Dusty,

You can get serviceable sailing rudder features, with all the bells and whistles described, from your Feathercraft unit if you do the following:

The business of using a metal core for a pair of wooden pieces on each side will work just fine. You will need to replace the aluminum blade with a stainless piece as the alu core will not hold-up to the side load bending moments that can be generated by the rig and the speed it can generate. Blades done in this fashion get a good loading hit at the point where they exit the rudder "cheekblock" assembly on the Feathercraft. Substituting an equal thickness of stainless will help absorb that load and it will not experience metal fatigue and breakage as quickly as will alu core material. The new core will slip right into the existing rudder assembly without the need for new bushings, spacers and rebuilding.

The core add on sections can be shaped from plywood, but I like to use solid material such as mahogany as all the grain is running in one direction and it will give substantially more strength to bending resistance along the length of the blade. Give the wooden pieces several really good coats of epoxy on both sides with and extra layer on the leading edges. Fasten the wooden pieces to the core with countersunk sheet metal screws and fill the screw heads to give a smooth, fair surface before painting/varnishing.

John's comment about building a balanced rudder is spot-on, though you won’t need as much of a balance as is suggested for larger, heavier sailboats. The feel of the rudder is already on the light side on a sailing kayak. You don't want that "feel" to go away as it gives good feedback from the tiller controls (foot pedals)

To get a flip-up potential from the Feathercraft, simply remove a section of the hold-down line on the rudder setup and substitute a section of bungee cord that is lead back to the cockpit. The inherent stretch of the bungee will allow the rudder to be held in the down position, but it will also give if the rudder blade hits a obstacle or when you drive the boat onto the beach under sail. You'll have to figure the proper length for the bungee when you rig the rudder on the kayak. It's all about the stretch component, the needed resistance against the water flow, etc. That line stays fixed on the kayak and the only one you now need to work with is the retrieval line. I place a clamcleat up by the cockpit to cleat the retrieval line when I manually pull the rudder into the "up" position, where it is then held, out of the way and not open to damage.

I'd make the wooden pieces for the rudder so that they are thick enough to achieve a NACA 0012 section. This is a good all-around foil section for sailing at the speeds you will likely experience in your kayak. It is not prone to stalling at low speeds, so you will retain good control for maneuvering and has only a small drag penalty at very high envelope speeds and that will not be of much consequence on this craft.

A nicely sectioned foil rudder is much better than a flat plate. It is stronger under side loads and looks a lot better for those times when your friends come around to give you grief because you smoked their butts on that very long crossing in a 15 knot breeze off the port bow.

If you would like to have a drawing showing a good rudder profile and some details showing a suggested rigging method, then write me off list and I'll send one out to you via email. I'd just like to see you end-up with a good rudder system for your sailing triple. (the guys are right. In the right breeze with good boat trim and sail handling, that waterline length is gonna give you some real pop) as long as the boat is not overloaded... lighter is better for multihulls.

Chris