Narrow or wide beam for low wake 12' punt?

Discussion in 'Boat Design' started by afie, May 10, 2021.

  1. afie
    Joined: May 2021
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    afie New Member

    Hi all,

    I'm after a aluminium tinny hull that produces a low wake and planes quickly to operate at 7-11 knot speeds in calm waters. What looks best is a square nose or V-nose punt around 3.75m long, needs to be that long to allow for a 10hp outboard. Outboard can preferably not be tiller steered, instead a centre steer console 2/3 along the hull from outboard. The hull choice available is:
    3.75m long, 1.52m beam, 80kg hull weight
    3.65m long, 1.26m beam, 58kg hull weight
    Lower hull weight is better, but is narrow or wide beam better?
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    The hull weight gap won't make much difference, 22kg, what you load it up with is more important, but I would go the wider one, it will hold plane better than the narrow one at those low speeds, and be less affected by variable loads. I don't think there will be any appreciable difference in wake, both will produce a wake beyond about 3 knots.
     
  3. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    That is dictated by your length-displacement ration, as that is linked to the wash height generated from the hull.

    In this case, with this single parameter, your best choice is the 3.65m, as its LD ratio 9.4, compared to the longer one at 8.7.

    Any value over 9 is good.
     
  4. afie
    Joined: May 2021
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    afie New Member

    Thanks for the answers.
    So, low wake its better to get something that has a high ratio of length to width, but wider beam will allow for quicker planing at low speeds? So I have a choice between lower wake and quicker planing?
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    no.

    I was clear and explicit in that your no.1 objective, of low wash.. is related to the length-displacement ratio. The higher the value the better.
    In this case the 3.65m hull.

    Whether this satisfies other parameters you have..is another question.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    When the thing is up and running, my money is on the wider boat staying on plane better, and especially with any kind of load. You are not going to be loitering at a hump speed that makes the most wake.
     
  7. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    58 kg is just the hull. You need about the weight of the engine, fuel, center console, operator, passenger (if any), gear, etc. Total displacement would be at least 150 kg and 250 kg is possible.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    Indeed.
    But I can only reply to the facts given and asked...
     

  9. Ike
    Joined: Apr 2006
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    Ike Senior Member

    For a 12' (3.75m) boat with a 10 hp engine, that planes, you want it to be as stable as possible. All else being equal, wider beam will be more stable. Less chance of it dumping you in the river with the crocs.
     
    bajansailor likes this.
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