Schilling Rudder Question

[Biggles]

Hello

I am building a schilling rudder for my boat. I have just noticed reading elsewhere that these will work at up to 2 x 70° The ram I have but not fitted yet is 2 x 35°.

My question is, is it a waste of time having a shilling rudder only working to 35°?

The boat is a wide beam narrowboat. Max speed is 7mph

Thanks

Biggles.

[daiquiri]

The answer will depend on the geometry of your rudder. Can you give some more info about it's dimensions?

[Biggles]

Originally Posted by daiquiri

The answer will depend on the geometry of your rudder. Can you give some more info about it's dimensions?

It's appox 560mm tall by 700mm long. I have no specific dimensions accept to say I have created it to look like a fish cut in half looking down on one.

The pivot point is 230mm from the front. The front is made from 60mm tube then it widens out to 100mm, 240mm back narrowing to 10mm, 400mm back then flat for 200 mm then a tail which is 100mm and about 30° angled.

Biggles

[Biggles]

On further reading I think mine that I'm building is probably a fishtail rudder. I read that these are good a 35°.

Still would welcome com met though.

Biggles

[daiquiri]

Some call it Schilling rudder, some call it MacLear Thistle rudder, some call it Mystic rudder (http://www.mysticrudder.com/index.html), go figure... It was probably invented and re-invented several times in history.

Anyways, apart the considerably higher drag at zero rudder angle it won't show you any sensational difference or advantage over a conventionally shaped foil, due to a very low aspect ratio of your rudder (AR=0.8). The lift characteristics of rudders of such low aspect ratio (or low height-to-length ratio, for rectangular platforms) are dominated mostly by tip-vortices, and in much lesser extent by the foil shape. End plates will somewhat improve things from the lift point of view, not when it comes to drag - as this rudder will anyways make some huge vortices at high angles.

Overall, you will probably gain some 5 degrees before it stalls, when compared to a conventional-foil rudder. But due to the said very low aspect ratio, the lift curve will be so flat that these 5 degrees will probably not yield much in terms of lateral (lift) force.

But anyways, it's probably still better than a flat-plate rudder, because the rounded leading edge area will prevent the creation of a leading-edge vortex, which is another important source of drag.

Cheers!

[Biggles]

Hello

Thanks for that. The link was very useful and the hand drawing could be mine. I will put it up on my blog when it's made and I will put a photo on here hopefully later today if I finish it. I just need to put the skin on and I'm not sure if I will be able to do that without heating it. If it needs heating I will have to take it to a local fabricators and borrow their oxy-propane kit. They are very accommodating.

Biggles

[Biggles]

Here is what I've made.

http://boatbuildblog.blogspot.com/20...ld-rudder.html

Thanks for the input.

Biggles