24-Foot DIY Tandem Trimaran Sailing in Florida
There is a DIY tandem trimaran sailing in the gin clear waters of Florida. It’s another design / build creation from Frank Smoot, who you can always check out at www.diy-tris.com
I asked Frank if he could answer a few questions from me and he shares (quite generously) below. I decided to include the questions I asked Frank this time. It may help to broaden out the conversation a bit.
It’s always fun seeing what the DIY-Tri fellow is up to … but this is a real treat today. Let’s get right to it ….
(Quick note: all of the pics below are owned by Frank, and are used here with his permission. Most of them are from his new diy-tri webpage).
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24-Foot DIY Tandem Trimaran Sailing in Florida
(A short interview with Frank Smoot)
Q: Why exactly did you design and build this 2-person model
A: Our very first sailing experiences (about 3 years ago) were in a pair of crudely attached kayaks, which created a marginally functional catamaran. The sail rig was way too small, the lee bow always wanted to submerge, and the helm balance was horrible. We eventually moved on to better cats, but were still always able to sail together in the “early days”.
Our first trimarans were made from those same kayaks. It was fun, and sailing independently was…novel. But we still wanted the ability to sail in the same boat, so I built out first “tandem” tri. It was 16’ long, and really wasn’t that great a boat. More of a “learning experience.” After it went to the landfill, we kinda forgot about a 2-person boat for a while.
By then, we each had our own small tris – 16 footers – which were a blast to sail. But my dear wife Laura took a notion that she might want to enter the Everglades Challenge. This would definitely require a larger, more seaworthy boat, which of course, would also be quicker because it was longer and would carry more sail.
So I started designing a 24-footer with twin rigs and tandem seating. It was intended to be a whole lot slicker boat than our first tandem tri, with a much slipperier hull and twin leeboards that could be remotely raised and lowered as a pair. The waterline length is just over 23 feet, and the waterline beam is just over 23 inches – a 12:1 ratio.
It also had more freeboard, a better rudder, and a lot more sail – a total of 170 sq ft. And with the addition of twin 1.5 sq ft skegs / fins on the amas, it now has a ton of lateral resistance, and goes upwind like a keelboat.
Q: Did you use some type of model or other inspiration to determine how long the boat would be … or how it would be rigged?
I can’t be sure, but the original inspiration may have come from the Adventure 24 tri. My boat was intended to be a “poor man’s” version of that boat. And I really wanted to try out a twin sail rig – which I’m told is called a “cat-ketch” – because you can get a lot of sail up without the complexity and bother of shrouds.
We were already big fans if freestanding rigs, so why not have a pair of them? And yes, I do generally build models of all the boats I build full-size. I built two different 1/4-scale models of this 24 footer. And they are almost 6’ long!
Q: How do you like the fore and aft rig system? Any advantages? Any drawbacks?
There are definite pros and cons to this kind of rig – most of which I was unaware of before sailing this boat. Initially, it just didn’t want to point. And if the main was at all close hauled, it was very obviously backwinding the mizzen.
But the reason this boat wouldn’t go upwind very well had much more to do with the fact that the big twin leeboards didn’t want to go down or stay down. Also, the original rudder (pilfered from one of my 16 foot boats) was much too small. Third, in shallow water, we had no way to create lateral resistance, so we tended to slide sideways with all that sail power.
Really, at this point, the boat was handling like a pig. I was pretty disappointed, but I sure wasn’t going to give up.
So I …
- devised a much better mechanism to raise and lower the leeboards
- made a brand new and much bigger rudder
- added the fins / skegs to the amas
- added vangs to both sails
What a difference!
Now the boat points beautifully, comes about quickly, and goes like a bandit. And it’s so smooth and quiet it’s almost eerie. And big waves (and powerboat wakes) which were a bit traumatic in our small boats don’t bother this big one a bit.
I also learned how to trim the sails to minimize the backwinding, and tacking (or gybing) is as simple is kicking the rudder over – no need to do anything with the sheets. I gotta say, we both love this boat!
If sailing gets any more painless than this, I probably don’t want to know about it!
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October 11th, 2012 at 6:06 pm
That is a heck of a lot of boat to approach with a “Just bend the ply until it looks like the boat you want!” structural plan, but with some thought and care it certainly can be done and there’s nothing at all wrong with that if you accept the risks and have some idea of what to expect and what side to err towards when it comes to structural considerations and material choices.
