MPX-11 Very Small High Power Trimaran

Discussion in 'Multihulls' started by Doug Lord, Jul 13, 2010.

  1. Doug Lord
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    Doug Lord Flight Ready

    MPX-12--FLASH TRItm

    --- Version 3 specifications revised and updated from 8/13/10 on.
    1. Version 1-top of page 1-estimated production specs.
    2. Version 2-top of page 2-one-off specifications reflecting higher weight of the one-off boat while maintaining ratios close to version 1. Refinement of some parameters as the design has progressed.

    ---As stated previously IF this thing is built it will be done as a one off which means it will be heavier that the production(molded) estimate in post #1.
    A small conceptual model is being built now-pictures will be posted in this thread. Work on the model has been instrumental in helping to refine the one-off design.
    And,this is a hot little boat as you'll see in a while........
    These are the revised specs:

    Note #1: the MPX-12 uses planing hulls because at this size displacement hulls carrying this kind of weight can't be "skinny" enough to take advantage of the low resistance characteristics of a high L/B hull-particularly with the main hull. It may be possible to use a skinny (L/B 14/1 or higher) ama hull coupled with a hydrofoil.
    Note#2: The MPX-12 uses two lifting hydrofoils-one on the rudder and one on the main foil. These foils are critical to the function of the boat. The system they comprise will be called the Flight Control System(FCS) and its derivation and application is detailed in subsequent posts. See post # 29, page 2 for more info.

    --Main hull beam-5.17'
    --Main hull beam at the waterline 3' (correction 8/7/10)
    --L/B-mainhull at waterline-4/1(planing hull/planing threshold: 6.9knots. (correction 8/7/10)
    --Overall beam- 16.5'(15' cl ama to cl ama) updated and corrected 8/19/10--NOTE: approx the same overall Beam/overall Length as Hydroptere.(not including gantry on MPX-12)
    --LOA- ama-10
    -- Ama LWL-6'
    --Ama beam- 1.5'(max and max at waterline)
    --Ama L/B- 4/1(planing hull/planing threshold-4.89 knots
    --Sail Area- 163 sq.ft /23.5' mast length. Slightly taller than a scaled down A Class Cat. updated 8/19/10
    --Main foil planform area-1.6 sq.ft.updated 8/19/10
    --Daggerboard immersed planform area(boat @ 10 degrees)- 1.195 sq.ft.
    --Rudder immersed planform area(boat @ 10 degrees) - .8 sq.ft.
    --Rudder foil planform area-1.3 sq.ft.
    --Draft(max) -3.5'
    --Draft @ 10 degrees -2.39'
    --Weight-155lb all up,ready to fly minus crew updated 8/13/10
    -- Total sailing weight- 395lb- updated and corrected 8/19/10
    --Max crew weight-240lb updated 8/7/10 ( note this gives a little wiggle room for hull weight)
    --Minimum crew weight(at max power)-120lb (boat can sail in same windstrength with minimum or maximum crew weight(!)
    --Max Mainfoil loading - 157.5 lb/sq.ft. in .3lb wind pressure @ takeoff @ 80% total load. NOTE: this is LESS mainfoil loading than a Moth with Veal(very light) updated and corrected 8/19/10---Loading DECREASES as speed increases.
    --Wand- altitude control system used in combination with the lifting hydrofoils on the daggerboard and rudder. Can be used to control sailing heel angle and compensate for different crew weights. Allows the boat to fly the main hull much earlier than it otherwise would.
    -- Max Pressure/w/o reefing 1.8 lb/sq.ft( 1.8 for F18 and 18 tri) The boat should be reefed(or the sail twisted off) in these conditions to prevent potential structural damage. After testing a warning label similar to the one installed in the Rave cockpit would probably refer to max speed or max apparent wind.
    --Designed Sailing Angle- 10 degrees from 5 knot wind. Maintained by wand surface sensor in conjunction with main hydrofoil and rudder hydrofoil.
    System allows hydrofoil to lift up or pull down automatically-regardless of wind(up to 1.8lb. per sq.ft) or crew weight(120-240lb.)
    -- SA/WS:
    a. not flying main hull-5/1
    b. flying main hull-13.8/1(moth on foils=13.65/1) updated 8/4/10
    -- SA/D= 47.47/1( updated 8/13/10 )
    -- W/SA= 2.42 (240lb crew-better than Moth w/Veal or Payne!) (Weight/ Sail Area="sail loading"-quick and dirty comparative ratio for low resistance boats-particularly foilers. 26' Mirabaud and 11' Moth about the same)-updated 8/13/10
    -- SCP/total weight*= 72.9% updated 8/13/10 -see note below
    --MAX RM-3322 foil downforce X 7.5)=3600 updated and corrected 8/19/10
    --MAX HM(before reefing/depowering) updated 8/13/10
    ---The crew will sit on a very comfortable sliding seat with a backrest.
    ---The seat will slide a maximum of 2' .
    ---The boat will have a simple robust folding system-nothing to take apart-ready to go in 5 min.
    --- See Wand above: this boat uses just two lifting hydrofoils which are critical to its operation.
    ---Ideas under consideration:
    a. jib pivot point traveler( see bottom of page 2)
    b. small "ballestron"/rotating whole rig( see bottom of page 2)

