Small trimarans under 20'

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

  1. Doug Lord
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    Doug Lord Flight Ready

    An oversquare catamaran wouldn't work anywhere near as well as an oversquare tri ,particularly in light air.And in heavy air there could be structural issues with the cat if it used the same system as Happy Feet. And that could have issues working on that wide of a cat. If it didn't use the "Happy Feet" solution, then it would need two sets of lifting foils. The Fire Arrow is 1.12 times length wide(19.5' LOA X 22' wide)*-and if I build a racing version vs the "sport" version of the current boat it would be 1.4 times length wide. The tri would definitely tack better.
    * Hydroptere is 1.2 times length wide.
     
  2. oldsailor7
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    oldsailor7 Senior Member

    Ask why the 18sq/m Cat class died out. (17ft Cat 12ft beam),----tube beams.
    Also the Shockwave 36, with super width and alloy tube crossbeams.
    Both these extra wide Cats suffered from torsion problems and crossbeam failures.
    The wider a Cat is in relation to it's length, the poorer it is at tacking, since both hulls are in the water.

    A very wide Trimaran in contrast, (unless it's a Piver or Horstman), does not have its amas
    deeply immersed when tacking. As it comes head to wind, neither are deeply immersed, like a cats are.
    The Buccaneer 24 is a case in point. At nearly 20ft wide it only has one ama in the water most of the time,
    and both hulls out of the water when head to wind during a tack. A big advantage when beating to windward.
     
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  3. hump101
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    hump101 Senior Member

    But if the cat has wand-controlled foils on both hulls then the windward foils are acting as if they are the centre hull foils with an even higher spacing, so to achieve the same righting moment the cat does not have to be as wide as the tri, and when tacking the windward foil can be used to keep the windward hull out of the water, hence allowing the boat to turn easily.

    Not wanting to further divert this thread, but the relative characteristics of cats and tris in displacement or foiling modes are completely different, and the benefits of tris tend to diminish once the boat is supported by foils.
     
  4. Doug Lord
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    Doug Lord Flight Ready

    H,.... I see your point but using a four foil(in the water) wand system on a wide cat(even if it is narrower than the tri) won't beat a tri with three foils in the water one of which unloads the faster the boat goes up to the point it generates downforce. The tri would be likely to be much faster in light air and maybe in heavy air as well-but it will be closer. RM for the tri would be greater, though by using wands both boats would have theoretically unlimited RM(up to the structural strength of the boat). Interesting-I'll think about it some more-thanks for the comment.
     
  5. hump101
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    hump101 Senior Member

    If you are providing downforce to aid RM, then if the downforce is provided from a greater distance to windward, then you need less, and hence less upforce to compensate it. Hence a cat need only be half the beam of a tri if the tri has the downforce-producing foils in its centre hull. However, if the tri has the downforce-producing foils in the windward hull, that is a different matter....
     
  6. Doug Lord
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    Doug Lord Flight Ready

    This is very interesting to think about. The cat would have to have wand controlled foils on both hulls though it would probably be faster with uptip foils and retracting the windward foil.
    So, it appears to me that the tri(oversquare with UptiP foils on the amas-used one at a time) would be faster up to the point downforce was required from the main foil in which case the cat(half the beam of the tri) could ,theoretically, have equal RM to the tri, but gained thru a foil system that would be more draggy than the tri foil system(UptiP foil on the lee ama) ? Up to the point of downforce being required the max RM of the Tri is greater than the max RM of the cat(w/o downforce).
    And wand systems on a cat* used for downforce may not be so good if Rocker is any example. The Whisper cat uses wands on the main foils and appears from the video to be very fast-perhaps because the two guys on trapezes prevent the windward foil from having to generate downforce. As far as I know Whisper hasn't been raced-I'd love to see results between it and the Flying Phantom.
    * half the beam of the tri
    And, of course, there's always the ultimate tri(?)Osprey-two main wand controlled foils-one on each ama-18' LOA X 22' foil tip to foil tip.
     

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  7. Doug Lord
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    Doug Lord Flight Ready

    Post 123-page 9:
    ====================
    Excellent post from Ted Warren, designer of the Ultralight 20 tri., picture below. Also Victor T very similar in appearance to Victor T.
    Pictures: 1&2=UL 20, 3-5=Victor T, 6=lines plan of Victor T by Lohring Miller:
    click for best view and to read Jack Knights commentary on Victor T's performance
     

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  8. Doug Lord
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    Doug Lord Flight Ready

    Small tri's(say under 14') are not seen too much but they are around. I believe that a little tri called the "3 meter" is raced in the Pacific Northwest. And in Italy they have something like a 10 foot class(I think it is Classe 10?).

    Pictures-1&2=Maora, 3&4=Marples 3meter, 5=Classe 10 :
     

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  9. hump101
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    hump101 Senior Member

    Exactly. I should add that I am not in favour of using foils to generate RM due to the drag penalty and the consequences of loss of downforce (instantaneous and violent capsize). Better to reduce the heeling moment if you want very high speed.
     
  10. rcnesneg
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    rcnesneg Senior Member

    Agreed. I can't justify the added expense and problem of full foils, especially ones that generate downforce. I wouldn't mind just having daggerboards in the amas that are slanted, so foil assist, but they will have to be light, dead simple, and easy to work with. Otherwise, I would prefer to focus time and effort on the sailplan, hull shape, canting mast, and above all, my own skill, as Randy showed us on sizzors.
     
