Extended transom

Discussion in 'Boat Design' started by Chuck Losness, Nov 20, 2012.

  1. Chuck Losness
    Joined: Apr 2008
    Posts: 332
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    Location: Central CA

    Chuck Losness Senior Member

    While you guys have been enjoying the good life over the last month, I have been sweating away in a very hot, humid dusty boatyard in Guaymas, Mexico extending the transom on my Gulfstar 37. I would classify the quality of my work as above average amateur. Certainly not even close to professional quality. But I am satisfied with how it all came out and that is what matters.
    I used plywood door skins to make the mold. The hull sides are one layer of mat followed by 4 layers of 1708 biaxl mat/cloth. The transom is similar but with a plywood stiffener sandwiched in the middle of the layup. The deck is 2 layers of 1/4 luan (I think) plywood sealed in epoxy. There is a slight curve to the deck. That is why I used 2 layers of 1/4 so it would conform to the curve. Not much choice in plywood in Guaymas. I got the best that I could find. I got the epoxy from US Composites. The epoxy is their slow cure intended for high heat and humidity. It was great to work with. The working time seemed to be over an hour and it took a full 24 hours to go off in 90 to 100 degree temperatures. The deck is covered with a layer of 1708 set in epoxy. I made 4" wide by 3" deep I beams with a plywood stiffener to support the deck. The hull sides above the deck are about 2 1/2" inches wide. The space between the inner and outer skins is filled with spray in foam. Other than for the deck I used polyester resin. I still have the final finish work to do above waterline. I have attached some photo's of the construction. Sorry no photo's of the deck supports. I forgot to take one.
    I am pleased with the performance increase. The old transom would squat under power or sail up to 12" into the water at 6 knots and you could see the turbulence that this caused. The new extended transom still squats but only a couple of inches at this speed and there is a smooth flow off of it. Speed increase is about 1/2 knot. Pre extension I would power at 2200 rpm to achieve 6.1 to 6.2 knots. With the extension I achieve this speed at 1900 rpm. Have only sailed down wind and the boat seemed to start to surf down waves sooner and hold it longer than before. Time will tell how much the extension helps under all points of sail.

    Attached Files:

    2 people like this.
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Nice job. Looks like it improved the boat
  3. Steve W
    Joined: Jul 2004
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    Location: Duluth, Minnesota

    Steve W Senior Member

    Nice job Chuck, it looks like it came from the factory that way, congrats.

  4. hoytedow
    Joined: Sep 2009
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    hoytedow Carbon Based Life Form


  5. Chuck Losness
    Joined: Apr 2008
    Posts: 332
    Likes: 43, Points: 28, Legacy Rep: 135
    Location: Central CA

    Chuck Losness Senior Member

    Thanks guys. I still have to finish it off to make it look nice. It is just rough gel coat right now. Hope I can get a decent color match. I don't want to have to paint the entire hull. Also have to mount the swim ladder, move the solar panel and make an opening in the stern pulpit for easier access. Hope to have it all done by the end of January.
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