Planing DIY Trimaran Amas

In this post, Frank Smoot shares some great information about how he came up with new amas for his DIY Trimaran. What I love about Frank’s work is that it’s based on “real-world, real-experience” small tri sailing.

After reading the below, you can see all of Frank’s ama construction photos beginning on this page at his website –> www.diy-tris.com/PA-1.htm

( Thanks again for sharing with us how you came up with the new amas Frank :-)

……………

Amazing DIY Trimaran Planing Amas
by Frank Smoot

My original amas were built more or less according to what I saw as “common practice” in the examples I found online. But I found that they submerged too easily when really pressed with a lot of sail power. Not only did this submerging cause the mast to lean sideways more than necessary (thus spilling wind needlessly), but this also brought the akas (crossrubes) in contact with the water — which creates exactly the same effect as putting on the brakes in your car.

So I set out to design some amas that would not only not submerge when pressed hard, but would actually rise higher as they went faster — like a powerboat hull. My goal was to get 15 mph out of a boat that cost me less than $1500 to build, and the amas were clearly a speed-limiting factor.

DIY trimaran ama side panels

Like most everything I do, it was a matter of trial and error. I sail my little tris several times a week, so I get a ton of real-world experience. Theory is great, but practice is the real source of understanding.

The very first amas I made (tortured plywood) only had about 200 lbs of flotation each. They were slippery and quiet, but submerged WAY too easily. My next set of amas was the same style, but bigger, with about 400 lbs of bouyancy each.

Unfortunately, I could also make them submerge when pushed really hard. But my new planing amas, which have about 800 lbs of flotation each, have solved that problem once and for all. I can’t make them submerge no matter how hard I try, and they actually rise farther out of the water the faster they go.

BTW, that 800 lbs of flotation on each side came in very handy when my (very under-designed) mast step blew out right through the side of my hull, back around Memorial Day. It made a hole about a foot square, which very quickly sunk my main hull. But those 1600 lbs of ama flotation saved the day!

DIY trimaran ama transom panels

I’d say it took me about 1-2 hours a day for a about a month. So maybe 45 hours all together? Of course, there were many more months of mental design work before I ever picked up a saw.

It took me that long to come up with a design that would (a) plane, (b) not slap when making the kind of intermittent contact with the surface that the windward ama always makes, and (c) provide maximum bouyancy at minimum immersion — my real #1 goal.

DIY trimaraninside ama transom

I will confess to buying ultra-cheap 1/8″ (3 mm) “doorskin” lauan ply (for bottoms and sides — the top is 6 mm ply), and using ultra-cheap porch & floor enamel (which works just great with just a single coat).

Since everything I do is experimental, and none of it will probably be around next year, why spend more? But I do fiberglass the sides and bottom (4 oz) because they take a lot of abuse. And I really, really hate it when things sink…

DIY trimaran ama bow construction

They have exceeded my expectations. I am just delighted with them. Since I first used the planing amas, I have’t been remotely tempted to use any of the old ones.

I can easily sustain 13 mph in any decent wind, even with a single 102 sf sail and freestanding (unstayed) mast. The only thing I’m not thrilled with is the weight. They came in at just over 30 lbs each. I’m sure I could knock off at least 5 lbs by going to better ply (okoume), which is also 30% lighter, and by not making these amas quite so strong (I need to be able to attach shrouds to them when I want to use my stayed masts).

DIY trimaran ama fiberglassing

As the size and power of our sails has increased this year, so has the speed and the “push” on the amas. My wife Laura (who has her own, lighter tri) has been using those original tortured-ply amas I mentioned.

In the beginning, she was a bit timid with her tri. But now that she’s not afraid to really push her boat, she finds herself burying those little amas all the time. So after seeing me pull away from her boat one too many times, she decided that she wanted some planing amas, too. So I made her an experimental set using foam, copying very closely the shape of my own planing amas.

Her planing amas are only slightly smaller than mine (because her boat has a bit less freeboard), and they weigh just 19 lbs! They will be field-tested next week, and I’m 100% confident she’ll love them. But now that she has her own high-tech amas, how will I keep her from passing me?

