Small trimarans under 20'

Discussion in 'Multihulls' started by Doug Lord, Jun 24, 2012.

  1. upchurchmr
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    upchurchmr Senior Member


    I agree the ama is way too small, everytime the power comes up they have to dump the sail. The other thing is the aka is the dumbest thing since dirt. First thing you ever get taught is not to put bends in a beam. And to make it two separate beams with the hull making the connection is just costly, heavy, and even dumber. It does look nice and I would take one for a couple hundred bucks. That is cause it would take a thousand to make it right.

  2. Ilan Voyager
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    Ilan Voyager Senior Member

    The small ama (less than 120% of the DISPLACEMENT) is a theory from the 60ties. With the materials of the time rigidity was the problem. Finally the tris of this school are not very safe (the buried ama makes you pitchpole suddenly)
    and the lack of power of this miserable little thing is absolutely disgusting.
    So in the eighties the amas begin to get bigger and bigger as it was possible to make better composites thus more rigid boats.

    Let's take one of the better cats the Tornado, the landmark. Despite of its great age, the hulls are absolutely remarkable, buoyant and fast. It has even been able to stand up all the successive transformations of the rig, with the same shape, volumes repartition and appendices...

    Crew 2 (twin trapeze, since 2000)
    LOA 6.09 m (20.0 ft)
    LWL 5.84 m (19 ft 2 in)
    Beam 3.08 m (10 ft 1 in)
    Draft 0.15 m (6 in)
    0.76 m (2 ft 6 in)
    Hull weight 155 kg (340 lb)
    Mast height 9.08 m (29 ft 9 in)
    Mainsail area 16.61 m2 (178.8 sq ft)
    Jib / Genoa area  5.33 m2 (57.4 sq ft)
    Spinnaker area 25.00 m2 (269.1 sq ft)
    A total of 46.94 m2 downwind...
    D-PN 59.0
    RYA PN 644

    Most of the Tornado are weighted at 160 kg, and the optimum crew weight is 150 kg, so the displacement is 310 kg. The Tornado hulls are huge with lot of volume and this video will show how the hulls behave full throttle.
    See the very flat sails, and the combination of mainsail, jib and spi working together. That shows that the cata is able to use all the power, the speed is very good as the relative wind is always in front. The cata is creating his own wind...

    A trimaran ama must behave in the same way...not to be buried in water if you want a decent speed.

    Illustration: Ylliam is the last of the F40 Biscuits Cantreau series designs by VDLP in 1990. As the F40 died, it was never called Biscuits Cantreau and sold to Swiss guys and fitted for lake sailing. Look at the size of the amas, just a bit smaller than the main hull. Displacement: 1800+ crew(75*5)= 2175 kg, the amas are about 220% of the displacement.

    Such a design is the direct ancestor of all the 60 feet tris post 1995 and even now 20 years later it will make at scale 1:2 a nice competition tri in the 20 feet, with some modern features added. Almost no rocker, very high prismatic and block coeffs. The Bonjean curves of longitudinal stability are remarkable, with very good good hydrodynamics.

    The main problem for making it at scale 1:2 is maths;
    - The minimal scantling whatever the size of a dinghy is to counteract the stresses induced by one 220 pounds guy jumping on one foot.
    - The displacement would be at scale 1:2 2175/2³= 272 kg. Minus 150 kg crew that leaves 122 kg for the tri...
    - At 1:2 scale the surfaces of the hulls are divided by only 2².
    A realistic weight with a careful airex-epox-glass with some carbon building is around 180-200 kg.
    So the displacement is 180+150=330 kg so the amas have a volume of 330*2.2= 0.736 m3. The resultant amas have the size if a Tornado hull...

    That means also at least 4 molds; main hull right and left part (vertical joint), ama right and left part, arm upper and lower part (horizontal joint) boards and rudders. That implies all the males, plus the molds.

    How much it would cost?

    A "competition" 30 feet tri has been made (6.09m by 4.80m 50m2) of total sail in 1991 in France. The cost has horrendous and the results in front of the Tornado, the BIM 20 and the protos were not so outstanding.

    Morality; to escape to the malediction of maths, a tri foiler is needed...another different story.

    A remark about beach boats. the Weta isa very good boat advertised for fun and nothing more, they never claimed that you'll smoke the Nacras. Do not mistake a beach toy like like the small tris of the videos with a beach race boat like a Tornado. Not the same world.

