Small trimarans under 20'

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

  1. idkfa
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    idkfa Senior Member

    The tri versus beach-cat is a non-starter, where are the open-water cats today?

    Alinghi versus Dogzilla was a match between two cats, when did you see Dogzilla's vaka used to stop the ama from burying, ie. used correctly, as reserved buoyancy for the ama? Actually when was it ever in the water? so how is it different from a pod? Alinghi lost to better sail design.

    A tri is faster than a cat not cause it is square or over-square, but because you can drive it harder than cat and recover, the vaka saves its *** from pitch-polling.

    Have a look at vid, how many times the vaka vol comes to the rescue?

    If you are off a beach with 20+cm waves, then the tri design has little inherent advantage, maybe a 50% longer vaka versus ama could be advantageous.

    imho idkfa.
  2. Doug Lord
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    Doug Lord Flight Ready

    Thats among the best offshore trimaran video I've ever seen- thanks. I'll post it in the "Great Multihull Video" thread.
    There is HUGE room for improvement in the design of small(under 20') trimarans-the surface has barely been scratched.
  3. TedWarren
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    TedWarren Junior Member

    I agree with Doug. It's always a matter of focus and trade-offs. We don't
    have a cockpit in the UltraLight 20 because of weight, windage, and sitting
    in the main hull of a small fast tri is like sitting in front of a fire hose, and we
    could not car-top the boat.

    The design is really a scaled down version of my personal racer the W27,
    which is actually 30 ft LOA, 27 ft BOA, 46' mast. It was arguably one of the
    fastest around-the-bouys boats in New England. It was undefeated in a
    season of racing with the local fleet.

    Freeboard is an interesting design parameter. You need enough to keep the
    boat moving in seas, but as little as possible. I noticed a direct relationship
    of freeboard to performance in my designs, especially to windward. Windward
    performance is a function of lift/drag in the air and lift/drag in the water.
    More freeboard equals more drag, period. One of the reasons that we are
    seeing cut-away bow shapes is that the boat with a smaller bow will have
    less drag and therefore better VMG to windward. In fact, there is no limit to
    this and if you really want to be daring you could eliminate all of the hull
    above the maximum dynamic waterlines. Seaworthiness dictates that you
    need some amount of freeboard. My rule for all of my performance trimarans
    is one inch of freeboard for every foot of hull. Check out all of the small
    high-performance multihulls and I think that you will find that is true, I know
    the Motive 25R, which we manufacture, is within that rule. The UltraLight 20
    meets that rule and has 20" of freeboard. I suspect that some folks are
    looking at the images and are thrown off by the BOA, which at 15 ft is wide
    by catamaran standards. Also we don't have any good pictures of the boat
    with decent wind. As the wind creates larger forces on the sails the boat
    heels and the main hull picks up significant freeboard.

    I know that skepticism of anything new is normal. As a designer I have to go
    by numbers. The numbers look good, better than an F18 or an A-cat or a
    Tornado. We have to sail the UltraLight 20 against these boats, but I would
    be shocked to find out the UL20 is not significantly faster.
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  4. Ilan Voyager
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    Ilan Voyager Senior Member

    TedWarren Many thanks for your detailed and solidly rational answer. I'm impatient to see the boat in the breeze. I wish you great success in racing and most important selling.
    Your tri is truly very interesting.
  5. Corley
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    Corley epoxy coated

    If a trimaran is flying the main hull it is not a cat and still benefits from the trimaran structure.

    VPLP thought the trimaran would have won in its initial format with a soft rig and the numbers seem to agree.

    A good article was written prior to the event for SAIL Magazine by Ian Campbell of the Wolfson Institute.
  6. Doug Lord
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    Doug Lord Flight Ready

    20' and under trimarans

    Thank you Corley-great read. It will blow the cat lovers minds that USA 17-a very wide trimaran -is lighter than the Alinghi Cat. It also lends a little credence to the specs I posted earlier showing a very wide 18' tri equal in weight to an F 18- something decried by some cat lovers as "impossible". Post 63
    And reflected in an actual small boat by Ted Warren....
    On my 18 with a 22' beam a single crew could sail the boat in the same pressure that requires 2 crew on trapezes in an F18. I wouldn't be surprised if Teds boat could do the same against the two cats below.

    Tornado Specs
    --LOA 20'
    --Beam 10' 1"
    --Sail area 236 sq.ft.
    --Weight 340lb
    Nacra 20 Carbon
    --LOA 20'
    --Beam 10.5'
    --Sail Area 279.8 sq. ft.
    --Weight 375lb
    Ultimate 20-race version(Ted Warren)
    --LOA 20'
    --Beam 15'
    --Sail Area 248 sq.ft.(+156sq.ft screecher)
    --Weight 175lb
  7. idkfa
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    idkfa Senior Member

    Thanks for the article.

    It does not generalise or suggest anywhere that the "structure" of a tri makes a tri inherently lighter than a cat,

    and when it references BOR weight advantage it states "if they can hold it together".

    I'm very suspect of the pod data; the pod of A5 is given as 4000lbs???? while the centre hull of BOR at 3000lbs? and it is twice the weight of the mast 2000lb? What gives? Did the Alinghi engineers get it so wrong, they obviously somewhat did compared to the BOR gang, but it is hard to think they got the mast right and 3 simple compression poles so wrong? That's suggesting a single one weights approx 1000lbs, why use steel here? more likely 100(-+50lbs) for a 60ft spin pole.

    Personally, in my books BOR is a cat (a big beach-cat). A plane has wheels but uses them for take-off and landing only, just like BOR uses its "hull" the rest of the time it's a pod structure.