DIY trimaran canting amas

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15 Responses to “Planing DIY Trimaran Amas”

  1. Stefano Says:

    Out of real world experience: your blowing the mast step is because it became under designed due to the OVER design of your floats.

    Be aware that cross bars are the second structures likely to fail under the load caused by no wind spilling off the sail when pressed hard, if the floats have no tendency to submerge and give some.

    Third chance is that the main hull becomes air borne and you may experience capsize with a tri, a great experience indeed. This can happen only if floats exceed whole boat displacement, and at 800 lbs you’re very probably at about 150% of loaded displacement.

    But I take your point: I also have given some angle and flat surface to my floats in order to have dynamic support ( like a planing hull) rather than just static ( volume) support.

    Striking a good balance is the whole design objective.
    I remember an Americas Cup race boat that tore the whole bow off the hull: the mast and stay did not give in, so the hull did. Another one cracked in two under mast compression after taking a couple small waves. Again, if too much load is applied, some part will fail. I’d rather have smaller parts fail with no potential risk, acting like fuses on an electric scheme, than larger ones without premonition. And believe me , I had quite a few failures on my tri :-) (excessive sail and pressing hard being my overloads)

    Looking forward to reading more real experience and perhaps some videos.

    Stefano

  2. Frank Says:

    Hi Stefano – Thanks for taking the time to post. As you note, it’s really all about striking a balance among design objectives.

    Going back to smaller amas would lead me back to the same problems I have worked to get away from, so the new planing amas are clearly a step in the right direction. Adding them actually caused no problems. The problem came, or at least manifested, when I upgraded to the bigger (102 sf) sail. In any case, reinforcing the mast step has solved the problem very nicely. Now I can push the boat as hard as I want without breaking anything. And I guaranteed future hulls will have sturdier steps (just as my wife’s tri already has).

    And yes, I have also had to add sturdier akas along the way, especially when I used the stayed mast with shrouds attached to the amas. Like I said, everything I do is part of the learning curve. And to paraphrase what Hobie Alter once said, I just build my boats, then take them out, push them as hard as I can, see what breaks, and fix it.

    I’m 100% convinced that these planing amas are perfect for this kind of boat. I wish you could personally experience the difference they have made. Now it’s back to the drawing board to design a hull worthy of these amas!

    I’d love to see some photos of what you are doing. I think sharing our thoughts and pix is a big part of what makes building these little boats so enjoyable and rewarding. And I do hope to have some new videos soon, but the cheap little camera that took the other one has stopped working. Maybe it’s time for that GoPro…

    Take care – Frank

  3. ian Says:

    The final pics of the boat with new amas installed just goes to show you that this kind of experimental design fabricated with less than the finest marine grade materials and techniques doesn’t need to look like a joke…I’ve always liked the look of this boat and it just gets more and more refined.

    I also love the fact that the designer has allowed form to follow function and embraced elements like nearly dead-straight runs and slab sides that so many sailboat designers dismiss out of hand- sometimes for good reasons, but sometimes it amounts to little more than sheer prejudice against anything that even hints at looking like a powerboat.

    Fact is that when you start talking about consistent speeds in the double digits in a boat this size, you need to start thinking in that direction anyway; the realities of hydrodynamics are such that any displacement hull even with no side/heeling loads and on a flat sea will eventually sink when driven hard enough, and anyone who has played around with over-powerful rigs in small boats knows that sailing such a hull under isn’t really that hard to do at all.

    There’s so much potential down this alley of planing hull forms on tris, especially for those whose needs don’t involve dealing with ocean sized wave conditions…pounding and associated stress are a big issue if you drive this kind of hull in any kind of waves or swell where the lift and water action can combine to lift nearly the entire forward half of the hull out of the water and then free fall into the next swell’s approaching face over and over and over…but this type of shape is a rocketship in good water ski conditions- just a faint wind chop to help get some air under it.

