Small trimarans under 20'

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

  1. Ilan Voyager
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    Ilan Voyager Senior Member

    The Weeta is a beach toy and has no other goal. Probably very fun, but no match with a serious cat. It would be very expensive to build a tri faster that an equivalent cat in these sizes, simple maths about minimal scantlings with the present building methods. After 30 to 40 feet it's another matter. For memory a Tornado with spi gets easily 22 knots downwind in flat sea.
     
  2. upchurchmr
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    upchurchmr Senior Member

    Ilan,

    Anything under 20 is a beach toy or a useless raft (too much cabin - any is too much).

    The Tornado is a great boat but it still is a beach toy. What difference does it make how fast it goes downwind? And what wind speed was that? Was it tacking downwind? Such a simple statement means nothing if you are not going to compare it to something. A power boat will go a lot faster downwind.

    If you want competitors on a Tornado, you probably need lots of Weetas to get them started.
     
  3. Doug Lord
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    Doug Lord Flight Ready

    ----------------------------
    Ilan, the results of a comparison of an 18' trimaran concept of mine with an F 18:


    This thread started out to try to see if there were any high performance 18' tris around that could beat an F18-either existing boats or designs whose numbers reflected the probable ability to do the job. To me, it is a very interesting design challenge that could produce an exciting, comfortable and very fast boat. It is clear that an 18' performance tri with small amas and lifting foils on the main hull(as per my suggestions earlier and below) and either foils or a planing hull to provide dynamic lift on the ama could be in the ball park pricing range of a Wildcat F18. It is further clear that with careful design and engineering the boats would be comparable in weight as well.( Keep in mind that as beachcats go the F18 is on the heavy side). The technical aspects of the boat show a high probability that the tri would be faster than the F18, would be able to sail in the same pressure as an F18 with one or two crew, and would do this while allowing the tri's crew to sit on the side of a center cockpit very comfortably:

    --the rig with 50 sq.ft.(277 all up-1' higher CE) more upwind SA(121 sq.ft. more downwind) than an F 18 would insure the power required to be faster than an F18
    -- using carbon tubes for the cross arms would assure the strength and light weight required for a 16' beam or greater.
    --Righting Moment: Max RM for the tri with two 175lb crew sitting on the side of a center cockpit would be 6700ft.lb. which means it could carry the 277 sq.ft. of sail(1' higher CE than an F18) in about the same pressure that an F18 can with two 175 pounders on trapezes (1.5lb./sq.ft. pressure). But while the F18 requires two 175lb crew to sail in this kind of pressure the tri would not. In fact, it could be sailed with a single crew in that pressure with the contribution from the mainfoil of 218.75lb. of downforce. The mainfoil, in concert with the rudder foil,(both on the main hull)act to control pitch and can be used to maintain the sailing angle of the boat with the main hull flying thru a significant variation in crew weight. The mainfoil would not be much larger than a Moth foil( 1.1=Moth; 1.4 sq.ft. tri). The F18 has 4 foils-the tri main hull four, as well, except that two of them are very small-about half an F18 foil-and lift vertically up or down. Learning from the F18 Capricorn(and other race boats) the tri would have a gybing daggerboard assuring excellent windward performance.
    -- Ama- the key to the design is that the main hull flys almost all the time. At max RM the ama must support 750lb.(boat weight+ 350lb of crew weight,or approx. 175lb crew +175lb main foil download). The ama could be a single rotating hull that would allow a displacement hull or a stepped planing hull as the case may be. Very experimental.
    OR: the ama could be a high L/B design incorporating a retractable (pivoting) foil with 1.4 sq.ft. of area in each ama. This would allow the ama foil to carry 70% of the boats weight(same % as an ORMA tri) using a proven foil system(DSS) that works somewhat differently than a "typical" curved foil: it develops no lateral resistance as a by-product so that 100% of its area is dedicated to vertical lift making it much more efficient than a curved foil. The least expensive of these two options may be the stepped planing hull but that still has to be proven. The DSS foil is proven....
    ====================

    If you look at the technical aspects it is undeniable that the tri would beat the cat-and that's with one hand tied behind its back! The crew of the tri sits on the side of a center cockpit while to sail in the same pressure(1.5lb.sq.ft-max design pressure for the F18) the F18 requires two crew on trapezes. Not only that but the tri can be sailed in the same pressure that an F18 requires two 175lb people on trapezes-singlehanded! More power ,more speed, much more comfort, much easier to sail fast-the tri could be a tremendous addition to "beach sailing" multihulls and the first of its kind(that I know of-even ostlind agrees with that!).
    Yes it can!
    NOTE: please see the SA/WS ratios for these two boats. They tell the story better than almost anything else showing that the tri has much less drag for its power than does the F18. And remember, this tri is not using all the power that the configuration allows-it is designed to be faster than an F19 AND extremely comfortable and much easier to sail.
    =====================
    F18
    Specifications:
    Length: 17' 11" / 5.46 m
    Beam: 8' 6" / 2.59
    Draft w/Rudder Up: 7.1" / 0.18
    Mast Length: 29' 6" / 8.99
    Sail Area:
    227 sq.ft. upwind SA
    454 ft2 / 42 m2 downwind SA
    SA/WS:
    --two hulls in water- 4.77/1
    -- single hull in water- 6.03/1

