Semiplaning / transitional Hull

Discussion in 'Boat Design' started by john zimmerlee, Apr 3, 2011.

  1. john zimmerlee
    Joined: Apr 2006
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    Location: Atlanta GA

    john zimmerlee Junior Member

    Our VersaBoat is a 9'-4" rescue boat with bow characteristics of both ends for equal reverse paddling.

    Rescuers now want an ability to use an outboard, so I notched out the stern and provided a pad on a 15 degree angle for the outboard.

    Both my 75 lb and 40 lb motors pitched the boat bow-up and powered it up to about 5 mph. More power just increaed the pitch and bogged it down. Both were mounted at different heights and tilt, but nothing seemed to approach planing.

    Admittedly, I have curved surfaces and not the typical sharp transition from hull to stern. Is there anyway to accomplish this without compromising the reverse motion ability?

    John.zimmerlee@gmail.com
     
  2. tom28571
    Joined: Dec 2001
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    Location: Oriental, NC

    tom28571 Senior Member

    Probably not. A boat that small needs some help in the aft bottom if it is expected to plane. What you describe does not sound like what is needed. Some more information and photos would be helpful. Double enders make questionable planing boats at best and usually need help in the form of aft wings or significant aft flat surfaces.
     
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  3. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Maybe some sort of horizontal foil on the outboard? The picture below is from the April/May issue of Professional Boatbuilder mag.
    The foil design by Russell Brown in Port Townsend WA is all carbon and unique compared to the other commercially available foils.
    Description"..... as evidenced here by a foil easily mounted to the lower unit of his outboard motor, which slightly raises the stern and reduces wake."
    The article is "Outside the Box" by Dan Spurr. You may be able to contact Russell Brown directly or reach Spur thru proboat@proboat.com
    This wouldn't change the hull at all and would help only when using the outboard...Hope this helps a bit.

    Russell Brown contact: http://www.ptfoils.com/

    click on image:
     

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  4. john zimmerlee
    Joined: Apr 2006
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    Location: Atlanta GA

    john zimmerlee Junior Member

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  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    With the "exit" you have on the aft sections, you'll never get it up on plane unless you provide some bearing area and most importantly a clean flow separation point. The wing that Doug mentions can work, though some experimentation would be necessary for size, shape and section. With the grotesque lack of power, I suspect you'll still never get it up on plane. The biggest motor you have is less then a single HP, so you're limited propulsive effort will keep you at low speeds.

    At the assumed LWL of 9.33' you are traveling at 1.63 S/L ratio which is above typical displacement speeds, but well below full plane. you'll need to be traveling at least 9 MPH to plane off and this will take a couple of HP (minimum), assuming your wave train is surmountable. Looking at the shape of your hull, I'd say 2 HP will do it, but there's a lot of drag with that hull shape (wheels and all?), so maybe 3 HP will be necessary just to sustain full plane, without "falling off" with every wave, contrary currents and winds.
     
  6. tom28571
    Joined: Dec 2001
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    Location: Oriental, NC

    tom28571 Senior Member

    That is just about opposite of any hull shape or size that I would expect to be designed as a planing boat. I don't think more power and/or wings are going to do it either. I count 16 holes through the hull that must be there for draining water. That is fine at paddling speed but there were probably 16 waterspouts when under power. If a planing rescue boat is needed, I suggest you should start over and forget about this hull. It is easy enough (but not optimum) to paddle a boat designed for planing but not so much the other way round.
     

  7. Guido
    Joined: Oct 2011
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    Location: Italy

    Guido Junior Member

    Poll

    Dear forum users,
    I'd appreciate very much your opinion on a new semidisplacement/low planing speed boat project.
    I'd be very grateful in you could spend few seconds in filling in the questionnaire I prepared at following link:
    https://docs.google.com/spreadsheet/...R1F3V3lHWWc6MQ


    As soon as the poll will be finished, I'll share with you the main overall results.
    Thanks for your collaboration.

    P.S. Sorry if in the questionnaire you'll find some italian words, it's a limit of Google tool I've used to prepare the poll.
     
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