multihull rudder rake

[bob fisher]

just a query.. is there any advantage of raking the tips of the rudders forward on catamaran rudders (transom hung) apart from shifting the CLR forward? i.e does it make them any easier to steer/bite in?

cheers

[dougfrolich]

By raking the rudders forward the center of pressure moves forward, so could aid in ballancing the rudder, also the spanwise flow would move from tip toward root wich I think would make them more resistant to blowout, but with the tips raked forward the blade is going to want to twist, and you don't want that, controlling that twist will require some high-tech thinking.

[frank marsden]

I think that the whole issue of rudder design is not well understood

[frank marsden]

as inthe rudder can steer the boat


hello!

what is this guy talkin about

that is what rudders are for.

Except, they can steer the boat of their on volition

[SailDesign]

Bob,
If you can allow the blade to "lip" under the transom, then follow a "normal" shap below (as in a balanced rudder with a chunk cut out to allow the transom to exist) then you have the best of all worlds - a balanced rudder but still not likely to "self-steer".
But... it really only works with a swing-up rudder.
Steve

[bob fisher]

to dougfrolich and saildesign, cheers heaps for your input it is a big help, that is basically what i am thinking of doing, a swing up rudder, sort of similar to a volvo 40 design, i think this will be more efficient than the typical daggerboard type.

to frank marsden, you obviosly have no idea mate, you should leave the technical comments to the experts.

cheers

bob fisher

[frank marsden]

Bob,

Please explain.

I have a fixed keel Superseal 26.

Lifting keel Superseal owners find that the angle of the lifting rudder blade can alter the steering characteristics from lee to weather helm, with no sailplan changes.


I peviously had a Trapper 500 (C&C 27 MkI)
If you left go of the tiller under power, the rudder would go hard to port in less than 6 seconds and the boat would turn to port tightly with the rudder at some 40deg.

Try this with the rudder hard to starboard and it would stay there, with it at about 20deg to starboard it would take about 45 seconds to go hard to port.

I still think that rudder design is not well understood.

I know that rudders can steer the boat if left to their own devices, and the helmsman may not notice it.