small sailboat wiring diagram

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Create Your Own Wiring Diagram

Photo: Ed Sherman

Whether you want to install a new stereo system or trace an intermittent electrical fault, a wiring diagram will save you hours of aggravation. The older your boat, the more likely you are to have either no wiring diagram or one that's worse than none because it's inaccurate. Making your own isn't rocket science, but it does take time, patience, and care. You won't get it all done in a day — or even several weekends — and don't let yourself get intimidated by complex electrical diagrams. Start by focusing on the simpler (and safer) 12-volt DC system aboard your boat. With each wire you trace, and circuit you complete, it gets easier. Eventually you'll have a map of your entire electrical system and a thorough understanding of how the pieces are tied together.

On many boats there are two types of current: alternating (AC) and direct (DC). Serious damage and even electrocution can result from confusing the two. In recently built boats, the two systems should be clearly differentiated and separated, including at the electrical panel. Wires and components associated with each should be distinct and, on newer boats built to American Boat and Yacht Council (ABYC) standards, will use standard color-coding. See chart at below.

AC wiring for 110 volts usually has white for neutral, black for hot, and green for ground (220-volt AC lines have a second hot wire, colored red). Those three wires typically are enclosed in white or gray insulation. You'll see the colored individual wires when they exit the common sheathing at each end. Your diagram should have one line for those three enclosed wires, except as necessary to differentiate them at the ends.

The wiring colors on your boat may be very different, especially if it's older and there's been a lot of "jury rigging" in its past. Make no assumptions about which wires do what. Trace each wire in the circuit from the electrical source to its use. Wire colors will assist you in doing that, even if they don't follow ABYC standards, by helping you identify the far end where it reappears from a conduit or a locker on its way to the equipment it powers.

On boats with both AC and DC systems, the DC system is generally simpler. DC power originates from the battery banks, so there is only one source. The DC electrical system is grounded through the negative bus of the distribution panel, which in turn is grounded through the engine negative terminal or its bus. That means that only two wires run from the distribution panel to each consumer of DC power — a DC positive and a DC negative — versus the three or four wires for each AC electrical user. The simplicity of the DC system, along with its relative safety in comparison to AC, makes it a good place to start.

Tip: Be very careful; don't confuse black DC negative wires on older boats with hot black wires on an AC circuit.

Big Picture: Sources & Uses

Take a careful look at the electrical systems on your boat, listing sources and uses for both AC and DC current. If it runs without the inverter when only battery power is available, it belongs on the DC list. A general idea of how each is connected will help you anticipate what to draw. If you have a good wiring diagram, copy it and blow it up so that you can make clear notes and changes in the future. Anytime you change the wiring or electrical components, write it on the diagram. If you don't have a good diagram, or you're intimidated by the arcane electrical symbols on the one you have, make one from scratch using large paper.

Starting with the batteries, follow the wires through to the end users, noting the selector equipment and any other equipment in line. Some people draw the wires within a sketch of their boat to indicate where they are. In a complex boat, this may ultimately be more confusing than drawing them in abstract and using industry conventions to show electrical components (see Online Extra). Start simply and make sure you know what you're drawing. Use a sharp pencil and try to avoid erasures. As you gain understanding and confidence, you'll likely redraw it several times. Indicate wire colors and gauges (thickness). The lower the gauge, the thicker the wire and the more current it can carry. The gauge should be imprinted on the insulation, with the number followed by "AWG," such as "12 AWG."

Using the list you made for the DC side, match up the breakers on the panel to the DC users. A few stragglers aside, the diagram of your DC system should come into focus. But don't jump ahead and make assumptions. All too often, a circuit breaker will have been reassigned in some past renovation, or a previous owner will have spliced into a wire to obtain power for an added item such as a fan. The only way to figure that out is to trace each wire to see where it really goes.

Tracing A Wire

After getting a basic understanding of your DC system, it's time to get down and dirty. First turn off all sources of power. Unplug from shore power, turn off any inverter and disconnect it from the battery, disable the generator, and remove the positive DC wires from the batteries. Although you're working on DC circuits, these actions will disable the AC side in case you mix up the two. Even after you've done this, DO NOT assume it's safe to touch any exposed wires, terminals, bus, etc.

Start at the source and trace each wire through to its end. The primary source wires will be heavy-duty wires running from your batteries to a distribution panel, or on smaller boats, a busbar. These wires should be few and simple, and much heavier gauge than the ones coming out of the panel/busbar because they supply the current for all those smaller wires. They may run through a selector switch before the panel.

The busbars or circuit breaker panels are the secondary source for most of your wiring, where the current "spreads out" following myriads of smaller wires to all the users on the boat. Hopefully your panel will have labels at the breakers, giving you some idea where these wires go. You may have to cut wire ties to isolate a particular wire contained in a tight bundle. Remember to re-tie the bundles when you're through. The wire you're tracing will often lead into a hole or conduit, but its color should distinguish it at the other end. If not, position a helper where you think the wire exits. Pull or carefully tug on your end, and hopefully your helper can see it moving. If not, try pulling back and forth like a seesaw.

If you just can't trace a wire, use a volt-ohm meter (VOM) to check for continuity (see "Five Ways To Use A Digital Multimeter," Dec. 2013). If you get continuity, you know in theory that the wire coming out of the hole is the same one going in. In some cases, wires going to certain equipment can indicate "ghost continuity" because of ground connections or other features. Physically tracing the wire is the most accurate method, especially on older boats. Once you've identified a wire from its source to its use, you can label it and add it to your wiring diagram.

Labeling And Diagramming

Attach labels to the wires at each end and at appropriate spots along the wire run. This helps when troubleshooting later. Buy labels or use high-quality yellow or white electrical tape and write on it with a quality indelible marker. Oil, grease, and other fumes in the boating atmosphere can cause the glue on labels or even good electrical tape to dissolve.

It's usually best to wrap the tape entirely around the wire, sticking it to itself. Office supply labels for label printers look neat but I've found that the glue on the back seldom lasts long and the labels end up in the bilge. Also label the wires and components on your diagram. You'll probably have to list and number these labels off to the side with a corresponding encircled number at the component. This avoids diagram clutter.

As you trace wires, look carefully for problems, including chafed insulation, hot spots indicated by browned or blackened insulation, little bumps in the insulation (indicates corrosion or overheating inside), a burnt insulation smell, or corroded terminals. Note the problems and fix them before you use the boat again. If you find an unfamiliar component, such as a diode, shunt, or transfer-solenoid switch, ask someone or research the part until you know what it does. This isn't just for accuracy; it will educate you, enabling you to diagnose problems more easily.

In older boats you might find dead wires, where an owner has removed something and disconnected (hopefully) its supply wire at the panel, but left it behind "just in case." Should you take it out, leave a strong nylon messenger string in its place to pull through another wire later. If you leave the wire, label it at both ends and be certain it's dead. Seal each end by wrapping it with electrical tape and then smear electrician's "liquid tape" over the actual tape to keep moisture out and the tape in place.

Voilá! The Final Product

By the time you get through diagramming the DC system, you'll have a good sense of how you want your wiring diagram to look. This is a good time to redraw it before starting on the AC system. AC systems can have more than one source (shore power, generator, inverter). If yours is particularly complex, consider hiring an ABYC-certified tech for an hour or two to walk you through it. Your diagram should clearly differentiate between AC and DC, or you can do a separate diagram for each system. Label which is which and make it obvious where the two types of current run close to, or could be confused with, each other. Make at least one copy to keep off the boat, and store your onboard diagram in a waterproof container such as a Ziploc bag. If it's very large, roll it up in a PVC pipe with two end caps. Glue one on, and use the other as a removable cap.

Diagramming your electrical system is a great winter project, and will be invaluable when you want to install something new.

Example Of A Draft Wiring Diagram For A Simple Boat

When you make your own wiring diagram use very large sheets of paper for clarity.
Most boats will have positive and negative busses where area wires come together.
Equipment coming off a switchboard or circuit panel should be straightforward to trace.
On a small boat, sketching circuits in the boat outline helps you locate wires later.
The next step would be to trace the wiring to the instrument cluster and related gauges.
Start with large cables leading from the batteries to the selector switch/busses.

