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Do-It-Yourself Small Trimarans

When we say, Do It Yourself Trimarans, in this post, we’re not kidding. Just recently, I was introduced to home-boatbuilder / weekly-sailor Frank Smoot. And as things turned out, meeting Frank became a real treat.

He didn’t just build 2 very low-cost small tris (for himself and his wife) — he designed them. (Not exactly an undertaking I’d recommend for most guys).

But see for yourself how things ended up.

Frank generously shares the following information (including photos and YouTube video) with us small trimaran fans. And he has even set up a website at www.DIY-tris.com to encourage others to pursue this outdoor passion … without spending a fortune.

Awesome! :-)


Do-It-Yourself Small Trimarans
by Frank B. Smoot

About two years ago, I was out cruising in the Gulf (Of Mexico) in my Kayak (a Pungo 140) a bit north of Sarasota. It’s a pretty quick boat, and I was paddling hard to catch I guy in what I later learned was a Sunfish. I was paddling my arms off, and he was just sitting there doing nothing. But I never even got close to him, so I thought,”What’s wrong with this picture.”

My wife, Laura, also had a Pungo 140 kayak, and I thought it might be cool to try and make a catamaran out of them, and rig a sail and rudder to it. It was, at best, a poor sailboat — especially because, at the time, I had no clue about CE (center of effort), CLR (center of lateral resistence), and the other important stuff you need to know to make a sailboat go where you want it to go.

I should mention that there was another BIG inspiration for going multihull. Laura and I briefly (very briefly) owned a Laser II, an old but quick and nimble monohull designed back in the ’70s. Since we knew next to nothing about sailing, we dumped it within the first 30 minutes of sailing it.

This was pretty traumatic, not to mention embarrassing. And since we’re both over 60, we decided that very day we wanted to “sail flat.” So I set out to build my first non-kayak-based catamaran. (Long story there, including snapping off a wooden mast like it was a toothpick.) It was a real dog to sail, but a great learning experience!

I am a cheapskate by nature, and I spent much of my working life as a remodeling contractor. I always use the least expensive materials that will produce a quality job. I kept hearing about “marine plywood” and “okume” and all that stuff, but I thought the price was ridiculous. And besides, nothing I built at that point was probably going to be worth keeping long enough to worry about rot :)

What really got us both into trimarans was when we rigged up sails, rudders, and outriggers to our Pungos. Crude, but amazingly effective. If you really want to learn about tris, cheap and quick, get an old kayak and rig it to sail.

I have now built about 10 different boats, the first several being catamarans, and all the recent ones being tris. The two latest ones (including the one in the video) are 16′ long, very narrow, and are much quicker, smoother, and drier than anything I built before. They also tack and point very well.

Frank's DIY Trimaran Under Construction

DIY Trimaran's Amas Half-Built

First, I built one for me, than another, lighter one for Laura. They have very different hull shapes, since everything I built is intended as a test-bed as well as a pleasure boat. Mine has gone 13 mph with just a single 84 sq. ft. sail on an unstayed, home-brew mast. Her boat is probably as quick, and was going at least 11 mph when she shot the video — with both hands free, I might add.

Our local bay gets very rough when the wind is westerly, and that interferes with both enjoyment and boat speed. So we like to sail most when the wind is at least 7-8 mph or more, up to about 15 mph, and not from the west.

Tortured Plywood Trimaran Amas

DIY Trimaran Boat Seat

Probably my favorite current story is when the video (shown below) was shot, just about a week ago. I forgot to bring the Garmin with the GPS, so our speeds are just estimated. But since I sail both of our tris several times every week, I’m good at estimating speed now. That day, the wind was northwesterly at 8-12 mph, so the waves were smallish and we could go fast without getting wet.

DIY Trimaran with 84-Sq Ft of Sail (Pre-Leeboards)

DIY Trimaran with Laser II Rig

Her hull is essentially flat on the very bottom, where mine is a V-hull. I had thought mine would be quicker, but hers planes very easily and goes faster with less sail. On that day, her tri was running our 84 sq. ft. sail, and I had just set my boat up to run the Laser II rig (124 sq. ft. with main and jib) that you see in the video. My mainsail was 89 sq. ft., and on that alone, I couldn’t catch her boat. (She’s an excellent, very intuitive sailor.)

Laura's DIY Trimaran is Slicker n' Quicker

DIY Trimarans on Trailer

Only when I put up the jib was my boat faster. And even with my full rig, I couldn’t catch her running downwind. On balance, we have concluded that a single, unstayed mast with a sail in the 80-90 sq. ft. range is perfect for these little boats. The much bigger Laser II rig is quicker, to be sure, especially close hauled. But it’s much more of a hassle to set up, and makes the boat lean more because the shrouds needed to be attached to the amas (outriggers). Plus, you have to tend two sails. Bottom line: one sail on one unstayed mast = best bang for the buck!

Laura's DIY Trimaran (w 84 Sq. Ft. of Sail)

My biggest regret is that I didn’t start doing this years ago! Of course, I also didn’t live in FL until about 4 years ago. This area is small sailboat heaven … as long as you can deal with some very shallow water now and then (another major factor influencing my designs).

I can sail 12 months of the year down here, as long as I can keep from getting splashed too much in Dec-Feb. That’s why my boats have lots more freeboard than our kayaks. Laura loves to sail, but maybe once a week. I’m a true “tri-junkie,” and have been known to take a boat out every day. Of course, being just 10 minutes away from a beach launch point is a big help. But I’d find a way no matter where I lived. When the wind is right, there’s just nothing like a small tri. Cleat the mainsheet, steer with your feet, and your hands — and spirit — are instantly free!

