Trimarans: Angle of Heel at Main Hull Takeoff

Discussion in 'Multihulls' started by Doug Lord, Sep 1, 2011.

  1. Doug Lord
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    Doug Lord Flight Ready

    I'd appreciate all the help I can get from designers and sailors with getting information on the main hull take off angle of heel of as many trimarans as possible.
    This is with the main hull "just kissing" (say 1mm above the water) .
    I've run into wide variations and I'm interested in getting lots more info for which I will be very grateful.
    Some that I know or have found:
    1) RC model-slightly oversquare moderate main hull rocker: 13 degrees, (accurate)
    2) My new design-wide main hull, little rocker: 10 degrees, (tentative)
    3) USA-17: 13 degrees, (accurate from Oracle)
    4) many other tris are much higher-one I measured here was 26 degrees!
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    Again, your help would be most appreciated!

    ------------
    --At this point I don't necessarily need analysis of why the angle is as it is(beam, weight SA, dihedral etc) just the angle will be ok. But analysis is ok-even great- just not absolutely required right now. Thanks.
    -
    -- Estimates are ok-just mention that's what it is.....
     
  2. Doug Lord
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    Doug Lord Flight Ready

  3. bruceb
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    bruceb Senior Member

    lift off

    Doug, I don't quite understand comparing such different designs, but lightly loaded (just me and some sails), my buc 24, with a lot of rocker, has all but the bottom few inches out at around 26-28 degrees. That really feels like a lot, almost mono type heel, but the Buc isn't really designed to lift the main hull. The floats are about the same displacement as the design load, so with normal loading, the float buries before the main hull ever lifts and the boat rounds up, so I have read- I haven't pushed it that far- yet:cool: I suspect many of the tris with smaller floats do the same. B
     
  4. Doug Lord
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    Doug Lord Flight Ready

    =========
    Thanks, Bruce-that's just the kind of info I was looking for. I'm just taking the info at face value -not necessarily analyzing what it means right now.
    I think there will be big differences between tri's designed to fly and those that aren't but there is a lot more to consider when attempting to determine which is better or worse and what it might be better or worse for.
    Again, appreciate it!
     
  5. Doug Lord
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    Doug Lord Flight Ready

    I'll tri to find a picture from a point with the main hull 1" off the water for the Sea Cart 26 but take a look at these pictures and compare to the ama submergence of the M23-and its not quite flying the main hull.
    These shots illustrate perfectly a curved lifting foil doing exactly what it is supposed to do-the ama bow is clear with the main hull way up-that is good design!
    http://seacart26.com/
    Can't find a suitable picture to measure takeoff angle but it looks like it would be fairly high....
    ------------------------
    UPDATE-9/15/11: According to a Sea Cart company employee the estimated takeoff angle when using the curved foil is 13-16 degrees.

    click on image:
     

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    Last edited: Sep 15, 2011
  6. Hussong

    Hussong Previous Member

    Isn't this fundamentally misleading?

    Price for M23 ready to sail: $38K

    Price for Seacart 26 ready to sail: $130K
     
  7. Doug Lord
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    Doug Lord Flight Ready

    ==================
    Hussong, this thread is about: "Trimarans: Angle of Heel at Main Hull Takeoff" and I would very much appreciate it if we could try hard to keep it on the original topic.
    Your question is interesting and you might want to go ahead and start a thread on pricing and the ramifications of certain pricing schemes-in fact I think it is a good idea!
     
  8. Hussong

    Hussong Previous Member

    The point is this: If you are going to say that, with reference to the Seacart 26, "...These shots illustrate perfectly a curved lifting foil doing exactly what it is supposed to do-the ama bow is clear with the main hull way up-that is good design!" By inference, you are also suggesting that the M23, which has no lifting foils, is a less than good design. The M23 is designed by VPLP out of France, They are responsible for many of the state of the art trimaran designs today. I hardly think that they are without the understanding to produce a "good design".

