Short Amas and Single Beam ?

Discussion in 'Multihulls' started by mcm, Feb 12, 2015.

  1. mcm
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    mcm Senior Member

    I'm interested to hear the opinions of others concerning the advantages and disadvantages of short ama, single beam trimarans.

    Looking at the short ama and single beam trimaran creations of Doug Lord and Gary Baigent is inspiring, but i know there must be some trade-offs.

    I'm especially curious about diagonal pitch stability, and of course whether those foils can really be depended on to replace the lost righting moment of smaller amas.
  2. Doug Lord
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    Doug Lord Flight Ready

    The advantage can be reduced weight and increased speed particularly if the platform is square or over square. Small amas can be planing with or without lifting foils. Probably most suited to under 30' speed boats and fast daysailers.
    By using the small ama single cross arm a small tri can easily equal or beat the weight of a cat the same length.
    The downside can be that the ama won't have much buoyancy and won't fly the main hull unless it is equipped with lifting foils. If the boat is square or over square and doesn't use lifting foils it is much more susceptible pitch pole downwind particularly in a gybe or bearaway. Planing amas work well with this configuration and planing amas+lifting foils work even better. Short amas should be designed to be able to plane because if they don't, as the boat speeds up, they will cause a lot of drag.
    Properly designed foils are extremely reliable particularly when they are used as "foil assist" because the ama planing surface works together with the foils to keep the ama up.
  3. mcm
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    mcm Senior Member

    But the loads on that single beam with the main hull flying between the amas must be huge, especially when you add the long span of a square / over square tri.

    Structurally, isn't it more sound to use the amas for righting moment, but lift from the main hull ?

    I like the idea of deep, adjustable lifting foils on both amas but only lifting enough to maintain stable pitch, roll, and righting moment while flying, and leave the real lifting to the main hull.

    Is there something wrong with my logic, and can't that be achieved with short amas and a single beam of an under 30'(9m), 1000lb.(450kg) boat ?
  4. Gary Baigent
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    Gary Baigent Senior Member

    I was going to keep out of this (because of a certain bias) but Doug has replied (knew he would) ... so I gave in.
    I've had 3 single beam, small float, foil trimarans. The first was Flash Harry which taught me a lot, mainly because of my own design mistakes. The floats were V shaped in cross section, very, very low buoyancy; the boat's health depended on the foils working. I had Harry for 30 years (note past tense) and only twice did I trip and bury the lee float and foil (carrying way too much sail, lumpy seas and heavy wind gusts) and each time the main beam appeared to be close to vertical. Both times it came back. You play the main attentively after that. On the other two larger boats the floats are U shaped and more buoyant but still around 50% the length of the main hull; as before, you are relying on the foils doing their job - which they, to date, have done, no problems.
    The bigger the boat, the more sympathetic it is.
    As Doug has said, the single beam, small float, foil design ... is light. Can't beat lightness on a multihull?
    Prediction: the way things are going with modern foil control development, soon the floats will disappear?
  5. Doug Lord
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    Doug Lord Flight Ready

    MCM, I'm not exactly sure what you mean by this but here is my take:
    As far as I know my test model is one of only two trimarans ever designed with an altitude controlled foil system on the main hull and the only one with its particular configuration. The advantage of an altitude controlled lifting foil on the main hull is that it can fly before it would fly due only to wind pressure which means you can fly in very light wind-like 5mph on an 18 footer.
    But up until the main foil starts pulling down it generates no righting moment. As the boat speeds up, the main foil is unloaded(because wind pressure begins to hold the main hull up) and becomes(with the rudder T-foil) the primary means of pitch control as well as being able to generate downforce adding to RM considerably.It is a system, for an over square tri,that develops tremendous pitch authority compared to a "normal" tri.
    This arrangement can be used with many different types of amas-long,short, planing ,displacement etc and still have the tremendous improvement in light air performance allowed by flying the main hull in light air-and the tremendous increase in pitch authority as the boat speeds up.
    An ama can generate RM(righting moment) by being on a main hull it can't lift-simply through the distance it is from the main hull and how much it submerges. OR, it can generate RM by having enough buoyancy to lift the main hull as it goes faster. The latter is by far faster but it has problems or "concerns" that need to be addressed during design:
    1) is the cross arm structure strong enough,
    2) what is the take off angle of heel when the main hull is just above kissing the water. This is important because some trimarans that fly the main hull do so at an excessive angle of heel-the range is about 10 degrees to over 26 degrees. The maximum initial takeoff angle of heel, that is relatively safe, would be around 15-17 degrees. Note, that I'm talking about the angle of heel at the instant the main hull flys-not the maximum angle the boat can be sailed at.
    3) a square or oversquare tri can carry a lot of sail upwind but when you round the weather mark and bearaway and/or gybe the pitch resistance of the boat is still about the same or worse than a "normal" tri. So a square or oversquare tri must be designed with some way of increasing pitch authority downwind-the best way ,in my opinion, is the use of lifting foils on the main hull and on the ama.