    The one negative that needs to be considered by anyone considering this planing ama route is that even a hull that develops gobs of dynamic lift at speed can be sunk, and having it attached to the weight of two more hulls and the drive of a sail by a big lever is a great way to do that…the Formula car-like sailing experience can get a whole lot more Formula car-like when your dynamic stability system gets pressed beyond its limits- when these types of systems fail, they tend to do so instantly and in a spectacular fashion, which is why so many ground effect assisted suspension schemes have been outlawed in formula car racing…when they go south you don’t just break something and limp home, instead the whole car flies off the ground like a kite when the critically necessary-by-design downforce goes away.

    In the case of an ama that *needs* the dynamic lift to develop enough righting moment to sail its boat safely without using live ballasting, one potentially not fun situation would be something like a sudden wind shift or possibly wave action that could cause the boats forward momentum to drop precipitously while there was still enough sidewards force from the sails to capsize the boat without the added upforce of the now missing dynamic lift.

    Of course there’s ways to avoid this- with light enough construction you can have all kinds of displacement hull-like reserve buoyancy above the planing surface, that because it only touches the water when needed can be shaped for other reasons besides pure in-the-water efficiency.

    And for those into pure performance, this kind of planing form combined with live ballast and plenty of sail is capable of truly astounding performance- if controlled and not at the expense of too much forward thrust, the type of lift on the main hull Stefano describes can be a very desirable thing, but as he points out, the safety margin becomes thinner and thinner and predictability is the tradeoff for the extra speed. Plus you’d have to put down your cigar and snifter of brandy and grab a tiller =0

    Unfortunately if it matters to you, the most efficient form to achieve quick and consistent planing at wind driven speeds with enough reserve buoyancy to be safe in real world conditions probably isn’t going to bring to mind the grace and beauty of golden age J-boats or graceful water-spiders-from-outer-space maxi tris, but will look more like something you’d tow water skiers with, or a surfboard- or possibly both….it worked here, just imagine if you got rid of all that dumb ballast-

    http://www.sailinganarchy.com/fringe/2008/1Ragtime.jpg

    http://www.sail-world.com/photos/Alt_Ragtime.JPG

  4. ian Says:

    One more thing re: the mast step failure-

    In my experience a lot of this type of thing and similar rig failures in tris is directly attributable to improper shroud placement, specifically going too far outboard with the shroud chainplates.

    While it may intuitively seem that a more widespread footprint would be more stable, in a sailboat there are other forces at play that make it an entirely different can of worms than something like a fixed antenna tower on dry land…as the chainplates move outwards the increasingly horizontal angle of the shrouds allows some catenary curve to develop, and that curve translates to gravity acting more or less perpendicular to the direction of tensioning, as opposed to helping add tension as it would if the cable were oriented vertically.

    The end result is some bit of added slop to the whole affair that can’t be tensioned out without pushing the shroud material/rig closer to its breaking point, often too close…so if everything isn’t stretched to the max, the mast is free to move but will likely do so in a “pumping” motion when wave action and hull motion is added in, especially in the type of spreaderless rig that many people are trying to achieve by placing the chainplates so far out.

    On top of that, all that added tension from trying to get that catenary out is working to drive the mast through the hull, when a more vertical shroud could do the same work with less initial tension. Add in some mast pumping and the working loads can spike far beyond the various parts’ capabilities in a flash.

    So- this may be nature’s way of telling you to move your chainplates farther inboard, which will also have the added benefit of allowing a lighter ama and simplifying the shroud attachment if you can manage to go to the aka itself.

  5. Stefano Says:

    Hi Frank:

    ” Like I said, everything I do is part of the learning curve. And to paraphrase what Hobie Alter once said, I just build my boats, then take them out, push them as hard as I can, see what breaks, and fix it.”

    JUST LIKE ME THEN :-) !!!

    I’m 100% convinced that these planing amas are perfect for this kind of boat. I wish you could personally experience the difference they have made.

