Tools For The Curves Of Your Boat

By Chris Landers

Fitting things to the complex shapes of a boat is a lot harder than hanging a shelf on your wall at home, but a few simple (and cheap) tools can make it a lot easier.


You've seen these before in elementary school or on your chart table — the geometry tool that helps you draw circles; in boat navigation, they're called dividers. Marine dividers have a thumbscrew to tighten the arms so they hold their position, but cheap ones from the stationery aisle of the drug store work just as well for this application, as long as the hinge is stiff enough to hold your angle. Use this to transfer, say, the curve of the hull onto a plywood shelf for a tight fit. Just hold the plywood perpendicular to the hull, set the dividers, and trace the curve onto the board. Now cut along that line. If the angle where it meets the hull is close to 90 degrees, you should have a good fit. If not, you may need the second tool.

Photo of using a scribe

Bevel Gauge

These are commercially available, or you can get used ones on eBay, but those are often too big for the confined spaces in a boat. For a small, cheap bevel gauge, look around for an engine feeler gauge that can be modified to do the job with a little grinding. Like the scribe, it should be stiff enough to hold its shape as you transfer angles from the hull to the work piece. For thin pieces, a carefully wielded angle grinder with a rough sanding disk should work for getting the desired angle.

Photo of a bevel gauge

Joggle Stick

For making things more complicated than shelves — like a bulkhead for instance — this is really indispensable. It's just a flat (eighth-inch or so thick) piece of material, shaped like an elongated teardrop and cut with irregular notches. Hardwood works great; mat board or thin plywood works in a pinch. To use it, clamp a thin piece of pattern stock (lauan plywood works well) in the space where the bulkhead will sit.

Photo of a joggle stick

The pattern stock should be roughly cut to shape but undersized so it mostly fills the space. Lay the joggle stick on the pattern so that the point touches the hull of the boat and trace the outline of the joggle stick onto the pattern. Do that as many times as you need to get a complete outline, picking up all the important points where the bulkhead will meet the hull. Once you're done, remove the pattern and clamp it flat to your final material. Lay the joggle stick in the outlines you've traced. Because of the irregular notches, there's only one way it can fit. Mark the final material at the pointy end of the stick. Once you have all your marks, remove the pattern and connect the dots. That should be the line you need to cut to match the hull (or close enough for a grinder to do the rest). 

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