Balancing the sail plan and board position

Regarding calculaltion of the hull's CLP, are you gents saying that the rudder should be included in the calculation? Logically I would have thought that you ignore the rudder with an eye to balancing the boat without it. The rudder is basically "along for the ride" (i.e., theoretically the AoA = 0 degrees), thus reducing the induced drag.

(I know I have Skeene's, Steve Killing's book and Elements of YD close by, but I'd like to hear the reasoning behind your advice here!)

Thanks,

Chuck

 

As far as I understand that is not reasonable to design a boat. If you are considering sailing the rudder "hands free" (i.e. let it flop around) it would be directionally unstable. IF you design the hull for zero tiller loads I think it would be difficult to keep the boat in a strait line. The rudder is a critical component of the directional stability and control of the boat, constant transient loads are always acting on all parts of a sailboat. Even with the rudder fixed it must still interact with the hull, wind, sail, and hydro forces alone with all of the other components of the boat. With the tiller hands-free these forces acting on the boat would have nothing to act against keeping it in line.

Perhaps someone more knowledgeable than me could add something if I am misunderstanding the function of the rudder.

 

It depends on the hull and appendage(s) configuration, but on this boat, with it's spade, then I'd include it in lateral area calculations.

 

I think for this boat the rudder is a fair proportion of the lateral area and will, for the most part, be lined up straight. Therefore I would include it, albeit on a 'weighted' scale - i.e. not contributing as much, size for size, as the daggerboard (because it is likely to be a lower lift section).

 

I'd back up what others have said here, particularly PI.

You don't want much, if any lead for a boat like this. Use the rudder and centerboard area and line 'em up with the sailplan area. The boat will be sailed flat, unless you are doing something wrong, so you won't get weather helm induced by heeling.
Look at other successful designs as a benchmark. If you can locate sailplan drawings, you can get a good idea of the sail and board centroids easily. Better still, coupled with that info, talk to a few who sail those boats and get their feel for how the boats balance.
One of the nicest sailing dingy types is the 505, just plain sweet. I'd use that as a real good starting point.

 

Banshee

Hi UK9

Is this David Lee's Banshee design? Are you still intending to do the dual role, single hander/UK Cherub?

http://www.sailingsource.com/cherub/test/doku.php/designs/banshee

 

Yes and Yes. Interested?

 

work in progress...