Rudder cavitation

[stevec22206]

Was wondering what causes rudder cavitation. Once we exceed a given speed the rudder on our O'day 23 begins to cavitate. My first thought is to replace the transom gudgeons as they appear to have developed some play. A friend also suggested it might be the leading edge of the rudder itself. Anyone else experience this? Remedy?

 

[NewportVic]

You mean vibration?

Some rudders do that. Had that on my R19 when it maxed out. Pretty good way to tell how fast I was going. If you decide to replace probably have to do both pintles and gudgeons. I used a couple of Nylon wire ties to tighten the joint... but it didn't last long ... so I just lived with it. Somewhere there are brass collars that might work. Vic "Seven"

 

[stevec22206]

I call it a cavitation

because after we reach the magic number the tiller will literally pulsate, or vibrate in one's hand, back and forth. I recall some discussion, maybe on this board, regarding the original gudgeons and pintels on this boat being undersized. As I said, my first thought is to replace them with a beefier set. There is enough slop in these now that it could be a contributing factor in the vibration. Before I endure the cost, and time required to replace them I wanted to feel certain this would eliminate most, if not all, of this annoyance. I have looked into your idea of the brass collar. Not sure there is enough material to work with.

 

[r.w.landau]

Steve, once the boat is powered to the max

by the sail you have up, the heel and the ammount of sail over powers the rudder. The rudder is then none functional. Leading up to that point the rudder is pulled to windward to correct for the desire of the boat to round up.The fact is, you are flying too much sail.The ideal condition is to fly the amount of sail so that the rudder creates the least amount of drag. That should be a heel of about 15 to 20 degrees.Once you get more than that, the sails over power the rudder.That cavatation is actually drag. The more you try to correct the overpowered sail, the more you have to compensate for it. The rudder is actually acting as a brake.If you are going ito the wind, find the place that takes the boat closest to the wind . You will have no rudder control but you will be sailing as fast as you can. It took a year to teach my wife this and I don't think that many people know how to find that groove. Let the wind round you up slowly and there will be a nitch that you have no control but the boat will be sailing into the wind at the boats max.Don't try this when there are boats near you unless you have a good insurance policy.That was a quick explaination. If you have questions, please ask again.r.w.landau

 

[Chuck R]

In the old'n days,,

This vibration meant the boat was happy. Your adjustments were at their max. I sailed cat boats during my youth, Nippers, Lyman Cats and the K-cats now after 50 years I forget if this occurred in a cat rig..?? The 222 O'Day I now own has done this and I attributed it to the Marconi rig.Steve, Good post! Is your 23 OD a shoal draft plus centerboard model? I wonder now if it is a centerboard thing and do full keel boats get this condition also? Lets see the replies.

 

[NewportVic]

Chuck ... now that you mention it ... the R19 ...

did seem to be happiest when it purred.That was the full keel modelVic "Seven"

 

[stevec22206]

She's old!

The holes in the gudgeons are no longer round. There is play, I can actually move the rudder fore and aft ever so slighty. This is a 1980 model shoal draft with a centerboard. They have some wear and tear on them. I had the luck to sail a new, at that time, O'day 25 many times and don't recall it having as much movement as mine does now. I understand the dynamics at work here, especially when the wind is approaching 15kts. and above. I'm curious to know if this is a characteristic of a transom hung rudder. Do the 22's, 222's, and 25's encounter this same issue? I would expect a fin keel to behave differently. Just thought I check with others to see if this is a common trait with this style hull and rudder set up. I am leaning towards replacement. Thanks for input.

 

[r.w.landau]

Steve, I have had two O'Day 25's

They all go wild at certian tacks and wind speeds. That is why I spent the time to type what I did earlier.Good luck in your search. It will not go away with replacement. It may be less but it is not worth the money and time to change the gudgeons.r.w.landau

 

[Kim]

Stalling

The rudder losing efficiency is due to hydrodynamic stalling.If you're familiar with airplanes, a wing stalls when losing aerodynamic efficiency; same principle.