    Change, 8/4/10: Definitely will add 2' gantry to boat. Will be adjustable in overhang and facillitate rudder hydrofoil angle of incidence change.

    Change, 8/13/10: Beam to increase to 15' CL ama to cl ama, 16.5' overall all. Allows nominal 9" clearance of main hull at a 10 degree angle of heel with amas at a 10 degree cant(bottom outboard with boat vertical). RM does NOT change.

    Change, 8/13/10: Boat to use gybing/canting daggerboard +mainfoil. Eliminates leeward component of hydrofoil at designed sailing angle of 10 degrees. Gybing board(F18 Capricorn and several dinghies) improves windward performance. As noted above the boat uses a sliding seat that moves a maximum of 2' and can be used to move the canting/gybing board from tack to tack(8/19/10)


    More Power, Much more Comfortable, Much easier to sail than ANY similarly powered up boat!

    More later.....
    --*SCP(sail carrying power)= the RM in ft.lbs divided by the distance in feet between the CE and CLR. To get Bethwaites ratio this number is then divided into the total weight in pounds.SCP/Total Weight- A ratio of 30% or better permits upwind planing.

    Revision of this page complete 10pm, 8/19/10 .
    Last edited: Aug 19, 2010
  2. Doug Lord
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    Doug Lord Flight Ready


    This is an update of post 19,p2 reflecting the changes to the specifications:

    The changes to the boat to facillitate a one off(and on which the model is based) shown in the post above reflect a very high SA/ws and a low W/SA.
    A) The Sail Area/wetted surface ratio:
    Wetted Surface, main hull flying-------------
    Main foil-(1.6 sq.ft. planform area)--------------3.2 sq.ft.
    Rudder foil-(1.3 sq.ft planform area)------------ 2.6 sq.ft.
    Vertical Fin/dggrbd(2' immersion)----------------2.39 sq.ft.
    Rudder----------------------------------------1.6 sq.ft.
    planing surface(ama)--------------------------2 sq.ft.
    TOTAL WETTED SURFACE---------------------11.79sq.ft.
    MXP-11(12) SA=163sq.ft.

    SA/ws= 163/11.59= 13.83/1

    Comparison to Moth:
    Main foil (planform area 1.1 sq.ft.)-------------2.2 sq.ft.
    Rudder foil( planform area .88 sq.ft.)-----------1.76 sq.ft.
    Vertical Fin/dggrbd(18" immersion)-------------1.17 sq.ft.
    TOTAL WETTED SURFACE-------------------- 6.3 sq.ft.
    Moth SA= 86 sq.ft.

