank capacity. 650 Ah bank = 162 amp alt: This is not going to happen easily on a small motor so charge times to 80% will take a while. 325 Ah bank = 81 amps This is achievable on a small motor with a 100 amp alt.. Going bigger on the alt is fine as it works it less hard and never puts out full "spec" when hot.. Being your basic Luddite, this electrical 'stuff' perplexes me. I have a 180 Ah charger running 4 X 130 Ah, deep-cycle, sealed batteries. Are you saying the best I will get is about 45Ah recharge rate?  

For a parallel discussion of how much comes OUT, please see the Energy Budget topic, here: PS You've just gotten the entire course on how to run a boat electrical system (other than battery switching) in one two page thread. Congratulations.[/QUOTE] Am I being a simpleton here (I've discovered Panadol does not cure this problem) but does it not follow that if the last 15-to-30% of battery recharge requires something to the order of 70% charging energy (running the motor) that it is better to leave the battery bank at 70-to-80% charge, from the motor, then let some trickle device do the rest?  

dpex said: Am I being a simpleton here (I've discovered Panadol does not cure this problem) but does it not follow tyhat if the last 15-to-30% of battery recharge requires something to the order of 70% charging energ (running the motor) that it is better to leave the battery bank at 70-to-80% charge, from the motor, then let some trickle device do the rest? Click to expand...

Yes, if you have shore power or wind or solar you can top up to 100%, but it takes quite a while. While cruising, if you use power every day trickle charging doesn't really help you (unless you can use slightly less power in a day than you can generate in a day). The alternator will put the power back in the batteries much faster. However the charge rate goes down as the batteries "fill". So, in my opinion, you need good batteries, good alternator, and a battery monitor before you spend money on solar or wind. They are nice to have but you need the bulk charging capability first.  

Solar system and battery bank Hello. I want to develop a system on solar that the load is 250 watt continous. the battery bank should support it to 2 day. can any one guide me in it like the solar panel should i have it's ratting and about battery bank. regards; taqi abrar  

Solar system and battery bank Hello. I want to develop a system on solar that the load is 250 watt continous. the battery bank should support it to 2 day. can anyone guide me in it like the solar panel should i have it's ratting and about battery bank. regards; taqi abrar  

Multiple postings are generally considered poor form. You probably should have started a new thread, but you definitely should have asked this question in only one place and then waited for an answer. Your question has been addressed in the other thread. Please see the answers there.  

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How Much Fuel Does a Sailboat Use?

Whenever I dream about long passages, I always wonder how much fuel a sailboat uses. I want to know how much fuel I should bring to carry on. So I crunched the numbers and in this article I'll share my results with you.

How much fuel does a sailboat use? Typically, an average sailboat uses between 1 - 2 gallons per hour. Small sailboats with smaller engines will use about 0.5 - 1 gallon per hour. Large sailboats use between 2 - 3 GPH. Of course, fuel consumption greatly varies with different engine sizes and water and weather conditions.

I'll go into the different factors that affect fuel consumption below. But first, let's get some ballpark figures for different sailboat sizes.

On this page:

Fuel consumption for different sizes, factors that affect fuel consumption, how to optimize fuel economy, how much fuel should i carry, related questions.

We measure fuel consumption in Gallons Per Hour (GPH), because the time the engine is running is the only fixed variable here. The distance you cover isn't fixed at all. Most sailboats cruise at a speed of 4 - 8 knots under engine. So the range on one hour of motoring can be anywhere from 4 - 8 nautical miles.

Of course, the size of the boat (and engine) and fuel consumption are related. So let's take a look at what different sizes use on average:

• small sailboats use on average 0.5 - 1 GPH
• mid-sized sailboats use on average 0.9 - 2 GPH
• large sailboats use on average 1.8 - 3.3 GPH

Larger 50HP engines may use up to 2.5 GPH if the conditions are bad and you max it out at, let's say, 8 knots.

Let's get a bit more detailed even. I want to know a range for each engine size. I've found the average fuel consumption in the Yanmar manual.

