performance rudder

[gabi]

 hi all,
we all know the benefits of a foiled rudder vs the flat plate,
but what about a different shape rudder for even more performance improvement,
something like a fin shape ,maybe deeper and narower, etc

just trying to get some ideas

[skip1930]

A no brainer for the foiled rudder. Do it for any number of reasons. For me the IdaSailer rudder gives me [when fully pushed down and bolted in place] a feeling of 'power steering at the tiller' because it is a bit balanced. Read further forward, some what under the transom.

skip.

[Pacman]

I added 2" to the leading edge of my rudder to balance the helm.

Adding some surface area in front of the pivot point to balance a portion of the surface area behind the pivot point made the  helm much lighter.

The additional surface area also makes it possible to turn the boat with less rudder angle (minimized slip angle).

I have made a faired rudder to NACA 12 shape and I have made a balanced rudder by adding aluminum plate to the leading edge.

Both experimental rudders were a success.

My next experiment will be a faired and balanced rudder.

[gabi]

well ..I've read that a longer narrower rudder is more efficient, so i was wondering if anybody tried to experiment with different lengths/widths ,and see what the improvement would be

the foiled rudder over the original dimensions is already a big difference,but who knows a different size/shape we might win some races...

[NateD]

well ..I've read that a longer narrower rudder is more efficient, so i was wondering if anybody tried to experiment with different lengths/widths ,and see what the improvement would be

the foiled rudder over the original dimensions is already a big difference,but who knows a different size/shape we might win some races...

Depends what you're racing....but I wouldn't count on much improvement beyond a standard foiled rudder. The rudder needs a certain amount of surface area to be effective and balance the forces on the boat, and in general the CP16 could use more surface area, not less than the stock plate rudder. I'm far from even an armchair engineer so I don't know how much of an improvement a skinnier and deeper foiled rudder would be, but I'm guessing it wouldn't be much of an improvement from a standard foiled rudder. This site (http://www.ikarus342000.com/Boardsandrudders.pdf) says a 1:4 aspect ratio is a good choice for a transom hung rudder, which is probably pretty close to the factory size. Making it narrow and long will obviously increase the minimum draft, which removes one of the benefits of a Com-Pac.

[gabi]

well , a sunfish rudder has more surface area than cp16'

in fact im thinking to get a used sunfish rudder from ebay, or a hobie cat rudder and try to mount it up,

[Bob23]

Gabi:
  I'm tending to agree with you. I replaced the stock wood rudder on my Force 5 with a stock foiled plastic rudder blade from a Hobiecat. Made a big difference for 2 reasons: First, the Hobie blade sat more plumb- not raked back like the stock Force 5 and second, it was indeed narrower. However, the Hobie blade has less surface area so, when conditions got nasty especially on a run, steering ability was a bit comprimised.
  I don't think a sunfish or Hobie blade has more surface area than a Compac 16 blade, at least not wetted surface area but I do admit to not having either here at the shop to compare.
  Here is a photo of the wood foiled rudder I made for my 23: It appears to not be plumb only because the downhaul is not tight.

 It worked great; the boat pointed higher, tacked through much easier and weather helm greatly reduced. However, it did come out wider than I planned (funny how stuff happens, eh?) so my thoughts were exactly as yours: make a deeper, much narrower blade with perhaps a fin shape which, coincedentally, is the shape of the little Hobiecat blade on my Force 5.
  I'll be watching this post. If all goes well, I may make a few prototype blades this winter to experiment with next spring.
Bob23

[gabi]

the hobie blade is about 34" long by 9" wide  and the cp16 is 23 by 13, so roughly the same area...

...but about the upper 3'd  of the hobie blade is where the casting mounts ,so i dont really know if thats foiled or not,

even so ,there could be an easy addapter plate that goes from the end of the hobie blade strait into the cp16  casting,

(a hobie rudder could be found for as little as 50 $ on ebay)

another part of the problem with the cp16 is that the casting is so low that the end of it is constantly in the water,... now how do you foil that casting....


on my boat the casting is about 2 " under water when sailing, just about to where the loking screw is.

now 2" out of 23" long thats about 10 % , ....and thats pure drag!!