    Pictures,L to R,1) Blue Arrow-British Americas Cup challenger -single crossarm with no amas-just foils at the point of max beam,2) Rave 16' foiler with a single cross arm :

    Attached Files:

  6. Gary Baigent
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    Gary Baigent Senior Member

    Doug may have a unique platform/foil design ... but in my humble opinion, he has too many foils ... and they cause drag. And therefore the boat doesn't work as well as it should do. One lee foil and one rudder T should be adequate to fly a boat with good equilibrium. KISS stuff, as Dick Newick said.
  7. Doug Lord
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    Doug Lord Flight Ready

    Of course, I disagree with Gary for the reasons in my last post. At any one time my foil configuration is only using three foils in the water(including the rudder) and one of those unloads 100% dramatically reducing drag and supporting the tri with basically just two foils. The main foil can also be used to generate downforce which is a proven, relatively low drag, way to increase righting moment. That allows my system to be sailed by a single lightweight person in both light and heavy air OR if you have the crew you need the main foil can just be used for pitch control.
    And the altitude controlled main foil can be used with UptiP ama foils(one at a time) or just a planing ama(with or without foil assist) or a long skinny ama.
    The system is extremely versatile and will be proven to develop more light air speed than any other system I'm familiar with-flying the main hull in very light air as well as using the wide beam of an oversquare platform(with the main foil, if desired) to develop truly awesome power to carry sail with better pitch control than any "normal" trimaran.

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  8. gonzo
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    gonzo Senior Member

    What's the size of that boat?
  9. Doug Lord
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    Doug Lord Flight Ready

    Fire Arrow

    Test model 5.5' LOA X 6.6' wide, 21.13lb, 3390 sqin(23.5 sq.ft).
    Full size 19.5 X 22' wide, 450lb, 350 sq.ft.
  10. waynemarlow
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    waynemarlow Senior Member

    As much as I think foils are the in thing at the moment, one only has to read back through the back catalogues of the AYRS to see that foils have been incredibly researched and huge sums spent on a very slow evolutionary path. I can remember building foils out of aluminium some 30 years ago for a client who became one of the fastest Tornados ever, I can also remember going across the English Channel on a fast hydrofoil and marvelling just how good it was.

    But the question has to be, why if so much time effort and money has been thrown at the problem, really only the moth at 35 kilos has proved to be a successful class. The rest such as the AC boats are at best one offs and would be soundly beaten by the sea hugging foil assist ORMA boats if the race was over 24 hours in varying conditions.

    The models that have been the next big thing have inevitably not panned out fully once built, the latest foil package such as being used on the A's are being revised on a weekly basis, after over 40 years of development that I know of, we are still just a tiny way forward. I'm not knocking the development, but just think we still have an awful long way yet to go to get that foil package that will truly be that all round package.
  11. Doug Lord
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    Doug Lord Flight Ready


    The problem is Wayne, you don't really know what has been accomplished or maybe you just don't understand what it means:
    Monitor an American boat that flew and tacked on foils in the 50's, Williwaw that foiled thousands of miles in the Pacific in the 70's, the first wand controlled foilers in the 70's, Hydroptere over the last 15 years setting records, in the last 10 years pioneering planing hulls coupled with retractable foils and setting records.
    And in the last 15 years, the foiling Moth using a bi-foil concept with altitude control for the first time in history and winding up as the fastest sailboat under 20' including beating all cats! An I14 flew on two foils in 1999, the R Class has adopted the bi-foil configuration as the first 2 person class to do so. Mirabaud, the 26' lake racer, and the largest bi-foiler in history, the I-14 class adopts rudder t-foils as do some other classes, all 60' and 70' racing tri's are equipped with ama foils.
    And the last 5 years: the largest increase in the use of lifting hydrofoils in the history of mankind!
    1) Hydroptere sets the world speed record,
    2) Sail Rocket using a hydrofoil that pulls down to set the latest world speed record,
    3) Kite boards using hydrofoils effectively in races against traditional boards for the first time,
    4) DSS invented and used to increase RM on monohull keelboats,
    5) Open60's use curved foils for foil assist for the first time in history,
    6) Open 60's allow DSS and new boats using DSS and other types of foils being designed and built specifically for the Vendee Globe coming up later this year,
    7) Verdier/VPLP develop a new version of DSS eliminating "normal" daggerboards for Open 60's,
    8) And perhaps the greatest event of all that signals that it is a revolution- not an evolution: the Americas Cup sailed on hydrofoils for the first time in the history of mankind!
    a. the development for the first time in history of a single main hydrofoil that can control the altitude of the boat it is attached to( UptiP foils),
    9) Numerous new catamaran classes have been and are being developed to use these UptiP foils:
    a. 18' Flying Phantom,
    b. 20' Nacra FCS
    c. 32' GC32
    d. Australian Stealth singlehander
    e. The C Class catamarans in the last Little Americas Cup in 2013,
    f. The California 45,
    g. The Gunboat G4 "cruising" foiler
    h. Exocet 19(trimaran) with Uptip ama foils and rudder T-foils on each ama,
    i. The new AC 45's using UptiP foils
    j. The new AC 62 being designed for UptiP foils,
    k. the Toro 34 cat-France (under development)
    l. Fast Fiber 20 cat-NZ
    10) The new Whisper cat using wand controlled foils on a very light platform,
    11) The Ultralight 20 being offered with ama foils as an option,
    12) The Vampire cat using wand controlled main foils at a 10-20 degree angle with a retractable windward foil,
    13) The S9 14' Italian single handed catamaran trapeze foiler,
    14) The Katana 50'(?) cruising cat with curved lifting foils for foil assist.
    15) The A Class cats struggling to develop full flying foiling with rules designed to prevent foiling.
    16) The Fire Arrow-the first trimaran of any size to use a wand controlled main foil coupled with UptiP ama foils,
    17) Gary Baigent's Foil assist trimarans using "L" foils on the amas,
    18) Doug Halsey's continued development of Broomstick, a 15' trimaran foiler using "V" foils-with and without amas.
    19) Paul Flados ongoing development of a small trimaran with experimental foils.
    20) 18' Osprey-Bradfield wand controlled foiler
    21) Team Cobalt surface piercing foiler, UK
    And that's all I can remember off the top of my head but foiler development across the world is at a higher level now than ever in history and , no Wayne: it's not evolution its a Revolution!
  12. P Flados
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    P Flados Senior Member

