While out racing last weekend I had experienced the hum that I believe is coming from my rudders and has been haunting me with this Prindle 18-2 I had recently acquired. When I had first noticed it; I had wet sanded the rudders and the centerboards going up to 1500 to a real smooth finish, cleaned up the leading edges, and shaped the trailing edge to almost a point and this had not stopped the noise, but it hasn't increased it either. I am now thinking maybe I should blunt (square it off) the training edge to elongate the flow off the edge of the rudder to maybe reduce the vibration.
Anyone have an thoughts about this?
Yep, Blunt the back edge.
I did the same thing with my P19. The answer was asymetry. On the positive side, I could always tell when I got her up to speed!
I get the same thing, nice spooky sound!
So, Is the consensus to blunt the trailing edges?
Yes this was letting me know that I was building speed, but it slowed us down. It seemed that someone was playing with the volume control and accelerator. As it got as loud as it could get the boat would slow, then start again.
Did you get rid of the noise?
I am going down to the yard today to get the rudders and reshape the trailing edges.
The way I've done mine (P-19 mx and I-20,boards rudders and centerboards) are to get a sharp pair of scissors ,hold the blades open over the trailing edge. Look at the angle of the blades and hold them at the angle you want the T.E. shaved to. Shave the T.E. with the scissors for a uniform (symetrical) edge, then sand and polish to finish. If you end up with a razor edge on the back ,blunt it with a sanding block.
Works for me, the whale sound is definitely slow, although Team Zhik/Layline have it and seem to go real fast. No telling how fast they'd be without it.
Todd
Un frigging believable - while looking at the rudders last night I had noticed something real odd - the port rudder casting is warped.
In place of taking the rudders off, bringing them home reshaping etc... I wanted to take them off and switch them to see if that would cure it and bench test things as outlined in the article from Jim Boyer. To my surprise, putting the starboard rudder on the port casting I had noted there was a hang up that existed with the original rudder. In really looking at it the bottom of the casting it is leaning inboard.
Never encountered this before