low wake design

Discussion in 'Boat Design' started by halfrhovsquared, Jan 9, 2020.

  1. rxcomposite
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    rxcomposite Senior Member

  2. rxcomposite
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    rxcomposite Senior Member

    Aerodynamically, a canard will work for flea powered watercrafts. Just a glimpse but at 1.00, you can see the small wing up front. At the back is a large high aspect ratio wing. This works like a two step hull.

     
  3. rxcomposite
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    rxcomposite Senior Member

    Here is a better view of the "wing" arrangement.

     
  4. goodwilltoall
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    goodwilltoall Senior Member

    Phil Bolger had many flat bottomed square hull boats slightly rockered that were well know for their low wakes
     
  5. DCockey
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    DCockey Senior Member

    bajansailor likes this.
  6. philSweet
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    philSweet Senior Member

    Those are a good sanity check. The catamarans require twice the power that the OP wants, and they weigh twice as much. Notice that the little monohull is under half the weight and requires 1/3 less power at the same capacity and same performance.
     
  7. BlueBell
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    BlueBell Ahhhhh...

    1. OP says stitch and glue is okay
    2. OP says pieces must be car toppable
    3. OP is considering that motor
    4. OP has given a max speed but no indication of cruising speed
     
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  8. halfrhovsquared
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    halfrhovsquared Junior Member

    Good advice all, thanks. Cruising speed will typically be about 10 mph but it still needs to go 15 mph top speed and I don't care how much fuel I burn at that speed. Needs to be really stable side to side so I can stand up, lean over, etc.- hence my desire for a trimaran or catamaran.

    Kind of leaning towards the rowing shell idea with sponsons on the ends of the outriggers. The really small outboards only weight about 30 lb so that should be good enough for 15 mph.

    Would have to think about how stable they are to stand up in though.
     
  9. BlueBell
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    BlueBell Ahhhhh...

    A single rowing scull is 27 feet, but you could cut off 5' to make your 22' bogie
    and have a flat transom to mount your tiny motor on.
    Variable width sponsons, amas, pontoons, floats, outriggers, whatever-you-want-to-call-them could be hugely useful.
    OR
    Two surf-skis (20') would make a nice catamaran with ample standing room.

    Are you really wanting to stitch and glue or modify used parts?
     
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  10. DogCavalry
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    DogCavalry Senior Member

    Angus rowboats has plans for a build it yourself racing shell. It's the boat I had in mind. A pair make a catamaran.
     
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  11. BlueBell
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    BlueBell Ahhhhh...

  12. Dolfiman
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    Dolfiman Senior Member

    If your first question can be within the following assumptions :
    - slender monohull Lw/Bw >7
    - Froude V/(g Lw)^0,5 in the range 0,4 - 0,9 (in metric units)
    , then (as already mentioned by members in this thread) the residuary (wave) drag can be considered mostly in function of the lenght displacement ratio Lw/D^(1/3) , (Lw in m, D in m3) , a global result
    based on various model series tests and back by good authors.

    >>> I did myself this investigation from the model series tests available and average/smooth them in the figure 1B page 17 of the attached document, giving the residuary drag Dr in % of the displacement Mg (Mg in weight = D in volume), in function of Froude and Lw/D^(1/3)

    The other two components of the total drag (on calm sea) to consider in your project is the friction drag (you need to know the wetted surface at displacement D) and the aerodynamical drag (you need an estimation of the aerial crossed sections)

    With the total drag x the design speed = the net power

    Net power / propulsion system efficiency = the engine power
     

    Attached Files:

  13. Squidly-Diddly
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    Squidly-Diddly Senior Member

    used small Hobie cats are a dime a dozen, but I hear they aren't suited to easy dismounting and car topping. Don't know the weight of smaller Hobie cat hull. Might be doable to butcher up a used free/cheap (because its lacking decent sails, rigging and trailer) Hobie and create an easy to dismount and car-top power-cat. Smaller Hobie cats have asymmetric hulls to aid sailing on beam wind, which isn't ideal for power-cat but not a deal breaker.
     
  14. gonzo
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    gonzo Senior Member

    I think the OP needs to quantify "very little wake". He should post the maximum wake height at a distance from the stern.
     

  15. BlueBell
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    BlueBell Ahhhhh...

    Correct, however it was their first priority and minimal would mean as near to zero as possible.
    It's going to be an inherent trait of this vessel anyway as there is no extra power for wake at this speed.
     
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