High Performance MPX Foil/Self-righting Trimaran-The Test Model

Discussion in 'Multihulls' started by Doug Lord, Dec 28, 2010.

  1. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model


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    OK: weight(displacement) varies as the cube of length:
    1) model length=60.75"=5.0625' ;5.0625' cubed=129.75
    2) full size= 18' ; 18 cubed = 5832
    3) model to full size= 5832/129.75=44.95, so multiply model weights by 44.95.
    4) full size to model=129.75/5832=.02225; (example:-.02225X 750 =16.688lb)
    ------
    model to full size(X 44.95)-all in pounds:

    mainhull=3.858=173.42
    amas(2)=1.25= 56.19
    mast and sails= 1.05=47.20
    curved pieces(2)=1.25=56.19
    2 cross arms=.74=33.26
    2 foil sets= .74= 33.26
    crew= 3.9=175.31
    ballast=3.9=175.31
    ===================
    Total 16.688=750.14lb (16.688X 44.95=750.13)
    --
    Notes: Mainhull (128lb now), ballast and "crew" provide leeway both on model and full size for mistakes and adjustments.
     
  2. AsterixDeGaul
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    AsterixDeGaul Junior Member

    Ok. this is exactly the same result i got but I simply use the SCALE cubed for the multiplyer ... notice (12/3.375)^3 = 44.94924556 (44.95)
     
  3. Doug Lord
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    Doug Lord Flight Ready

    =======
    Seems to work well!
     
  4. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran:The Test Model

    Part 1 of 2:
    ----------------------------

    Possible small design change: ( originally posted 1/3/12)
    In going over everything for assembly one last time (which involved looking at the testing I want to accomplish) I realized that the center of lift of the planing part of this ama-particularly when modified later for testing the MPX planing ama-is a bit too far aft. Moving it forward may be a possibility-I'll know after checking the CG calcs. Doesn't appear that anything else would be negatively affected. I'll know later....
    =================
    UPDATE 1/4/12: The amas don't need to be moved at all. The additional planing surface added to the ama for the test( to Test the planing ama*) has its center of lift just forward of the center of lift of the main foil+rudder foil(mainfoil carries 80% of the boats weight) so its in an ideal position.
    I calculated the approximate total planing area at a running angle of 2.5-4 degrees(controlled by the foils on the main hull) to be 6 sq.ft for 750lb @ 15 knots.
    *in the past I haven't been real satisfied with planing surfaces on smaller models-which the ama surface is. So model testing of a planing surface may not be very worthwhile at this size. But the area and position of the ama for full size testing is ideal.


    pix-1 & 2 MPX-12 planing ama, 3) red line shows approximate position of SRT ama transom if it is moved forward relative to curved piece:
    click on image-
     

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  5. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    Part 2 of 2:
    ---------------------------------

    Below are images of the tentative planing surface(cardboard cut out) to be tried on the model and the full size boat. More details in Part 1. For those who wonder how the Center of Lift of the ama can be so far behind the CG of the ama it should be pointed out that the Center of Lift of the ama is 3.375"(1' full size) ahead of the fore and aft location of the CG of the boat.
    The CG of the boat coincides exactly with the fore and aft location of the Center of Lift of the main foils(at takeoff)-with or without ballast.
    Another important point is that the Center of Lift of the curved lifting foil is just slightly ahead of the Center of Lift of the main foil(which is ahead of the combined static Center of Lift of the main and rudder foils together) and is about 3"(just under 1' fullsize) ahead of the center of lift of the planing surface of the ama. The idea is to build in a bit of pitch resistance to supplement the rudder foil. The ama CB is at the Center of lift of the curved lifting foil.
    Testing will include:
    1) the planing surface and curved lifting foil ,each separately, lifting the total weight of the boat,
    2) the combination each lifting different proportions of the total boat weight.
    3) Of particular interest to me is evaluating the degree to which the curved lifting foil could help the ama to plane and the effect of the curved lifting foil on the ama planing characteristics in waves.
    =================
    The most important thing to understand about the foil system on the SRT(MPX foil system) is that the curved lifting foil or the planing surface or the two in combination must be able to carry the full weight of the boat. This is a critical function for this system to work. At the point that the full load is carried by the ama( curved foil ,planing surface, or both) the two main foils are unloaded except for their work of controlling angle of heel and pitch. The two mainhull foils(rudder and daggerboard lifting foils +altitude control system-wand) control the running angle of the planing surface and/or the angle of attack of the curved lifting foil. This is the essence of this foil system design.
    One more thing: this system could also work with a low volume, high L/B displacement hull with the curved foil.


    Click on image to see Center of Lift and Ama CG in pictures 1 & 2. Note that the modification of the ama to include this lifting surface is not being done now but the design had to be done to make sure the ama is in the right position-it is.....
     

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  6. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    ====================
    Just for the heck of it I called the Technical Support number on a can of "Dynalite"( bondo like filler but works better) to ask about applying it to an epoxy substrate. A tech rep called back today saying that as long as the epoxy was well cured and sanded with 80 grit the stuff would bond well. This stuff works better than any epoxy based material I've yet tried so I'll probably use it just to test it. On a full size epoxy boat I'd probably use the stuff in the post above....... I hate one offs and will avoid them as much as possible! Building tooling for this boat would have resulted in a much lighter boat that was virtually finished out of the mold(using paint, not gel coat) but it would have cost much more than this thing and would have forced me to lock in things that aren't ready to be locked in. Now if this boat works well it could become a plug-maybe.......or not.
    UPDATE: In addition to the Dynalite and Adtech filler I found this-see pdf below:
     

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  7. Gary Baigent
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    Gary Baigent Senior Member

    Doug, the float shape is very interesting but I wonder about the delta flat shape centre and aft. I know what you're aiming for (planing) but once that shape buries into the back of a wave at high speed, it is going to act like a very large horizontal dart shaped foil at negative angle of attack and keep on going down and won't lift up like a reverse bow shape, say on an A Class, shedding water from the curved upper sections of the bow; it is going to keep on plunging ... or am I completely off course with this interpretation?
     
