Curved Transom

[JimM]

I am hopeing to start building William Gardens 12 foot catboat - Tom Cat. The plans call for a curved transom. The transom is about 4' 6" wide. The radius of the transom is 9' 2.5" for a total deflection of about 3" from a flat surface. The transom is 3/4" thick.

I haven't laminated something this big before. Should I use veneer all the way through or use plywood for part of it? How should I hide the plywood edge if it is used? I would welcome any helpful suggestions.

Thanks
Jim McGee

[Dan McCosh]

That would be bendable with two layers 3/8 ins. thick. I laminated a transom with a slightly sharper radius out of two 1/2 ins. layers, but that was about the limit for mahogany. The 3/8 ins. layers would be easier to keep fair than thinner veneers. A couple of staggered blocks on a strongback make a good bending jig.

[Buddy Sharpton]

I would be tempted to make this out of three layers of very easily bent 1/4" plywood. I have built similarly curved cabin tops ( two layers) this way with no problem at all. Are you going to put your own veneer on the faces? If so you can drill lots of 1/8" "vent" holes and pull the layers together with drywall screws to squeeze out air pockets and actually see the epoxy squeeze out the holes. My work was geting a painted underside and a Dynel fabric out surface though.

What plywood edge are you having to hide and why?
As I recall this is a unusual epoxy/ carvel construction, but the planks should still lay outside the transom along the bottom and topsides.

Isn't this a so called half decked catboat with a completely oval coming. I would then expect the deck would cover the top edge of your transom. If I have misremembered and this boat has only a oval coaming forward with foredeck and washboards but the transom "clear", you could create a 3/4" by 3/8" trim mould of the same wood (mahogany?) that would be applied like a very low "toerail" across the top of the transom to cover your visible plys. Usually the tops of transoms are not left perpendicular to the face which is itself is raked 7 to 12 degrees from vertical.
Rather the top surface is planed away level, parallel to the waterline, resulting in a sort of rolling bevel.

You could start by trimmimg your transom's top edge 90" to the face. Be sure your trim piece has enough thickness to allow for this slope to be planed in and dressed after the rectangular trim strip is glued in place.
I made a dinghy transom this way and it wrapped around the gentle compound curve easily- no steaming or soaking.

[Lulworth]

Jim,

If it's a single radius of curvature you could use plywood but laminating a curved transom is fairly easy. Three layers of thin strips of cedar maybe 1/8" thick (or less) and 3-4" wide and each layer at +/- 45 degrees stapled onto a curved form then a nice vacuum bagged layer of something nice (I used teak)

Comme sa:

http://www.imagestation.com/picture/sraid60/pea88051c607737d82fecda53cdd86e36/fc50b916.jpg

et:

http://www.imagestation.com/picture/sraid69/p5c42ea3aeeea4fb56ff5545660749413/fbb56623.jpg

Well, you get the idea...

David

[JimM]

Thanks Dan, Buddy and David.

Buddy sorry for the confusion. The transom on the Tom Cat stands proud of the stern deck and has a sculling notch in the center. I was trying to figure out how to hide the edges of the plywood along the top edge and in the round notch. It was deffinetly past my bedtime last night when I wrote my last post.

Thanks for the information.

Jim McGee

[JimD]

Please allow me to change the subject just a bit but anyone know why this boat would be designed with a curved transom besides the fact that Mr Garden thought it would look nice and he can be a very artistic designer? Is there any other advantage?

[Buddy Sharpton]

I believe you've got it. Typically a wooden catboat had a flat transom in spite of all those many other curves. It was more practical to build that way. Certainly a curved panel in modern plywood will be stiffer for its weight and more effective resisting the torque, particularly fore and aft, of the rudder. That's why fiberglass boats are almost always made with curved transoms when an outboard rudder is involved. On a catboat, especially a small one, a transom knee is usually used to transfer that load into the keel(son}. But curved transom would look good, demonstrate a higher standard of build, and eliminate a tad more weight ( might have been 1" ply were it flat) and keep the cockpit clear of the transom knee.