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Bulkheads

January 5th, 2015

This whole plywood boat building thing has a bunch of advantages. Clearly, the biggest is the ability to construct a hull out of four strakes, rather than 20, But there are others, and the biggest of those is the ease of creating bulkheads. Ratty, like most other boats, gains strength from a series of transverse bulkeads. These help maintain the proper shape of the hull, resist racking, and also (conveniently) serve as the basis for benches and other internal furniture. Ratty has 5 of them.

Numbers 1 and 5 are solid, at least for now, and will form the footing for the foredeck, and whatever the dinghy equivalent of a poopdeck is.  Later on, that after bulkhead will also serve as the mount for the engine.  Numbers 2, 3, and 4 have big holes in the middle, and will support  (and be stiffened by) the rowing thwarts. The big holes in the middle will eventually have floorboards running through them.

As I’ve written previously, I put bulkheads 1 & 2, and 4 & 5, in as soon as I could after I flipped the boat. Then I procrastinated putting  the center bulkhead in for months. It’s bifurcated by the centerboard trunk, and I figured fitting its 2 halves would be a pain in the butt. It was.

In order to fit that center bulkhead, I had first to fit the centerboard trunk. The trunk is actually mortised into the keelson, and then sandwiched between two bits of wood called case logs. The bulkhead pieces serve to keep the trunk plumb, and the whole structure is a bit complex. Stupidly, I decided to glue the whole structure – trunk, caselogs, and bulkhead – up at once. Next time I won’t. I used epoxy hardener that began to kick too quickly, and found myself racing the clock. In future, I’d register the bulkheads in place (I’ve been using hot glue to “chock” bits of plywood against the workpiece for this purpose, and it seems to work quite well), then saran wrap any surface I don’t want glue on, glue the trunk up, remove the bulkheads, and then glue them in place using the trunk as a guide.

Learning. Yay.

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This photo shows the assembly dry fit. the “chocks” of plywood are visible on the hull. Getting things lined up just so was difficult in the extreme, and I didn’t end up getting it quite right. (It’ll work, and be invisible). That 2×4 over the top of the boat is my level stick– I took measurements  along the flat top of the bulkhead to make sure things were level from port to starboard.

 

 

 

 

Post glue-up (and beginning to lay out the “tanks”).  Impossible to see from his — or any– photo, but the bottoms of the 2 bulkhead halves did not end up quite in the same place fore-and-aft– one is a bit behin the other. A matter of a half-inch or so. But once the thwart is laid on top, it’ll be impossible to see. Also, the centerboard case assembly warps toward starboard a little at the front end. The case top and the thwart on #3 will fix that.

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Entry Filed under: Building Ratty

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