    A full power Tornado, or a proto cat are beasts, accelerating like motorcycles. I know of what I'm speaking as I have sailed on several beach cats from 14 to 20 feet, on F40 cats and tris and a few 60 feet trimarans...

    Attached Files:

  3. Submarine Tom

    Submarine Tom Previous Member

    Great video Ilan, thank you, I watched it twice!

    Shame the top decks aren't a bit fuller forward and the hardware a little more hydrodynamically blended in.

    Isn't speed great!
  4. warwick
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    warwick Senior Member

    I would think weather conditions would have to be considered. As a boat that relies on some wind may restrict usage (enjoyment). Compared to an easily driven boat like Gary Baigents Sid & Old Sailor 7 mentions with the buccaneer 24, that does not require much wind to get moving.

    Its all about how one wants to sail, and how much physical activity in return the fun.
  5. Doug Lord
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    Doug Lord Flight Ready

    Fast tri's under 20'

    I'm convinced that tri's, designed to play in the same world as beach cats could beat them. I think it was Randy Smythes Scissors that beat a Tornado in last years Everglades challenge. And way back in 1969 the Gougeon Brothers "Victor T" beat the C Class cats of the day. And they didn't even use lifting foils.
    I don't think small trimarans designed to beat beachcats need large amas but,in my opinion, they would benefit a great deal from foil assist-at least curved,"L" or "J" foils in the amas. Best performance would be with small amas with lifting foils and an oversquare platform with lifting foils on the main hull. Some small cats are being manufactured with lifting foils(Nacra 20, Nacra 17 Olympic,A Class Cats (several manufacturers) and others and it's past time that small tri's are designed with them as well. The unfortunate fact is that most if not all under 20' tri's are slower than beach cats and it doesn't have to be that way. Using foil technology, like a lot of the fast cats are, would be a big improvement as would using an oversquare platform for the tri with small amas.
  6. Ilan Voyager
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    Ilan Voyager Senior Member

    Doug, I do not know what is your experience in racing, or engineering of race boats. I have some experience of the problems of racing multis.

    There is no results if the hulls are not able to pass the power of the sails. The video of the Tornado shows perfectly trimmed sails (and not twisted leech sails like a 1930 skerry cruiser like in the tris videos) and a hull staying in line with no parasitic movements slicing the water.
    The explanation is very simple and very hard to obtain; enough general volume, and good repartition of these volumes. No boat (even monohulls) escapes to this rule. Or you replace the hulls by underwater wings in the hope of better hydrodynamics.

    The Scissors was beating " a well driven Tornado" when it had a structural failure in the Everglades 2011...not the good example. The Scissor looks like a DIY "duct tape", not a "pro" tri, using Class A hulls. Good for one person in light weather.

    The good example is to go to the Texel race in Netherlands (1000 multis competing with all the European cream) and to beat frankly any 20 feet on the water. And be the yearś winner of all the races open to small multis. Seule la victoire est jolie (only winning is nice).

    Victor T won ONE race in front of the C cats in a local regatta in 1968 in very light conditions. Nothing more. Unhappily the C class did not allowed tris. When you compare the C Class in 1968 and now there is a complete world of difference. The Gougeon tris have always been plagued by the too small amas.

    In F40 the tris crushed the catas at very high cost; a Jeanneau Composites cata was in 1987 at 125000 USD the platform. Complete for less than 300000 USD. Biscuits Cantreau III cost was more than 800.000 USD. The F40 died because it was too expensive, no sponsor followed.
    The F40 Adrenalin lost the F40 championship because of its amas (110% of the displacement) The boat could never keep its speed because the lack of buoyancy of the amas; acceleration followed by deceleration when the ama went under water. And began to break structurally when they tried to follow Biscuits Cantreau, able to fly on one hull.
    But I agree with you that tris can be at least as fast as the equivalent cats if they become all around foilers able to fly in good conditions and to have decent perfs in light weather.
  7. Doug Lord
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    Doug Lord Flight Ready