    The absolute max in the "small ama" department is no amas. I believe Broomstick has been operated this way. Probably an exciting ride, but not much for practical every day sailing.

    On my, I also tried out an ama on one side and foil only on the other. Interesting, but boy is it easy to mess up and roll the boat big time during tacks and other slow maneuvering. Being "ready to swim" is a must.

    Single beam and very short amas are possible. If foils are used for the bulk of the lift, planing surfaces are worth considering for amas. I have been playing around with this on my small tri test platform. I like them better than when I used 4" thinwall PVC for a low displacement skinny ama.

    My planing amas are very small. 2' long by 1' wide provides adequate lift even for my bigger (95 sq ft) sail once I get above say 5 kts. At times, the 3" thickness of the foam was marginal in terms of flotation for times where I was not moving. Specifically this was with:

    • Near zero speed
    • No sheet tension
    • 8 - 15 kts wind
    • Trying to adjust the boat in some way with no attention on "sailing"
    Note that the nose tends to stay around say 45° to 60° off of the wind in this mode for this boat.

    I have added more foam thickness for more low speed stability for next season.
  13. cavalier mk2
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    cavalier mk2 Senior Member

    From my years in a ULDB I tend to think that a hybrid will emerge, light enough to plane and surf, enough ballast to self right and what I always wanted, some foils to stand up to the wind and go faster. Pretty much what Gary said except...I don't think multihulls will go away because they do so many things well. I think a new craft will join the mix and people will keep mixing it up because its fun and that's how things evolve. To answer the question about Gary and Doug and single beam short ama tris....I think they are having fun and isn't that what boating is about? IMHO it is more important to ask yourself what you think and start a journey of discovery because you may wind up in some surprising and interesting places.
  14. mcm
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    mcm Senior Member

    i meant the main hull having the main lifting foil.
    which seems to be your 'Fire Arrow' set-up.

    Wind pressure ? So, the main hull foil is unloaded because it hasn't started to pull down, or because the increasing wind pressure forces down the lee ama causing its foil to generate enough lift to hold the whole boat up ?

    A single up-tip foil on the lee ama can do that ?

    Do you think such a system is applicable to off-shore racing ?

    And About the 'Fire Arrow' amas; will that stage one planning half hit the water mainly at sub-5knts ?

    I see that, but this ?
    i understood the ama buoyancy generates RM by lifting itself - how can it also lift the main hull way over there ?

    By the way, i do appreciate you taking the time to help me grok this.

  15. Gary Baigent
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    Gary Baigent Senior Member

    A few shots of small float, wide, single beam tri foilers:
    !. Fildou a Marc Lombard F40 with 45 degree angled foils, no T rudder, in fresh conditions; this is a 30 odd year old design - still going strong with the French Golden Oldies.
    2. Groucho, also 30 odd years old, in very light conditions; only main hull and the lower section of the leeward foil (inverted Y that year) are in water, boat is magically fast in such conditions.
    3. Eric Tabarly's first model foiler, mid 1970's, which eventuated into Paul Ricard and later, Hydroptere.
    4. Nothing is new, Daru trimaran, probably Centuries old design - yet still modern. Okay, it has a double beam - but if covered, would be a single.

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