One thing to keep in mind for anyone considering scaling something up like this is that as the boat and the loads of rigs and amas and such increase, you very quickly lose the benefit of scale where small plywood hulls of this type can be overbuilt without a big weight penalty…
for example, say you build an 8′ hull with 1/4″ ply and 1×2″ stringers and frames- that’s a pretty average dinghy/tender and reasonably light for its strength…if you wanted to go lighter and designed/built with care you could easily halve those dimensions, because the originals are overbuilt as far as bare essentials go.
but if you were to double the length of that hull to 16′ and doubled the framing and sheathing dimensions, you’d have something incredibly heavy that would be strong but unsuitable as a fast sailboat…obviously that ability to develop strength with lighter relative weight is a huge benefit to plywood and wood and glass, but as you get bigger the engineering gets more and more critical and you find that the forces acting on the various parts and the boat as a whole don’t necessarily scale up at the same rate the materials do.
With that in mind I would suggest that maybe higher aspect ratio sails may be far more trouble than they are worth, considering the potential changes to the boats static and dynamic structural loads they could create. The ketch rig makes a lot of sense here because a tall sloop rig of the same area would present some serious loads that could overwhelm the rest of the structure or the ama righting moment…otherwise conventional spilt rigs are always something of a compromise that sacrifices performance for safety and ease of sail handling, which is why as a racing rig they are only really favored on offshore racers that tend to do most of their work off the wind or as rule beaters in handicap racing (many racing yawls were really just sloops with a tiny mizzen added to take advantage of rating rules).
The mizzen luffing and general weirdness between sails when you aren’t reaching is one of the drawbacks of a more or less traditional ketch or yawl rig even on a slow displacement cruiser, and combined with the significant changes that occur to apparent wind as multihulls get up to speed- and the fact that you’ve got half your sail area in the mizzen- the inherent limitations of conventional soft sails on booms are the bricks in the wall preventing maximum performance.
Most attempts to get better performance with split rigged cruising boats involve doing away with conventional booms and using a wishbone or loose footed sail(s), which allows for better air flow between the sails and better performance to weather, and also allows for far flatter construction/trimming of sails- which is a huge benefit when your boat speed has you essentially going to weather all the time.
Also the loose footed rigs allow for the sails to overlap and actually work as one unit and generate more power and lift via the “slot” effect…this is one of the odder looking ideas for creating a better performing split rig that by all accounts works pretty well-
http://www.runningtideyachts.com/sail/
October 11th, 2012 at 7:45 pm
WOW!!! Great great job Frank ! I love the boat, read your site and it could not fall in a better moment since I am about to build a trimaran of 22 ft, larger in volume, but with a split rig.
I partially agree with Ian and would have gone with a heftier 6 mm planking and an internal longitudinal backbone, but that is just an opinion, and I do not cover in glass my ply… Here are the questions:
1) what is the fabric weight over the foam bottom? Does it have any tendency to crush? any backbone needed to the styrofoam core after trial?
2) can you expand on the boom-mast fittings ? They look pretty neat
3) what does ” a mean 18 inches beam” mean ? I understand wl beam and sheer beam, but not the latter 18 inch stuff.
4) Any idea of the prismatic coefficient of this boat?
5) what about the akas.. are they simple tubing or coaxial two tubes? And the hull-aka fastening system ? Can yu expand ( even with simple pics)
6) what is the rise of keel at bow and at transom? In other words, how much rocker ?
Thanks so much for sharing your experience, Stefano
PS I will send on e-mail something that I think is a very useful smart and efficient solution for higher aspect sail with low masts
October 12th, 2012 at 2:42 pm
Again very neat, I like the conjionrd use of foam and ply and glass to create a lite but stiff hull.
You didn’t utlize your clever folding ama’s, whats your reasoning, given the EC need to pass through limited space/hight, are they simpley telescoping ?
Enjoy following your builds.
John Farrell
October 12th, 2012 at 6:03 pm
I think the foam/glass/plywood bottom section could be fairly easily engineered to provide a great deal of longitudinal/torsional strength for minimal weight gain, and that’s the kind of out of the box thinking that can allow simple plywood forms like this to be scaled to their limits while dodging many of the weight penalties involved in scaling up traditional hull framing to get the same shapes.