    SA/ws-86/6.3= 13.65/1


    B) Main foil loading(assuming that the main foil supports 80% of the weight/load). On the MPX-12 the foil lifts both up and down.

    ---Because of the nature of the foil system on this boat the highest foil loading occurs in the lightest air(.3lb. per sq.ft. wind pressure) at takeoff. In this case the main foil loading is 252lb. of vertical lift( 157.5 lbs. per sq.ft. main foil area).
    The next highest loading is with the minimum weight crew in maximum conditions(1.8lb. per sq.ft. SA pressure) where the the load is 187 lb. down force ( 116.8 lb. per sq.ft. main foil area).
    Heavy Crew-Max vertical lift: 252lb(157.5 lbs per sq.ft.)
    Lite Crew-Max downforce: 187lb( 116.8 lbs per sq.ft.)

    ---Comparison to a Moth(vertical lift only-main foil @ 80% only) :
    Lite crew(154lb)=160 lb/per sq.ft.
    Heavy crew(180lb)=178.9 lb. per sq.ft.
    C) W/SA=weight in pounds divided by sail area in sq.ft.( sail loading-smaller=better )

    --MPX-12=all revised:
    a. Heavy=395/163= 2.42
    b. Lite= 275/160= 1.69

    a. Heavy= 246/86= 2.86
    b. Lite= 220/86 = 2.56

    Interesting A Class & C Class Cat comparisons with Moth and MPX-12--ALL WITH 175 lb* crew:
    *(2 X 175lb. for C Class)

    1) W/SA(weight in pounds divided by sail area in sq.ft.) smaller better :
    a. Moth(66+175=241lb) 241/86= 2.8
    b. A Class Cat( 150+175= 325) 325/150= 2.16
    c. MPX-12( 155+175= 330) 330/163= 2.02
    d. C Class Cat(approx.)-680/300= 2.27

    2) SA/WS(sail area in sq.ft. divided by wetted surface in sq.ft.)
    Note: A Class calculated with one board, one rudder and flying one hull. In addition 10% of its wetted surface is deducted to account for lift from the new curved boards.

    A) FLYING:
    a. Moth(from above) SA/ws= 13.65/1
    b. A Class Cat(wetted surface=21.53 sq.ft) SA/ws= 6.96/1(corrected)
    c. MPX-12(from above) SA/ws= 13.83/1
    d. C Class Cat (wetted surface incl 1 board,1 rudder=35.63sq.ft./approx.) SA/ws= 8.42/1

    a. Moth- SA/ws= 3.51/1
    b. A Class- SA/ws= 5.56/1
    c. MPX-12- SA/ws= 6.17/1
    d. C Class Cat(approx.)- SA/ws= 7.5/1

    I would think that anyone who might be interested in fast small boats-particularly multihulls should study these results very carefully. The Moth is a good benchmark since it has regularly beaten A class Cats, F18s etc. The results above go a long way to explain why.....

    page updated and corrected 8/19/10
    Last edited: Aug 19, 2010
  3. Doug Lord
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    Doug Lord Flight Ready


    Making steady progress on the model-just completed the 2nd fill. Lot more sanding, a bit more filling and you will see an interesting model of the potential prototype. Looks wild....
  4. Doug Lord
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    Doug Lord Flight Ready


    The model is almost finished-at least the hard part and I've been giving the "mini ama foils", first mentioned in the post below(# 13 this thread), more thought. I think they could be beneficial. They would be retractable and I think testing them on at least one side would be the way to go on a prototype should one be built. No altitude control system but adjustable angle of incidence. Less than half a square foot area(very tentative), no flap, asymmetrical section.They would retract aft of and above(slightly) the planing surface and extend below the planing surface 1.5-2'.
    63412, area=.375sq.ft.,foil lift(one side only):
    a. at Cl= .6, speed 10k= 62lb.
    b. at Cl= .31, speed 20k= 128lb.
    c. at Cl= .31, speed 25k= 200lb.
    Note: angle of attack=2.2 degrees=Cl of .6,
    angle of attack of 0 degrees= Cl of .31 . To achieve this, angle of incidence of foil is "shifted" based on speed.

