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J121 SPEED GUIDE

North Sails experts Kimo Worthington and Chuck Allen answer questions in this speed guide for the J121 class.

Who sails a J121?

There are several distinct types of people who sail a J121, and most are experienced sailors. Some race the boat one design, some race shorthanded or fully crewed offshore, and some head south and cruise the Caribbean. Many are individualists who have been changing keels and adding sails. In the 2018 Newport Bermuda Race, four J121s raced in three different configurations. The point is, the J121 is a versatile boat that’s ready to sail offshore, and the sailors who do buy one all seem to agree that they’d rather do something other than race windward-leeward course configurations.

The J121 is a versatile boat that’s ready to sail shorthanded and/or offshore.

What’s the ideal J121 crew size?

That’s a trick question for this boat. The most crew you’ll ever need is five or six, total, for an event like Block Island Race Week, but the boat was designed for sailing doublehanded. It sails well without water ballast, but it really shines when you fill the windward tank with 850 pounds of water; that’s like having four or five extra people on the rail. Testing in a strong breeze, we have found the performance is spectacular with a reefed main and inner jib.

The most crew you’ll ever need on a J121 is five or six, and the boat is designed for doublehanding.

How do you move a J121 around between races?

The boat is 40 feet long and weighs 11,900 pounds with 4,800 pounds of ballast, so you’re going to move this boat on its own bottom or with a professional trucker. It’s equipped with a 30hp Yanmar diesel and saildrive, so it moves along well under power. And remember, even with only a couple of delivery crew you can add water ballast and power right up.

What sails are recommended?

The boat is billed as a five-sail boat. There’s one mainsail and two jibs, one that roller-furls on the headstay and the other that roller-furls on the inner headstay. The boat has an extendable sprit that can fly a Code Zero/gennaker on a roller-furler, or you can use an all-purpose asymmetric spinnaker. For a closer look at all these sails, view the

North Sails product page

, but it’s worth talking to a North class expert to make sure you match your sails to sailing style and location. Other speciality sails include smaller and flatter spinnakers and spinnaker staysails.

J121 Tuning

What are the keys to rig set-up.

The rig is set up for heavy air with 52 on the uppers.

Any tricks to tuning a boat with multiple headstays?

The inner jib is a big upgrade for most people. Now, instead of wrestling to set and douse a heavy air jib, you can raise and furl it anytime on the inner headstay, which has a halyard lock-off. The lower end of the inner headstay has a 3:1 purchase, and before deploying the heavy air jib we grind the daylights out of it—enough to make the forward headstay just start going slack.

What’s involved in setting up and hoisting the mainsail?

The mainsail has luff slides that live on the mast track. Before bending them on for the first time, tension and secure the battens and check that the main halyard purchase has no twists. Be sure the headboard is on the track and that the battens aren’t too tight. Check that the pressure is evenly distributed between the bottom car and the tack point, which is adjustable. You should be able to hoist the sail by hand; don’t use a winch, because you might over-hoist the sail.

With track cars and batten tension set correctly and no twists in the two-part halyard, you should be able to hoist the sail by hand.

What’s involved in adjusting the bobstay tension?

The bobstay on a J121 counters the upward pressure on the pole from the Code Zero or spinnaker, and your goal is to keep the pole projecting forward in alignment with the sheer line of the hull. The adjustment is in the center of the bobstay and can be set at the beginning of the season. Be sure that the pole is all the way out and that you have a mark on the pole control line before adjusting the bobstay tension.

When the pole is extended all the way, there should be a ½ inch between bulkhead and turning block.

J121 Upwind Sailing

What sail combinations do you use upwind on a j121.

One of the exciting things about this boat is that you can use different combinations depending on the situation. Standard upwind configuration is a full main and J1 (the bigger jib). As the wind builds, you might reef the main and keep the big jib going; offshore, you might not reef and use the inner jib instead. In enough wind, of course, you’ll use the inner jib with a reefed main.

The inner jib sets up on the inner forestay. Note the furling line, which should be rigged along the windward side.

Upwind, where does the crew sit?

The goal is to keep your “bow knuckle” in contact with the water. So if you have a full crew of five or six, in light air most should be sitting well forward. At 10 knots, you’ll still have two crew sitting in front of the shrouds. At 14 knots, one crew is forward; at 18 knots, everyone will move back to normal hiking position.

If your weight is too far aft, the bow knuckle will always be out of the water.

