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

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

  1. rapscallion
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    rapscallion Senior Member

    interesting next generation amas!
     
  2. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    ----
    Yeah, if they work! These amas are designed to contact the water -either slow or fast- intermittently. They will support a curved lifting foil that will support most of the boats weight as speed increases with the two foils on the main hull gradually unloading after lifting the main hull in relatively light air.
    Thanks for checking in, Raps!

    PS-the "curved pieces" mentioned earlier and the next pieces to be built(very difficult) are critical to allowing the amas to function......


    click on image---
     

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  3. rapscallion
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    rapscallion Senior Member

    I have read tspeers awesome curved foil papers of awesomeness. I would love to hear about how you are going to make them...

    And I think the "fins" are clever. At low speeds they may create less drag than a flat bottomed Ama... are their any examples of such a hull form out there that you know of?
     
  4. Doug Lord
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    Doug Lord Flight Ready

    =================
    Not exactly-at least that I know of(but its a big world!). The curved foils will be made in molds and I'll document the process. They have to support 16 pounds plus a fairly substantial factor of safety. I'll make them and the trunks exactly like I'll build the fullsize foils.

    Let me clarify this: Raps if you look at the picture of the balsa(unglassed) hull you'll notice that they are not really fins but a continuation of the planing surface.

    --click on image:
     

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  5. troy2000
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    troy2000 Senior Member

    This is good stuff.

    I can almost absodamnlutely guarantee I'll never build or sail anything remotely like what Doug is working on, but I love to keep track of it anyway.
     
  6. DennisRB
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    DennisRB Senior Member

    I also like the ama design. A flat bottomed transom will create huge drag before it planes. This design will not create anywhere near as much drag even when the ama is half submerged at low speeds. Was this the intent Doug? Do you think these planing style surfaces would be usable on a design that is to be sailed in choppy/rough conditions?
     
  7. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    -------------------------------------
    Dennis, the main thing is that these amas are designed for intermittent contact-either slow or fast. They will not be sailed "on" for long since the curved lifting foil in the ama will begin to work as soon as the boat starts moving. The amas have the absolute minimum buoyancy that I've learned thru experiments(2 full size tri's, several RC tri's including the F3) is possible. That means they will work in all conditions to give buoyancy when required with the least drag allowing speed to build quickly so that the foils will work.
    They are variations on the MPX-12( see thread and previous mention in this thread as well as pictures) amas tailored specifically for this boat which, hopefully, will be a self-righting trimaran. So, for instance, the fixed keel adds a bit of RM with heel and helps the boat stay level with no ama immersion at static displacement.
    ----
    Only if they're used as they are in this boat for intermittent contact. The MPX-12 amas are designed to support the whole weight of the boat in most inshore conditions while planing-but they are extremely experimental and would probably require foil assist in rougher conditions. The SRT amas are a bit less experimental and more based on proven experience.
     
  8. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

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    Glad you said almost! Thanks for checking in-and if it works-and you're in Florida, well............
     
  9. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    Here is some additional testing mainly to the rig with the high aspect square top jib.
    1) I have considered what the effect of moving the tack of the headsail-especially one like this or the aeroskiff-to leeward would be. Now thanks to Daniel and Eric Sponberg in this thread I know for sure: http://www.boatdesign.net/forums/hy...eadsail-vs-shroud-angle-39379.html#post481427
    It will improve pointing ability and will definitely be set up on the model.
    --
    2) A problem with a rig with a tall narrow jib like this is forestay sag to leeward in the middle so I'm going to experiment with matching that sag with bend to leeward of the mast-like a DN iceboat but much less bend.

    pictures- original experimental aeroskiff rig with square top jib and rough sketch of SRT rig:
     

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  10. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    Good news. I've sorta been dreading building the "curved pieces" I mentioned earlier because the way I was going to build it was tedious and heavy.
    So, you may remember that right at the begining I bought a large piece of 1.5lb styrofoam to use as a base to build the hull. That didn't work out so I still have the foam. I got the stuff from a local architectural foam place and it turns out they have a computer controlled hot wire and they can cut the pieces in one fell swoop, so to speak. But not until sometime next week.
    When I get the foam pieces there will be some light shaping, installing crossarm receptacles and then they will be carbonated. Pretty quick and light enough.
     
