Rudder turbulance noise

[mdgann]

My 1976 E23 MK II has a montrous slab of mahogony (sp?) for a rudder. Last Saturday as I was enjoying a 10 knot breeze, sailing at about 4.5 knots I had to raise my voice to be heard over the noise of the water going around my transom hung rudder. The boat balances very well, so I was not dragging it sideways through the water or anything. It was so loud that I thought I had left the outboard down.

As I was watching it over the transom, I noticed that it has a very blunt leading edge and the water would build up around this. I realize that a well rounded leading edge and fat cross section helps with stalling at slow speeds, but was wondering if I would notice any difference if I shaped the leading edge a bit to promote more laminar flow and less noise (turbulance)?

Any experience or ideas out there? Thanks.

 

[Seth]

I would do it

Couldn't hurt! Noise is slow!

 

[mdgann]

Thanks for your reply Seth. I was beginning to think that no one cared Maybe it's a size thing. Less than 30 feet, who cares.

Anyway, I think that I will do it. I have not done this before, but I would suppose that it would be critical to get the shape symetrical and would even use a template. Maybe a NACA foil number or something. Any experience out there?

 

[Loren Beach]

Sometimes silence just means that no one has thought up anything to contribute...

I like Seth's idea that noise = turbulence and that must be slowing you down a nano-knot or three. I went from a Niagara 26 to my present boat and the N-26 did have a transom hung rudder. I remember that it had a really nice foil shape and the trailing edge was fairly sharp. It made no particular noises, but once the boat was over 8 kts you could hear the stern wave and also the transom-mounted LS outboard would partly get its prop under water from the same wave...

The boat could not plane, but would surf well, having flatish bottom shape aft. (It was designed by Geo. Hinterhoeller as a sort of scaled-up version of his Shark.)

Loren in PDX

 

[HGSail]

A rudder and Keel are like a wing on an airplane. You should have smooth flow over all surfaces, Leading and Trailing edges and everything in between. Without the smooth and uniformed flow around the foil, It will act like a brake.
So I agree with Seth, it couldn't hurt.

Pat
E29
'73
#224
Holy Guacamole

 

[rssailor]

Fair the foil

Yes, try and make your rudder more like a foil, with the leading edge slighly less tappered than the trailing edge. Check out 3M catalog, they make some long sanding boards that work real well. Just bought a longer one for the hook-it sand paper, think its like eighteen inches long or so. After you are done, soak the bugger in penetrating epoxy to make the wood less likely to absorb water. Ryan