Upwind on the J121, when do you add water ballast?

As soon as you’re heeling 18 to 20 degrees, start adding water to the tanks to maintain a constant angle of heel. With a full crew, that’s likely to be around 15 knots true wind. Doublehanded, it might be at 12 knots. Don’t forget to add water when you’re cruising or doing a delivery, too. Not only will it reduce heel and improve speed, it can also settle the motion of the boat.

The boat is heeled too much; it's time to add water ballast (or depower).

How do you trim the main and jib upwind?

In light to medium air, center the boom by raising the traveler, and then sheet as hard as you dare to get some rudder angle and heel the boat over 12 to 15 degrees. Don’t head up and slow down; let the foils work and the boat will gain height. Look for the top telltale to be stalling about 25 percent of the time in light air, 50 percent in medium air. When the breeze comes up, keep the traveler high; ease the sheet to add twist when you have trouble reaching the target numbers.

In medium air, the traveler should be raised well to windward to keep the boom on centerline.

For the jib, add three marks on the spreader that line up with the leech for eased, normal, and tight trim. We also recommend marking the deck for the inhauler to set the lead angle between 7 and 12 degrees. Set the angle tightest in flat water and moderate breeze.

The inhauler is set at 8 degrees.

How do you trim the heavy-air jib on the inner headstay?

As mentioned, you need to crank on the inner headstay until it is carrying about three-quarters of the rig load and the forward headstay loosens just a little. The jib sheets lead to the same floating lead as the J1 and you will still trim to the same spreader marks, as well as watching to keep the leech telltales flowing.

What are the key gear changes for sailing upwind?

We’ve developed a playbook for five wind speeds. It goes like this:

• Zone 1 (0-8 knots): You’re looking for power; move weight forward, and keep backstay and headstay loose and outhaul eased. Try to get some heel; pull in the mainsheet.

Start moving weight to the rail. Pull on backstay, jib halyard, and outhaul. Sail shape should still be deep. Trim the mainsheet hard.

Max outhaul, backstay, cunningham, and jib halyard. Find “magic heel angle” (12 to 15 degrees). Crew weight starts moving aft, sail shape becomes flatter. Consider moving jib leads back.

Now you need less power. Consider a single reef. All controls should be maxed. Find the “magic heel angle” (12-15 degrees). Sail shape should be really flat. Trim sails so the boat is easy to steer and fast; ease main (if it flogs, open the slot by easing the jib or moving the jib lead back).

Smaller jib on inner headstay and/or reefed main. Strive for “magic heel angle” (12-15 degrees). Make the boat easy to sail and keep it going fast through the water.

The Magic Heel angle for the J121 is 12-15 degrees.

J121 Reaching and Downwind Sailing

What are the best j121 sail combinations when reaching.

When close reaching in lighter winds, an eased J1 is very efficient because it has leech battens. As you bear off, switch to the Code Zero well before you think it’s time—about 70 to 80 degrees true wind. By easing the tension on the front of the Code Zero and letting it scallop you can sail even higher, but don’t overdo it. Crew should remain forward, in upwind position.

Not all Code Zeros are the same.

Learning the crossover from spinnaker to Code Zero is a key to best reaching speeds on the J121.

What are the crossovers between downwind sails?

Learn your sail crossover chart (see below) to determine the correct angles for the two jibs, Code Zero, and A3 and A2 spinnakers—and keep the leech of your main and headsail well-matched.

The main and Code Zero leeches are well-matched, a fast combination.

he top end of Zone 3 (18 knots) from 90 to 125 degrees true wind angle, sail with a double-slotted Code Zero and inner jib. In winds over 18 knots, you may be able to carry the combination to 135 degrees. If you have one, you can use a spinnaker staysail at 135 degrees and deeper. When it’s really windy, an A4 (small spinnaker) and inner jib can be a very effective double-slot reaching combination.

Where does the J121 crew sit when sailing downwind?

Under spinnaker in light air, crew weight should be forward and on the leeward rail, similar to upwind sailing. As the breeze comes up to 8 to 10 knots, you’ll sail with three in front of the shrouds to windward. For wind in the low to mid teens, those crew come aft of the shrouds. When power reaching, they will move halfway back to companionway, or even right back to the skipper.

Both upwind and downwind, light air crew position is well forward to keep the bow knuckle touching the water.

Video of power reaching:

J121 Maneuvers

How do you set and drop the code zero.