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How to Safely Wire a Boat: A Beginners Guide

Electric technician working on a fuse box or switch board, using pliers or engineering tool

1 Wiring a Boat
2 Have a Wiring Diagram and a Plan
3 Gather the Right Materials
4 Use the Right Tools
5 Follow These Steps to Wire Your Boat
6 Conclusion

Wiring a boat can be an intimidating task. Maybe you have never done it before and feel overwhelmed about how to do it, where to start, and most importantly, the safety of it. But with the right knowledge and tools, it can be a manageable project. Properly wiring your boat is critical for safety and functionality. In this beginner’s guide, we’ll provide an overview of the wiring process, including the necessary materials, tools, and steps on how you can effectively wire your boat. Continue reading below for more information and you will be on your way to becoming a boat wiring expert in no time.

Wiring a Boat

Have a wiring diagram and a plan.

Before starting the wiring process, it is crucial to have a wiring diagram and a plan. A wiring diagram is a visual representation of the boat’s electrical system and helps you identify the wires and their functions. A plan will help you organize the wiring, identify the locations of switches, panels, and other components, as well as ensure that the wiring is properly connected.

Gather the Right Materials

It is important to be sure that you have the right materials before wiring your boat. The materials you’ll need for wiring a boat include marine-grade wire, connectors, terminals, heat shrink tubing , fuses, and a fuse block or panel. It’s crucial to use marine-grade materials as they are specifically designed to withstand the harsh marine environment and prevent corrosion.

Use the Right Tools

Not only is it a priority to have the right materials for wiring, but you will also need to be sure that you have the proper tools. The tools required for wiring a boat include wire strippers, crimping tools , a heat gun or lighter, a multimeter, and a soldering iron. These tools will help you strip and crimp wires, heat shrink tubing, test circuits, and solder connections.

Follow These Steps to Wire Your Boat

Now we will discuss the essential steps required when wiring your boat. The wiring process involves several steps, which are running wires, connecting wires, and testing the circuits. It is also important to follow the wiring diagram and plan to ensure that all wires are connected correctly. The step-by-step process for wiring your boat is as follows:

First, you’ll need to run the wires from the battery to the components and devices on the boat. It’s crucial to label the wires and keep them organized to prevent confusion during the wiring process.

Next, you’ll need to connect the wires using the appropriate connectors and terminals. Crimping or soldering connections is recommended for a secure and reliable connection. Be sure to use heat shrink tubing to protect the connections from moisture and corrosion.

After all the wires are connected, you’ll need to test the circuits using a multimeter to ensure that they are properly connected and functioning. It’s important to check for continuity, voltage, and proper grounding.

Wiring a boat may seem like a daunting task, but with the right knowledge and tools, it can be a manageable project. Remember that it is important to have a wiring diagram and plan, use marine-grade materials, choose the correct tools, and follow the proper steps for running, connecting, and testing the wires. With these tips, you’ll be able to safely and efficiently wire your boat and enjoy all of its electrical features and components.

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1. Panel Buyer’s Guide
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How to…

We get many questions over and over again, and in an effort to provide great content to our customers we’ve this how-to section with some guides below:

1. Wire A Boat

We’ve put together a this little newbie guide on How To Wire A Boat . It is by all means not-all inclusive, but should help some folks pickup some of the basics. View the complete guide here .

2. Wire A Bilge Pump

We recommend an ON-OFF switch for small boat bilge pumps with a a separate fused feed to the float switch direct from the battery. This makes sure your bilge pump is never accidentally shut of. It also gives a visual indicator at the switch when the float switch is working. View the complete guide here .

3. Create a Panel Template or Tracing

Often people want or need to mail their old switch panel in to have us duplicate a unique shape. Here’s our guide on how to mail in your switch panel with good results.

Practical Boat Owner

Digital edition

Boat wiring explained for the practical sailor

Pat Manley and Oliver Ballam
February 13, 2024

Pat Manley and Oliver Ballam demystify boat electrics and explain wiring and the best techniques for its installation

Inserting a draw rod while sorting out boat wiring

Inserting a draw rod. Credit: Fernhurst Books Credit: Fernhurst Books

Electrical wire used on boats should be tinned (covered in solder) along its whole length.

This is expensive, so most production boats have ‘automotive-type’ wire, which allows corrosion to spread along the strands of wire under the insulation.

Automotive-type wire. Credit: Fernhurst Books

This makes it impossible to remake joints successfully. Where one end of a wire is located in a damp atmosphere, tinned wire should always be used.

Tinned marine wire. Credit: Fernhurst Books

Unless it’s unavoidable, don’t run wires through the bilge where their condition will deteriorate.

Running boat wiring

Use a push wiring threader to run wires through conduits and pipes.

Insert one end into the conduit or gap through which you need to run the wire.
Then push the threader through.
Then use the threader to pull the electric wire all the way back through.

If you need to run wires straight through inaccessible spaces then draw rods are better because they are rigid and you can angle them to come out of, or go into, a space. They screw together and can be assembled ‘as you go’.

A set of draw rods. Credit: Fernhurst Books

Most alloy masts have internal conduits, provided to carry wiring running up the mast. Sometimes these are extruded as part of the mast and sometimes they are plastic conduits clipped or riveted onto the side of the mast.

Wires dropped through the main section of the mast will slap and chafe.

An alloy mast with conduits. Credit: Fernhurst Books

A push threader can be used to run mouse lines and cables up the mast’s conduit.

If possible, it’s usually easier to pull one existing cable back with a mouse line attached, and then attach the new cable and the old cable together to the mouse line.

Grommets to protect insulation. Credit: Fernhurst Books

Ducting used to protect insulation in boat wiring

Ducting to protect insulation. Credit: Fernhurst Books

Supported cable. Credit: Fernhurst Books

Cable should not come under strain, which could cause connections to be pulled apart.

Corrugated trunking used with boat wiring

Corrugated trunking. Credit: Fernhurst Books

Beta duct trunking. Credit: Fernhurst Books

Make a wiring diagram of any new work to be stored with the boat’s manual. If there are joints/junctions access points, try to indicate on the diagram where these points are.

Heavy-duty circuits

A DC electric motor will overheat and suffer early failure if the supply voltage is reduced.

Motors with high current requirements need special care with their wiring circuits to maintain an adequate voltage. Normally, a voltage drop of 10% is the maximum allowed.

The operating switch will not handle the required current, so a relay is introduced into the circuit.

A relay consists of an electromagnet that can be operated by the low current; its contactors then carry the high current required to operate the motor, or whatever.

This keeps the switching current low, but heavy-duty contacts handle the high current load of the motor.

Proper siting of the relay will keep the length of the high-current circuit to a minimum.

Let’s see why an electric windlass, for instance, might fail prematurely if its wiring has too much resistance: Say it has a maximum power of 1,000W and should be run at 12V:

The current would be 83.33A at maximum pulling power: 1,000W ÷ 12V = 83.33A
Say the resistance of the wire is such that there is a 10% voltage drop: 2V x 90% = 10.8V
The current would now need to be 92.59A if required to pull its maximum load: 1,000W ÷ 10.8V = 92.59A because it would try to maintain power by drawing more current from the battery at the reduced voltage
With a 20% voltage drop (to 9.6V), the current would be 104.2A: 1,000W ÷ 9.6V = 104.17A
This would give a 25% current overload: 104.17A ÷ 83.33A = 1.25 leading to rapid failure

For the same reason, if you had the engine running, the voltage at the windlass would be about 13.5V.

With the engine stopped and the battery down from overnight use, the windlass voltage could easily be reduced to 10V or so.

Engine running: 1,000W ÷ 13.5V = 74A

Engine off: 1,000W ÷ 10 V = 100A

Which windlass motor is going to last longer?

You might think that the windlass motor is a fixed resistance so by Ohms Law, as the voltage decreases, so does the current. However, motors produce something called back EMF (voltage) which acts against the current flow.

This means that the operating current is optimal at rated speed. It’s at its highest when the motor is stationary.

Back EMF is too detailed to discuss here, but it’s why poorly supplied motors fail early.

Starter motors and sheet winches

These are operated with the engine stopped. Starter motors normally run for a very short time and have a relatively short run of very heavy cable.

Provided connections are clean and well made, they make only small demands on a dedicated engine start battery.

Relay to keep the switching current low

Sheet winches may have relatively long cable runs and the demands on the battery system can be significant, so that voltage drop at the motor needs to be minimised.

Adhere strictly to the manufacturer’s wiring requirements.

Bow thrusters and anchor windlasses

To keep voltage drop to a minimum, these are normally used with the engine running to prolong the life of their electric motors and to minimise battery drain.

Bow thrusters especially can’t be powered directly from the engine alternator , as it won’t produce enough current.

