Post your design ideas

Discussion in 'Multihulls' started by Brorsan, Mar 11, 2011.

  1. Brorsan
    Joined: Nov 2007
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    Brorsan Junior Member

    I would like to start a thread where people can post and discuss their multihull design, even if they are not planed to be built. Post pictures and descriptions of your designs and share thoughts and comments. This means that a person can post a number of different designs just for the fun of designing.
    This is after all a boat design forum :)
     
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  2. Brorsan
    Joined: Nov 2007
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    Location: Gothenburg/Sweden

    Brorsan Junior Member

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

    Design Ideas

    Here is a link to my MPX-12(11) 12' trimaran thread. It uses a unique foil assist system with experimental planing amas.
    http://www.boatdesign.net/forums/multihulls/mpx-11-very-small-high-power-trimaran-33686-15.html
    Comments, ideas, suggestions and constructive criticism welcome.



    MPX-12 Specs

    -- LOA-12' 7"
    -- LWL-12' 7"
    -- Main hull beam-5.29'-
    -- Main hull beam at the waterline -3'
    -- Overall beam- 17.5'*(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) *tentative as of 11/10/10
    -- LOA- ama-10'
    -- Ama Buoyancy - 3.25 cu.ft/ 208lb / 53% of sailing weight
    -- Sail Area- 178 sq.ft /25.5' mast length. Slightly taller than a scaled down A Class Cat.
    -- Draft(max) -3.5' tentative
    -- Weight-159lb all up,ready to fly minus crew
    -- Total sailing weight(displacement)- 395lb-
    -- Max crew weight-236lb
    -- Minimum crew weight(at max power)-120lb (boat can sail in same windstrength with minimum or maximum crew weight(!)
    -- Max Pressure/w/o reefing 1.8 lb/sq.ft( 1.8 for F18 cat)
    -- 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)
    -- SA/D= 47.47/1
    -- W/SA= 2.42 (With a 236lb crew on MPX this ratio is still 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.
    -- SCP/total weight= 72.9% (according to Bethwaite above 30%=capable of upwind planing)
     

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  4. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Design Ideas: High Performance Self-Righting Trimaran

    These are the preliminary specs of an experimental high performance self-righting trimaran. I'm building a model now that will test this concept and elements of the MPX-12 in the other post. Comments, ideas, suggestions and constructive criticism welcome.

    Thread that provides details of the model being built now to test this concept: http://www.boatdesign.net/forums/mu...-self-righting-trimaran-test-model-36058.html

    ======================
    These first preliminary design numbers are based on work I did for a two person 18' tri in another thread in the multihulls forum.. They have been "massaged" to meet the goals of an automatically self-righting small trimaran. No consideration of cost is given here since the boat is highly experimental. The numbers show that this boat will probably right itself from a capsize or a pitchpole-this must be confirmed by model and fullsize testing.
    This boat is designed as a SINGLEHANDER. For this version the ama will be either full flying (preferably) or foil assist only. These dimensions are preliminary and are bound to change as a result of testing and/or design refinement:

    Self-Righting Trimaran(SRT) / Preliminary Specifications:

    Length: 18' / 5.49m
    Beam: 22' / 6.7m (foldable for trailering)
    Ama LOA: 12'
    100% ama buoyancy: 375lb.
    Draft w/boards Up: 6.4"
    Draft, daggerkeel down: 4' 8"
    Mast Length: 28' / 8.3mm
    Sail Area:
    --277 sq.ft. upwind SA
    --575 ft2 / 53.4 m2 downwind SA
    Weight (with spinnaker): 400 lbs / 181.9 kg
    Crew weight: wide range-for these numbers 175lb.
    Ballast: (at the juncture of the daggerboard and main foil)- 175lb.
    =====================

    COMPARITIVE RATIOS:

    Bruce Number: 1.83 F18=1.66

    SA/WS:
    -- not flying-5.73/1 F18=4.77/1

    -- flying main hull-10.26/1 F18(flying one hull)=6.03/1

    SA/D: 53.89 F18=44.16

    W/SA-smaller better): 2.71 F18=3.29

    =====================
    Picture: small model of main hull-large(5') model underway now. Model will test the SRT concept, and elements of the MPX concept.The full size hull will test the trapwing movable ballast concept in addition to the MPX and SRT if the model tests prove out:
     

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  5. redreuben
    Joined: Jan 2009
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    Location: Beaconsfield Western Australia

    redreuben redreuben

    Gee didn't see that coming !
     
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  6. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Design Ideas

    ----------
    I think it looks great. Do you expect it to fly the main hull? Do you plan to build it? Great thread-thanks again.
     
  7. Brorsan
    Joined: Nov 2007
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    Brorsan Junior Member

    It is not intended to fly the mainhull. Foils in the amas will help the short and skinny amas to stay above water, but not fly.
    Forgot to mention that crew sits inside the mainhull, and that it will be steered with a steering wheel somewhat like old fighter airplanes. It will probably not be built, but who knows? :)


    MPX12: I like the couch seating, but what is the function of the rounded part in the cockpit? structural to carry the loads from the aft beams? The lifting foils on the mainhull, is that the only ones or will there also be foils on the "amas"?

    Trapwing: Love the shape of that hull. It is intended for some other building method than plywood, or is that possible? How does the amas look?

    Finaly, PLEASE keep it down with the amount of text. No one is interested in pages of technical info. Also, the designs dont have to be finnished by any means, early sketches are as good as anything - this is a discuss thread.
     
