Carl

Very interesting! That endplate or horizontal stabilizer on the end of the rudder reminds me similar devices used on aircraft.

Wing tip (whatever you want to call them, tipsails, endplates, etc) curved up and down stop the flow of high pressure air under the wing, migrating to the top of the wing. This prevents wing tip vortices and makes control surfaces(ailerons) much more effective. This leads to a more efficient wing. Somewhere in the vicinity of 5 to 7% less Induced drag.

Induced drag is drag that is created by creating lift.

All this to explain that by putting the foil on the bottom of the rudder you are making the rudder more efficient, so it could conceivably be smaller and thus lighter and less draggy.

However the tip foil might create structural issues in that the rudder would have to be kept strong so it would not distort when under load. (probably not an issue)

The other thing is that the added rudder tips would probably be susceptible to damage and dragging weeds.

This issue could be pacified by placing the foils up from the bottom of the rudder say a few inches and making the foils sacrificial, in other words if you hit a rock they might break off and be replaceable as a cheap part or a do it yourself, carve one out and screw it on type of repair. Also by sweeping the foils back more they would hook less.

Makes me wonder if the same endplate could be used on the daggerboard, so it wouldn't have to be so long....

Easy to find out...Has anyone tried an endplate on the daggerboard?