Always hoist a Code Zero on the weather side of the headstay. Raise it until the tack is 1 meter above the pole and tie off the halyard, then tension the luff via the 2:1 tack line. The Code Zero should run through a twing and then aft to the primary block. Unfurl when ready.

To drop a Code Zero: Furl the sail and bear away, tensioning the windward sheet to pull the sail to weather of the headstay as you ease halyard. Accordion it onto the foredeck. When dropping the sail while going upwind, you may have to luff up to get the furled sail to weather of the headstay.

How do you furl the Code Zero?

The key to furling this big sail when it’s windy is to ease the sheet far enough to take the pressure off the sail—but not so far that the sail completely luffs. Maintain a little tension to ensure a tight furl.

How do you reef the main?

Mainsail reefing is straightforward on the J121. Ease the halyard and take up the tack line until the new tackpoint is snug. Next, trim the reefing line until the clew is snug against the boom and put a sail tie around the loose sail aft. Then raise the halyard enough for proper luff tension.

How do you change from J1 to inner jib?

Hoist the furled inner jib to its halyard lock with the tack eased off one meter. Then tighten the tack until the luff rope is quite tight—with significantly more load than the headstay. Keep the tack line on a winch for further adjustment and deploy the inner jib, then furl the J1. Your furling lines should run along the weather side of the boat.

How do you set the J121 spinnaker?

The key jobs when setting the J121 spinnaker with a crew are as follows: The sail starts in the bag, typically zipped up and tied off to the foredeck. Bear off to hoist, and raise the sail at least halfway before pulling out the tack and pole. The driver should call for the set when the boat is sailing at the right angle—if windy, bear off so it’s well hoisted before it fills. Also, don’t furl the jib(s) until the kite is up and flying, or you may mistakenly furl a lazy sheet or other part of the spinnaker. For shorthanded sailing, use a snuffer system or spinnaker zipper system.

How do you jibe the J121 spinnaker?

We recommend an outside jibe, so the clew travels forward around the luff before sheeting in on the new leeward side. The new sheet must be in the “gybulator” or “sheet catcher” before the jibe begins so it doesn’t accidentally drop below the sprit pole. (The gybulator is mounted about six inches above the tack on the luff of the sail.)

The “gybulator” is located about six inches above the tack and the sheet must be in it for jibing. https://youtu.be/nZjE3G0vN7U

Any tips on the starting line?

Be careful not to sail too slowly when approaching the starting line. If your speed falls below 2.5 knots, it can take a long time to get back up to speed and you’ll make a lot of leeway until the water starts flowing effectively over the foils again.

How do you tack a J121?

In light air, roll tacking the J121 is important; use all the crew weight you have. When using water ballast, plan ahead and start shifting the water from one side to the other a minute or two ahead of time. The goal is to come onto the new tack with the water ballast already transferred.

How long does it take to fill, move, and empty the J121’s water ballast?

It takes five minutes to fill the windward tank, one minute to transfer it to leeward before a tack, and two minutes to empty the tank.

The water ballast tanks are filled and drained with three control lines.

What are the keys to sailing a J121 well?

Keep your crew weight out of the aft end of the boat.

Plan ahead for tacks so you have time to shift the water ballast.

In most breezes, max out the backstay to improve headstay tension.

What is the coolest thing about sailing J121s?

We think what’s best about the boat is all the different types of sailors it attracts. J/Boats listened to its clients and introduced a boat that people can sail fast with their families or a few friends, either near shore and for long-distance adventuring.

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2023 J Boats J/121

The J/121 is a 40’ offshore speedster that can be day raced or distance sailed by just 5 or fewer crew…. the best short-handed J ever…. capable of winning on any race track while also excelling in daysailing and weekend mode. Here’s a boat, class and program that redefines sailboat racing as a recreation and shared adventure with friends, reducing the focus on specialization and athletic short-course W/L racing.  The J/121 fulfills the growing need to simplify life and reconnect with those you really want to sail with on a boat that’s pure magic to sail.

Why a New 40 Footer? Sailing continues to adapt to the rapidly changing demographics, technology and social trends of an ever more hectic world.  As our lives become more fast-paced so does the need to escape from the time constraints, pressures and burdens.  “Always on, always connected” is leading the drive to “get away” to a place that can nourish and recharge the soul.  Nowhere is that more evident than the extraordinary growth of adventure travel, providing people a much needed outlet through outdoor, shared experiences with others.