    NOT FAR FROM TRYING ;-)) JUST WANT TO MAKE SURE THE CROSSBEAM WILL SUPPORT THE INCREASED PRESSURE OF OVER 220 FT OF CANVAS ;-)

    I’d love to see some photos of what you are doing.

    My boat is Nepau and is already in this blog… also on youtube. All current improvements will be recorded and submitted.

    All the best, Stefano

  6. Stefano Says:

    Mast compression:

    I just forgot to say: my mast has a double support: it has a mast step on the floor of the hull, bracing the sides, 3/4 inch plywood, and a mast partner bracing also the hull sides with a box beam 2 ft above the floor.

    Plus, it takes shrouds out to chainplates brought out to the “terrace” seats ( 2.5 ft away from the mast). The shrouds can snap, the mast will keep going ( happened).

    The loads: the mast partner takes bending loads, while the shrouds convert this bending load into a compression load vertically.My shrouds are sufficiently elastic ( dyneema) to allow for load sharing between the two structures. My sail is from a 420 international dinghy ( 130 ft circa) + 150 ft of downwind gennaker that I fly occasionally.

    All damages were to winward with wind + wave load . Future improvements will include a second pair of textile shrouds to the amas

    Yours friendly Stefano

  7. Frank Says:

    Ian, you certainly raise a number of worthy points. Thanks for your kind words about my form-follows-function designs. I’m not sure why so many sailboaters dislike straight lines or sides, but the folks who design and build powerboats don’t let tradition stand in the way of performance. And it’s amazing what you can do with cheap 3 mm plywood, epoxy, and fiberglas. I have found these boats to be almost indestructable (in normal use) as long as you don’t underdesign critical parts — like mast steps for unstayed masts.

    Even though it was one of my unstayed masts that broke through the hull, your notes about chainplate location are definitely on target. I have never experienced any damage or failure while using my stayed mast rigs, but it is clear that having the shrouds at a wide angle to the mast brings its own set of problems, especialy when they are attached to a point on the amas. When I first tried the stayed mast rig, it was painfully clear that the flexibility of the akas would keep me from ever experiencing the shroud tension I wanted. But since my hull is just 24″ wide at the gunwales, I didn’t have any other options. I did increase the diameter of the aka tubes, but it was by no means a perfect solution.

    And as you say, the variety of dynamic forces can create some pretty scary interactive motions in rough weather and the mast flops from side to side a bit, and the amas move up and down as the water surfaces does, and the jibstay alternately slackens and tightens on a run.

    Overall, the sails on my unstayed masts have produced the same top speed as my larger sails on stayed masts. But I believe that’s because my speed is limited by what is at best a semi-planing hull. The bow of my V-hull boat seems to start getting lower in the water at about 12 mph. I could try moving my seating position back, but I suspect a better hull is going to be the answer. My new design, which I’m about to start, is essentially a long (well, 16′ long), skinny powerboat hull.

    Re the issue of going fast enough to get in trouble (1.e., pitchpole, bury an ama too far, or otherwise capsize), I really can’t see that happening with these designs. The bigger amas won’t submerge even under maximum loads, and the additional forward bouyancy I’m building into my new hull will make such problems even less likely.

    I don’t smoke cigars, but I definitely love having my hands free while zipping along. I have always disliked tillers, which seem to me to be the only part of trimarans that are still in the 19th century. Of course, if your boat is bigger than mine, you’ll probably want the option of moving around, in which case the tiller is a necessary evil. But for me, foot steering just can’t be beat.

    Finally, I’m planning a small tri with fold-out amas. It will by necessity have aka supports that extend out to 6′ or so. Shouls I opt to power it with a stayed rig, this will give me a sufficiently broad base to attach shrouds not subject to all the problems of ama-located chainplates. Unlike my current tri, which shares a trailer with my wife’s tri, this one will have it own dedicated trailer. Between the folding amas and my new mast design, I think I can cut my launch-prep time from about 15 minutes down to under 5 minutes. Onward and upward!