  5. Doug Lord
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    Doug Lord Flight Ready

  6. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    MPX-12 (Flash Tri)

    Well, its not finished but I thought you might like to see these first pictures.
    -- the seats slide
    -- the rudder gantry slides in and out as well(in for trailering)
    -- the boat(and model) folds for trailering. It can also be disassembled and "plugged in"(Weta style) instead of folding.
    -- rig not done yet
    -- planing amas angled 10 degrees which is the sailing angle of the boat-automatically controlled by the wand(not shown yet).

    Note: see post #45 ; crossarm angle to be changed as of 9/19/10-these original pictures will remain to compare with the modifications.

    click on image and then again on resulting image

    Attached Files:

  7. gypsy28
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    gypsy28 Senior Member

    Speaking as a mold maker, if you can produce the molds for that for a similar price to a 11 (or 12 or 13) foot cat I'll eat my shoes, looks cool tho
  8. Doug Lord
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    Doug Lord Flight Ready

    No chance. This thing offers much more than any cat in those sizes and will cost more.
    --much faster
    --much more comfortable
    --much easier to sail
    Thanks-you can save your shoes.......
  9. Eralnd44
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    Eralnd44 Wanderer

    moth is no concequence.

    comment maybe runs away for the wind drag on ama things? drag always there. every step you think goes front is then two steps to make it behind. not design progress and also ugly

    if noodle looks right then must be spaghetti. you forget the taste
  10. Gary Baigent
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    Gary Baigent Senior Member

    Doug, I admire your tenacity for pages and pages of figures and to your model making but perhaps you became too enamoured with joining curving lines in this model. Putting these shapes together just increases weight and windage and the surface area of this small boat is very large. The flattened areas towards the bow sections of the amas, the devils tails pointing forward, would be conducive to sudden burying in waves should the lifting foils trip. IMO you need to take your model saw to many of these areas and return to simplicity. Because a small, powerful, foiling tri would definitely be a good time sailing boat.
  11. Doug Lord
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    Doug Lord Flight Ready

    Thanks for your comments ,Gary.
  12. Munter
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    Munter Amateur

    Doug - did you ever see that episode of the Simpsons where Homer designs his dream car? It was called "The Homer". I think what you have presented here is "The Doug".

    I like how you have multiplied the load on the front beam by cantilevering the outer hulls. Why not get rid of the rear beam and just rely on the torsional capability of a single beam?

    Edited to be more constructive:

    Distribution of buoyancy
    What stops the design tipping over diagonally backwards? Given there is no bouyancy out at the floats wouldn't a decent gust just off head to wind be enough to tip it? At low speed the floats will supply minimal righting moment so how does one keep the boat under the rig?

    Why have you gone for long narrow planing floats? Long narrow floats gives you a low aspect ratio planing surface and is quite different to the solution that sailboards have gone to where short and fat boards are used to give a low planing thresh-hold. Why are you apparently trying to combine a planing surface with a wave piercing design?

    What stops this design from going sideways if it got to the point of being on one hull? Given the large sail area how will the minimal remaining foil area actually cope? I think the verticals may be prone to ventilating, particularly when you consider that they are surface piercing. Having a gybing dagger board doesn't seem like a sensible solution partly because it implies the board has a degree of freedom to move that is the exact opposite of what experienced foilers aim for (ie a rigid connection between the foil and hull). A gybing board won't be any less prone to ventilate and may actually be more prone to it I would guess. Other multihulls minimise leeway using the vertical area of the leeward hull - you design does not appear to be designed to do this and I suspect you have significantly underestimated this problem.