The challenge is trying to align 8-10 people onto the same schedule.  This obstacle alone is impacting keelboat racing participation across the board in most areas. Just as technology is making it easier to sail, the over-reliance on crew is making it more complicated.  Two of the positive growth areas in sailing today are one-design class racing in trailerable boats, and short-handed day racing and fun point to point events.   The global success of the new J/70 is a direct result of pent-up demand for an affordable one-design with a pre-planned circuit and easy entry.  The travel and event logistics for four people are infinitely easier than that of 8-10.  For those sailing larger keelboats, it’s the charity pursuit races and day distance events like San Francisco’s Three Bridge Fiasco that are becoming increasingly popular.  And it’s no surprise why.  These events pack a lot of sailing fun and adventure into more acceptable, smaller doses that require less practice and time to manage.

The J/121 is designed with both of these trends in mind.  Imagine a fleet of high- performance, offshore-capable speedsters sprinting along point-to-point, around- the-island, and adventure-style races with half the normal crew size, with owners enjoying a “dream circuit” of events that tie into regional “classic” races that everyone aspires to sail in.

Specifications

Basic boat info, contact form submission, more from j boats, send request.

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Sailboat specifications

• Last update: 25th April 2020

J/121's main features

• 2018: Sailing World - Boat of the Year: Best Crossover
• 2018: SAIL magazine - Best Performance Boat 30 to 40ft

J/121's main dimensions

J/121's rig and sails, j/121's performances, j/121's auxiliary engine, j/121's accommodations and layout.

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2023 J Boats J/121

The J/121 is a 40’ offshore speedster that can be day raced or distance sailed by just 5 or fewer crew…. the best short-handed J ever…. capable of winning on any race track while also excelling in daysailing and weekend mode. Here’s a boat, class and program that redefines sailboat racing as a recreation and shared adventure with friends, reducing the focus on specialization and athletic short-course W/L racing.  The J/121 fulfills the growing need to simplify life and reconnect with those you really want to sail with on a boat that’s pure magic to sail.

Why a New 40 Footer? Sailing continues to adapt to the rapidly changing demographics, technology and social trends of an ever more hectic world.  As our lives become more fast-paced so does the need to escape from the time constraints, pressures and burdens.  “Always on, always connected” is leading the drive to “get away” to a place that can nourish and recharge the soul.  Nowhere is that more evident than the extraordinary growth of adventure travel, providing people a much needed outlet through outdoor, shared experiences with others.

The challenge is trying to align 8-10 people onto the same schedule.  This obstacle alone is impacting keelboat racing participation across the board in most areas. Just as technology is making it easier to sail, the over-reliance on crew is making it more complicated.  Two of the positive growth areas in sailing today are one-design class racing in trailerable boats, and short-handed day racing and fun point to point events.   The global success of the new J/70 is a direct result of pent-up demand for an affordable one-design with a pre-planned circuit and easy entry.  The travel and event logistics for four people are infinitely easier than that of 8-10.  For those sailing larger keelboats, it’s the charity pursuit races and day distance events like San Francisco’s Three Bridge Fiasco that are becoming increasingly popular.  And it’s no surprise why.  These events pack a lot of sailing fun and adventure into more acceptable, smaller doses that require less practice and time to manage.

The J/121 is designed with both of these trends in mind.  Imagine a fleet of high- performance, offshore-capable speedsters sprinting along point-to-point, around- the-island, and adventure-style races with half the normal crew size, with owners enjoying a “dream circuit” of events that tie into regional “classic” races that everyone aspires to sail in.

Specifications

Basic boat info, contact form submission, more from j boats.