    Attached Files:

  8. Doug Lord
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    Doug Lord Flight Ready

    It's too bad you look at it that way,idkfa.

    Small tri's can be designed to be faster,weigh equal or less, handle better, be more comfortable and be in the same pricing ballpark as a beachcat. That's just a fact. It's too bad there are so few doing that but thanks to Ted Warren for proving a point I've been trying to make for some time. I hope he sells a bunch of those excellent boats!
  9. upchurchmr
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    upchurchmr Senior Member


    So when the wind is below 8kts BOR is a Trimaran since it can't fly the main hull, but above that it is a Cat?
    This is a simple English lesson.
    3 hulls Trimaran
    2 hulls Catamaran.

    The boat does not change its description depending on the wind speed.
    It sure is disappointing to have to fight people distorting simple language for their own point of view.
    Hard enough to understand each other without intentionally causing problems.

    Every major competitive trimaran has endless pictures flying the main hull. Would you persist in calling them catamarans?
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  10. Corley
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    Corley epoxy coated

    Extreme wide beam is difficult to achieve on a catamaran the structure just doesn't allow it even with the best carbon fibre tricks, maxi cats or even inshore monsters like Alinghi V and even AC72 catamarans don't escape that conundrum. Loick Peyron has commented in Seahorse about how tender the AC72 is versus the offshore multihulls he has sailed due to the relatively low amount of righting moment. That's why I'm a bit disappointed that we wont see an AC72 trimaran in this episode of the America's Cup because there is no doubt it could be a better mousetrap. Something to look forward to if the Cup stays multi I hope.

    The wide beam equals horsepower as it increases the righting moment and the safe sail carrying capacity of the craft without an excessive increase in weight. The modern trimaran structure benefits from being able to embed the beams into the main hull structure at the beam root. Have you seen the video of the walkthrough of Banque Populaire V? The interior of the main beam is hollow inside the main hull it doesn't sit in a trench. I don't know the details of it's composite engineering but I'd guess that the carbon unidirectionals from the main beam fan out and pass well onto and possibly even under the main hull and that gives massive strength while retaining light weight. You just cant get that kind of beam structural efficiency in a catamaran in any sane way in a non immersed pod. I'd be interested to hear Ted's thoughts on this as he designed a concept and structural strategy for a maxi pod catamaran for "The Race". If I'm miles off base in the modern context I'd appreciate the correction.

    This is ancient history by the way as Ilan Voyager can vouch through his involvement in the Formula 40 program and what they learnt about structure. The later Formula 40 trimarans sailed on one hull as well with the main hull barely immersed or flying nearly all the time even in low wind strengths.
  11. Skyak
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    Skyak Senior Member

    You can call it what you like but nobody will understand you. The fact remains that in all out, cost no object competition (length limited) a trimaran will win over a cat. The structural and aerodynamic requirements favor a big stiff hull down the middle that produces less drag than a dolphin striker when it hits the water. The one caveat is the sloop rig. I don't know if the structure to support the jib favors the tri enough that a cat could win a main only battle.

    The main hull may not spend much time in the water, but when it did in tacking it was much faster. Did you watch the last race? Alinghi's last tack took forever! The reason is simple, Alinghi has two thin sharp hulls with negligible rocker in the water and the striker dangling in the waves. Look at the main hull rocker on Dogzilla. When it tacks the speed hulls are out of the water. Even if the tri wasn't faster (it is) it would have out maneuvered the cat in the match race.
  12. idkfa
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    idkfa Senior Member

    "No problem man:p" tris are faster tacking.....

    Any takers on the "proper use of a vaka", ie. "reserve buoyancy for amas"? Look at vaka rocker shape?

    I'm just calling it as I see it, tri off-shore, cat in-shore. Cause in principle, cats are lighter and lighter is faster.

    But in practice the sea has bumps,, and then the vakas come into play,, and then tris are faster.

    I like to see a tri try to beat-up on a cat at the Little America's Cup, don't know if the rules will allow?

    Gladly hear other explanations for the past decades of racing multihull evolution history.

    And, yes BOR was in-shore and never used its vaka to advantage, except as a water-balast carring pod! So it may have looked like a chicken but it walked like a duck and quacked like a duck, you can call it chicken, I'll say duck, no misunderstand necessary, form is secondary to function... In my books anyway.
  13. Doug Lord
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    Doug Lord Flight Ready

    Me too! Problem is the beam-a tri utilizing the attributes of a trimaran among which is the ability to use square or oversquare beam would be illegal. However, there is an historical precedent and that was when Victor T raced the C Class cats in 1969 and beat them in several races to win the North American Multihull Championship. I'm not sure but I think thats when the C Class may have changed their rule to limit beam-not positive though. It was either that or convert to tri's. Didn't the same thing happen in the F40 class-the tri won so they changed the rule?
    PS I'd like to see a monohull challenge the C's-a monohull with just two foils-the Moth is close right now if not faster....
  14. Jetboy
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    Jetboy Senior Member

    It's also fair to say that in an all out, cost no object (beam limited) competition a cat will always win? How about in a length plus beam combined limit competition?

    What I believe is a hell of a lot more important is in a cost limited competition, which is faster.

  15. Doug Lord
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    Doug Lord Flight Ready

    Of course, if you limit the beam of a trimaran it's going to affect potential speed. The thing is that one of the major differences between a well designed cat and a well designed tri is that the tri can be designed to handle oversquare beam-it's one of the advantages of a trimaran platform.
    I think I remember that thats how the Formula 40 guys got rid of boats like Adrenalin: just changed the max beam!
    On a small tri, the ultra wide beam can be a detriment unless you use foils to lift the main hull in light air.
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