Cat sponsons- displacement forward,planning?

Discussion in 'Boat Design' started by Bullshipper, May 3, 2008.

  1. Bullshipper
    Joined: May 2008
    Posts: 106
    Likes: 2, Points: 18, Legacy Rep: 21
    Location: Mexico

    Bullshipper Bullshipper

    1st post here.

    Meant to say displacement forward, planning aft.

    Looking for your thoughts on a new to me concept for designing power cat sponsons for 50 kph crusing speeds.

    The idea is to go with a sponson bottom that is

    knife like forward, protuding forward of the deck area to lessen tunnel slap and be efficient at low trolling speeds.

    Transition to semi displacement midships with slightly deeper sponson camel height to provide more lift to bow and stern

    Transition into 13 degree planning surfaces aft so that when more power is applied and the bows tilt up, the aft planning surfaces lift the to get better speed on smaller wetted surface area.

    Stern heavy flat attitude when trolling, with more bow lift at speed.
     
  2. CTMD
    Joined: Dec 2007
    Posts: 198
    Likes: 9, Points: 0, Legacy Rep: 117
    Location: Melbourne, Aus

    CTMD Naval Architect

    How big is the boat? The is a big difference in required hull form for a 7m and 17m cat at 27 knots.
     
  3. Bullshipper
    Joined: May 2008
    Posts: 106
    Likes: 2, Points: 18, Legacy Rep: 21
    Location: Mexico

    Bullshipper Bullshipper

    Hi Chris,

    I believe you helped Roger Hill and I with the design on a 7 m trailer hull for Mexico a while back.


    This is for a 29'x11'11" project.
     

  4. CTMD
    Joined: Dec 2007
    Posts: 198
    Likes: 9, Points: 0, Legacy Rep: 117
    Location: Melbourne, Aus

    CTMD Naval Architect

    Yes, that's me, I worked with Roger for a number of years and we still work together on occasion. How did the boat turn out? If there is anything I can help you with please don't hesitate to ask, either here or via email (chris (at) ctmd.com.au) .

    At 30' you'll definitely be looking for some lift at 27 knots. It sounds counter intuitive, but your efficiency at low speed on a power cat has more to do with the stern than the forefoot (bow). Obviously a pointy front will help but a planning stern will be like dragging a bucket when you are going slow. I'm assuming this will be an Aluminium boat so you'll also need to make sure all the plates are developable or it could get very expensive to build.
     
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