  8. Frank Says:

    Stefano, I read your very interesting article on this site and watched your (too short :) video. I had a very similar experience with a leeboard failure causing, in turn, a rudder failure. It was a “double-whammy” lesson in the perils or underbuilding both the leeboard (foam-core…never again..) and the rudder mount, which is much sturdier now.

    I see you have made steady improvements to your boat. I doubt I’d have the courage to buy a hull made by somebody else and push it hard. The one thing that struck me was the beam, after the trimaran conversion. From the bow view, it struck me as being overall too narrow. The measurements you provided served to confirm this. I’ll be that taking your overall beam out to 12′ or even 4m would add a whole bunch of stability, and enhance top speed as well.

    Of course, the aka tubes will need to be up to the job. I have found that 3″ drawn aluminum (6061 T6) tubes with .065 walls are quite sturdy and well as lightweight, and all my future boats will have them.

    Finally, I understand why you might want synthetic shrouds, but I have gone back to stainless steel shrouds, which are a lot cheaper and have a lot less windage. And I can assemble them myself at the local marine supply store.

    Happy sailing – Frank

  9. ian Says:

    Hi Frank-

    Thanks for the response and for accepting the stuff about chainplate locations in the spirit in which it was intended even though it turned out to be erroneous in this particular case…one thing you mention that I forgot to add re: mast pumping is that any kind of aka flex can contribute greatly to this problem and needs to be considered by anyone using this kind of tubular design on a small scale, especially if they are using tubes/alloys that were never intended for use as spars…even some of the high tech aluminum out there that *is* intended for that purpose may have built in deflection qualities that can allow for rig tension to come and go to an unacceptable degree.

    That said, the worst mast pumping I ever personally experienced was in a Piver Victress with solid wings decks that we were amazed to get back to the slip from a sea trial with the rig intact.

    As for the sit-in/foot steering thing- again, thanks for taking *that* in the spirit of gentle fun that was intended…I’ve gone on record on this blog before about my feelings in this regard so I won’t belabor the point further, except to specifically address your comments about things being antiquated…

    one aspect of modern tri design I see as a possible pitfall (especially for amateur designers) is a tendency to go overboard (no pun intended) with modernization for modernization’s sake…and one modern idea related to tris is the notion that movement of live ballast is more or less irrelevant.

    For boats operated in protected waters by people who aren’t pushing their limits or who do so with eyes wide open and enough experience to know when to back off, that may very well be a valid position…but there is always the risk that less experienced sailors and designers reading blogs like this will treat the trimaran concept as being essentially a monohull with training wheels that requires no special skills to operate safely, which it isn’t.

    It bears considering that the original Polynesian proas relied on live ballast via an ama oriented to windward as an integral part of their design and operation…and that the most successful Atlantic style proas with this layout reversed use leeward amas that are proportionally far larger than what we see in most trimaran designs that not at all coincidentally are always burying their amas.

    So when I see people talking about this age old issue, I can’t help but have a bit of a chuckle when the boat design in question has pretty much tossed aside the concept of moving some dead weight around to keep it on its lines- it seems especially odd since even ballasted monohull boat sailors do it and it’s part and parcel of non-ballasted performance dinghy and cat sailing.

    You have obviously thought this out in relation to your needs and have walked the walk with trial and error experiments, so this isn’t directed at you personally….but I do see a trend where people who maybe don’t have a lot of experience, who might want to sail but want to cut corners and aren’t aware where the safety limits lie, are drawn/led to trimarans under the erroneous idea that their initial stability is a constant that can be relied on in order to completely avoid having to learn about and deal with things like hiking and related trimming of the hull(s).

    I see this trend in advertising surrounding many of the sit-in offerings out there, most notably some Windrider ad copy-

    “Give us the clumsy, out of shape, land bound masses longing for wind and spray while hoisting a frosty beverage in one hand and a pastrami on rye in the other. ”

    “Have a cabin, waterfront home, resort, rental operation? No experience necessary and your guests will always come back without capsizing!”