• Yanmar uses an average fuel consumption of 170 grams per hour per horsepower . - I want to remind you that these are the manufacturer's numbers, so they're probably optimistic.
• So I've also added a more conservative estimate, based on 250 grams per hour per horsepower .

So if you want to calculate your engine's fuel consumption, simply multiply 170 or 250 with the amount of HP. The number is in liters, you have to convert it to gallons.

Here are the manufacturers estimates:

Here are my estimates for bad conditions:.

As you can see, fuel use widely varies. There are a lot of factors that determine how much your engine actually burn. Some of them are:

• engine size, type, and power
• hull type and shape
• wind direction
• water conditions

Engine size and power - Larger engines use more fuel. But if you're engine is too small, it could potentially use more fuel. The engine has to work too hard making it rev up (it runs on maximum RPM), burning more fuel. Most of the times people have too big of an engine, and sailboats don't require very large engines. But if you're on the open sea and have a large boat (let's say 40' and up), you want something stronger to deal with the current and wind. Most sailboats are fine with a 30HP engine in most circumstances.

There are some other engine factors, like type the number of cylinders. 2-stroke engines are more powerful but also use a lot more fuel for example. The right size propellor is also important.

If you want to read more on how to choose the right engine size, I've written this short guide on calculating the right size. You can find it here .

Hull type and shape - The shape of the hull determines how much water it displaces. The bulkier the shape, the more water it has to push away, so the more fuel it uses. Also, multihulls displace a lot less water, making them way more efficient. You'll see when you drive a catamaran: it uses WAY less fuel. Flat bottom boats use even less (but are less appropriate for sailing).

Wind direction - Driving straight into a headwind could almost double fuel consumption. Strong winds create high waves which will cause your fuel economy to sink.

Water conditions - As mentioned, high waves are not good for fuel consumption. If you have to head into a strong current, that's not good as well. Very strong (ocean) currents can also double the burn rate.

If you need to save your fuel, but you need to get out, for example in an emergency, you want to make sure you get as far as possible as fast as possible. So how to make it happen?

Don't drive at hull speed . This will cause the engine to rev up to maximum RPM. Engines are most efficient between 75-85% of their maximum RPM. It really improves mileage a lot if you take it down a knot.

Find the right course . Take the wind direction and current into account. Just as you would while sailing (but don't go overboard with this either).

Reduce the weight . If you carry ballast, now is the time to unload it. Lowering weight means a lot more range on that tank.

Pick the right engine size . Don't overpower and don't underpower your boat. You want your engine to run at the optimal RPM.

Choose the right prop size - The right propellor is crucial to get an efficiently-running motor. Too small and the engine will rev up in the red, too large and the engine won't even come near the sweet spot.

Make sure your hull is clean. A clean and waxed hull really helps with reducing friction from the water, so it increases your mileage.

Don't drive at maximal hull speed. If you have the right engine size, the optimal speed should be about 2/3 of the maximum hull speed.

Want to know the maximum hull speed for different boat lengths? Check my article with lots of examples here .

If you want to find the sweet spot for your motor, you need to find the specific fuel consumption curve of the engine (SFC) and also the propulsion efficiency curve. The best advice I can give here is to ask the salesperson you've bought the engine from. He or she usually has the data.

Taking it easy on speed is also better for the engine, so it will last longer and require less maintenance.

But it might not be worth your time. Sometimes you just want to get out there fast. Sure, by cruising at 6 knots instead of 8, you increased your range with (let's say) 10%, but you've also increased your drive time by dozens of hours.

Some sailors would argue the more the better. And sure, it's tempting to rev up the engine once you reach 3 or 4 knots. Especially if you have a long way ahead of you. But more fuel means more weight means more fuel consumption. So what's the sweet spot?

I'd say the ideal range for ocean passage is about 400-500 NM of fuel. The average motoring speed of sailboats is 6 knots. That translates to roughly 60-80 hours of motor time. At 2 GPH, you would need about 125-160 gallons of fuel.

If your boat is a bit more efficient, let's say 1 GPH, you would need about 60 - 80 gallons.

