[quote]Really? [/quote]
Simpler and a lot less time than building a kayak.

The simplest, the Smarttrack type is an aluminium blade (could even be wood), A block of plastic (PVC?) ~20-25 mm thick by 100 mm x 100 mm. A SS piece of rod 4 mm and a nut and bolt, say 6 mm x 20mm.

The pivots that it steers in can be plywood, one at deck level, the other below the rudder block, the up and down from suitable "string".

The whole thing could be made from wood including pivots.

The Don Currie 90 degree retracting one needs a few more bits (3 more bits?). Total about 12 bits OK 16 if I include the nuts also necessary if the metal isn't threaded.

The Sea-Lect version has 76 components !