There are two schools of thought on powering these machines:

An existing battery – engine or domestic Long, very heavy and expensive cables run from the aft battery bank. For a bow thruster these cables may carry 400A and may have a circuit length of 20m, in which case a cross-sectional area of 200mm2 may be needed for cables. That’s a diameter of 16mm! Windlass cables will be appreciably smaller as most windlasses draw more like 80-100A (typically 35-70mm²). If no bow thruster is installed this is the most common method for a windlass.
A separate battery close to the demand The heavy cable length is kept to a minimum by placing a dedicated battery close to the windlass or bow thruster. This is charged by a smaller cable from the engine/charger. The charging cable needs to be rated to carry the maximum charging current and associated voltage drop only. The lower cost of the lighter cable, however, may be outweighed by the cost of the extra battery. The disadvantage of this method is the weight of this battery forward in the boat, although the total weight of cable and battery may be similar for both methods. It also complicates the charging system significantly, but this is the favoured option for bow thrusters.

Wire current rates

A wire must be capable of carrying the maximum current in the circuit. All wires have a current rating. A 5A wire must carry no more than 5A, and so on.

Note that wires bundled together can carry less current because they will heat up. Wiring for sensitive equipment should not allow more than a 3% voltage drop.

Normally this is more restrictive than the current rating because it depends on the length of the wires (both positive and negative).

Other wiring may be allowed a 10% voltage drop along its total length. Even 10% will usually require a larger diameter of cable than the current carrying capacity.

The cable should be specified to suit the largest requirement. 12V circuits will always require heavier cable than 24V circuits, because with 24V the current is halved for the same power appliance. This is why larger boats (with longer runs and heavier loads) will run a 24V system.

Wire sizes required for a given length of cable run

(Length is the sum of the positive and negative wires) – see tables below

When installing new equipment you’ll need to:

Decide where you will need to power the equipment from: The battery (if it needs to be on all the time); The battery isolator (best if it is turned off by the battery isolator); An existing bus bar or circuit breaker.
Check the wire size required, according to its length and the current it has to carry, from the table above.
Run a new positive wire from the above source to a fuse holder or circuit breaker.
Run a new positive wire from the new fuse holder to the new equipment.
Run a new negative wire from the existing negative bus bar or a new one as appropriate.
Once you’ve checked your work, fit an appropriately-sized fuse, as recommended by the equipment manufacturer.

A table showing sizes for a dive length of cable run for boat wiring

Credit: Fernhurst Books

The fuse or circuit breaker should be fitted as close as practicable to the positive source.
If you have an ammeter, its shunt should be fitted in the negative battery cable.
Equipment supplied direct from the battery MUST have the negative cable connected via the shunt and NOT taken direct to the battery’s negative terminal.
If you are planning to add more than one device, you may need to add a positive and/or negative bus bar.
When connection to the battery is necessary, some vessels will have a bus bar already – can you connect to this rather than adding more wires to the battery? Is the bus bar and supply wiring capable of carrying the extra current?

A diagram showing New protected wiring insulation

New protected wiring insulation. Credit: Fernhurst Books

Continues below…

Switches turn on or off the flow of electricity in a circuit' relays provide control over the flow. Credit: Fernhurst

Understanding boat electrics: switches and relays

Pat Manley and Oliver Ballam demystify boat electrics, starting with switches and relays

Spraying a connector for electrical wiring

Understanding electrical wiring connections for boats

Pat Manley and Oliver Ballam demystify boat electrics and explain how to use and make secure electrical wiring connections

Signal wire connectors allow a permanent joint to be made. Credit: Fernhurst

Understanding electrics: insulating & signal wire connectors

Oliver Ballam and Pat Manley demystify boat electrics and explain various types of electrical connectors and their uses on board

Soldering boat wire: joints and connections

Oliver Ballam and Pat Manley demystify boat electrics and explain the best techniques for soldering and de-soldering connections

The third edition of Essential Boat Electrics (Fernhurst Books, £16.99) is available at fernhurstbooks.com .

Written by Oliver Ballam and the late Pat Manley, it’s a practical guide – with simple language and clear diagrams – to allow owners to tackle electrical jobs on board.

There are tutorials, from wiring a circuit, understanding switches and relays to troubleshooting electrical faults, all using easy-to-follow photo sequences.

The book also looks at tasks such as choosing solar panels and batteries and connecting navigational instruments.

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14 Steps To Wiring Your Boat

What you need to know to install or re-wire the electrical system on your boat. a step-by-step practical guide. covers planning, diagrams, wiring, batteries, over current protection and more..

I want to thank Ed Sherman for reviewing this page for accuracy.

A question often asked on boating and boat building forums, and by visitors to my web site, is: “I need a simple wiring diagram for a small outboard boat to wire up the lights and few other things, but no one seems to have one. Is there one, and where can I find it? Are there a set of step-by-step instructions?”

There are wiring diagrams, websites and forums that tell you how to wire an electrical system for large boats and bigger sailboats. But when it comes to small boats there is a distinct lack of information and diagrams for how to install a simple, safe, and reliable electrical system.

The following is meant to apply only to small outboard boats under 16 feet with 50 or 60 horsepower or less. It can be applied to slightly larger boats that have a simple 12V DC system using one or two 12V batteries.

Note 1 : I will not deal with the wiring specifically for the outboard motor and controls. Here is a web site where you can obtain wiring diagrams for most outboard motors. Most new outboards come with a wiring harness and a manual that has wiring diagrams. See Master Tech Marine Outboard Wiring Diagrams .

Note 2: If you are re-wiring a boat with an electrical system installed: Don't rip out that old system yet ! Use the old system to help make a plan in steps 1 through 7. Trace out each wire and put that on your diagram. This will make it far easier to locate wires and equipment. Wait until you actually start installing wiring in step 12. Then replace each set of wires with new. This may take a little more time, but will result in far fewer mistakes and less troubleshooting.

Note 3: Throughout this I will give references to the US Code of Federal Regulations (CFR) requirements that apply to boat manufacturers, and to the American Boat and Yacht Council industry standards. Examples: 33 CFR 183.401, or ABYC E-11. The US Coast Guard Regulations (the CFR) and the ABYC standards are good guidelines to follow for a safe and reliable electrical system. They are used by marine electricians, professional boatbuilders, designers, marine surveyors, and marine repairers. If that’s how the pros do it, so should you.

Step 1. Make a Plan. Decide what you want to install, and where it will go. See Electrical Planning

Step 2. Draw a simple electrical schematic (diagram) that shows each piece of equipment, the fuses, switches, and how all of this will be connected. This is not a diagram of where the equipment is located on the boat. That will come in Step 8. It is simply a diagram of the electrical circuits. Here are two alternative examples. (Click on the diagram to expand.) The first diagram uses a positive buss bar. The second omits the positive buss bar. For clarity I did not use color codes except red (positive) and black (negative).

Do not be concerned if you don’t know electrical symbols. Just make a box or circle and write in what it is, or you can use a picture of the item. As long as you understand what goes where, and how they are connected, it’s Ok. Remember, any 12V DC device must have at least a positive and negative wire connected to it. Put a plus or minus next to the wire or use red for positive and black for negative. On metal boats do not use the hull as a return (negative) path. Connecting your electrical system to a metal hull can result in stray current corrosion.

See also BoatUS diagram:

There are several ways to draw wiring diagrams. The most important thing is that you understand what you are diagraming. It needs to be simple enough and clear enough for you to be able to refer to it in the future and still understand what each item is, what the wiring is and how each item of equipment is connected to the electrical system. That way, in the future if you want to add or subtract equipment you can do so by referring to your diagram and determining where and how the new item fits into the system.

Step 3. Batteries: Decide where you will put the battery. Later we will decide the capacity and type of battery but for now we only need to decide where to put it.

The battery is the source of power for starting, instrumentation, and lighting. There may be a second battery on some boats for running a trolling motor or other equipment.

Batteries should not be too close to anything that can cause an accidental short. There should be 12 inches of space all around them. Batteries must not be directly under or over fuel lines or under other electrical equipment such as a charger or inverter. If they are, there must be a floor or panel separating them. ABYC E-10.7.5 and 10.7.6 Storage Batteries

Batteries need to be in a space that is ventilated to the atmosphere. 33 CFR 183.420(e) This applies to all batteries, not just lead/acid batteries.

Batteries must not move, so they have to be fastened down. 33 CFR 183.420(a)

There should be a tray under a battery for spilled electrolyte, or it should be in a battery box, and fastened down so it won’t move under any conditions. (ABYC E-10.7.2) The Coast Guard does not require a tray or a battery box but ABYC does require some means to contain spills. If it is strapped down in a tray, spilled acid won’t damage the boat and the battery won’t move. The terminals need to be covered with a boot or some other device that protects them from accidental contact with metal tools. But, if the battery is in a box the terminals are protected against accidental contact with tools, spills are contained, and it won’t move.