How Many Gallons of Fuel Does a Sailboat Hold? On average, a sailboat holds anywhere between 30 - 60 gallons of fuel on board. This provides a theoretical range of 350 - 600 nautical miles at a fuel consumption of 0.5 GPH. In practice, fuel consumption averages at 1 GPH, making the range 200 - 300 NM.

shane johnson

man i had a real hard time trying to find real info on fuel regards sail and power vessels. ime tearing my hair out deciding on a liveaboard for me over here in australia, i will be working sometimes so at a marina and other times out on the reef or werever the fish are. ime looking at a great fitted out light 50 footer with 2 yanmar 40 hp in her at the same time a steel 40 fter with sails and 2 50 hp diesels in her.all sails are furling including the mainsail and in my head i think sail would be a safety advantage wouldnt it? but the other is top shelf with room fitout electrics and weight. being 8 ton the steel being 12 ton.

Shawn Buckles

Hi Shane, glad you find the article helpful. If you’re a sailor, I’d say sails are definitely a great backup to have. Personally, I’d only go for the one with sails if I plan on actually sailing the vessel. If not, I’d opt for the larger, fully-outfitted one.

Well, in any case, you’ll have plenty of horses!

Great article. I did spot a calculation error in the fuel numbers. Try applying the specific gravity of diesel fuel to convert from mass in grams to liters of diesel fuel. A typical number for diesel is .823 g/L.

Multiply the results in the tables above by 1/.823 = 1.215 to get the correct consumption results.

e.g. 10 HP @ BSFC of 250g/hr would be 2.5Kg/hr * 1.215 = 3.04L/hr.

David van Niekerk

Dankie Shown Buckles I’m from the Boland (South Africa). I find your article very OK. I know now the fuel consumption of a normal sailboat@ 8kn (14.64km/u) is about 5.1 LPH. BUT, wat is the fuel consumption of a catamaran or even the newe hydrofoil’s? (A small aircraft is about 10+ LPH @80-100km/h)

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Sailo's Boat Calculator

The Sailo Boat Calculator is a tool that allows you to explore, predict, and plan costs and revenues associated to boat ownership. The most important user inputs can be found on the left side of the Cost of Ownership tab. The calculator has built-in models that compute costs as a function of the information provided.

The calculator is organized in multiple tabs that show costs breakdown and allow for detailed customization. For example, the fuel cost tab computes fuel consumption based on the type and size of your boat, estimated HP, and average current gas prices. To make this calculation more accurate you can enter a more exact fuel consumption for your boat and more accurate local gas prices.

The last two tabs are probably the most interesting. The Charter Profit section estimates the income your boat can generate on a platform like Sailo based on charter rates and days rented. Of course we increase maintenance costs due to chartering based on the number of extra days on the water. The Rent vs Buy tab shows a comparison between renting and owning an identical boat to find which option is the most economical and by how much. Note: we assume identical fuel consumption and cost for both rental and personal use. Read more about it here .

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Renting vs owning (per year), calculator feedback, sailo boat ownership calculator, thank you for taking time to give us feedback. you feedback is important in improving the accuracy of the calculator results., the results for my boat were reasonable, ease of use, the calculator is easy to use and understand, the calculator design is clean and appealing, the calculator is useful.

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The Sailboats Calculators below will enable you to calculate the main Sailboat Ratios, using data that you can retrieve from the Boat table or your own data.

We will be adding more calculators along the way and more in-depth explanations of how they work and what they can help you with., hopefully you will enjoy them and find them useful to search or understand the characteristics of your or any given sailboat ..

SA/D range of values

16 to 18 Heavy offshore cruisers 18 to 22 Medium cruisers 22 to 26 Inshore cruisers, racing boats 26 to 30+ Extreme racing boats

Ballast/Displacement:

A Ballast/Displacement ratio of 40 or more translates into a stiffer, more powerful boat that will be better able to stand up to the wind.