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San Juan 21 Review

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This is a review for a 1976 San Juan 21 Mark II. I bought my boat 4 years ago and had a hard time finding reviews for it at the time, so I am just returning my bit of info into the intertubes for others to find. I won’t be monitoring this post reliably. The SJ21 is a “good old boat” in that the maker is no longer around, but many of these were produced and they are not especially hard to come by. There is still a solid following of these boats and there are several racing classes out there still active. I contribute and use the SJ21 forums and they are a great resource which is attractive if you are a new boat owner in that you can get support if needed. This wasn’t my first boat, but it was my first boat of this size and complexity, so the forums have been invaluable. Mine is a Mark II, distinguished from the Mark I by the fact that coach roof and the deck are all at one level continuous to the edge of the boat. The Mark I has a more traditional look with a raised coach roof, though presumably less interior space. There are Mark IIIs that look the same as the II, but I am unsure of what differences exist. Mine was built in 1976 is a mid-lifecycle example. San Juans are moderately well built compared to some other cheaply made boats, though I am sure there are higher quality boats made. The fiberglass is relatively thick and the construction feels durable. The deck and transom have balsa cores which, like all cored hulls, can be a problem if not properly maintained. This is not unique to the SJ21, it is a generally accepted build practice to add strength to the deck by sandwiching a ¾ inch piece of wood between two skins of fiberglass. When bolts or other hardware are put through this sandwich, water will eventually creep in if not properly handled and rot out the inner wood. More on this later. It is a light boat compared to many of its competitors which make it quick in light airs. The reason it is light is that the keel is only about 400 lbs. It is a retractable keel that swings up into a raised trunk inside of the cabin. When fully retracted, the boat only draws about 12 inches of water, allowing it to beach easily. This aspect is great for my use as it makes shore stops effortless. It also means you don’t need to keep a dingy or tender onboard, assuming you live where sandy shores are the norm. The retractable keel also makes running aground a non-issue as you can just crank up the keel. If you are gunkholing and already have the keel up and you run aground, just step out and push it off. There are downsides to the light keel as well though. This boat is very tender. I primarily cruise and day sail with my boat. The best days sailing to me include steady wind where we make solid progress without having to mind the tiller constantly. I started on small boats and know how to handle them, but sometimes you just want to drink your beer and not actively sail. Certainly there are days that this happens, but a heavier keeled boat would be more stable in heavy or confused wind. I didn’t realize now much difference some weight makes until I had my parents onboard recently on a pretty windy day. These winds would normally have me turning upwind and minding the mainsheet in gusts, but the extra weight allowed the boat to take gusts without healing excessively. I assume this is what a heavier keel would do. Conversely, if you are new to sailing and want to learn to sail competitively I think the tender nature is a good thing as it will teach you to sail better and more efficiently. The cockpit on the Mark II is reasonably spacious and one of the reasons I liked this boat. The Mark I has even more cockpit and less cabin space which might be attractive if you primarily day sail. I can fit my wife and two kids on board with no problem, though 4 adults are too much. My son (11) and I have ample room to maneuver; he even lays down to sleep regularly. The mainsheet is on the floor at the stern of the cockpit when traditionally rigged. I have tried other rigs, but like the factory mainsheet rig best. I have re-rigged my boat to lead all the lines to the cockpit. This is not uncommon and a nice upgrade when done well, but the quality can vary and it means more holes in the deck for potential leakage if not done properly. There are no safety stanchions on this boat and going forward in moderate seas can be a bit harrowing. Even with lines led aft, this seems inevitable. There is a lazarette in the back of the boat for storing gas, anchors, etc. It is sealed off from the rest of the cabin so you can store semi-noxious materials there without concern. The original transom has a built in motor mount though many replace them with retracting mounts. The standard mount requires a long shaft outboard, which I have and works great. Many racers use a 2 horse motor, but I have a 2-stroke 4 horse Yamaha that is awesome and I wouldn’t want any less engine on the back. In my experience, when you need an engine, it is always better to have a little extra umpf and the 4 horse is plenty. The cabin on an SJ21 is moderately cramped. If you are coming off a sunfish, it will feel like a palace and in general when I got this boat it felt huge compared to my previous boats. However, humans are fickle beings and now it feels small at times. There are two coffin berths where the majority of your body is under the cockpit seats while lying down. These double as the general seats when below. There is no standing headroom. The keel trunk sticks up in the middle of the cabin and you pay for the convenience of shallow water depth by this intrusion. This limits cabin floor and storage space as well since you must have containers that can fit between the trunk and bunk if you want to store supplies for a cruise. There is a compression post and a forward v-berth with a forward hatch above for ventilation and pulling sails down. Two boxes are built into the hull, one for a house battery and one just for general storage. Under the v-berth is also a shallow storage area. The floor of the cabin is the bottom of the boat and there is no false bottom. In turn there is no plug for draining water which was new to me. Thus when water finds its way in, you must bail and sponge it out. Water will get into the boat through the keel trunk depending on the waves, wind and the last time you replaced the keel gasket on the bottom of the boat. Not a lot of water, but it happens. There is a basic electrical system that consists of cabin lights, accessories and running lights. Most boats will have neglected this and it will need repair/replacement if you intend to cruise. Racers won’t need any of this. The battery box is slanted at the same angle as the side of the boat and makes securing the battery a chore. Re-wiring the boat is not complicated though I guess it depends on your electronics skills. In general, this boat should be considered a competent daysailor with the potential for overnight excursions. I sailed my family of four to Shackleford Banks and Cape Lookout on the NC coast, sleeping overnight at Shackleford. We all fit, but the wife has since declared she has no interest in doing it again. Me and the boy have done a 2 night trip to the coast since and loved it. Just think of it as car-camping in a hard topped, spacious tent and you will be happy. If you want to hang out below in a yacht, you will be disappointed. The other important aspect of the keel set up is trailerability. The boat sits very low on the trailer, below the roof line of my Toyota Highlander. It is light and thus doesn’t require a real truck to pull (see Toyota Highlander). We have a reasonably steep ramp at my marina and I have never had a problem with my front wheel drive 4-cylinder. It also tows well as a result of its low profile. Putting in and taking out is easy since you do not have to have a deep water ramp and no tongue extension is required for this boat. I have never had a boat with the keel trunk on the bottom as many of the SJ21 peers have, but hitting the slot on the trailer seems like it would be tough compared to the ease with which the SJ slides on. I believe time spent sailing is directly related to how easy a boat is to set up, particularly a sailboat. Therefore, I leave mine on a trailer at a marina with the mast up at a local lake. If I had to set up the mast every time I wanted to sail, or to deal with a significant keel that make loading and unloading a problem, I would sail less. This boat is easy to hook up and drop in if you leave it with mast up. It takes me 30minutes from pulling up to my boat, to pulling sails up after having parked the car and motored away from the dock. My trailering set up allows me to sail often on a local lake, but I can also strike the mast and set her up for a 2-hour coastal haul if needed. I can easily put up and take down the mast now that I have practice and I use the jib down haul I installed a brake. Once mastered, you can have her ready to ride in about 30 mins and another 30 mins to set her back up. Keeping it at my house or off site storage would quickly sap my interest (not to mention the waiting family) in day sailing unless I devoted the whole day. Parts are no problem with this boat as there is still an active aftermarket and most parts have found modern replacements by major manufacturers. I have completely restored my boat from stem to stern by myself in my garage, including new paint, hardware and running/standing rigging. The boat is exactly 21 feet and I have been able to shoe horn it into two different garages for the winter on a homemade lift. I successfully dropped and re-fit the keel by myself as well. Working on any boat of this size is a lot of work and not for those with a passing fancy, but the SJ21 does not pose any specific challenges. When looking for a SJ 21 to buy, much of the advice used for other boats applies. That said, the cored deck and transom to me is the most critical. Don’t trust the guy selling. Have him pull the lower gudgeon to see if he has properly sealed it, or if there is water intrusion in the transom. Make your purchase contingent on drilling several small holes from inside the cabin up into the deck, but not penetrating the deck to check on the core. White wood is good, dry brown wood is okay, wet or soggy mush is a potential deal breaker. I wouldn’t personally buy one with more than a third of the deck containing any moisture. Sure you can re-core the deck, but it will cost you much more than finding a better boat. Thankfully my deck was in great shape despite my ignorance, but I had to completely rebuild my transom (it sucked). Sails are expensive. I am still using the original sails that came from the manufacturer and wish I had haggled down the price more as a result. They work, but are tired. Check out all the hardware, is it original? If so, it should probably be replaced and is a bad sign for core issues if the owner has never re-bedded them. In general I think the SJ 21 is somewhat unique in its class. There are an abundance of 21 foot pocket cruisers, but only a few other large scale manufactured boats offer the flush keel in this length. It does well in races in light airs, but is pretty tender in heavier air. I think it is a great boat to step into from dinghies given the easy of trailerability and the ability to overnight. Just do your homework and don’t buy a deck re-core project unless you know what you are doing! Cheers, Kuriti  