The battery should be close to the engine. Since starting current is so high, and the wires to the starter are not fused, you want to keep the wires as short as is practical.

The battery should be a combo starting/deep cycle battery, usually sold as a marine battery. An auto battery would do for starting and lights. But, for running a radio, and other electronics while anchored or fishing, a battery with a little deep cycle capacity is needed so the battery doesn’t go flat and leave you stranded when you try to restart the engine.

How big a battery (capacity, not physical size) do you need? That depends on the amount of load on the battery. I will show how to determine that in Step 12.

There is one non-electrical consideration; weight. Lead acid batteries can weigh up to 50 lb. Think about how the weight of the battery will affect weight distribution on your boat, especially if it is on the same side as the helm and controls. You may have to move it to balance the boat side to side. If you have a very low transom, how will the weight of the battery affect the water line at the transom?

Step 4. Battery Switch: Some people think that a battery switch is not necessary on a small boat. I think a battery switch is necessary to turn everything off when you are not using the boat.

Where the battery is located determines where the battery switch goes. It should be close to the battery but easily accessible to be switched off in an emergency. ABYC E-11.6.2.

A good brand is Perko but there are others. Avoid any battery switch that is not UL Marine Listed. There are cheap ones on the market that are not UL listed and can get hot and melt.

A battery switch must be ignition protected. (33 CFR 183.410)

Ignition protection means that it will not ignite gas fumes if they are present. This is extremely important if you have a gasoline fuel tank in the same compartment as the battery.

Use only ignition protected electrical components. You don't want anything in there that will set fuel vapors off. Batteries are not considered a source of ignition because there are no moving parts, but if you make accidental contact with metal tools it can create an arc. So, the terminals must be protected, and battery switches and other electrical equipment in this compartment must be ignition protected.

Buy a switch that has a provision for two batteries because you may want to add a battery in the future. The switch will have three positions. OFF, 1, 2, and BOTH. The 1 position connects the one battery and allows charging of that battery when the engine is running (if your outboard is large enough to have an alternator). The 2 position connects and charges the second battery, if there is one, and the BOTH position puts the two batteries in parallel doubling the battery capacity and charging both at the same time. You won’t need the BOTH and 2 positions now, but this gives you the option to add a second battery.

Step 5. Fuses: Next, install a fuse block close to the battery switch. Fuses must be within seven inches of the source of power (33 CFR 183.455) but you can go up to forty inches if the wire is sheathed. Standard wire loom is fine as a sheath. Be aware, the fuse is there to protect the wire, not the equipment. If you overload wiring it gets hot, melts and starts a fire. We will determine the size of the fuse later. See Step 12. Buy a fuse block with two fuse holders. That way you have a spare if the fuse blows. This is generally a good idea. When installing fuse blocks get ones with more fuse holders than you think you need. You will need them eventually. One or two extra fuse holders is good.

Step 6. Equipment Location: Determine where each piece of equipment will be.

Think about where you want things to go. Depth finders need to be where they are easy to see, but not blocking your vision when operating the boat. Radios should be where they can be easily reached, and for VHF, reach the mike. The back of the console or surface you are mounting them on needs to be easily accessible for access to the wiring.

Step 7 . Locate the fuses, buss bars and switch panels.

Decide where to put fuse boxes, buss bars, switch panels, etc. Each of these must be close to the equipment they power, and easily accessible to be worked on. They cannot be hidden behind equipment or inaccessible panels. This may sound obvious, but I have seen some very bad installations. Also, they should be protected from spray or rain.

Most electrical and electronic equipment comes with pigtails. Pigtails are wires coming out of the equipment and may only be a few inches to several feet long. Sometimes they have a connector attached to the ends of the wire. When determining where stuff goes consider the length of the pigtails, because you don’t want a rat’s nest of wires hanging loose.

Switch boxes: A box or panel where switches can be mounted to control stuff. On a small outboard boat this is usually the dash or the console.

Fuse block: A panel with fuse sockets on it. It can be open or covered.

Buss bar: A block with studs for connecting wires.

Typical Buss Bar: This buss bar is for the negative wires. The large wire on the left is the battery negative.

There are some devices that are connected directly to the source of power and do not go through fuse blocks and switches. They need to always have power. One is the bilge pump. Bilge pumps may have a float switch that automatically turns the pump on when water in the bilge gets to a preset height. This won’t work if the pump is not wired directly to the battery. It is not good practice to wire it directly to the battery though. Wire it to the power input side of the battery switch. It is good to install a switch at the helm that turns the pump on manually.

If your boat has an anchor light, you may also want to wire the switch for the light directly to the power input side of the battery switch. That way you can turn on the anchor light when the battery switch is off.

Step 8. Make a diagram of the boat showing where the wiring, equipment and fuse blocks will be located.

Make a rough drawing of the boat looking down from the top. This is called a general arrangement and shows how the boat is laid out. Using your electrical schematic, put in where the equipment, fuse boxes, buss bars, switch boxes and wiring are going to go. Check this against the actual boat to make sure you aren’t missing something.

Wiring cannot go through pieces of equipment, pipes, tubes, and other solid objects. They can go through walls and bulkheads and panels. Wiring must be easily accessible for installation, trouble shooting and replacement. It must be fastened down at least every 18 inches (ABYC 11.15.4.1.9) so it isn’t or chafing on something. Where wiring goes through a bulkhead, wall or panel, it must have a grommet or padding to protect the wire. 33 CFR 183.445(a)

Your diagram may look something like this; (Click on image to expand)

Step 9. Wiring: Figure out how much wire you need, what size wire you need, and what color it should be. Wire standards.

What about the wires from the battery Switch to the starter? The wire needs to be a very heavy gauge, at least a 4 AWG on small outboard boats, because starters draw a lot of current. Both the positive and negative wires should be the same size. If the outboard has the wires for the starter already installed, the wires from the battery to the switch should be the same size as those wires. The engine manufacturer has determined the amount of amperage the starter draws and correctly sized the wires for the load.

The positive wire (red) goes from the battery to the input side of the battery switch. The negative (black) wire goes to a buss bar. One post on the buss is for the wire from battery to the engine block (ground). Another wire goes from the buss up forward to the dash. The others are for other equipment. There should be as many terminal posts as you need plus a few extra.

Color Codes: The positive wire should be red. Negative can be black, or yellow, or black with a yellow stripe. Throughout the boat negative wires should be black or yellow or a combination. AT the dash or console, all positive wires from the fuse block to the instruments and the equipment, should be color coded using the standard color codes for marine wiring. Direct Current Color Codes: From ABYC E-11.15.2.3 Table 11 and Table 12.

Direct Current Color Codes: From ABYC E-11.15.2.3 Table 11 and Table 12.

Color codes tell you what the wire is for. But label the wire on both ends. A simple piece of tape with a name written on it will do. They do not need to be fancy labels, but if you prefer, you can buy labels at electrical suppliers or hardware stores.

Wire must be marine wire. (33 CFR Sec. 183.435) Do not use auto wire. It is not made to the same standards as marine. Most marine wire is labeled UL 1426. It must be copper stranded wire. It does not have to be tinned, although tinned wire will last longer. On a small boat it is not necessary. Do not scrimp on wire though! Cheap wire could mean the difference between a reliable system and one that you constantly have trouble with. Buy good quality wire. I have seen 100 ft spools of Ancor 16 AWG Tinned Marine Wire for sale on-line for as little as $24.00 USD.

What size wire? American Wire Gauge (AWG) is in reverse order. The larger the number, the thinner the wire. The thickest wires are 00 or 0 AWG. The smallest gauge allowed on boats for a single wire is 16 AWG, or 18 AWG if it’s in a bundle or sheath (33CFR 183.425), but this may be way too thin for the equipment or the length of the wire run. The only exception to this is wire inside electronic devices or part of the electronic controls on the engine. 33 CFR 183.425(g)

The thicker a wire is, the less resistance it has. The longer a wire is the more resistance it has, and so there is a larger voltage drop. You want to minimize the resistance and the voltage drop. So you first need to figure out the wire size based on how many amps are being used, and then by how long the wire is. Use the tables in Appendix A, at the end of this page, to determine the correct size. Don't just guess at wire size and buy larger diameter wire such as 14 or 12 AWG. See Wire Size:

For the purpose of determining wire size, the fuse block the wire is coming from is considered the source of power. For the wires running from the battery to the starter, or to the under-dash fuse block, the battery is the source of power. In the two examples below the fuse block under the dash or console is the source of power.