  8. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran:The Test Model

    ----------------
    Gary, I think you may be off course but thats why its going to be tested. The running angle of the ama is controlled by the foils on the main hull-and is fully adjustable. My initial thoughts are to keep the planing surface leading edge relatively sharp to allow it to penetrate waves without a lot of extra drag.Thats the idea on the whole ama design: a planing surface(and/or curved lifting foil) coupled to a high L/B wave piercing hull. May not work with the planing surface but I think its got a good chance because the boat is not relying on the ama for pitch control or control of running angle. The main foils "impose" control on the ama. The use of the planing surface in combination with the ama's curved lifting foil may wind up being the best solution-we'll see. The planing surface will be set at between 3-4 degrees positive running angle, and again, is controlled by the foils on the main hull.(as is the angle of attack of the curved lifting foil)
    Thanks for your comments!

    PS-Greg Ketterman does not think a planing surface will work at all.
     
  9. cavalier mk2
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    cavalier mk2 Senior Member

    3-4 degrees is the low end of the planing angle of attack curve. Can you adjust to the upper 5-6 degree end of things if needed?
     
  10. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    -----------------
    Sure. Interesting you should say that. A windsurfer designer I know said it should be no more that 2 degrees! All the more reason to test-though I don't have high expectations about any results determined in model testing for the planing surface. We know that the results for the curved foil and main foils will scale up well(thanks to Bradfield and Ketterman). My feeling is not so much that the planing ama will be a breakthru performance wise but maybe a breakthru fun wise especially on a small boat like the MPX-12. We'll see....
    Thanks for the info and question.
    More:
    Just ran into this:
    In an interesting professional paper presented to the Society of Naval Architects and Marine Engineers (SNAME), ON THE SUBJECT OF HIGH-SPEED MONOHULLS, by Daniel Savitsky, I came across this assessment of the influence of a planing hull's trim angle (what we non-naval architects might call the running angle when on plane) on the effort needed to propel the hull:

    "...the performance of a planing hull is very dependent upon the longitudinal location of the center-of-gravity that controls the trim angle of the craft when planning. The trim angle in turn has a major effect upon the resistance/weight ratio. Typically, the resistance of a planing hull is a minimum at trim angles between 3-4 degrees and increases for both higher and lower values of trim. If the center of gravity for a given hull cannot be varied, then transom flaps or transom interceptors [i.e., trim tabs] can be used to change the trim. Analytical methods are available for evaluating the effect of center-of-gravity position or transom flap design on the equilibrium running trim angle."
    Cf.: http://legacy.sname.org/newsletter/Savitskyreport.pdf Note: this was reported on a Boston Whaler forum and this paper is about high speed planing monohulls.
    =========
    In "Design of Sailing Yachts" by Pierre Gutelle, he has a table that shows the resistance of a flat plate planing lowest between 4-6 degrees:

    click on image-
     

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    Last edited: Jan 10, 2012
  11. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-righting Trimaran: The Test Model

    This may help to explain how the MPX foil system works. This video animation was done to illustrate how the wand works in relationship to the foil on a Rave(or SKAT,or Osprey, or F3).
    Applying this to my foil system, you need to envision a wand on each side of the main hull connected with each other and to the main foil flap as shown in the video. The system then works as shown but what is being regulated is the altitude of the main hull and therefore the angle of heel of the whole boat.
    In addition, the ama in the MPX system can be a planing hull, a planing hull with foil assist, a low volume high L/B hull with a curved lifting foil for foil assist or full flying as a surface piercing foil. Model testing will help determine which solution is the best, but full size testing will answer the question definitively.
    The advantage of this system in a small, very wide performance tri, is that it will allow the main hull to fly in very light air which then permits the main foils to unload until one of the ama configurations supports the whole weight of the boat.

    http://www.youtube.com/watch?NR=1&feature=endscreen&v=yuFwDm8t3IM
     
  12. rapscallion
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    rapscallion Senior Member

    I feel your pain when it comes to tooling and building one offs.... I just bought a 3D printer to play with... I'm going to use it for work mostly... I'm working on resins for 3D printing applications in my spare time. 3D print your tooling! Hell, 3D print the damn boat!
     
  13. Doug Lord
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    Doug Lord Flight Ready

    =======
    Hmmmmm... how big an object can you "print"? I love those machines!
     
  14. rapscallion
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    rapscallion Senior Member

    The one I bought is small, but it has two extruder heads. Right now I don't see why you couldn't double or triple the size of the controller arms so you could print bigger objects. I'll know more after the weekend. The software will take some getting used to.
     

  15. Schoonner
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    Schoonner Senior Member

    Now THAT sounds like something I'd like to try. Why not make a modular model that you just glass together after printing all the pieces?

    Nice model Doug Lord!! I dunno why I didn't see it before. I admire the curved pieces between the main hull and ama. They remind me of the stub wings between the fuselage and engine nacelles of the P-38 Lightning WW2 fighter. Might even be able to get a little lift out of them when pointing windward. Just figure some foils for them that will be more effective on the leeward side at 45 degrees from straight on that way the windward side doesn't see as much lift as the leeward side. You could also use longitudinal fins on them to reduce their lift coefficient at angles you don't want as well as increase drag when running. (Just my two pesos)
     
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