    I think that they are two totally different boats with entirely different slices of the market. One is $38K and the boat that you say is good design, is significantly more at $130K. It seems to me that if a manufacturer wishes to keep costs under control and produce a truly fabulous trimaran in the under $40K region, that lifting foils become a unique and very pricey add-on that will certainly take the boat into the $50K region and well out of the targeted market segment.

    Comparing the less expensive boat to the radically more expensive boat and then further coupling the expensive product with a good design claim is inappropriate in my estimation.

    Perhaps if you compared boats with equal costs and features, your comparison would be more valuable. As it is, this is not a direct comparison and has little value.
     
  9. Doug Lord
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    Doug Lord Flight Ready

    This thread has nothing to do with "slices of the market"- only the technical differences related to the main hull takeoff angle of heel. Please start your own thread about "slices of the market", pricing as they may relate to a boat's technology etc.
    --
    My remarks were not intended as inferring anything about the M23. My comment about "good design" was related to the functioning of the curved lifting boards on the Sea Cart 26. Both boats appear to be good trimaran designs. Because of the differences in design the comparison of the M23 ama submergence and Sea Cart ama submergence(or lack thereof) at or near hull flying angle is within the topic of this thread.
    ----
     
  10. bruceb
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    bruceb Senior Member

    lift off

    Doug, thanks for posting the Sea cart pics- I am interested, even if my budget is somewhat:rolleyes: less. The under-body views tell a lot. I did notice quite a lot of rudder angle in both pics- I wonder if they were trying for "air". In the budget department, I have one of my foils finished and working- at last. I built the trunks before the foils and didn't get the fit quite right, but with enough sanding in the trunk, all is well. I will get some pics up soon, but with my first test sail, the a-board feels great. It definitely is lifting the float both up and to weather- of course, I don't know yet how much drag has increased. I do know that my budget for both trunks and boards is about $500 US, so lifting a-boards are not just for the wealthy:cool: B
     
  11. Doug Lord
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    Doug Lord Flight Ready

    ====================
    Looking forward to seeing them, Bruce! Are they curved or straight angled boards? Check out the video here of the Catri 23-straight angled boards plus a couple of small anhedral foils off the transom:

    http://www.youtube.com/watch?v=20tULUapaMM&NR=1 Didn't get a good measurement but I'd guess just about 13 degrees with the main hull just kissing. Fairly small amas and the foils are doing their job.....
     
  12. bruceb
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    bruceb Senior Member

    more lift

    my boards are also straight, little smaller and are right behind the crossbeam, and mine are probably 5 degrees more vertical so I won't get as much lift as the Catri. I have bigger floats and the Buc isn't as fast, so I was looking for more lift to weather. A friend has a Nacra 20, and from watching his boat, curved foils do require some adjustment for conditions, where the straight boards are somewhat less effective but also more forgiving. Also, I have enough trouble making a straight board, and a pair of curved ones would probably take me all winter:mad: I like to experiment, but I also like to sail, not sand. B
     
  13. Hussong

    Hussong Previous Member

    Spot on, bruceb. You've touched on the very reason why the M23 is not equipped with curved foils as suggested by others here. Cost/Time effectiveness in the build, which is the same as the manufacturer saying they are too expensive and not needed for what is already a great design.

    Ama foils play an insignificant part in the angle of heel when the main hull leaves the water.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    ------------------
    Bruce, is your boat a Buccaneer 24?(update-just read your earlier post about your Buc 24!--I guess it helps to read those earlier posts!) What's the scuttlebutt about foils on those boats-any info?
     

  15. Hussong

    Hussong Previous Member

    It is true and if you actually work out the physics accurately, you will see it to be so.

    Simply put; what forces cause the main hull to rise and what forces prevent it from doing so? Where does the center of gravity location benefit the lifting of the hull and under what conditions does the COG have a more difficult time of lifting the main hull?

    Lift from foils is not generated immediately, where heeling moments happen long before the foil is accelerated and capable of generating lift. The function of main hull lift has everything to do with the design of the base structure of the boat and the designed flotation of the ama relative to the heeling moment potential of the rig.
     
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