— the blade is laminated of 5 layers of 1/4” lauan ply, ground to a NACA 0012 profile and then glassed with two layers of 6 oz glass fabric in WEST epoxy.

— it’s housed in a cassette with a kick-up pivot, and the cassette is 1/4’ lauan ply too, 1 layer thick at the top and two layers down where it sandwiches the blade, with solid lumber 1 1/4 square or so around the front, top, and half the back (the places that don’t interfere with the blade, down or up).

The original was sort of a halfway-barn-door layout but I ditched that for narrow and deep to have better performance, which I definitely got (but paid for with the kick-up complication, necessary if the rudder were to reach deep in a beachable boat. ?When it kicks up then it functions as a long barn-door shape.

For light?and stiff, I’d try?

— one piece, no kick-up scheme

— ‘glass/epoxy over a styrofoam core, probably at least four layers of 6 oz glass (maybe 6 near the tiller joint and leading edge), and with something like a 1” x 4” (full inches) stick of wood as the front edge of the core, to receive the tiller torque and to bolt the pintles into without crushing it.

(DO NOT attempt to use polyester resin, including Bondo, on a styrofoam core — you’ll find the core dissolving.)

— I think a wood core along the lower edge would also be prudent for when it runs aground.

For barn-door rudders, NACA profiles are a bit silly but still if the rudder protrudes below the transom I’d round the nose of that portion with something like a 2” long half-ellipse. ?Otherwise just shape it to fit the pintles.

I’d ?taper the trailing edge for about 4”, but not to so thin an edge it became fragile — maybe to 1/4” or so, and maybe put a wood core in the aft inch or so.

For extra stiffness and sturdiness, I’d use 1.5” foam instead of 1” and taper it a bit to the leading edge, maybe with some filler to fair the joint there. (Thickened epoxy — silica for thickener and microballoons to minimize weight) (NOT BONDO). ?And taper the trailing 6” instead of 4”.

Bending load is going to be max at the leading edge and taper off to near zero at the trailing ?edge, so you might use only 2-3 layers of glass full length but build up steadily as you go forward, to 6 layers wrapped around the leading edge and reaching back a foot or so. ?Every layer should wrap the leading edge, to help pick up the tension from the tiller torque and deliver it aft.

Minimize weight by taking care to use only just barely as much resin as you need to get each layer of glass fully wet, with diligent stippling with your chip brush. ?Do get it fully wetted, no entrained air, but count on stippling each layer for some minutes to get it there. ?If you just slather it and drown it, you get much thicker epoxy layers than you need, and extra weight.

To minimize the stair-step effect from the successively fewer layers of glass, you could glass it with all but the last layer of glass, then fair it with thickened epoxy (silica for thickener and microballoons to minimize weight) and sand it (sparingly — don’t go through the glass you just put on)?

— and then put on the last layer of glass.

If you let the epoxy set between applying one layer and the next (which does keep the work more controllable — you might manage two layers at a time but I wouldn’t attempt more), then take steps to remove the “amine blush” that will interfere with adhesion of the next layer, and also sand off any projecting glass fibers and resin that would prop up the next layer.

Rounding and tapering are prior to glassing, of course. ?I’d blue up the core including whatever wooden edges you fit into it, and then fair the whole thing, then glass it. ?Do beware that the sander will chew way faster on the foam than on the wood.

… and be warned that when you sand styrofoam it goes everywhere, and it clings. ?Wear breathing protection and keep a shop vac close by. ?If at all possible use a sander with a vac hose on it.

have fun

Crispin Miller