    Ilan, I've designed and built rc and full size multihulls since the early 60's including a 14' tri, a 12' cat(Kona Cat), 16' cat , 18' tri (not built yet)and a 20' tri and a 66' power cat. I've designed and built numerous other boats during that period as well ,for what its worth.
    When you look at small tri's, say from 12' on up to 20', you find enormous righting moment but ,in many cases, the RM is so great that the tri can't fly the main hull. In fact, as best I can tell there is not a single under 20' production trimaran built today that is designed for the main hull to fly.
    The Weta offers the old "bury the ama safety valve" solution so the skipper can depower as soon as the ama starts to bury(and he/she better had because the main hull isn't going to fly except during a pitchpole).
    My new and unique solution to designing a high speed small trimaran is to go oversquare with the platform, use lifting foils on the main hull with a wand altitude control system that "sets" the angle of heel of the boat and maintains it and use an ama foil or combination planing ama+ foil to support almost 100% of the load at "X" speed. In this boat, which I'm building a large test model for now, the main hull will fly in a 5-6 knot wind. As soon as it flys the main foils begin to unload and the single ama foil(or ama foil + planing ama) begins to load up. That eliminates 95% of the induced drag on the main foils whose sole mission from that point on is pitch control, not vertical lift.
    I believe such a boat opens up the small trimaran platform to very high performance,particularly in light air! It allows an oversquare platform because the boat doesn't rely on heeling force to fly the main hull initially. A wide, small tri like this w/o foils would be a dog(unless it was exceptionally light)-not flying the main hull until it was blowing 15-20knots. Most sailing in the states is done in 10 knots and under so this unique concept opens up light air trimaran performance like never before while at the same time enhancing heavy air performance. The model should prove this concept and ,if I'm lucky I'll get to build a full size version.
    The use of lifting foils on small trimarans will make them directly competitive and probably substantially faster then the fastest beach cats. This probable performance will erase the myth of the small trimaran as slow and show what the trimaran platform can do when designed for the highest performance.
    There is a side benefit to all this as well: an 18' performance tri using the system described above could be sailed singlehanded with the skipper sitting in a comfortable cockpit(bucket seat on my boat) while the F18 it just passed has two people on trapezes that have to run to the other side every time they tack or gybe.
    Foil assist is a revolutionary tool that designers can use to reconfigure small trimarans into pretty close to the fastest small multihulls around. And it will completely change the perception of a small trimaran.
    About Victor T-this is from the book "The Evolution of Modern Sailboat Design" by Meade Gougeon and Ty Knoy,page 160:

    "Gougeon perfected downwind tacking in 1969 with his fourth trimaran, Victor T, which won the North American Multihull Championship that summer at Hamilton, Ontario.(beating C Class cats) At the One-of-a-Kind regatta at Chicago that fall he posted the fastest time time around a set of marks ever recorded in the second race before having to quit the series because of structural failure."

    Pictures: a model of a 12 footer(17'wide) using the concept above:

    Attached Files:

  8. idkfa
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    idkfa Senior Member

    A large tri has 2-3m of ama freeboard, bank pop has 5m, they can afford to go through the waves, hence little rocker and "v" transom, don't think a small tri will have that choice with say 60cm of freeboard, going over may ultimately prove faster. Let beach cats be just that, "beach" cats; falling forwards on the wire when you stuff the bow, coastal and off-shore is the domain of tris!

  9. Richard Woods
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    Richard Woods Woods Designs


    Why do you think the Moths use fixed foils when it would be much easier to launch/recover them if they could be raised as you propose on your design. Does it make them too heavy? too weak? too expensive? Just asking as I don't know the answer and I assume you do as you've studied foil design so much

    And (although it is not a great photo, google image search isn't as good as its web search) how would your design cope with sailing off a beach with moderate surf like this, taken at the start of the Texel beach cat race - the worlds biggest such race. As Ilan says, it has 1000 starters and thus is an essential race for you to compete in to prove your concept. You'll sell a lot of boats if you could race round Texel and beat the F18's while sitting down (how DO you get out through surf without getting wet?) 156.jpg

    Last year I watched a RS800 overtake a well sailed Spitfire 16 beach cat to windward. Imagine a skiff like that with small outriggers. Keep it flat and the outriggers will stay out of the water. Because they will add very little weight and windage an outriggered RS800 should still beat a similar length beach cat and be easier to sail than a true skiff because it has the buoyancy of its "training wheels"

    So is it really necessary to fly the main hull to go fast in a trimaran?

    Your quote "he posted the fastest time time around a set of marks ever recorded in the second race before having to quit the series because of structural failure" may not be the best advert. You have to finish to win!