  8. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    ============
    1) MX-12: The rounded part is to support the rear cross arm primarily and allow a place to sit in the center of the boat. The foils on the main hull are there to allow it to fly in very light air*, to enhance pitch stability and to automatically control the heeling angle of the boat at about 10 degrees. The first amas-very experimental-are planing amas and one can support the weight of the boat at about 15 knots. The two foils on the main hull control the trim angle of the planing amas. If the planing amas don't work then I'll use very small narrow amas with foils.

    2) Thanks. The hull model with "Trapwing" on it is a likeness of a full size hull that will be used experimentally for the Trapwing movable ballast prototype AND the SRT(self-righting trimaran) if the model SRT proves that the concept works. The amas will be relatively high L/B with lifting foils and the boat will be quite wide and use the MPX foil system but with 175lb. ballast at the mainfoil/daggerboard juncture.

    * The bi-foiler arrangement makes it possible to have a very wide small tri that will also fly the main hull in light air. Without the foils the main hull would not fly until 15 knots, or so, of wind. The foils also make it possible for a lightweight crew to sail with the same maximum RM as a heavyweight crew since with the wand altitude control system the main foil automatically pulls down if the angle of heel exceeds 10 degrees or so.

    -----
    About the text: I posted only the minimum to give an accurate representation of the boat. I posted comparative ratios to show how the proposed design stacks up against other boats.
     
  9. rayaldridge
    Joined: Jun 2006
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    rayaldridge Senior Member

    This is what I'm building now-- a folding cat for cruising two people that can be trailed behind a compact car.

    [​IMG]
     
  10. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    ==================
    Ray, you've got some nice ideas for a mini cruising boat-how does this one compare to your first boat?
     
  11. rayaldridge
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    rayaldridge Senior Member

    Slider is an open cat with fixed beam of 8.5 feet. The new boat will be 4 feet longer, with sitting headroom cabins, and a mechanism to fold it out to a beam of 12 feet. The rig is from a Nacra 5.2

    The idea is to build a boat for modest offshore use-- maybe to the Bahamas or a bit further.

    Baby steps.
     
  12. John Perry
    Joined: Nov 2003
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    John Perry Senior Member

    OK, this is what I have been playing with recently. Its a cruising catamaran, about 10m LOA. Recently I have been doing the structural details as separate models that will later get joined together as a new whole boat model, so the whole boat model in these pics is out of date but the best I have right now.

    Construction: strip planking glass sheathed in and out up to the shallow knuckle in the lower topsides, rest would be plywood with external glass sheath.
    Keels would be lifting centreboards, pivoted type, with an arrangment to close the slot behind the lowered board, as I already designed for a dinghy.
    Hulls to provide standing headroom but only over a very limited floor area in the galley, the loo and the space under hatches where you change cloths. Rest of the cabin space would be sitting headroom only.
    About 650 clearance under central part of bridgedeck, thats reasonable for this size of boat, but maybe even more would be better. Probably two outboards, not one in the middle as shown here.
    Sheltered steering position shown with fabric hood, but could be a lightweight ridgid shelter instead. The whole shelter slides for and aft so as to either provide sitting headroom under the shelter behind the steering position or to allow standing behind the shelter. The shelter folds down, then the mast will lower with a tabernacle, thats quite an important feature for me.
    This aft view omits transom hung dinghy style lifting rudders that swing up vertical for beaching. These would be controlled from the wheel by a cable and rod system I have worked out but it is a bit complicated to describe in words. I dont think you can easily beat that type of rudder for damage resistance and accessibility if repair is needed.
    Rig would be conventional multihull style fully battened sloop with roller foresail. Undecided about a rotating mast or not. Doesent seem easy to get the right extrusions in UK these days, any ideas?
    I am wondering whether I can omit trampolines forward since I have shown a ridgid structure extending forward on the centreline which could provide access to the forestay attachment. Trampolines do seem to be a maintainance problem and they can catch wind and waves.
    The part of the bridgdeck structure forward of the cockpit provides lots of locker space for sailing gear, anchors etc.
    The two main cross beams connect into sockets in the hulls using an arrangement of wedges to lock them tight in the sockets. It must be fairly easily demountable to transport on a flat bed lorry. OK to make several lorry trips, one for each bit since its only five miles to the marina. Mast would be hardest part to move perhaps.

    Will it be built - I dont know yet - When our military are thinking of a big aquisition they have a point called 'main gate'. There can be millions, billions even, spent on design work prior to main gate, but until you get past main gate you dont cut steel (or plywood in this case). Main gate for this project is at least 9 months ahead, need to have a costed design, FEA analysis etc. also work out whether I have enough space to build, and whether life is long enough to both build and sail a larger boat. I do realise that building a boat makes no financial sense when you can buy a good second hand one much cheaper than the materials for a new one, but I like woodwork and have built my previous boats, albeit they were much smaller. If I dont build this one, will probably build a new smaller boat.
     

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  13. Lister

    Lister Previous Member

    I very much like this one. Stylish, go fast even at rest.
    Lister

    [​IMG]
     
  14. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Trapwing / SRT

    -----
    Thanks, Lister!
     

  15. Brorsan
    Joined: Nov 2007
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    Brorsan Junior Member

    John, that is a nice looking cat you've got.
    Do you have to stand up to steer it from the wheel? I cant see any where to sit down for the rest of the crew either, is this accomplished with normal moveble garden chairs?

    Ray, how yhought out a folding mechanism yet, or is the slinger demounteble instead? How wide will the berths be aprox? Do you sit in the hull, just aft from the cabin, or between the hulls? Keep it up, i love your ideas of these micro crusers.

    /Brorsan
     
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