Displacement/Length:

The lower a boat’s Displacement/Length (LWL) ratio, the less power it takes to drive the boat to its nominal hull speed.

less than 100 = Ultralight;

100-200 = Light;

200-275 = Moderate;

275-350 = Heavy;

350+ = Ultraheavy;

Comfort Ratio:

This is a ratio created by Ted Brewer as a measure of motion comfort. It provides a reasonable comparison between yachts of similar size and type. It is based on the fact that the faster the motion the more upsetting it is to the average person. Consider, though, that the typical summertime coastal cruiser will rarely encounter the wind and seas that an ocean going yacht will meet.

Numbers below 20 indicate a lightweight racing boat;

20 to 30 indicates a coastal cruiser;

30 to 40 indicates a moderate bluewater cruising boat;

40 to 50 indicates a heavy bluewater boat ;

over 50 indicates an extremely heavy bluewater boat.

Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam^1.33), where displacement is expressed in pounds, and length is expressed in feet.

Capsize Screening Formula (CSF):

Designed to determine if a boat has blue water capability. The CSF compares beam with displacement since excess beam contributes to capsize and heavy displacement reduces capsize vulnerability. The boat is better suited for ocean passages (vs coastal cruising) if the result of the calculation is 2.0 or less. The lower the better.

Hull Speed Calculator

Hull speed calculator is a simple calculator that determines a vessel’s hull speed based on the length of the vessel’s waterline.

Boat Speed Calculator

The boat speed calculator calculates the top speed of a boat based on the boat’s power and her displacement. If you try to understand how fast a boat can go, this calculator will help you answer that. The boat speed calculator utilizes a constant known as Crouch constant which differs based on the type of the boat.  

FOR MULTIHULLS ONLY:

Bn – bruce number:.

The Bruce Number is a power-to-weight ratio for relative speed potential for comparing two or more boats. It takes into consideration the displacement and sail area of main and jib. 100% fore-triangle only, no overlapping sails.

Chris White, “The Cruising Multihull”, (International Marine, Camden, Maine, 1997), states that a boat with a BN of less than 1.3 will be slow in light winds. A boat with a BN of 1.6 or greater is a boat that will be reefed often in offshore cruising.

Derek Harvey, “Multihulls for Cruising and Racing”, International Marine, Camden, Maine, 1991, states that a BN of 1 is generally accepted as the dividing line between so-called slow and fast multihulls.

BN = SA^0.5/(Disp. in pounds)^.333

Kelsall Sailing Performance (KSP):

Another measure of relative speed potential of a boat. It takes into consideration “reported” sail area, displacement and length at waterline. The higher the number the faster speed prediction for the boat. A cat with a number 0.6 is likely to sail 6kts in 10kts wind, a cat with a number of 0.7 is likely to sail at 7kts in 10kts wind.

KSP = (Lwl*SA÷D)^0.5*.05

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City council votes to change electricity fee calculation

If approved, the new model would come into effect in 2027.

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With electricity bills soaring over the past year in Calgary, city council has voted in favour of changing the way it calculates the local access fee. 

Instead of the fee being tied to the province's regulated rate option — which reached record-high prices in 2023 — the city says it's aiming to move to a consumption-based model, charging customers based on how much power they use. 

Mayor Jyoti Gondek said the change will bring more long-term stability and predictability for Calgarians. 

"It's not the surprise that you see with the volatility of pricing of the regulated rate option," she said. 

"It was a revenue stream for us, but the time to focus on Calgarians and their stability is more important right now." 

• Calgarians pay higher access fees than other Albertans as regulated rate soars
• Alberta's regulated rate option expected to soar next month — to its highest level in history

Last year, the city collected an additional $200 million in fees from Calgarians, owing largely to skyrocketing electricity prices. 

Under the current local access fee model, the City of Calgary, through Enmax and other retailers, charges 11.11 per cent of the monthly RRO per kilowatt hour consumed, plus 11.11 per cent of transmission and distribution costs for the access fee.

The local access fee works in lieu of a property tax to run power equipment through the city.

Coun. Evan Spencer said the fee has been a point of tension for Calgarians, and that he's glad to see it changing. 

