Peformance Rudder profile and Shape

[savageseadog]

I know there are accepted optimum aerofoil sections for rudders which covers the streamline section, but what about the shape in elevation? I've seen all kinds of tapers, thick, raked aft, thin, curved etc. Is there an optimum profile?

 

[Birdseye]

Do you mean sideways on? If so there are two criteria. Balance is an issue relating to the pivot point and how heavy the boat is on the helm. That apart, rudders are just another foil like a keel so its an issue of chord against overall length.

 

[adwuk]

Most effective when the leading edge is at right angles to the flow. Everything else is tradeoffs between foil efficiency, strength, stock position and balance. The taper is there counter the increased lever that the generated force has on the stock. The challenge comes from wanting 1) a low drag efficient foil operating in clear flow and 2) the turning force generated at the waterline. Now design around those conflicting requirements.

 

[Foolish Muse]

http://www.thedailysail.com/dinghy/12/61366/0/turbocoles-rudder

Look at the above article. There is a lot of thought going into tubercules on the leading edge. I'm even considering it for my own rudder.

 

[savageseadog]

http://www.thedailysail.com/dinghy/12/61366/0/turbocoles-rudder

Look at the above article. There is a lot of thought going into tubercules on the leading edge. I'm even considering it for my own rudder.

Put a sharp edge on it and it would see off the lobster pots

 

[bignick]

Most effective when the leading edge is at right angles to the flow. Everything else is tradeoffs between foil efficiency, strength, stock position and balance. The taper is there counter the increased lever that the generated force has on the stock. The challenge comes from wanting 1) a low drag efficient foil operating in clear flow and 2) the turning force generated at the waterline. Now design around those conflicting requirements.

Small section nose radius combined with a rectangular planform can also lead to abrupt and sudden stall.

 

[Keen_Ed]

start here:
http://www.ericwsponberg.com/wp-content/uploads/keel-and-rudder-design.pdf

"Tapering a planform to match the characteristics of one half an ellipse produces optimum lift distribution and the least vortex drag"

Then I would look at things like TP52 rudders, Merlin Rocket rudders etc and go and ask a naval architect.

IANANA, but I would think that it depends also a lot on the boat. Plus planforms with a straight bottom are easier to build and more resistant to damage than pointed tips. Higher aspect foils are easier to stall and give less feel than lower aspect.