Making the Transom Bows

Shaving to the line
Shaving the upper transom bow to the line of the deck camber.

The transom bows are the curved top and bottom pieces that give you the shape of that beautiful transom you see on classic runabouts.  Nelson Zimmer’s plan calls for a 5 foot radius curve.  He also calls for a deck crown or “camber” of 2-1/2 inches at the transom.

So we’ve got two pieces to make, bent to a 5 foot radius.  And the top one has to have a curve cut on top of it to support the crown of the deck as well.

Building a form for a curve
Building a form for a 5 foot radius curve.

The first step is to find something around the shop that has the curve you need that you can bend lumber to.  If you’re not lucky enough to find something like that, you’ve got to make a form.  When you’re drawing your curve on the plywood for the form, don’t forget to subtract the thickness of your planking, and the framing piece you’re making.  If you want the outside of the planking to be at a 5 foot radius, and your planking is 9/16 inch thick, and your framing is 2″ thick, the radius of your form needs to be 4′ 9-7/16″.




Beam Compass
A Beam Compass is two points you attach to the length of board you need.

How do you draw a curve to that specific radius?  Well, you use a beam compass.  It’s really just two points you attach to a board with the exact measurement you need.  We know how wide our transom is from the lofting, and we know that Zimmer wants a 2-1/2″ crown in the deck at the transom.  If you know those two things, calculate the radius of the circle you need.  Pretty easy!  And you thought that high-school math would never be useful to you.





Shop form for laminating lumber to a curve
Here’s the nearly complete form. Note the 2×4 stiffener on edge.

I build my forms fairly stout.  I nearly pulled one apart once trying to clamp the veneers to it.  So I decided the extra lumber and screws were worth it.








Transferring a curve to a curved piece of wood.
Transferring the curve drawn on the flat surface of the workbench to the curved surface of the transom bow requires transferring points on the curve at intervals to the bow. Then connect the points with a batten and you have your line to cut to.

So, we’ve got our curved blank, and we’ve drawn our curve.  But it’s based on a flat, 2 dimensional view from the plans and lofting.  To transfer that to the curved surface of the bow, we’ll need to do our old trick of measuring the depth of the curve at intervals and transfer those measurements to the bow with a batten.  After that, it’s just a matter of cutting it on the bandsaw and shaving to the line as in our first picture.

Next we make the bottom bow, and then figure out how to glue this whole thing together!


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