Transom Angle Origins

Discussion in 'Boat Design' started by boatbum10, Dec 18, 2018.

  1. boatbum10
    Joined: Jan 2012
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    Location: Warrenton, Oregon

    boatbum10 Junior Member

    Does anyone know how we ended up with 12 degree powerboat transoms at the norm? I'm not looking for answers like that's what motors are built for so that's what everyone uses. Way back in the early days, why was that angle picked? Random? Ideal motor setback for performance on outboard boats? Best angle to keep water out when in reverse at reasonable speeds? Based on the thickness of some special board or shop roof angle or other easy to reference device back in the day? Maybe it's what the first outboards were capable of tilting to? Ideas, theories, any old timers with secret knowledge?
  2. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    I don't think it is too much of a secret, a bit of "flam" keeps water from easily splashing into the boat, especially when reversing into a little chop. The 12-13 degrees was pretty much adopted and the design of outboards catered to that. When hydraulic trim came along, and it was possible to change the drive angle of outboards underway, it was desirable to have a greater range of trim to utilise, because while one might not run an engine trimmed heavily down, 95% of the time, it was good to have that ability for the occasion you might want it. So the transom angle was increased to more like 16-17 degrees, for a lot of boats. The change is pretty much about power trim, and getting more "tuck-under".
  3. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    You can still read the name on the transom, but the sun and weather damage is minimized. Remember varnished mahogany transoms? You don't want the sun heating and cooing those planks every day. Flam really helped to keep the joints tight and the weather out of the woodwork. And stern anchor chain had some place to fall - not on the coined gold lettering.
    kapnD likes this.

  4. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Transom rake isn't much different in degree to topsides flam on a hard chine hull, part of the function of which is to stop waves slapping against the side of the boat being easily able to land water into the boat, especially as there is usually wind involved.
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