    Richard Woods of Woods Designs
  10. Doug Lord
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    Doug Lord Flight Ready

    Richard one of the greatest weaknesses of the Moth is the fact that they keep the foil down all the time which they pretty much have to do. But Bladerider introduced a Moth with retactable foils and it was apparently a failure because the main hull is so narrow and the wing pod bouyancy didn't help enough that it didn't go over well- it was too hard to connect up the pushrod to the wand. But retractable foils were used to good effect on the short lived RS600FF monofoiler and it beat the Moth in several races in the UK.
    The Rave and the new Osprey have 100% retractable foils controlled by the skipper and each also has two foiling positions that allows the boat to fly at two different altitudes. Both boats are beach sailable.
    At this point I don't think sailing off a beach thru surf would be a good idea with my boat but most of the cat races around here start in the intercoastal and there are many in Florida that are not surf races ---plenty of chances to compete against beach cats. Down the line maybe we'll try the surf assuming I have a back up boat(!)
    The boat I have in mind takes advantage of an oversquare platform and yes it would be critical to fly the main hull. I'm not saying every tri should fly the main hull only those 20' and under that want to be faster than a beach cat and use an oversquare platform. I don't know anything about an RS 800 or Spitfire 16 cat but no cat could carry the same upwind SA my 18 will have in the same maximum pressure. And even if they could they couldn't match the SA/WS ratio this boat can achieve. I'll look them up and comment further.

    Pictures: Osprey multifoiler and RS600FF monofoiler both with retactable foils:

    Attached Files:

  11. Richard Woods
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    Richard Woods Woods Designs

    Although I haven't sailed one I have raced against RS600's many times

    You are designing an over-square 18ft trimaran. That implies it is maybe 20ft wide? I assume the beams will fold to reduce the width, otherwise you won't find many places you can store it, or even launch. I assume it will take less than 30 minutes from road trailer to sailing

    Richard Woods
  12. Doug Lord
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    Doug Lord Flight Ready

    22' wide, folds in a couple minutes, should be 10-15min. from trailer to water.
    Will have a beach dolly.
    Bradfields Osprey in the previous post is 18' X 20' wide (foil tip to foil tip) but has to be assembed for a couple of hours before it is sailed-but it is just a prototype.
    Using the dual independent wands gives the boat RM limited only by the structure of the boat. The designer has to tell the customer what the limit is. On the 16' Rave it was 30 knots( but that was very conservative-probably written by a lawyer). My boat doesn't use dual independent wands but uses dual wands that work separately depending on the angle of heel. The system, like on Bradfields boats, is capable of creating RM unless it is prevented from doing so.
  13. Corley
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    Corley epoxy coated

    Victor T actually raced a regatta against the fastest C Class cats of the day and won convincingly. I'll have to check in Richard Harris's book for more details. The interesting thing was that Victor T was faster downwind which is somewhat counterintuitive and carried a smaller sailplan than the C Class cats.

    I've dug up some more details it was the 1969 NAMSA regatta here is an extract from the following article about Victor T

    The Brothers built several high-profile racing sailboats that advanced and refined the construction techniques they developed while building iceboats and a series of experimental trimarans beginning in the late 1950s. Together they built an experimental 25' trimaran to IYRU Class C rules that marks the start of their early racing success at the 1963–1964 NAMSA Championships at Stamford, Conn.Building on this success and experience, Meade constructed Victor T in 1967–1968. He got the boat’s weight down to 320 lb and it earned the distinction of being the lightest Class C competitor in the 1969 Nationals in Hamilton, Ontario. There, Victor T took home the win against a strong field of wingmast-powered catamarans.
  14. Doug Lord
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    Doug Lord Flight Ready

    Corley, the info I quoted above was from the Meade Gougeon book-what is the name of the Richard Harris book? More detail than my book....

  15. Ilan Voyager
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    Ilan Voyager Senior Member

    Corley that for the input about Victor T. It remains that's very old, cats have changed and I doubt this tri would have the shadow of a possibility to beat a modern one. But it showed the way, and for a 1967 design it's absolutely remarkable. It remains that it won only one regatta (ie one race) of some significance: the 1969 Nationals in Hamilton, Ontario in very light wind conditions.

    Another comment about the link in Wst System site: The change of the rules of the F40 in 1990 or 1991, came not because of Adrenalin -clearly beaten by Biscuits Cantreau III- smashing the cats but simply because a problem of cost. A tri like Biscuits Cantreau III, 20 to 25% better than the cats, is 2 to 3 times more expensive than cats like the F40 Irens design. No sponsor was following and the F40 was simply dying, with one impossible-to beat tri and nothing behind.
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