Posted by: Wayne | September 6, 2010

Transom Framing 1

I have not gotten very much done on the boat over the past couple of weeks.  A combination of a busy schedule at work and fighting a cough will do that to a person.  I had been slowly cutting the framing for the transom and I finished that project on Sunday.  I also got the bumpkin hole cut, as well as the two plywood doublers (around the tiller cut-out, and around the bumpkin hole).

This evening after work I glued the lower portion of the transom framing in place, as well as the bumpkin hole doubler.  I also glued the top piece back together (a 20x20mm notch in a 25mm wide piece really weakens it).

Pieces glued up on the port side of the transom. The squarish piece above the seat support brace is the bumpkin hole support. The round hole is for one of two drain bungs.

The center and starboard sides of the transom.

While doing this glue-up, I also glued in the blocking between bulkheads 2 and 3.  The mainmast step sits on top of this blocking when it is installed.

The filler blocks to support the mainmast step.

Finally, I made the reinforcing fillets on the starboard side of the centercase.  Since the holes for the through-bolts got plugged, I figured I would make sure I could clear them out without too much trouble BEFORE I filled both sides.  It seems like common sense.

Fillet between bulkheads 4 and 5. It is truly amazing how much epoxy this takes.

The fillet between bulkheads 5 and 6. This one also took a ton of epoxy.

Aft end of centercase. I added a bit of a fillet here as well.

None of these steps are terribly impressive.  The next glue-up will finish framing the transom, as well as doing the other side of the centercase and adding some vertical stiffeners to bulkhead 2.  Then I get to do the big one: gluing in both seat fronts, the cross-braces on bulkheads 6 and 8, and the transom.  Then I get to start playing with stringers.  It should be fun!

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Responses

  1. So what did shipwrights use before epoxy? I know tar was used in repair, but was it used in construction?

  2. Wow, that is a simple question with a long answer. Way back when, there were no glues that could really survive immersion, so all fastening was mechanical. The two big traditional types of wooden construction are carvel and clinker.

    Carvel was usually used on larger vessels, and used a network of the keel and frames, usually sawn (cut into shape) or steamed (bent into shape). Onto this network, the planks were fitted to shape and nailed into place. The gaps between the planks were caulked, I believe primarily with cotton. This is also why you hear about ships “taking up”. When a vessel constructed this way is launched, the wood hasn’t swollen to seal the cracks, so the boat leaks. As the wood swells, the leaks slowly stop. If the pieces were fitted so closely as to not leak at launch, the force of the wood swelling would tear things apart.

    Clinker was usually used with smaller vessels, especially those constructed up in Scandenavia. A clinker vessel has the planks overlapping at the edges with no caulking. It relies on a close fit between the planks, and uses riveted nails to hold it together. It also uses frames, but usually there are fewer and they are less massive.

    One of the earliest waterproof glues was resorcinol. This is a two-part glue invented around WWII in Britain and used to make the famous Mosquito bomber. This is also the glue used to make vast quantities of waterproof plywood. It can be recognized by the dark purple glue line. It is a truly magnificent glue, but it requires very well fitted glue joints and high clamping pressure. Nevertheless, many boats have been built using resorcinol and hold up very well indeed.

    Like resorcinol, epoxy can withstand sustained immersion. Unlike resorcinol, properly thickened epoxy can bridge rather large gaps. Ironically, it is possible to over-clamp an epoxy joint, creating a weaker than normal bond.

    Epoxy is really the strongest, most waterproof glue that can be easily used by a person of limited woodworking ability.

    I hope this answers your question.

    God bless!

  3. Yes, that was a marvelous answer. Boatbuilding is a fascinating art.


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