A Scribe’s Scribe or How to Make Replacement Bulkheads

I’ve hired a few house carpenters and tried to train them to be boat carpenters and the first thing the yard foreman would always tell them was to throw away their T-squares. Boat lines are curved and the sooner they learned to match what they were building with a hull’s lines, the more successful they would be.  It didn’t have to be straight or even level on the rolling ocean, but it did have to be “eye sweet;” it had to look right.

An Architectural Drawing Compass will reproduce your vessels curves when making repairs

So when this scribe writes about replacing rotting bulkheads in a boat for the do-it-yourselfer, the first thing I need to teach you is how to scribe.  That is, to trace the curve of the hull exactly, so that you can produce a piece of wood that fits and supports the fiberglass structure.

Bulkheads on production fiberglass boats are traditionally made of plywood.  Years ago, people wondered how long a fiberglass boat would last.  Today, we know the answer is typically much longer than the plumbing and electrical systems, or, for that matter, the bulkheads.  The plywood would wick up moisture over the years and rot–weakening the boat from the inside out.

Here’s how to replace rotted bulkheads: After cutting the fiberglass tabbing that holds the rotted bulkheads in place, remove all the wood with a roto-zip. Sand the fiberglass flush to the hull so it provides a mechanical bond for the replacement tabbing to hold the new bulkheads. The job of scribing the exact shape is next.

First, make an exact template of the bulkhead in cardboard.  To make the cardboard template you will need an architect’s drawing compass, duct tape, cardboard, and a box cutter knife.

Rough cut a large piece of cardboard to approximate the curve of the hull—it doesn’t have to be perfect to start. Now push your curved piece of cardboard as close as you can to the curve of the hull. Open your drawing compass and with the pencil end on the cardboard, use the pointed end to follow the curvature of the hull—scribing the hull’s curve on the cardboard. Cut along the pencil line and if necessary repeat until the cardboard conforms to the shape of the hull.  Tape it in place and add “extensions,” other pieces of cardboard to complete the entire template.  You should have one big piece of cardboard with lots of taped-on extensions to approximate your bulkhead. It may look agricultural but it will be an effective template.

Using your cardboard template, trace out the pattern on a piece of marine plywood.  Cut and dry fit your plywood in the boat to make sure it fits.  Make any adjustments you need to the plywood and don’t forget to add limber holes for any plywood that touches the bilge. I use epoxy to coat and seal the plywood. This prevents the new bulkhead from wicking up moisture and rotting like the original.  Now you are ready to tab the bulkhead into position using glass matte or roving and make your boat as strong as ever.  Once you’ve mastered the use of a drawing compass to scribe the contours of your boat onto a template, you’ll find that you won’t be limited to simply re-building bulkheads.

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