    While the first example can be cut some slack as a bit of humorous copywriting and shouldn’t be taken 100% literally, I’d still contend that clumsy out of shape potential sailors would be far better served by a few weeks on a Laser with a hiking strap than a tri that lets them stuff their mouths with pastrami and soft drinks uninterrupted…

    but that second example is, in my opinion as a former sailing instructor, bordering on criminal negligence…even allowing some license for advertising hyperbole, to advertise ANY boat- let alone a sailboat being aimed at beginners- as being incapable of being capsized is just unconscionable, period.

    Again, this has nothing to do with you personally or your boat, but in the interests of avoiding some kind of tragedy related to these small trimarans I feel it is important to address the various safety issues surrounding small tri design trends whenever possible even if most people will never be exposed to these risks or have a problem…let’s not forget what happened to the three wheeled ATV- it’s not at all outside the realm of possibility that a few drowning deaths of inexperienced people who believed this crap could lead to a virtual moratorium on production tris like the Windriders on similar grounds that they are “inherently unstable” and unsafe.

    It’s been a hard enough slog getting past the missteps and tragedies of the past when it comes to trimarans in general; now that they have some degree of mainstream acceptance it is important to prevent a similar situation from happening again at the hands of people trying to cash in on it with at least in some cases little regard for who might get hurt in the process.

    Just my two cents, off my soapboax, now back to your regularly scheduled programming…

    Ian

  10. Frank Says:

    Hi Ian – I always assume that my fellow tri enthusiasts want to help, so unless a comment is overtly negative, I see it as positive. You are right about the aluminum tubes. I’m sure they were not made for this kind of use. Clearly, the first tubes I used were not up to the job. But the 3″dia tubing with .065″ walls I am upgrading to are both very light end very strong, and seem well able to handle any of the stresses I impose on it, even when I use an unstayed mast and attach the shrouds to the fittings / chainplates on my amas.

    As for the modernization issue, as you noted, my “prime directive” is that form follows function. I don’t like tillers on my own boats simply because I like to sit facing forward and in one place. My boats aren’t big / wide enough to hike out anyway, and there’d be no place to sit if I did, so foot pedal steering is the logical choice. But for those who wish to use their own weight as shiftable ballast, that clearly is a great aid to both stability and performance. And in such cases, a tiller is the obvious choice. It’s just not my choice.

    And having already experienced a few traumatic events in my various sailboats, I completely agree that it’s unwise and even irresponsible to minimize or downplay the risks inherent in operating these little tris (or any boats, for that matter). Without question, we can get in serious trouble if our boat or our brain isn’t up to the challenges at hand. And the quicker the boat, the faster problems can manifest.

    I had been corresponding with tri guru Jim Brown prior to this year’s Cedar Key meetup. We hooked up with him there and he spent about 45 minutes talking with us about our little tris, both of which he examined “hands on” due to his failing eyesight. He is of the opinion that smallish, submersible amas are kind of a safety feature that keeps the inexperienced trimaran pilot from getting into a pitch-pole situation or other potential dangers of high-speed sailing. I support his position when it comes to inexperienced sailors zipping around in rental tris. But for those of us trying to squeeze out maximum performance from our minimalist craft, it’s clear to me that bigger amas = better performance. In any case, I sure do love my new plaing amas. Now I just need a planing main hull to go with them.

    BTW, I would be delighted to see some photos or videos of your own boats. Can you provide any links or pix?

    Cheers – Frank

  11. Stefano Says:

    To Frank and Ian

    As for stability: I have added two “terraces”, visible on the video. This is not only to sit or even lie comfortably enough (9 inch wide by 7 ft) but also dramatically increase stiffens and resistance to torsion motion of the hull, making it much faster. They provide also two excellent fastening points for removable oarlocks and on the lower side, I tied two inflatable cylinders for about 60 liters volume each, that have a double function of rollers to pull the tri on pebbles or beaches, and also act as reserve buoyancy (came in very useful a couple of times ;-).