    Bruce Number: 1.66
    SA/D: 44.16
    W/SA: 3.29
    Weight (with spinnaker): 397 lbs / 180 kg
    Price as of 6/21/10= $22,500 including everything except trailer
    ---------------------------------------------------
    18 Tri
    Specifications:
    Length: 18' / 5.49m
    Beam: 16' / 4.88m
    Draft w/Rudder Up: 6.4"
    Mast Length: 31.5' / 9.6m
    Sail Area:
    277 sq.ft. upwind SA
    575 ft2 / 53.4 m2 downwind SA
    SA/WS:
    -- not flying-5.73/1
    -- flying main hull-10.26/1

    Bruce Number: 1.83
    SA/D: 53.89
    W/SA: 2.71
    Weight (with spinnaker): 400 lbs / 181.9 kg
    Hull Construction: Fiberglass/Foam Sandwich and some carbon/foam sandwich
    Price estimate-$22,500-24,500
    (Note: skin area and volume of tri ama about 1/3rd that of an F18 hull!)
    -------------
    Ama foil area corrected 6/22/10
    SA/WS added 6/23/10


    Note: for those that only see numbers and not the picture they paint you should really do something about that. Without analyzing the technical characteristics of a boat you know nothing about it. If you judge a boat by a pretty rendering without at the same time analyzing the technical data for the pretty picture you're not getting the full story. When comparing two boats such as the F18 cat and 18' tri the technical data is critical. You should insist that posters/"designers" who are telling you about a boat and/or comparing one with another provide the applicable ratio's and other details. You should probably make an effort to understand this information.



    =====================

    Note: the key to understanding this is to realize that the tri works like no other tri currently in existence utilizing two lifting foils on the main hull augmented by a wide beam and and VERY SMALL ama using either a small lifting foil or a planing surface-or maybe both in certain conditions. The two foils allow the mainhull to fly long before a conventional tri this small and this wide would. The two foils,and this is real important, unload the faster the boat goes! The pitch control is greater than almost any equivalent length multihull. This is a "daysailing" version of the concept since an all out racing machine could be considerably more powerful(and expensive).
    This was done to show the potential of new thinking that allows the full attributes of a trimaran to be used more effectively than they have been to date in "conventional" small trimaran designs under 20' or so.
     
  4. Richard Woods
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    Richard Woods Woods Designs

    Can't wait to see yours sailing. Please post videos when you do

    I was racing today in a RS400 dinghy, like this (in wind)

    http://www.youtube.com/watch?v=U2QCyQsrqlg

    while this was actually the boat I crewed on (and no, that's not me crewing)

    http://www.youtube.com/watch?v=P-IWCZdE3Ro

    The owner of the boat I was crewing for said that last year he was measured by gps at 22 knots over pretty much a mile. Years ago I sailed a sistership at 15 knots ( it took us 4 mins to do the nautical mile between two buoys)

    Also out on the water today were a few Int Moths. Incredibly quick, but an absolute nightmare to launch and recover, even on an inland lake. Totally impossible to use one in a tidal muddy estuary or even by yourself, as it takes two people to launch them

    As always boats are not about ultimate speed. They have to be practical

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  5. Doug Lord
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    Doug Lord Flight Ready

    ===========================================
    My 18 design concept uses retractable foils as opposed to Moth foils. It can be sailed off a beach and folded or unfolded in 5 min or less. It is designed to fly the main hull in light air and to unload the main foils soon after take off.
    It is designed to be comfortable, dry, easy to sail and very fast. I'm building a test model as a start.....
     
  6. Richard Woods
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    Richard Woods Woods Designs

    so which of the many sketches in your gallery is the one you mean?

    Richard Woods
     
  7. oldsailor7
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    oldsailor7 Senior Member

    (Quote).- Three hulls perform better in a light wind, which face it, is where a lot of the sailing occurs.- (Quote).

    Which is why the Buccaneer 24 has been such a successful design.
     
  8. Corley
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    Corley epoxy coated

    It's too bad there are not any plans around for the Crowther Bunyip that was a simple to build small trimaran 20' IIRC.
     
  9. oldsailor7
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    oldsailor7 Senior Member

    Yup. The Bunyip was a good Tri.
    It is inconceivable that there isn't a set of the plans lurking around somewhere which can be re-vitalised as I did with the B24.
    Under Australian Copyright law, which includes technical specifications, (ie: Plans and instructions), all of Crowthers early sailboat designs are now out of copyright time limit and are free to re-print or build.
    Perhaps a call on the appropriate internet forums for a set of plans which can be restored and re-printed might be a good idea.
     
  10. Doug Lord
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    Doug Lord Flight Ready

    Are there any pictures or details that you remember about the boat?
     
  11. oldsailor7
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    oldsailor7 Senior Member

    Yes.
    As Corley says, it was a smaller version of the Kraken 25, with simple plywood chined hulls and laminated wood crossarms.
     
  12. Corley
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    Corley epoxy coated

    Attached Files:

  13. oldsailor7
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    oldsailor7 Senior Member

    Corley, If you blow that dwg up you can see thats a Bunyip emblem on the sail, and it says Bunyip on the bows :D
    Also it says it is a plywood chined version of the Kraken 18.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    Thanks guys. Ah,....whats a "Bunyip"?
     

  15. Corley
    Joined: Oct 2009
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    Corley epoxy coated

    I'm just back from crewing on the delivery of a catamaran between Port Lincoln and Melbourne so the room is still moving around let alone the computer screen :D
     
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