  11. rapscallion
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    rapscallion Senior Member

    WOW! That is good news! It's good to hear things are still moving along
     
  12. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    Design Notes on Ama Foils:
    Here is a rough sketch of the curved ama foil(see left picture below). The position of the foil marked "3" is the length of the foil at maximum deployment. On the full size boat the foil will be 8' long with a 2.25' radius, a chord of .85'(may be changed). The foil sticks out under the ama 6' with the immersed(from bottom of ama) portion having an aspect ratio of 7/1(may be changed). It has a fairly tight curve to maximize vertical lift.
    The foil only draws 2.25 ' at max deployment from the bottom of the ama.
    It will be capable of supporting the entire weight of the boat at 13 knots( 15mph) within the drag bucket of the foil. Of course , being a curved foil it will be completely adjustable- with a variable angle of incidence( +1 to + 4 degrees-nominally set at +2.5 degrees) of the vertical lift section without interfering with the lateral resistance developed by the board. The vertical section of the curved foil will be designed to unload the daggerboard that supports the main foil and the leading edge will be adjustably toed in between 1 and 3 degrees(maybe). You can get the model dimensions by multiplying the above by 3.375,so under the boat: 20.25" with a 7.59" radius, and a 2.87" chord and a 64312 section(for now). An interesting thing I'm going to test is to extend the end of the foil 6-8" tangent to the curve which will help to maximize vertical lift. It will also mean that 6-8" of the foil will always stick down....The foil requires no altitude control and will, at times, behave as a surface piercing foil. Because of the lifting foils on the main hull this foil is designed to carry a larger percentage of the total load than a "normal" ama curved foil does and the ama itself has nothing to do with pitch control as it does on "normal" curved foil equipped amas. Further, as the load increases on the ama foil, it decreases on the main foil(s) until they are virtually unloaded except for their requirements of sailing angle control and pitch control.
    ------

    Ama Foil + Trunk Build Plan(and notes):

    I'm going to use the same technique on the test model I'm building as I will on the full size. I haven't built curved foils yet but I have designed and built tooling for 40 years and know it well. I've built numerous examples of straight foil tooling including foils with matching trunks for models and full size boats.
    So heres the plan:
    1) build a curved platform with the surface equal to the centerline thru the foil,
    2) build one half the foil on the surface,
    3)* add sheet wax equivalent to the allowance for foil clearance in one half the trunk. I haven't decided on this yet but I notice that Farrier includes some kind of material like outdoor carpet in the trunk for their cassette rudder to allow the thing to slide while still being held relatively firmly.
    4) use wax and/or clay to make a pivot point(s) for one half of the trunk . The pivot point allows the head of the foil to be able to be moved fore and aft to tune the angle of incidence. A molded "round" should be included at the bottom of the trunk in front and in back( or just above any molded insert-see below). The clearance should be a maximum of 1/16" and the round can be designed to have a small thin piece of delron glued to it. Note that the foil angle of incidence will not be adjusted under load.This method doesn't allow for adjustment of the toe-in of the foil except by moving the trunk. Also ,it doesn't allow any 'cant' but I don't think that is necessary on my boat. The trunk will allow for the foil to pivot fore and aft approximately -3 degrees(forward) to + 6 degrees(aft) or slightly more.
    5) wax the edges and possibly spray with partall ,
    6) lay up one half the trunk----before pulling attach a light, removable framework to prevent the trunk half from warping.
    7) pull trunk half #1,
    8) Since my foil is constant chord I'll go ahead and lay up the second trunk half. Reminder: make sure to move the pivot point!
    9) remove the sheet wax and clay from the foil half plug, clean up and rewax,
    10) lay up the mold for this half of the foil,
    11) pull the mold and build a one off foil inside the mold using the exact same patterns you used to build the first half,
    12) Repeat 3,4,5,6, 7 and 8 for this second half foil mold and two trunk halves.
    -------
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    Rough Sketches, L to R, 1) Final design of the SRT curved ama foil, 2) *trunk illustration showing pivot points and removable insert to facillitate sliding board, 3) Farrier F32 curved foil + trunk- note room at the top of the trunk(left of picture) for the head of the foil to move fore and aft:

    click on image for better detail:
     

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  13. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    ======================
    They're done!
     
  14. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    Here is one "curved piece" mocked up in not quite the most precise way to give you an idea of how it will work. Also, another picture of the MPX-12 ama
    and its "curved piece" to compare to.( more MPX-12 info: http://www.boatdesign.net/forums/multihulls/mpx-11-very-small-high-power-trimaran-33686-15.html )
    Again these pieces connect the carbon tube cross arms to the ama. On the model the ama running angle will be able to be adjusted slightly by moving the forward cross arm vertically on the main hull, with more adjustment possible by selective-but simple-grinder surgery facilitated by built in carbon pins. Nominal running angle when on foils = 4 degrees. And ,again, the ama is designed for intermittent contact-not to be sailed "on"(necessarily). Also the "curved piece" has about the same static buoyancy as does the ama itself with both together(and the lee side carbon tubes) a bit less than the boat displacement-about 80%. The curved piece keeps the center of buoyancy of the combined ama/curved piece fairly high and that and cross arm dihedral and forward sweep should play a role in the self -righting characteristic of the boat(if it works).
     

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  15. Doug Lord
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    Doug Lord Flight Ready

    High Performance Self-Righting Trimaran: The Test Model

    ====================
    Tomorrow I should have pictures of the first accurate mock up of the complete boat-stay tuned........
     
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