Here is an example:

A Hummingbird Model 345C depth sounder draws 380ma (milliamps from the specifications). The installation includes a 6 foot power cable of 18 AWG wire. This may be fine for connecting it to a fuse block near the dash. But we need to size the cable running from the battery to the dash. It is going to be at least 10-12 feet long on a 16 foot boat. Double that length for the negative return wire.

Use table 3 in The Appendix for voltage drop. Most boat manufactures use wire rated for 105C (degrees Celsius - the temperature rating of the insulation on the wire). Looking at the table under the column for 105C we see amperages starting at 20 amps, 25 amps, 30 amps, and so on. Following the row for 20 amps to the left column we find 18 AWG.

From the table on voltage drop an 18 AWG wire 20-24 feet long (30 feet in the table) with a 15-ampere load will have less than a 10% voltage drop. But it can only be 18 if it’s in a sheath or bundle. So go up one size to 16 AWG.

Another Example:

Suppose I have three electronics running off a fuse block in the dash or console. Each piece of equipment requires 1 amp at 12 volts to run. The total amperage for the three items is 3 amps. From the fuse block in the dash or console to each item of equipment, there is a positive wire from the fuse to the equipment, and a negative wire running back to the buss. Using 1 ampere, we determine the size the wire should be, by using table 1 and 3 in Appendix A. For instance, if the positive wire is two feet long then the total length of positive and negative wires is 4 feet. Looking at the Table 1, the line for 18 AWG wire at 105C allows up to 20 amps.

So, we could use 18 AWG. Look at Table 3. We see that an 18 AWG wire, 10 feet long, will have less than a 10% voltage drop for up to 5 amperes. Again, we could use 18 AWG but since 18 AWG wire has to be in a bundle or a sheath we add a level of safety by using 16 AWG.

This is done using the tables developed by the US Coast Guard and ABYC. You don’t have to know any formulas to figure it out. The first table determines the wire size based on the load in amps and the second table the size depending on length and voltage drop. You use the larger wire if there is a difference.

See the table in Appendix A at the bottom of this page. or ELECTRICAL TABLE: 33 CFR 183.42: ALLOWABLE AMPERAGE OF CONDUCTORS FOR UNDER 50 VOLTS or: ELECTRICAL SYSTEMS VOLTAGE DROP

Step 10. Wiring tools. Wire connections (terminals). See Connectors :

Tools: Use good quality tools, especially good quality crimpers and wire strippers. Cheap crimpers make bad crimps. Bad crimps make bad connections. Poor wire strippers nick the metal conductor which may cause the wire to break or have a high resistance. See My Page on Practical:

Wire terminals must be used . Connections should never be a bare wire wrapped around a stud or post. This is bad practice, and can easily come loose or result in a high resistance connection. High resistance equals heat, which results in fire. Never use wire nuts to connect wires on a boat! They are prone to vibration and corrosion. ABYC E-11.15.3.7 Twist-on connectors (i.e., wire nuts) shall not be used.

Use crimp type ring or captive spade terminals. Captive spade terminals have a tang on the ends. This prevents them from being pulled off or slipping off the stud or post. Connections must resist being pulled off. In the ABYC wire standard there is a table listing how much of a pull they must withstand depending on the size of the wire. A 16 AWG wire must withstand a ten lb. pull. A 4 AWG wire must withstand a 70lb pull.

You can solder connections if you like but crimp them first . ABYC standards do not prohibit soldering, but they do not allow soldering to be the sole source of support for the connection. (ABYC E-11.5.3.8) This is because solder creates a hard spot in the wire which is not as flexible as the wire itself and not as resistant to flexing and vibration. So, if you solder you must also crimp. Crimp first, then solder.

Seal wire connections with a good waterproof sealant , usually marketed as dielectric grease. There is no requirement to do this, but it prevents water from getting in the connection and wicking up the inside of the wire insulation or corroding the connector.

My method. I do not solder. First I slide a short length of heat shrink tubing onto the wire. https://en.wikipedia.org/wiki/Heat-shrink_tubing How long it is depends on the wire and connector size. Usually if the tubing extends about 1/2 inch (1 centimeter) beyond the end of the connector, that is enough. Then I use dielectric grease. See Wikipedia on Dielectric grease . Dielectric grease is non-conductive grease, usually silicone that is also waterproof and can be used to seal connectors. Before crimping the wire in the connector, I squirt a little dielectric grease into the connector where the wire goes. I then insert the wire and crimp it. Then I slide the tubing down over the connector and shrink it with a heat gun or hair drier so it seals itself around the wire and connector. The combination of grease and heat shrink tubing should keep the water out.

Heat Shrink Tubing And Connectors, AAA protection, How to install and repair. http://youtu.be/jCRsx38WRw8

How to get a good crimp: Marine How to: Wire terminations: https://marinehowto.com/marine-wire-termination/

Step 11. Fuses . How big should your fuses be?

Fuses are rated by amperage and protect the wire from overheating and fire. Fuses must be rated at the same or less rating of the wire. If you have a wire that is rated at 15 amps you need a 15 amp fuse. Each circuit is rated for a certain amperage, such as 15 amps or 20 amps, and more equipment is not added to the circuit if it would cause it to draw more current than the fuse is rated for.

This can become an issue on little boats too if you have more equipment, or something like a powerful stereo system that draws a lot of amperage. Then it should have its own circuit and its own fuse for the circuit.

The question is how many fuses in the block? That depends on how much stuff you are running. I would have a fuse for the lights, one for the instrumentation, and one for any electronic devices, plus a spare. That is four. But for expansion maybe a six or 8 fuse block would be better. Again, in the future you won’t have to buy a new block. See Overcurrent Protection:

Step 12. Installing equipment .

Start with the battery, the battery switch, and the main fuse block.

Selecting a Battery: Batteries are rated by voltage and capacity. We are using a 12V battery. There are two ratings, CCA and MCA See Batteries at:

CCA Means Cold Cranking Amps. MCA means Marine Cranking Amps. These are measures of how many amps the battery can deliver for 30 seconds and maintain the voltage at 12V. Basically the higher the CCA rating the longer the battery will maintain its voltage. Batteries are also rated by amp-hours. 1 amp for 1 hour is 1 amp-hr. Generally the rating is based on how many amps the battery will discharge for 20 hours until the charge drops to 10.5 volts. The higher the amp hour rating, the longer the battery will power your equipment. Also, batteries are rated for Reserve Capacity which is how many minutes it will deliver the same voltage at 80 degrees. An average marine battery should have a Reserve Capacity of 60 to 90 minutes. Anything less is not adequate.

There are four types of batteries commonly used on boats, Wet Cell (also called lead acid, flooded, or flooded lead acid, and sometimes abbreviated FLA), AGM (Absorbed Glass Mat, Gel, and Lithium, but for now I’ll stick with the standard wet-cell battery. They are relatively inexpensive, can be purchased anywhere, and for a small boat, more than adequate. A battery with a CCA or MCA rating of 200-300 should do but we’ll determine that when we calculate the loads. See table below on how to calculate loads. Battery Capacity should be at least twice the load.

To calculate loads, list the equipment you are planning on installing. In the chart below the following items are listed. Navigation lights Bilge Pump Radio (Only when receiving) Depth Sounder engine electrical Instruments GPS Bait well pump Horn Radio TX. (VHF Marine radio. It draws more when transmitting)

Determine from the specifications for each item what the current load is in amps. Separate them into continuous loads (on all the time) and intermittent loads (only on when used). Determine how many hours they will be used. Multiply the amps times the hours to get amp hours. Add up the amp hours.

Learn boat wiring from the experts

By Author Fiona McGlynn

Posted on Last updated: August 18, 2023

Our review of Boat Electrics 101 , a new online course, co-developed by marine electrics expert, Nigel Calder.

When we bought our 1970s-era sailboat, the boat wiring was a disaster.

We soon discovered a rainbow spaghetti mess of unlabeled electrical wires behind our DC electrical panel. Legacy marine electrical systems from a previous “rewiring” made trouble-shooting and tracing wiring runs exasperating. Lights and pumps regularly failed and we once lost power entirely (despite being on shore power).

In short, living on a poorly wired boat was a nightmare. We needed to learn about our boat’s electrical if we were ever going to go bluewater cruising.

A quick note that this post contains affiliate links (so if you purchase through a link we’ll earn a small commission). We received free access to this course in exchange for a fair and honest review. All the opinions are our own.

