Paul Thompson wrote:

Annie Hill wrote:

To do as you suggest, Paul, would require some heavy metalwork, to ensure that the rudder is sufficiently strong.  I'm trying to avoid any more metal below the water so that I don't have to worry about electrolysis.  Moreover, I want to attach the rudders using James Wharram's method, with rope hinges.  Cheap, low tech, and incredibly easy to check or replace.  And doesn't require bushing.

I've just posted on my blog, for those who are interested.

You misunderstood, I did not mean to suggest that you should do it. Only to show that you can have a fully balanced rudder that is supported at both ends.

Arne, if you look very closely at the cross section through the middle of the rudder, I drew a trim tab, which is what Annie wants for her self steering. It’s good to hear that you found no friction in the renewed Wharram figure 8 Dyneema cord hinge, as trim tabs are very sensitive to stiff rudders, to the point of not working at all well. When that’s the case, the fallback position is to reverse the linkage and convert the trim tab into an auxiliary rudder (which just happens to be mounted on the main rudder, which is fixed when the vane is in operation). 

To do as you suggest, Paul, would require some heavy metalwork, to ensure that the rudder is sufficiently strong.  I'm trying to avoid any more metal below the water so that I don't have to worry about electrolysis.  Moreover, I want to attach the rudders using James Wharram's method, with rope hinges.  Cheap, low tech, and incredibly easy to check or replace.  And doesn't require bushing.

I've just posted on my blog, for those who are interested.

"I may be making progress, but I still have to fit out the saloon, the galley and the cockpit, lay the decks (including the teak- sorry Mr Tyler), put on the rubbing strakes, make the rudders and bilgeboards, make tillers, build a mast, make a sail, wire the boat, make cushions, paint the hull and around the cockpit and no doubt dozens of smaller jobs that presently escape my mind."

Almost inaudible sigh. You will be reducing the thickness of plywood by the same amount as the thickness of the teak, won't you? Please?

Annie Hill wrote:

David Tyler wrote:

But, but, but...

I made the drawing back in January last year. It lacks dimensions, that's all.

I dare say you did, chuck.  But I can't find that drawing anywhere in my files!  Dimensions wouldn't go amiss ;-) if you could manage them. 

http://www.windknife.com/full-foil 

Cheap enough for what they are but I have not used them myself.

Even the "nose only" section may not be big enough enough though.

Not sure I am terribly impressed with their asym section, and its hard to see that nose scaling to an 800 mm chord.

Then again David's asym foils would be dead easy to construct and those box sections look pretty strong to me.