Are squared hull/transoms essential for a planing catamaran hull?

Discussion in 'Hydrodynamics and Aerodynamics' started by NoviceJoe, Jul 22, 2020.

  1. Will Gilmore
    Joined: Aug 2017
    Posts: 193
    Likes: 68, Points: 28
    Location: Littleton, nh

    Will Gilmore Senior Member

    Before a boat can plane, it needs to power up the bow wave. Planing happens when the CG clears the crest of the wave and the boat flattens back out over the top.

    Move the CG aft and the stern falls more naturally into the wave trough. You get a little more speed over hull speed before you labor the engine. However, you have to drive it farther up the bow wave before it clears the crest.

    Move the CG forward and you don't have to drive the boat up the wave as far to clear the crest, but you have more initial effort just to reach hull speed.

    Perhaps a movable weight, such as your body, can improve the dynamics by starting out aft and jumping forward to help get her up. As kids, we use to do this when a boat was under powered, we'd send two of us up to the bow to force the boat over the top of the bow wave.

    -Will (Dragonfly)
     
  2. sandhammaren05
    Joined: May 2009
    Posts: 409
    Likes: 16, Points: 18, Legacy Rep: 138
    Location: Texas & Austria

    sandhammaren05 Senior Member

    Yes, square it, but get a bigger motor. An older 2-stroke OMC 7.5 will guarantee planing.
     

  3. sailhand
    Joined: Jan 2017
    Posts: 102
    Likes: 20, Points: 18, Legacy Rep: 29
    Location: australia

    sailhand Senior Member

    Lots of interesting comments here. But somewhat distressed to discover that there is no medal for going the fastest with a small motor. Oh well I guess Im off to discover the real meaning of life. Hmm lets start at 42 and work from there and see what happens.
     
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