If the foam and plywood false bottom was glassed to the proper thickness to become one unit and integrated into the plywood hull sides effectively, the foam could become largely irrelevant as a structural consideration and would mostly just serve as a plug for the bottom contours…but the positive flotation and ease of repair aspect is a nice dividend as well.
One thing I really like about this design is that it avoids a big issue with larger open cockpit ply or similarly lightly sheathed hulls with traditional framing, which is that as the distances get bigger so do loads from things like people stepping or falling off of gunwales to the cockpit floor…having one continuous plywood web on that plane that isn’t also holding water out eliminates having to build a floor that can handle the structural loads of using the hull skin to stand on or to jump into without tearing the skin off the frames.
It’s also a great solution for mounting bulkheads and mast steps and the like, and offers a large expanse of area underneath where blocking, stringers and other structural elements could also reside without cluttering things up in the cockpit.
October 13th, 2012 at 8:00 pm
Hi guys – sorry for the slow replies. For whatever reason, I’m not getting notified of anything that happens here on Joe’s site – no emails for nre articles, your posts…sure hope Joe can fix that.
Ian – To put your mind at ease, the boat is quite robust. I always build “by eye” but I hate failures due to breakage as much as anybody. Without becoming long-winded, let me just say that everything about the boat has exceeded my expectations. As you note, swapping out the sails for higher aspect ones probably won’t help much. Just two days ago we managed an astonishing (to me) 9 mph close hauled – about 45 degrees off the wind. And you know what? I think that’s plenty! We zipped past a close-hauled monohull like he was at anchor. Whoever says tris don’t point and cat-ketch rigs don’t go upwind is welcome to come along next time we go out. We also managed 12 mph ona reach in 12 mph of wind. The only problem is it just doesn’t “feel” fast when you’re used to 16 foot boats. But I can live with it :)
Stefano – The blue foam was initially covered with 4 oz glass, and then the whole hull was covered with 6 oz glass. Additionally, the floor (6mm ply) os covered in the cockpit areas with 6 oz glass. It all seems very sturdy. The 5 bulkheads in combination with the foam “enclosed semi-circle” make a hull that is virtually torque proof. And the total of 170 sq ft of sail is really pretty conservative for a 24′ boat.
Re the homemade goosenecks, once again my cheapness trumps all other considerations. I’ll try to take soem close-ups. They are really just pieces of PVC pipe and some aluminum straps and other bits assembles to that they are free to spin 360 degrees around the round masts. Haven’t managed to break one yet, despite being out there in WAY too much wind a couple of times. Maybe I should do an article on how truly cheap people solve boatbuilding problems :)
As with all my boats, this is an experimental design. I don’t expect it to be around three years from now, so I sure don’t overbuild. I think the bottom is tough enough for the places we launch and beach (mostly sand) bur probably wouldn’t stand up to gravel or big stones – let alone concrete launch ramps.
Improvements over previous boats include: the aforementioned bulkheads, greater “bury” on the unstayed masts, bigger and deeper leeboards, fins added to the amas, and the fact thet the floor of the boat site about 2″ above water level. If I drilled some holes, it would be self-bailing. In fact, the drain plug in the transom fell out and got lost, so we sailed without it. Of course, with so much freeboard, we don’t take on much spray.
I really wish all you folks could see the boat up close. I’m pretty sure you’d see why I do what I do, and I’m even more sure I could learn a bunch of useful things from hearing your feedback.
Cheers – Frank
October 13th, 2012 at 8:08 pm
Oops – I see I left a few questions unanswered.
- Not sure what your 3rd question is, Stefano. Can you tell me where you saw that?
- I’m thinking the prismatic coefficient will be quite large, as the bilge curves are small radius (just 4″) and the hull is dead vertical for the first few inches below the waterline amidships.
- Rocker is about 7″ overall, in a nearly smooth curve from bow to transom. The foam alone provides about 1300 lbs of bouyancy, so both bow and transom and about 2″ out of the water when underway.
- The akas don’t telescope, but are simply made from a 12′ piece of 3″ aluminum tubing with pieces of 2 1/2″ tubing pop riveted into the ends for an overall beam of 18′. I’ll try to get detail shots of the attachment.
Gotta go for now – Frank