MAKING A NEW TRANSOM FOR HULL #113

[bob mitchell]

   This definitely a work in progress as well as a documentation of the transom area, so since there are a lot of photos, and as far as I can tell you only get 3 photos per blog, there will be TRANSOM 1, Transom 2, etc. In Transom 1 I will start out with a photo from Dennis Gaffeny's Le Batteau Sans Souci (now gone, but I have her masts and sails), showing the transom without a transom.

Note the vertical plywood at the top, above the horizontal deck layer, that forms the bulwark. The plywood layers of the transom here came off intact, leaving the bottom and side framing. The next graphic is a Clyde Phillips diagram (actually, as we found out, the edges end flush with the framing, and the boat sides overlap the transom), followed by a description of how the transom was built.

FROM CLYDE: The drawing shows the transom, transom knee, and transom frame.  Note that the three layers of 3/8 plywood that makes up the “planking” of the transom extends beyond the transom frame across the bottom and up each side to catch the end of the bottom and side planking.  OR it doesn’t. (THE SIDE AND BOTTOM PLANKING EXTEND, AND THE TRANSOM FITS INSIDE, RCM) Hopefully you can discover which covers what when you take out the old.  It could be that the frame extends beyond the plywood (so the inside surface of the frame comes out to the inside surface of the planks if the planks overlap the transom).  Ask for other drawings if they are needed.  I don’t really remember and am looking at it both ways.  It’s always good to have plywood end grain covered but some end grain will show regardless at this point.

 

I only show the transom frame following the edges of the transom.  There may be some vertical pieces, and a crowned piece of the frame that hold up the end of the deck.  The frame piece I show at the inside top of the transom may not be there (it may be at the deck level).  There is no need for it at the top.  The cap rail sits on top of the transom and the transom may have at least one layer of 3/4” ply sitting on top of the deck, a la bulwarks.

 

The three layers of 3/8th were marine grade Douglas Fir (inside two layers) and the outside layer had an outside veneer of ribbon grain mahogany.  That made for a beautiful varnished transom for those who wanted the wood to show.  The frame could have been white oak to match the other frames and have much the same nail holding power.

 

The transom was built on a mold that had recesses to receive the frame sections and a place to hold the knee.  The three layers were tacked down (just at the top and bottom on the vertical center line) to hold them in place (gluing as you go) and the mold top was lowered over it all and clamped down for gluing pressure.  It’s possible, I suppose, to first build the mold, but for a “one off” transom you should be able to build it on the boat.  But that will require some well thought-out clamps in order to hold the inside of the plywood where it belongs and apply sufficient pressure from the outside.  No big deal!!!??? (end of Clyde stuff)

    And finally for an introduction, is a shot of my transom area - a complete rebuild, but where to start (been struggling with that question for three weeks).

     The frame of the left is frame 36, completely rebuilt with premo quarter sawn oak, new plywood gussets (see frame 36 posts if interested) and a quarter sawn 1 1/2 x 4" yellow pine cross member (visible above) to stabilize the hull shape and support the new cockpit sole. Frame 36 is my last contact with reality until I get to the transom. Frames 37 and 38 are gone, even though I had left them in place for reference. And worst of all, the chine in this area is gone. Fortunately the transom knee is in great shape. But today the port side bottom planking about fell off, so I went ahead and let it go.

     There is a 4 x 4 (not especilly visible, but above old floor: far vertical brace is visible) that goes under the three layers of the douglas fir inner clamp on each side I use this to support and level athwartships the whole transom area.

I will also add some blocks  that I can screw the sides to stabilize them for reference when refitting the new transom.

        So the current order of operations is -add 1 x 6 pressure treated lumber layer to inner clamp with premium polyurethane adhesive (the inner clamp is in good shape, but has some checks, and is just so critical to everything, that I am going to "refresh" it while all is open. The ends of the three layers of the inner clamps are visible in the first photo

right below the deck blocking. The inner clamps run the full length of the boat. All frame tops are fastened to the inner clamps, and the deck beams are bolted to the inner clamps) Next, after new clamp layer is set up, I will put epoxy between the new apron and the transom knee, relieve the support the 4x4 is giving, and drill a bolt the knee to the apron (long 1/2" galvanized bolts, like for the floors). Then the weight of the aft section of the boat will be on the new apron. I will check for level athwartships, and refirm up the 4x4 for stability (not to carry weight immediately, but I don't know what shifts will ocurr when I remove the transom - and I will screw some blocks into the 4x4 to stabilize the sides in position).

         Then I will sawsall out the transom (be sure  to support), and rebuild - that will be the TRANSOM 2 post. After that I will reinstall, then fair and scarf in a few feet of new chine on both sides. Once that is done fitting frames 37 and 38 should not be to bad. Then back to the engine, or on to the cockpit, or maybe start the planking. I guess I will save the mast till after the fiberglass. Damn I wish I had something to do.