Learning how to wire a boat

The good news is that while boat electrical may seem intimidating, it’s actually not all that difficult to get the hang of—but it does have to be done right!

The challenging part was finding a good teacher. We hired an electrician we found on Craigslist to show us the ropes, but this proved to be a complete disaster (with him shorting out the dock mains at our marina and frying our inverter).

After that experience, we resolved to teach ourselves, sorting through the good, bad, (and sometimes, downright dangerous) boat electrical advice available online.

Fortunately, there is now a FAR better way to learn boat wiring…

Boat Electrics 101

Boat Electrics 101 is the online course I desperately wish we’d had at the time. It launched in 2021 and was created by arguably the world’s smartest people on marine electrics including boat systems guru, Nigel Calder.

If you’re not familiar with Nigel, you’ll find his mechanical and electric books in just bout every bluewater cruiser’s library. These guys really know what they’re talking about!

In the course you’ll learn:

The basics of how electricity works
Electrical system components and how to safely connect them
How batteries work (and what you can do to double or triple their lifetime)
Energy system design: how to balance your energy storage, consumption, and generation
How to plan a (re)wiring of your boat (including making your own boat wiring diagram)

Unlike my grade 10 science teacher, the course does a great job of taking an important concept and breaking it down with animations, diagrams, and videos.

For example, In one module, Calder demonstrates the importance of circuit breakers by driving a screw through an unprotected wire. The cable immediately went up in flames, filling the room with smoke! Lesson learned.

Best of all, all of their materials follow ABYC and ISO standards. Both Nigel and Michael have been members of American Boat and Yacht Council (ABYC) and the International Organization for Standardization (ISO) committees, so they know the rules and best practices better than anyone.

I’ve taken Boat Electrics 101 and can’t say enough good things about it. If you sign up now, you can take advantage of their early bird offer ($199) and save $100 . Oh, and you keep your access to the course forever (even as they add new material). Even if it saves you hiring a marine electrician just once, the course more than pays for itself.

The rewards of doing it yourself

Learning how to wire a boat was not only rewarding but it made us more capable, self-sufficient boat owners. It’s an essential skill for people with older boats, but even new boat owners will find there comes a day when an electrical component fails or they want to add more bells and whistles.

We’ve saved a lot of money by doing our own marine electrical work (not to mention avoided days stuck in port waiting for a professional marine electrician). So, don’t let marine wiring intimidate you. With the right knowledge and tools, you’ll be well on your way to doing your own marine electrical.

Fiona McGlynn is an award-winning boating writer who created Waterborne as a place to learn about living aboard and traveling the world by sailboat. She has written for boating magazines including BoatUS, SAIL, Cruising World, and Good Old Boat. She’s also a contributing editor at Good Old Boat and BoatUS Magazine. In 2017, Fiona and her husband completed a 3-year, 13,000-mile voyage from Vancouver to Mexico to Australia on their 35-foot sailboat.

Sunday 23rd of January 2022

I learned the hard way about boat electrics when locked onto the engine block and a battery charger on a sailboat connected to shore power with a faulty ground. I was being tazered by 240v.

My friend saved my life by pushing me off the engine with a broom handle!

Yes, understanding boat electrics is something that is as important as navigation!

Oh my gosh, that sounds terrifying! What a nightmare. I'm glad you're okay. That was some good quick thinking on your friend's part!

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How To Create A Wiring Diagram For Your Boat

Most new boats include a drawing that outlines the entire electrical system, however these become outdated very quickly as new equipment is installed. For older boats, they can be completely out-of-date or non-existent. Putting together a simple diagram of your boat's electrical system may seem overwhelming but it isn't as hard as you think. It just takes time, patience and the realization that it cannot be completed in a day and will be an on-going project.

Where to Start? If you have an existing drawing, we recommend you enlarge it and make clear notes regarding any changes. If you don't have a drawing, start with a large sheet of paper, and begin with the batteries and the main DC system such as battery chargers, inverter, busbars, and switches. Also include wire size and fuses.

Labelling - In order to complete the schematic drawing, you will have to figure out what each wire is for and where it goes. Once you have established the purpose of the wire, attach a label to identify it. Use marine specific labels or a high-quality labeller. Oils and moisture in the engine room can cause most home office labels to dissolve. While you are tracing each wire, look for signs of chafing or small bumps and change as required.

Many electrical problems start with the connectors, the wires are in a damp environment and are subject to constant vibration. A good connection starts with a good crimp and the secret to a great crimp tool is that it does not pierce the insulation on the wire. Our favourite is the FTZ Cycle Crimp tool that is specifically designed for heat shrink terminals and splices. The bare wire at each end of the connector sleeve must be sealed with heat shrink. Make sure you have a number of different sizes on board, both for correct wire gauge and ring size, along with a good heat shrink torch, such as the Ancor Mini Butane or Butane Pro.

Marine terminals feature pure electrolytic copper to offer the least electrical resistance for best current flow. They are tinned to prevent corrosion from salt and moisture. Ensure that they are UL listed and designed to be used on flexible stranded wire. Look for terminals with a seamless, flared barrel design that makes it easy to insert the wire and gives maximum strength when crimped. A closed-end seals out moisture so your cables stay dry and do not corrode over time. You may be tempted to use less expensive terminals designed for your car or truck but don't.

Along with your crimper, terminals and heat shrink, you should pick up a small tinned wire brush. To ensure you have the best connection possible, keep the posts and connectors free of corrosion. Your onboard fuse kit should include a complete set of both glass and blade (automotive style) fuses. As you are going through and identifying each wire run, make a list of fuses you use. Many marine stores carry small, inexpensive kits with a great assortment. A really great tip is to zap strap or tape an extra fuse in or near the location of the actual fuse. If you have an inverter/charger, make sure you have a Class T fuse onboard as they can be difficult to source while boating

ABYC Standards - If you are thinking of doing any wiring as a DIY project, get a copy of the appropriate American Boat and Yacht Council (ABYC) standards. Boat manufacturers use these standards as an absolute rulebook to design and build safer boats.

There are symbols used by designers and electricians for each device, but if you don’t know the symbols don’t worry. Draw a square, label it with the name of the device (inverter, switch) and show the wires that are connected to it. For DC wiring, positive wires are red, negative wires are yellow (or black in some cases).

Your boat wiring system should have a marine grade main battery disconnect switch which allows you to open the switch to turn everything off at once. There are some devices on your boat that you do not want to shut off when you turn off the battery switch such as the automatic bilge pump, an automatic fire-fighting system, or propane detector. These will be wired directly to the battery and must be protected with an inline fuse at the beginning of the circuit.

On most boats the ground reference is the engine block which is, in turn, connected to the water via the propeller shaft. Determine if you have a bonding buss for the underwater metals, this is a green wire (or a copper strap) that runs through the length of the boat and connects all of the underwater metals. Although grounding and bonding are frequently referred to interchangeably, a bonding system electrically connects the boat’s underwater metal fittings, such as through-hulls, seacocks, rudders and struts through zincs to protect it from corrosion.

While you are putting together your schematic, make a note of each of the components (ie inverter, charger, generator) with the model number. Then collect all of your Owner’s Manuals, we recommend storing them in an accordion file or binder. While all of this information is available on-line, boaters do not always have access to the internet. The back pages of these manuals typically contain a list of common error messages and resets along with proper installation wiring diagrams. Many boaters include the original bill of sale inside the front cover of the actual manual, which includes a description and date of purchase.

Most yacht clubs, cruising groups or Power Squadrons offer electrical courses either in the evening or on the weekend. For those of you who really want to get to the next step of understanding the what and the why of marine electrical, purchase and read Nigel Calder’s book called “Boatowner’s Mechanical and Electrical Manual”, it is the industry "go to" for marine electrical repair.

A good electrical diagram will save you money because there is nothing more beneficial to a technician or mechanic than an up-to-date schematic. It can save hours of trouble-shooting. As well, the process of spending time with your electrical will help you become more familiar with your boat and get you back on the water faster.

About the author: Jeff Cote is the owner of Pacific Yacht Systems, a full service shop delivering marine electrical and navigation solutions for recreational boats. Visit their website and blog for info and articles on marine electrical systems, projects and more: www.pysystems.ca.

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Simple wiring diagram for small craft

Discussion in ' OnBoard Electronics & Controls ' started by CDK , Jun 8, 2009 .

