Powerboat and dagger boards

Discussion in 'Powerboats' started by merryfisherman, May 6, 2014.

  1. merryfisherman
    Joined: May 2014
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    Location: Scotland

    merryfisherman New Member

    Having had semi-displacement shaft drive boats, I now have an outboard powered boat, with a planning hull. It's very good save for the fact that it is tricky in a tight harbour especially with a good wind.

    The problem I find with a planning hull is that the boat “skids” in a turn, unlike a yacht that seems to “pivot” around its keel.

    It therefore occurred to me that some form of dagger board that could be lowered when entering and leaving harbour and then raised before accelerating onto the plane might be a neat solution to the slow speed handling problems of a planning hull.

    I came across a link to a folding keel for a small boat designed (I think) by Stuart Roy. He in turn said that he had seen drawings of a dagger board employed on a powerboat very successfully for the same reasons. The boat was designed by Eivind Amble and Tor Stokke of Norway.

    Does any one have any contact details or any other details about a dagger board for a powerboat?

    Sorry for the duplicate post - posted originally in the design section in error!

    Thanks in advance
  2. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    I am attaching a photo taken from a book which is dated 1973. What you can notice there is a small fin placed at around 60% of the LWL (measured from the transom), which has a purpose of creating a pivot point during turns. So the basic idea you had is not new. It is commonly used on hydroplane boats to help their flat hulls bite the water during fast turns.
    However, I am not aware of daggerboard versions of the skid fin, and am also not aware of them being used to improve the low-speed handling of the boat. But the idea is sound, and should work. The problem is - you'll have to create a through-hull opening for the daggerboard. It will weaken the structure right where it needs most of it's strength and might trigger concentrated stress-induced cracks around the base of the daggerboard well. And it will also be a costly modification. If you feel confident that you can resolve these issues, I see no reasons why it shouldn't work.

    Attached Files:

  3. bob perry
    Joined: May 2014
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    bob perry Junior Member

    My problem was that kept forgetting that I could not steer the whaler when it was in neutral! I'm a slow learner.

  4. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    A daggerboard trunk opening will also add drag if submerged even with the board retracted.

    We rented pontoon houseboats several times and I thougt a retractable board in the bow would be a great help for low speed maneuvering, particularly in a cross wind.
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