Rudder flex

[Guest]

I know some like flexing/twisting rudder like things and in fact build it into their gear to great advantage but does a 30fter want a flexing or twistable rudder? By flexing I mean under load looks a little like one of the curve foils off Timberwolf than it does a plank of 12 x 2, some of that is probably refraction though. By twisting I mean the bottom end twists a bit, which I don't think my rudder is doing but do know some boats built that in on purpose, mind you all the ones I know are a lot faster and massively lighter. I was planning on whacking a pile of carbon/whatever down the sides to stiffen it up but thought 'lets ask the audience' to see if there is any better idea worth sussing first.

 

Anyone have any thoughts on what you'd do if you had zero restrictions, bar the total allowed area I think.

[Atom Ant 0]

Just glue 3 bits of 4 x 2 together KM. Use PVA. Ross 930's go well with that set up I hear.

[Guest]

If your after performance my I suggest ferro cement...................

[wheels 543]

You don't want movement or "bending". Any movement is the opposite direction to the force applied. Seeing as the force in this case is lift, then you don't want to lose that lift. So you then need to apply more angle to make up the difference. Problem is, the angle is in the Horizontal plane and the "bending" is in the vertical plane. The result is lost energy or inefficiency.

Then aside from all that, add in stress and fatigue. Unless you have a material that can cope with constant bending and unbending, eventually something is going to break.

[Kestrahl 6]

On the old Shaw 6.5 we built the foils very light, hollow carbon with a spar. The keel fin was 7kg and the rudder blade was 3kg, half the weight of Rob's plans. There was 4 layers of double bias in the layup so took some of the twisting loads. However it was quite scary how much flex was in the keel fin when the boat was hoisted in the air, and I'm sure the rudder wouldn't have been much different. But the boat was a rocket and the quickest 6.5 in NZ especially upwind in a breeze and neither of the foils cracked or broke!

[Guest]

knot me you fly, so just think a wing, or elevator, and weather or not you would want it doing the wild thing.

from my experence most 930's rudders don't actually meet cat 3 structures

[Guest]

Used to experiment with flexible surfboard fins years ago and it seems they would load up and release energy which felt like acceleration. They did not last long though. So maybe some flex in the rudder will "store" energy and release it when the load lessens, something like an unstayed mast is known to do. For racing I think it would hold merit. Rather than the rudder pushing sideways some of that energy would be stored and released as acceleration and may even lessen the loads on the helm. All this may be absolute bullshit too.