"You can look at it through a long time horizon and it kind of averages out. But the fact that we were doing it during the middle of an affordability crisis really is what brought a lot of this conversation to a head."

But Calgarians won't see any savings yet. 

The proposed change still needs to be approved by the Alberta Utilities Commission, and even then, it wouldn't take effect until 2027. 

"Anytime you go to make a change, you have an awful lot of people sitting around that table that you have to consult with and work with before you can ultimately sign the dotted line," said Spencer. 

With files from Scott Dippel and Karina Zapata

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What household appliances use the most energy? Here's a breakdown, plus tips on how to save money

With no relief on the cards from high electricity prices, it could be time to identify where you could be saving on your energy use. 

While you may know some of the main energy-suckers (we're looking at you, aircon), you might not know just how much power they use.

Here are some of the top household appliances that may be eating up your power bill, and how to use them efficiently to help cut down on costs.

What's the average electricity bill in Australia?

A survey of more than 4,100 households by financial comparison site Canstar Blue identified the average quarterly electricity bills across the states and territories.

But keep in mind the cost of electricity in Australia can vary significantly depending on location, consumption, and energy providers.

Here's the state-by-state breakdown, ranked from cheapest to the most expensive:

SOURCE: Canstar Blue. Research conducted in December 2023 for households of all sizes. Northern Territory excluded due to insufficient data

The big energy users in your home

So what appliances are sucking up all that energy?

Here's which parts of your home use the most power so you can see where you may be able to make some savings.

The data was obtained from the Department of Climate Change, Energy, Environment and Water, and the SA Department of Energy and Mining.

Heating/cooling — 40 per cent

It's no surprise heating and cooling tops the list — we're suckers for turning the air conditioner on when it's too hot, and the heater on when it's freezing.

In the summertime, try using a fan before switching on the air conditioner .

They are cheap to run at only around 2 cents per hour.

But if you find it's so hot and humid that an air conditioner is desperately needed, try to set the temperature between 23 and 26 degrees Celsius .

The Energy Efficiency Council says each degree below this can increase your electricity bill by as much as 15 per cent.

If you're looking to use the heating , set it between 18C and 20C .

But if you're trying to keep cool, you could also combine your air conditioner with a fan . 

Instead of having the air conditioner on a low temperature, set it a bit higher and move the air around with a fan.

This could save you 70 per cent of your electricity usage, according to research by Ollie Jay, a professor of heat and health at the University of Sydney.

"If you move air more in an indoor environment, the temperature at which you [feel like you're too hot] is hotter," Professor Jay says. 

"So you feel the same at 23 degrees with still air as you will at 27 degrees with air moving, because we're cooling the person, instead of cooling the air."

And remember, if you're heating or cooling a room, close off the areas that you're not using .

Choice product category manager Chris Barnes has a few other cost-saving tips:

• Stop draughts and seal air leaks
• Clean the aircon regularly to help it run efficiently
• Use reverse-cycle aircons rather than gas heaters or portable electric heaters

Hot water — 25 per cent

Let's break our water usage down even further.

This time, the data comes from Sydney Water:

• Showers use 26 per cent of a household's water consumption
• Toilets use 20 per cent
• Washing machines  use 12 per cent
• Inside taps use 12 per cent
• Bath tubs use 6  per cent
• Dishwashers use 1  per cent

So what's the best way to reduce your hot water consumption?

Mr Barnes says it's all about the shower.

"Have shorter showers [4 minutes or less] , and install a low-flow shower head ."

The SA Department of Energy says some shower heads can use up to 25 litres of water a minute — so  try installing one that uses 9 litres instead .

You may also find that replacing your old hot water system with a more efficient model could reduce your running costs.

"Check your hot water system occasionally to make sure it's not leaking and that the exposed hot water pipes are properly insulated , as this can perish over time," Mr Barnes says.