CDK retired engineer

Regularly I've seen questions on this forum about electrical wiring because that is still a mystery for many boat owners. Here is a simple wiring diagram for motor- and sailing boats with one engine and just the basic equipment. There are only 7 wires shown that connect the engine bay; I omitted temp. gauges, rev counters etc. which all have their own wires or cables. The ignition wire is not used for diesels, but there it can be used for the fuel valve. A friendly reader in the US is invited to translate my wire sizes from mm2 to AWG numbers. Parts like the diode bridge and 4-way battery switch are available from Vetus in Europe, I did not look for US suppliers. Drawings are shown as .JPG, but also available as .CDR (Corel draw). Boat owners who have no idea what this all means should of course hire a qualified technician!

Attached Files:

Electrical1.jpg, electrical2.jpg.

apex1 Guest

C OMPACT D UTCH K NOWLEDGE as usual......................

Knut Sand Senior Member

Pretty. I once, somewhere suggested automatic 12 vdc diode light in the engine compartment, biwired together with the bilge pump. Also on the same biwire an alarm/ buzzer located at the steering position (with on/ off switch, normally set at "on") telling the driver that something is going on down under..... In case, it can cive you a few extra minutes....:?: For a low cost....

BillyDoc Senior Member

Nice, Knut, very useful! BillyDoc

Delane Senior Member

Small Boat Wiring Pictures Re-wired my J-24. Basically pulled everything and started over. The goal was simplicity in design and to not use one of those typical switch panels. I used a 100 volt A/C switches. Have any questions, please ask.

Electrical Panel.JPG

Power panel 1.jpg, power, bilge, controller.jpg.

BeauVrolyk Sailor

Delane said: ↑ Re-wired my J-24. Basically pulled everything and started over. The goal was simplicity in design and to not use one of those typical switch panels. I used a 100 volt A/C switches. Have any questions, please ask. Click to expand...

Dry Boat My wiring is inside of a closed compartment and the boat is very dry. Tabernacle mast set up and everything has been re-beaded. Bone dry and I have a solar vent to circulate air.

Delane said: ↑ My wiring is inside of a closed compartment and the boat is very dry. Tabernacle mast set up and everything has been re-beaded. Bone dry and I have a solar vent to circulate air. Click to expand...

CDK said: ↑ Regularly I've seen questions on this forum about electrical wiring because that is still a mystery for many boat owners. Here is a simple wiring diagram for motor- and sailing boats with one engine and just the basic equipment. There are only 7 wires shown that connect the engine bay; I omitted temp. gauges, rev counters etc. which all have their own wires or cables. The ignition wire is not used for diesels, but there it can be used for the fuel valve. A friendly reader in the US is invited to translate my wire sizes from mm2 to AWG numbers. Parts like the diode bridge and 4-way battery switch are available from Vetus in Europe, I did not look for US suppliers. Drawings are shown as .JPG, but also available as .CDR (Corel draw). Boat owners who have no idea what this all means should of course hire a qualified technician! Click to expand...

Only Switches & Fuses The switches are not the breaker type. That little fuse box was the most expensive part of the whole panel at $40 by the time it arrived.

BeauVrolyk said: ↑ I am curious why you've used both circuit breakers and fuses. Is there a specific reason? I have had great luck with waterproof circuit breakers and pretty bad luck with the contacts on fuses. Beau Click to expand...

zamgod Junior Member

CDK, can I ask what the box at the bottom left of your drawing is? The one where most of the wires feed into. Thanks.

That box is the engine compartment. There are only 7 wires connecting it to the rest of electrical parts that is located elsewhere on board, i.e. under the steering console or in the cabin.

TollyWally Senior Member

Very nice basic set up to get people started. I've wondered about taking common cheap ac switches like Delane used and attaching pigtails potting them with epoxy.

gonzo Senior Member

If you have fuel onboard, those switches are not spark protected. That means the possibility of fire or explosion.

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10 Basic Rules for Wiring a Boat

Terry brown.

Jan 08, 2019

After many decades of troubleshooting and repairing boat wiring issues, I’ve become pretty darn good at figuring things out. Today’s boat wiring is one of the most difficult problems you’ll run across due to requirements of the numerous accessories.

For the last several weeks, I have been chasing a problem that has been causing me to lose sleep at night. Every time I think I have it fixed, it seems like another issue pops up and I’m back to square one. I finally conquered it by fixing a ground and using isolated power with a heavier guage wire.

This issue got me thinking that I’m probably not the only one that has experienced these headaches. So I wanted to make a short checklist that might help you if you run into a similar issue. If you’re just getting started working on your own boat wiring, these are some rules you should certainly follow.

Check for a wiring schematic

Unfortunately, not all boats have them. For as long as I can remember, however, Ranger has included one in most of their boats. Rather than purely guessing, having that roadmap can be huge when you’re tracking down problems.

Make detailed notes of any repairs

When adding accessories, it’s imperative to make clear notes in your phone or on a sheet of paper detailing how you rigged it. If a problem arises a few months after you did the work, you’re probably not going to remember exactly how everything is laid out.

I always use color-coded wire with red for positive and black for negative. This takes a lot the guesswork out of the problem solving.

High-grade connections and dielectric grease

Use high-grade connections and always use dielectric grease and shrink tubing on connections. You should never skip this step because it will save you a lot of trouble over time.

A good set of powerful crimpers are an excellent investment, too. Liquid tape is another inexpensive purchase that can protect against shorts. If you’re using electrical tape, make sure to cut it instead of pulling it when wrapping; it will stay on the wire much better.

Tighten terminals

Always tighten battery terminals snugly on the battery posts. A good rule of thumb is to put the smallest leads on the bottom. Use the box-end of the wrench when tightening as it is less likely to slip and bloody your knuckles.

Loose connections

A loose connection can cause a short or more resistance and which will keep your battery from performing optimally. Loose leads can use more power and significantly decrease your battery life.

Always hook up the positive lead first, too. I also replace all wing-style nuts with nylock. They hold much better and are less susceptible to loosening due to vibration.

Buy a good multi-meter

They are inexpensive and can solve a problem quickly. Battery power is DC, or direct current, so set up your meter for that. I also have a battery load tester, too. These can point out a bad cell quickly and save you a lot of time.

Here’s a good selection of multi-meters from Amazon.

Modern electronics eat power

Today’s electronics are big-time power hogs. A good group 27 or 31 battery is the best choice to power them and I strongly ecommend a deep cycle over a starting battery for this application because they hold a longer charge.

Use cable lubrication

When applicable, use lubrication when pulling wire through chases and never pull too hard; this can shred everything in the wire if you’re not careful. If it gets snug during the pull, back up and re-pull as nicks and scarring of the shielding can cause problems down the road including dead shorts.

Not only will your equipment not work, but bad wires can result in a fire.

Use zip ties to bundle wire

A limited amount of zip ties is the best choice as they can snag if wiring need to be worked on.

Never pull zip ties into a chase. Use ferrite rings or RF coils around electronics to dampen radio frequency interference. You can get ‘em cheap and they can be huge for removing trolling motor interference on electronics screens.

Use the proper wire gauge for the application

Load requirement and distance from the battery will help determine proper gauge wire and fuse requirements. For example, a trolling motor on a 20-foot boat should have 4 or 6 gauge wire for best battery utilization.

Every problem cannot be solved with this checklist, but it will give you a good starting place. Study schematics, never be afraid to attempt the job and if necessary, enlist expert help in the form of a reputable dealer or manufacturer and you can cut the down time significantly. Boat owners should never cut corners on wiring jobs.

With a BS in Radio/Television from Illinois State University, Terry Brown had the vision for Wired2fish. He currently serves as the President of Sales for Wired2fish. Prior to that he was director of sales at Bassfan. Brown is not only the best connector in the fishing industry, but he’s also the handiest man around a boat. He can fix just about anything on a boat from electronics to motors and everything in between, and the other team members always rely on him for answers on boat issues. He’s also an accomplished angler, radio host and writer. Another jack of all trades on this avid angling team.

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How to make wiring diagrams for your boat

Smits Marine
Friday, Jul 9, 2021

How To Create A Wiring Diagram For Your Boat

Most new boats include a drawing that outlines the entire electrical system, however these become outdated very quickly as new equipment is installed. For older boats, they can be completely out-of-date or non-existent. Putting together a simple diagram of your boat’s electrical system may seem overwhelming but it isn’t as hard as you think. It just takes time, patience and the realization that it cannot be completed in a day and will be an on-going project.

Where to Start? If you have an existing drawing, we recommend you enlarge it and make clear notes regarding any changes. If you don’t have a drawing, start with a large sheet of paper, and begin with the batteries and the main DC system such as battery chargers, inverter, busbars, and switches. Also include wire size and fuses.