  11. Doug Lord
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    Doug Lord Flight Ready

    ==================
    The Rave, Osprey, Skat, Hobie Trifoiler and the record setting Long Shot and probably others use windward foil downforce. On all these boats the designers have shown that the RM generated by the foils is faster than not using the foils for RM.

    Heres what Ketterman says about the foil system used on the Hobie Trifoiler and on Long Shot:

    HYDROFOIL SAILBOATS IN GENERAL

    "Hydrofoil boats can be categorized into two categories; 1) Incidence controlled hydrofoils* and 2) surface piercing hydrofoils. The difference lies in the way the boat maintains the proper altitude above the water surface. A surface piercing hydrofoil boat maintains proper height by varying the amount of foil submerged. The boat raises up as the speed increases and reduces the amount of foil submerged and therefore the lift. The boat finds equilibrium at the proper altitude. An incidence controlled hydrofoil sailboat has a mechanism that controls the angle of attack of the foil to maintain the proper altitude. It is generally believed that surface piercing is simpler, but incidence control is more efficient. In reality, it is the method that works with fewer problems that is simpler.
    From the beginning it was felt that incidence control was better suited for a sailboat even though most of the existing hydrofoil sailboats were of the surface piercing type. There are many advantages of the incidence controlled foils; however, the most important is what I call the DLA (dynamic leveling affect). This is the increase in righting moment or stability due to the ability of the windward foil to pull down. The DLA has little affect on the low wind performance, but it essentially makes the top speed of the boat limited to the strength of the boat. Conventional boats with a finite amount of righting moment can only extract so much power from the wind, but with the DLA, the righting moment is virtually unlimited.
    Intuitively many people think that the added drag of the windward foil plus the increased induced drag of the leeward foil would offset the gain in righting moment, but calculations show and practice proves otherwise. The dynamic leveling affect not only produces a dramatic increase in top speed, but is also responsible for all the other key features that this stability provides.
    The other major advantage of the incidence controlled foils is they are less affected by the waves and other surface affects. Drag and losses associated with the surface are the major reason incidence controlled foils are more efficient.
    All hydrofoil sailboats have problems with ventilation; however, surface piercing foils have larger problems, because the foils are piercing the surface at a smaller dihedral angle which makes it easier to ventilate."

    ------
    * On the Trifoiler the entire foil was moved to control RM, lift and negative lift hence the term "incidence controlled foils". On the Rave the incidence was generally fixed at +2.5 degrees for the main foils though some owners found a way to decrease the incidence on the windward foil. Lift and negative lift on a Rave foiler is generated by the wand (designed by Dr. Sam Bradfield), a surface sensor(dragging in the water) and attached directly via linkage to a flap on each main foil. The wands are independent just like the trifoiler "incidence controlled" foil sensors.
     
  12. waynemarlow
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    waynemarlow Senior Member

    Yes creating downward force on the windward ama is an option but the complexity and problems associated with it are a minus.

    All the boats quoted using this system are now almost entirely defunct classes, no longer made, one off builds or dedicated speed machines, is that not telling us that they are probably not suited to 95% of the time most boats are used.

    Yes foils have a place and oddly enough the next planned boat I build, will have foil assist on the Amas, but they will not be used for main stream mass production designs ( is the A class a mass production design ) in the short term future.
     
  13. Doug Lord
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    Doug Lord Flight Ready

    ==================
    They're already being used on at least three under 20 designs. The Exocet 19(tooling almost complete) uses one UptiP foil and one rudder T-foil on each ama. Ted Warren offers ama lifting foils on his Ultralight 20. And on my Fire Arrow 19.5' design undergoing model testing.
    ---
    Wayne, you're truly amazing-you start a thread where you attempt to ban the word "foils" from the discussion, while knowing all along that you planned to use foils on your own personal tri!!!! Why don't you tell the good people in this thread WHY you chose to use ama lifting foils. Then your comment will become part of the "discussion"!?
    It's been my contention all along that the use of modern foils on a small trimaran will be an advantage and you have been so against that publicly while privately using them on your own boat. Like I said: "Amazing!"
    ---
    POST 287:
    ---
    POST 187:
     
  14. hump101
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    hump101 Senior Member

    There is no dispute that foil downforce can be made to work, and will result in a quick boat if done well, but if you want to go REALLY quick, then you need to eliminate the heeling moment (e.g. kites, sailrocket, etc.), or use a geometry where the weight provides the rm, but is carried by the sail, not the water (windsurfer, moth, etc.).

    For me, the real world downsides of using foils to generate downforce outweigh the benefits, there are more elegant options.
     

  15. Richard Woods
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    Richard Woods Woods Designs

    The 3m tris aren't raced any more.

    But there is also my nesting Tryst, dozens now building

    http://sailingcatamarans.com/index.php/designs/27-trimarans-under-25/428-tryst-trimaran

    which was built in Canada and has been in the back of our pickup for 10,000 miles. Currently I'm sailing it in Mexico.

    2 sheets 4mm ply for the main hull. 1 sheet 3mm ply for both outriggers. Sail is from a Walker Bay 10 but I'd like a Moth or Byte C11 sail instead, and of course a mast that is NOT an old fence post

    Richard Woods
     
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