Electronics — 14 per cent

This includes appliances and devices such as:

• Gaming consoles
• Music and entertainment systems
• Home office equipment

And if you're curious how much a 43-59 inch TV costs to run for 10 hours per day for 90 days, here's that info:

• LED: $18-$81
• LCD: $18-$108
• Plasma: $27-$126

Generally, most electronic appliances tend to enter a stand-by mode rather than fully powering down.

So while you're asleep or away from home, they're working behind the scenes, sucking your electricity and cash.

According to Canstar Blue estimates, appliances on stand-by mode could cost you up to 10 per cent of your electricity bill each. That's more than $100 annually.

Mr Barnes says the best way to save on stand-by costs is to make a habit of switching devices off at the wall when you're not using them.

"We tend to have more and more devices plugged in or charging nowadays than ever before; routers, phones, and stick vacuums, which all adds up.

"Think about whether they all need to be plugged in all the time."

Fridge and freezers — 8 per cent

The fridge is one of those appliances that unfortunately, you have no choice but to run 24/7.

This is why choosing the right size and efficiency for your requirements can make all the difference to your energy bill.

Here are some simple ways to reduce fridge costs according to Mr Barnes:

• Check the temperature: Adjust your fridge to 3C  and freezer to -18C  for the best balance between coolness, food safety, and energy efficiency
• Check the placement: Fridges placed in warm areas use more energy to stay cool. Make sure it's in a well-ventilated space and that there are sufficient gaps around the unit
• Maintenance: Is food going off faster than it used to? Is it noisy? It could be worth checking the door seals are clean and brushing off any dusty coils on the back of the fridge
• Contents: A full fridge is a happy fridge because the thermal mass of its contents help maintain temperature and reduce running costs

Cooking appliances — 5 per cent

From the refrigerator and freezer to the dishwasher, coffee machine and oven, all of these appliances use energy to run.

Here's a breakdown:

For those of you wondering about gas appliances, here are the hourly running costs:

• Oven — $0.48
• Cooktop (per burner) — $0.48
• Griller — $0.24 - $0.48

Mr Barnes says small kitchen appliances are generally cheaper to run than ovens and cooktops.

"For small one or two-person households, it may be more cost effective to use benchtop appliances such as an air fryer or microwave rather than an oven or cooktop."

For example, a sandwich press will grill a toasted sandwich faster than the oven grill, and use less energy.

And if you've got one, only run a dishwasher when it's full .

You can head to the SA Department of Energy and Environment to get the cost per cycle for different-sized dishwashers .

Laundry — 4 per cent

As with fridges, how much energy it will cost to run a washing machine and dryer will come down to the size and type .

When it comes to washing, the simplest tip Mr Barnes suggests is to choose a cold wash .

"The cleaning power is much the same in most cases, and the electricity costs are lower."

The Department of Energy says washing clothes with cold water "can save up to 10 times more energy" than a warm wash.

Here are some other energy saving behaviours the SA Department of Energy recommends:

• Wash a full load
• Adjust the wash cycle to match the load
• Pre-soak or pre-treat soiled items
• Select the economy or energy saving cycles  on your machine

The best clothes dryer is the sun and it costs nothing to run, so dry your clothes on a washing line whenever you can.

And if that's not an option, try not to overfill the clothes dryer as this can slow down the drying process and lead to greater energy usage.

How do I calculate the running cost of an appliance?

The CSIRO has a handy set of instructions you can follow to do this yourself.

1. Find the wattage

The wattage is usually printed on the actual appliance or on the packaging.

To turn your wattage into kilowatts just divide by 1,000.

So if your air conditioner is 3,000 watts, then the kW would be 3kW.

A 50 watt light bulb would be 0.05 kW.

2. Calculate the cost

You first need to work out the kilowatt hours (kWh) consumed for that period.

So multiply your kW by the length of time, in hours, that the appliance is being used for.

Then multiply this by $0.22 (retailers' tariffs will differ so just use this as a guide)

This will give you the running cost. 

For example, you used your 3kW air conditioner for four hours.

That's three multiplied by four, which works out to be 12kWh.

Now multiply that number by 0.22 and you'll get 2.64.

That means it costs $2.64 to run, or $0.66 an hour.

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