Excellent first boat. Good for daysailing on protected waters, or longer cruises for hardy souls in reliable conditions. The SJ21 came in two versions: a doghouse coachroof (Mk1) or a flush deck (Mks 2&3). The former has a longer cockpit (seats 5) but small interior; the latter has a shorter cockpit but more space below. Sitting headroom, barely; not much stowage. Keel winch awkwardly located in the V-berth. The SJ21 sails like a big dinghy & is best treated that way. Its sailplan is balanced, with slight lee helm in low winds and slight weather helm above 18 kts or 20 degrees of heel. The boat generally rounds up if overdriven. It prefers winds between 6-15kts and has a narrow groove of 10-15 degrees of heel. It moves well in light air. The flat bottom and swept keel mean the boat points only so-so. It is very quick from a close reach to a deep reach but gets a little loose in a following swell. It is not overly prone to broaching, and indeed the SJ21 has no glaring vices at all. The SJ21 sails brilliantly on main or reefed main only, and we have survived 50 kts that way on flat water. Its bluff bows make it slam a bit to windward and struggle in chop. With the keel up, the boat floats in 8" of water and is easy to launch and, at ~2000# on the trailer, a small vehicle can tow it. Build quality is so-so. Most common problems are wet balsa in decks and transom; leaking portlights; and wobbly keel pivot bolts. It is a simple boat to maintain and inexpensive to own. Typically sells for $2000-3000 USD. Look for upgrades like backstay adjuster, improved mainsheet system, braking keel winch, larger stern cleats, and rebedded deck hardware with proper backing plates. If sailing qualities are more important than interior space or foul-weather hardiness, the SJ21 is a good choice. Click to expand...