There are symbols used by engineers and electricians for each device, but if you don’t know the symbols don’t worry. Draw a square, label it with the name of the device (inverter, switch) and show the wires that are connected to it. For DC wiring, positive wires are red, negative wires are yellow (or black in some cases).

Boat Wiring Guide With Diagrams. How To Wire A Boat

When you buy a new Jon boat it is usually just a shell. But even after you have bought a new outboard motor to power your boat your job is not yet done. Not only do you need to wire your trolling motor to a battery but if you plan to navigate waters at night you may need to wire up navigational lights as well.

If you include fishfinders, search lights and other electronic goodies to your build then the wiring of your Jon boat can start to seem like a messy and daunting task.

Not to worry we are here to show you the basics of wiring your boat.

Staying safe should be your top priority when wiring a boat!

Plan and organize your boat wiring set-up before you begin – use boat wiring diagrams, 9 key points for wiring a boat switch panel, how to hide the boat wires after wiring a boat, how to insulate boat wires, video with easy practical steps for wiring a boat, additional resources that will help you build up knowledge on boat wiring, organizations to contact to learn more about boat wiring, a simple boat wiring diagram – basic 12 volt boat wiring diagram, 2 battery boat wiring diagram, full spec small boat wiring diagram, jon boat wiring diagram, in conclusion: how to wire boat lights & other boat electrical systems, when you need to know a bit about boat wiring.

If you are ready to do more with your Jon boat than resting on your oars, you will need to add power to your set-up.

Obviously the most common component on a boat, especially a Jon boat, which requires power is the trolling motor.

But, depending on the use of your boat there are a wide variety of other components and accessories that may need to be battery powered.

Battery operated boat components that need to be wired include:

Navigation lights.
Deck lighting and accessory lights.
Bilge pump.
Fish finders and Sonar.
Control panels.
On-board power banks and charging points.

Simultaneously connecting a range of items that a Jon boat needs to perform well for recreational boating, angling or hunting requires some basic electrical knowledge. It also requires a sound and logical approach to wiring your boat.

There are various approaches you can take for your Jon boat wiring set-up, and the approach you take will depend on your resources, the equipment and tools you have to hand and the functionality you want to achieve.

The most important thing to keep in mind before you start any electrical work on your boat is that electric is dangers even from a relatively small 12 V battery.

This is never more important than it is on a boat where you will be surrounded by water.

Boat wiring must be 100% protected from the elements as water is an electrical conductor – electric and water don’t mix well!

Untidy, piecemeal patch wiring jobs are dangerous and carry the risk of damage to your equipment, can start fires or even cause bodily harm or a fatality from electrocution.

55% of US Coastguard investigated boat fires are caused by faulty wiring. So, it is critical that you get the wiring of your boat right.

We have provided this information to give you an approach for wiring your boat effectively.

We strongly advise calling a professional marine electrician or surveyor if you feel out of your depth.

Be sure to also to use an electrician to review and ensure that the work you have undertaken yourself is electrically sound.

Key principles to wiring a boat

In this article we will outline key points and principles for basic wiring of your Jon boat with inclusion of a control panel to keep everything organized.

Wiring your Jon boat is as simple as following a boat wiring diagram. However you need to be aware of how to insulate and protect your electrical wires and connections before you begin.

We have included a video for wiring a Jon boat and several electrical boat wiring diagrams as well as links to some excellent additional resources.

These will assist you in accomplishing this task more effectively.

There is also a list of key pieces of kit that you will need to complete the job and also that will give a more resilient finish to your work.

11 items you will need to wire your Jon boat:

A battery. Ideally you should have 2 batteries though for light electrical loads 1 battery will probably suffice.
A main battery switch.
A control panel.
A reel of marine grade primary wire 8-14 AWG depending on the size of your boat.
A negative bus bar.
Waterproof in-line fuses.
Spiral wrap or wire conduits.
Wire tie mounts.
Marine-grade butt connectors.
Heat shrink wire wrap.

In addition you will need a regular selection of tools including a pencil or marker, wire cutters, pliers, drill, screwdrivers, a heat gun, hole saw and handheld power saw.

Protective eye-wear, gloves and a face-mask are also advisable.

Wiring a Jon boat can appear to be a daunting task when you first approach it but with careful planning and a good guide you can wire your boat in a single evening.

You will need to sketch out or acquire a simple wiring plan for your boat which outlines the layout of the circuitry that needs to be connected. This will help in planning the equipment you need, wire lengths and key connections in your boat wiring. We have included several layout boat wiring diagrams (including a basic boat wiring diagram, a 2 battery boat wiring diagram, a full spec small boat wiring diagram and a Jon boat wiring diagram), at the end of this article.
Ensure you identify and distinguish your positive (usually red) and negative (typically black) terminals on your battery, the control panel, and all the accessories that will become part of your Jon boat wiring set-up. Match like with like at all times.
Power runs from your onboard battery to your control panel from which the power will be distributed to your connected equipment. The switches on the control panel essentially act as circuit-breakers that cut off power to the equipment that is not in use.
You will need to correctly position all accessories and boat equipment, that is to be wired, in the correct place on your boat so you can run adequate lengths of your marine cabling to them. For example, if you are connecting a deck light make sure you position the light in the exact location on the deck where it will be used before you connect it to the battery or you may find that the cable you allocated for the connection is too short!
Lay out and cut all the relevant lengths of cable on the boat according to your set-up boat wiring diagram. How many cables do you need? Cut that amount making sure you have enough length in each cable.
When working with marine grade wire, have plenty on hand, and leave slack in your work for re-positioning, making corrections, upgrades and for making your final connections.
It may be helpful to approach dealing with all positive wiring first and once that is completed focusing on the negative wiring connections afterwards.
Your control panel will have connectors that allow you to splice wiring from your equipment into the control panel. You will need to attach complementary connectors to all wiring coming from your Jon boat equipment.
Wire ends should be connected with appropriate marine-grade butt connectors. Install these heat shrink terminals using a heat gun to create a watertight seal. Heat shrink wire wrap can also be used to group wires together if needed.
The connectors you use must be marine grade (corrosion resistant) and match the gauge of wire you are working with.
A negative bus bar is used prior to connection of the negative wiring to the negative battery terminal to handle your boat’s negative load.

Masses of tangled and improperly connected boat wires are not only unsightly, they are dangerous!

Once you have established your wiring arrangement you can hold all your wiring together using a flexible wiring conduit of appropriate length.

Jon boat electrical wires fastened to hull

You can also use cable ties and cable tie mounts.

In keeping with The American Boat and Yacht Council recommendation make sure electrical wires are secured at a minimum of at least every 18 inches.

3 ways to ensure that your boat electrics are properly protected

Avoid overloading your writing, as this can cause short circuiting and fires.
Fuses and circuit breakers should be sized below the amp rating of the equipment and accessories that are being protected.
The American Boat and Yacht Council advises that they should be located within 7 inches of wire length from your power source.
Do not use wire nuts for connections in your boat wiring, use ring or spade terminals with heat shrink tubing.

This wire is specifically manufactured to withstand the corrosive and abrasive environment experienced on boats.

Electrical tape, sleeves, padding and seals can also be used to insulate and protect your wiring, especially if it is run behind the ribs of the boat.

Videos and resources for successful & safe boat wiring

This is a relaxed run-through of the key steps you need to take to successfully wire your Jon boat.

Boat circuits checklist
Step-by-step guide for wiring any boat
The boat builder’s handbook
The American Boat and Yacht Council provides industry standards and education resources for wiring recreational vessels.

4 Boat wiring diagrams

If you are used to DIY projects on your Jon boat, wiring is going to be a task you will have to encounter at some point.

Despite the apparent simplicity of Jon boat wiring, safety is always paramount. Getting assistance from a professional or at least a boater who is experienced in marine wiring is prudent.

Once you have mastered the principles of safe wiring, the scope of your projects and the performance of your boat will increase massively.

Mick McGrath

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Simple wiring diagram for small craft

CDK retired engineer

Attached Files:

apex1 Guest

Knut Sand Senior Member

BillyDoc Senior Member

Delane Senior Member

Electrical Panel.JPG

BeauVrolyk Sailor

zamgod Junior Member

TollyWally Senior Member

gonzo Senior Member

Simple solar charge design question

Simple electric kayak

simple remote steering

Looking for simple loudhailer

Wiring Diagram Services?

Help with fish finder wiring

Proper wiring advice please

Ammeter wiring