Re: Rudder Performance

I suppose that one might not be too worried about increased drag from the rudder on a downwind because you've got "free" energy from the wave you're turning on? As long as the rudder is effective in steering the boat, right? The rudder on my mako 6 seems to work very well until it's thrown way, way over.

Does anyone know how much a non-NACA shaped rudder, like the Fenn rudders, needs to turn until it gets to a point where it is no longer effective in steering? Or, in other words, would a NACA shaped rudder be noticably better on a downwind?

Actually, I'm in way over my head here, so I'll just listen.

how about if the course is flatwater with wide 90 degree turns? We have many races here that are like that. In fact, one is a canal race with no turns- only course corrections!!!

Would you swap out a full size blade for something smaller?

Any gain in performance on flatwater?

In flatwater for a mostly straight course I would definitely go small. What you are describing is close to a K1 race so go look at a typical K1 rudder. They are tiny compared to a typical ski rudder. A surfski is a bit harder to turn than a K1 so I might go slightly larger than a k1 rudder but not much. I have a flatwater rudder I made myself that is 4" deep and works very well for ocean racing in mild conditions.

An idea that I have had for some time but never got round to trying is to replicate the effect of a keel rudder as used on yachts. This is best described by imagining that one cuts off the all of the rudder forward of the shaft and mounts the removed peice on the hull as a weed deflector. The remaining portion (obviously after being reinforced and made good) is then installed in the usual way. The result id a fixed front portion and a moving rear portion with the following benefits:
1. A trailing rudder with progressive resistance to deflection = smoother operation and better "feel"
2. Greater lift/drag due to "flap" effect of deflection (as in flaps on on aircraft wing)
3. Integrated built in weed deflector
4. Eliminates the drag caused by turbulence generated in the gap between the hull and the top of the rudder as the leading edge delects over the centre line of the hull.