: My rudder idea for the Sea racer looks like the attached image
: (perhaps not everybody in the thread has access to the plans ;-)
: The idea was to have an extremely light and simple but
: hydrodynamically efficient solution (retracted or employed),
: with few parts and put together witout fasteners of any kind and
: therefore serviceable anywhere.

: The rudder blade hangs on a pin, held in place in the shaft. The
: cylinder is kept in place by the two-part uphaul, tightened in
: front of the cockpit with a piece of bungy cord. The cylinder
: top fits into a square hole in the line sheave, that lies
: loosely in the top compartment of the shaft and connected to the
: rudder lines.

: All parts are manufactured from glassfiber and epoxy, and as molds
: were used standard plastic plumbing pipes of different sizes.
: The cylinder is foam-filled to be light.
: Everything can be assembled/disassembled in a minute without tools:
: just release the bungy cord, drop the rudder cylinder and remove
: the pin...

I think your rudder is just great – few parts, simple, and light. And uses the same simple retract and deploy that your skeg uses.

**

: The comment on being not autoretractable is of course valid –
: unless the rudder happens to be in neutral position. But the
: prototype rudder is controlled by a another new (?) idea – a
: pedal set made out of 3 mm plywood cut to produce two pedal
: plates with rudder lines attached to outer upper corners. These
: "pedals" conform to the shape of the foot when bent
: – and they flex back to neutral when released, meaning that
: the rudder always will be in neutral and retractable (by the
: paddler or by a rock) immidiately when not engaged.

That’ll work fine, but might it not be even simpler using an off the shelf gas pedal rudder with the addition of a fixed bungee on the front of each.
With the same adjustment, that would self centre but has the addition of having a varied spring response. (And I still think a detent would be helpful to the setup).
In both cases, though not shown, you’ll have to fix the lines to the tiller pulley so that no slip happens (because things slip, that’s why a detent may also be helpful, heh heh).

**

: The comment on rounded corners are also valid – I did that after
: testing – but not too much, since it creates turbulence!

I didn’t mean to apply that comment for the foil section view (that probably should have a blunt/angled edge to stop variable vortex shedding) but for the side view of the blade.
If you look at Willn’s last post, you’ll see the area just above the retract line is rounded. If you shape cut your your blade at this location there is a slim possibility that under slight angles the blade would still ‘carve’ its way back in (– but nitpicking details).