Hey Diarmuid! I didn't realize that review was yours. I read it long ago and always remember the line about heeling as my son is climbing the gunnel in a gust. I thought a review on the SJ21 forum would be viewed as biased, so just pitching in my 2 cents for anyone else. Basically, I didn't want to work yesterday morning....  

Great info!! I have been sailing my MII for five years now. Her name is NAUJA, I refurbished her myself. I sail her on Lake Erie and I am considering the loop next year or so. Thank you for this article!  

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San Juan 21

San Juan 21 is a 20 ′ 6 ″ / 6.3 m monohull sailboat designed by Don Clark and built by Clark Boat Company between 1970 and 1977.

Rig and Sails

Auxilary power, accomodations, calculations.

The theoretical maximum speed that a displacement hull can move efficiently through the water is determined by it's waterline length and displacement. It may be unable to reach this speed if the boat is underpowered or heavily loaded, though it may exceed this speed given enough power. Read more.

Classic hull speed formula:

Hull Speed = 1.34 x √LWL

Max Speed/Length ratio = 8.26 ÷ Displacement/Length ratio .311 Hull Speed = Max Speed/Length ratio x √LWL

Sail Area / Displacement Ratio

A measure of the power of the sails relative to the weight of the boat. The higher the number, the higher the performance, but the harder the boat will be to handle. This ratio is a "non-dimensional" value that facilitates comparisons between boats of different types and sizes. Read more.

SA/D = SA ÷ (D ÷ 64) 2/3

• SA : Sail area in square feet, derived by adding the mainsail area to 100% of the foretriangle area (the lateral area above the deck between the mast and the forestay).
• D : Displacement in pounds.

Ballast / Displacement Ratio

A measure of the stability of a boat's hull that suggests how well a monohull will stand up to its sails. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing and is an indicator of stiffness and resistance to capsize.

Ballast / Displacement * 100

Displacement / Length Ratio

A measure of the weight of the boat relative to it's length at the waterline. The higher a boat’s D/L ratio, the more easily it will carry a load and the more comfortable its motion will be. The lower a boat's ratio is, the less power it takes to drive the boat to its nominal hull speed or beyond. Read more.

D/L = (D ÷ 2240) ÷ (0.01 x LWL)³

• D: Displacement of the boat in pounds.
• LWL: Waterline length in feet

Comfort Ratio

This ratio assess how quickly and abruptly a boat’s hull reacts to waves in a significant seaway, these being the elements of a boat’s motion most likely to cause seasickness. Read more.

Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam 1.33 )

• D: Displacement of the boat in pounds
• LOA: Length overall in feet
• Beam: Width of boat at the widest point in feet

Capsize Screening Formula

This formula attempts to indicate whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions. Read more.

CSV = Beam ÷ ³√(D / 64)

Clark Boat Co. had previously built a number of One-Design Dinghy’s, but this was the first ‘SAN JUAN’ and a huge success. Designed displacement was 1250 lbs. but it was found that most ended up at 1400 lbs. Thanks to Samuel Tricky for providing corrected information for this and number of other boats in this category.

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