    In between the two akas is stretched a trampoline mesh net 2.5 ft by 6.5, making it very attractive for all lazy friends or sun-bathing keen female friends to act as “live” ballast. Further out is a narrow board 4 inch, that has a double purpose of hiking board and also connecting the two akas, so that the first one up front has a rigid element to distribute part of the load to the other aft aka. It works fine and you can also sit or walk on them.

    I’m looking forward to complete the boat in mid July, sail it hard again, make some videos and report soon after. Keep an eye on this site by then

    A rudder can be steered and connected via small blocks and line circuit to a vertical leverage on one side of the boat or two..freeing the boat from its length and making it possible to look forward and sit on one side while steering. A friend made the circuit with sufficient friction to allow for self steering of the boat with minimal corrections (a shock cord is also part of the system).

    cheers, Stefano

  12. Frank Says:

    Hi Stefano – Sure, let’s correspond directly. Email is much quicker, plus we can add photos. BTW, how did your English get to be so good?

    Re folding systems, I have developed one that I plan to use, but I have no way yet to show you drawings. I’ll work on that.

    As for bouyancy in amas, you already know my thoughts there. A lot of static bouyanck with a good amount of dynamic lift as well. I just finished the new foam planing amas for Laura’s boat, an I plan to test them out today. I also moved the seating position 14″ farther back to try to correct what I think was a bow that was lowering a bit at speed, instead of lifting. I’ll let you know how it goes.

    We had 13 consecutive days where we couldn’t sail, due to no wind or too much rain! I have never seen that before in the “Sunshine State” as Florida is called.

    I’m not sure how you plan to use stepped hulls, or how they are appropriate at these relatively low speeds, but I would like to hear your thoughts and see any photos or drawings you can provide. I’m making a new main hull for my tri, based on discoveries I made from the current one. It will have a very shallow V-bottom for the aft 2/3, transitioning quickly to a powerboat-type bow for the forward 1/3. Rocker will be only about 1″. I’m trying to get the hull to act more like a windsurfing board than a sailboat. I think if we can get these boats light enough and give them enough planing surface, they will plane at very low speeds. I built a model first, as I always do, so I can see how the lines look in 3-D. The bow was a bit too severe, so I will smooth it out a bit. Photo to follow.

    How did you shorten your tri? I wish I could get 12.5 ft long tubes in my desired size, but most of them come just 12′. I have upgraded to 2″ dia and .125″ walls (1/8″) from the original .065 walls (1/16″) for my current boat, but the 3″ .065 tubing is both stronger and lighter, so my next boat will be designed around that.

    How long does it take you to assemble your boat so you can launch and sail? I can now do Laura’s boat in about 13 minutes, but I have plans for a system with fold-out amas and a tilt-up sail that will be pre-rigged, and I think I will be able to do it in about 3 minutes. Anyway, that’s the plan!

    Have you considered building your own hull and amas?

    Take care – Frank

  13. Bryan Says:

    Dear Frank,

    The amas have 800 lbs of flowtation — Does that mean that they are filled with foam or just hollow? And when you talk about planing is there a small step on the amas?

    Bryan

  14. JACK SPOERING Says:

    WELL. IF NOBODY ELSE WILL SAY IT I WILL — ” DR. SMOOT’S TRIMARAN INOVATIONS ARE THE GREATEST THING TO HAPPEN TO SMALL TRIMARANS SINCE PIVER CAME UP WITH THE NUGGET”. IF HE EVER COMES OUT WITH PLANS THEY’LL BE ALL OVER LIKE HOBIE CATS.

  15. TomK Says:

    I hear a lot about how having amas with too much floatation will cause a tri to capsize. Well, having amas that are too small will capsize a tri even more quickly. If the ama floatation isn’t enough to offset the sail power before the ama goes under, you’re in dangerous territory.

    Conversely, larger amas that require more force to submerge don’t automatically cause the center hull to fly. That takes a great deal more power because of the weight the sail plan has to lift.

    I’d rather have amas that are a little too large than a little too small. The former isn’t likely to a capsize, while the latter almost guarantees it.

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