I’m planning lots of articles about what I’ve learned and done (and what I’ll do in the future) at www.DIY-tris.com. I want to spread the word to others, and help inspire them to build and sail small tris!


  1. Very nicely done…simplicity and function combined to create a naturally elegant form.

    While obviously it’s easy to get in over one’s head designing boats from scratch and testing the results can be quite hazardous for someone who doesn’t already know what they are doing, it’s worth noting that multi’s and especially tris are about as forgiving as boats come in this regard, not just due to their inherent stability and flotation but also because of their modular nature- you have some leeway (no pun intended) when a particular part needs to be re-engineered and can even have completely different configurations of amas, rigs, etc. for different conditions uses.

    As for the smaller rig being a better overall option, determining sail areas and aspect ratios is somewhat counterintuitive with multis; larger and especially taller rigs reach a point of diminishing returns very quickly and with no big pendulum of a weighted keel to counteract their forces can have a far greater effect on boat motion and seahandling than adding an extra few feet to a monohull’s rig does, not to mention the stresses involved when you start moving chainplates outwards to support that taller stick (I’ve sailed original Pivers that I thought were going to come apart from mast pumping due to hideously ill-placed standing rigging).

    Many early modern tris suffered greatly from a tendency to just assume that if a rig was good for a monohull it’d be good for a trimaran, and in my opinion far too little effort has gone into developing better rig options that update the positive aspects of ancient Polynesian sail forms while taking advantage of modern materials and construction techniques….I’m not knocking the choice of bermuda rig here; they’re plentiful and relatively cheap and easy to acquire but their development had nothing to do with what a multihull needs, and ultimately they hit a brick wall when the boat starts making its own wind, if they make it that far :)

  2. Great stuff…. and located close to me, too! I’ll be looking up Frank in the near future to see his boats, view his construction methodology, and just talk boats (and, just POSSIBLY challenge him to a race against Clarity!).

  3. Thanks for taking the time to make a post, guys. I much appreciate the kind words. As I note on my site, I am very new at this, and very far from being professionally knowledgable. Tris are indeed very forgiving, which is why I love them. I agree with Ian that tris may do best with sails specifically built for their unique characteristics — which is why I’m having a 102-sq. ft. sail made for an unstayed mast I’m making. It will be boomless so I can (a) furl it around the round alumimum mast, and (b) see how well boomless sails actually work! If not so good, I will definitely put a boom on it. As for that race, Mike, bring it on. There’s no such thing as a looser in a trimaran! – Frank

  4. As someone who has sailed with Frank and watched his boats in action, I can say he knows what he is talking about. They are very user friendly boats but with quite a bit of knowledge that Frank has gleaned from reading a lot of books and experimenting he has made some boats that will really move well and look good to boot :)

    I look forward to my own experimentation with a homebuilt trimaran. I recently purchased an old Hobie 18 to steal parts off of and for the trailer as well. Would love to get out on the water with Mike and Frank sometime, maybe up in Tampa Bay by the “Shadow Bay” area.
    -Peter (Cleric)

  5. Huge fan, we think alike. I also want to start by modifying my current Kayak, one of the small squatty 10′ models, but it is just a first attempt, I’ve built one simple monohull from scratch, and it is really slow, but I still like it, because I made it. Anyway, what I’m not sure of is, do you have some kind of formula you use to figure out the size of the amas? Because there is a LOT of buoyancy in the kayak I have, plus I’ve been “blessed” with plenty of “ballast” (my doctor wouldn’t consider it blessed) I don’t know if that would make a difference in the size or not. I have a few home made sails, as well as a windsurfer sail, and even some larger sails from a 20′ sailboat that are “retired” that I can cut down in the future. I’d love to see some drawings or plans to show more detail of what you’ve done, but thanks so much for sharing what you have so far.

  6. Hi Bob – Thank you for your kind words. The bouyancy of the kayak / main hull is, in my view, irrelevant to the size of the amas. So is the “ballast” weight :) The main purpose of the amas is to keep the main hull as upright as possible. If you can also get them to plane, so much the better. I don’t have any actual plans for what I build, as they are all just made from sketches. (Though I will soon be posting lots of detailed photos of my new planing ama design, which I absolutely love.) I am bit concerned that you’ll be disappointed with a such a short main hull, but if speed’s not too important, then no problem. I’m curious to know how you will attach the akas to your kayak, how much sail you intend to use, and how you will attach your mast. Please feel free to provide as much detail as you wish. I will be happy to help you get your project going in any way I can.
    Take care – Frank

  7. I’ve been following Dr. Smoot’s Small Trimaran adventures for some time now. I’ve said it before and I’ll say it again – “If Frank ever comes out with a set of plans, we’ll see his design all over … just like Hobie Cats.”

  8. Hi Frank: I have been admiring your designs for the past few years. I am currently welding a main hull for a Dick Newick
    Tri Design using Hobie Cat Outriggers, but I want the simplest rigging possible. Your lastest Crab Claw setup looks like the best I’ve ever seen. I’m planning something simular but bigger as my main hull will be 24 ft long. I have a piece of land in Port Charlotte & if I ever make it down would like to talk boats.
    Greetings George

  9. Hello Dr. Frank,

    I’m wondering about your project about planing ama’s.

    Did you stop with them ? and if so: What was the reason for that.

    I am asking because I have tried waterski’s as amas and they did alright untill they got submerged. Then drag is increasing a lot.

    Kind Regards,

    Do you have any experience with foils at/in/under you ama’s ?


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