    In our previous discussion of your proposed design I raised some concerns over the mass. You have since deleted most of your contributions to that thread but the mass issue hasn't gone away. Those floats are really quite a bit larger than I had imagined in terms of surface area. Have you actually found a functional use for all the parts or have significant parts of this design been predetermined by the apparent re-use of a previous model? What are the big vertical sections at the rear of the floats about? They will surely add significant weight if you expect them to be strong enough to handle more than 10kts of boatspeed. Have you just glued a bit onto a previous model to come up with this design? With a design philosophy like that I think it is exceedingly unlikely that this vessel will come in at the revised target mass.

    Structural Integrity
    Why does the planing float extend so far in front of the amas? The further the lifting point is from the amas, the more stress they will be under. It doesn't look like a sensible way of transferring the load from the planing surface to the main hull.

    A little day dreaming and fantasy boat design is fun and a big part of what I think this forum is about. A little chop and change of a previous model is fine and fun but I think it is pretty misleading to suggest that this design is the result of any serious analysis or investigation. It seems way too early to be making definite statements about speed, comfort and ease of use when it isn't really clear that the vessel will work at all? How about modestly under-promising and then over-delivering instead?
  13. Eralnd44
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    Eralnd44 Wanderer

    Flash is slang for the sensation felt immediately after injecting a narcotic.
    Flash is slang for ostentatious.
    Flash is British slang for to expose oneself indecently.
    Flash is slang for, To fill suddenly with water.
    Flash is slang for relating to thieves, swindlers, and underworld figures.
    Flash is slang for the act of vomiting.
    A flash in the pan
  14. Doug Lord
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    Doug Lord Flight Ready

    I made a big mistake allowing the cross arms to come across the main hull straight-it screws up the "look" of the main hull and is not as strong as it could be.Further, the crew sits 4" too high. So the cross arms will be changed and will be re done-right this time. Should make a major difference in appearance w/o too many negatives except the time. But that is why I built the model-to get it right.
    No other changes, Gary......

  15. Doug Lord
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    Doug Lord Flight Ready

    Gary, I don't see the flat areas you refer to. The forward half of the ama is designed as a wavepiercing hull that is integrated into the aft planing sections in such a way as to allow the ama to take wave impacts with little fuss. The whole ama would have to pitch down 8-10 degrees for the hull to cause a pitchpole. The design running angle of the planing surface is +4 degrees which is adjustable and controlled and maintained by the two main foils. The main foils are more deeply submerged than, say,Moth foils and are much less loaded in heavy air to the point that at max pressure(1.8lb/sq.ft of SA) with a 240lb crew the main foil is developing less than a 100lbs of downforce and between .8 and 1.7lbs/sq.ft wind pressure the foils develop no lift or downforce. Their main "mission" is pitch control with a far greater ability to control pitch and heave since they have little to no load through out the medium to high speed range.
    Back to the ama:the design utilizes curves to create a very light weight structure. The ama is designed to be able to be fully submerged inadvertently with the lowest possible resulting drag and to be able to get back to max speed quickly. The whole ama has about 200lb buoyancy when immersed up to the crossarms-that is a lot on a 155lb 16' wide trimaran(50+% of total sailing weight)-but nowhere near what one would want on a cruising tri. But its perfect for this boat-low drag and light weight. The weights quoted above are for a one off and could be reduced 20-30% if the boat was molded.
    The planing amas do not work like normal planing hull boats do. Most planing hulls -say, like a sailboard-have to start from zero with the same load they'll have at 20 knots. Not these amas: they don't begin to carry the full load until the boat is moving at 13-18 knots which allows them to be much smaller than they would otherwise have to be. In fact, that and the integration of wavepiercing geometry to the forward half of the ama are the keys to what I hope will be exceptional performance. Of course, the ama design would be useless without the foils so it all has to come together to perform well-and I think it will.

    click on image and then again on resulting image:

    Attached Files:

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