Rudder Wobble(?)

bluefin

New Member
Just spent my first season sailing a J24! I bought a 2003 boat built in Argentina and we had a blast this summer on Lake Tahoe!

One issue I had that I'd like some advice on is the rudder had a distinct wobble at speed. The "wobble" was not a vibration. The tiller would move 2 to 3 inches back and forth approx. 3 or 4 times per second. This would only happen off the wind at or about hull speed. I checked the gudgeon straps and pins and there is no play whatsoever. I looked closely at both foils and could not see/feel any anomalies. I do not have class templates so the foils could be out of spec, but if they are, it would be so minor that I don't think it would cause the problem.

I faired a rudder on a Santana 35 once and did encounter a cavitation/vibration at the trailing edge. A pro told me to bevel one side of the trailing edge and that cured the problem. The J24 rudder trailing edge is so narrow that I don't think that is the issue either.

So as you can see, I'm at a loss as to the problem and solution. What I do know is this problem will become a much bigger problem if I don't figure out how to fix it. Any thoughts/advice would be much appreciated. Thanks...........
 
Wow! That sounds like a tough one. Certainly beyond my pay scale or experience.

If there's no loose hardware it sounds like it's some sort of hydrodynamic problem. Interesting that you don't see anything odd about the rudder shape. I think you need to consult with someone who has real experience with yacht design. Here's somebody who might be able to help you. I haven't had any contact with him, but it's apparent that he has experience working with the DIY crowd. Maybe he'd be willing to talk to you and offer you some suggestions.
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We'd be interested to know what you find out!
 
I have been think about this one since your posted. We used to race J22's and the "ridden hard and put away wet" boats sometimes suffered from a soft keel mount. Although J22's and J24's did not have an exceptionally deep keel sump, the older ones and perhaps the ones with higher flex cycles of the fiberglass resin layup tended to move more. New boats are unquestionable stiffer, you can tell by the ring when you thump them. Older boats not so much. You could be getting movement of the keel fin as it "swims" through the water due to a soft keep sump. This movement may indeed be the hydrodynamic problem the above writer eluded to. That movement or swimming would then be transferred back to the rudder as it sympathetically reacts. Far fetched but indeed possible.
The 24 has tabbed in wooden keel stringers that are designed to stiffen the sump spreading the load over the bottom of the hull. Perhaps the core material in those stringers are no longer with us and now the bottom of the hull is adding to the flex.
On a 22 it is most noticeable down hill. You could actually feel the boat hunt right to left without moving the rudder as the keel would "adjust" itself to the waves. Weird feeling.
Fin moan or hum is indeed a function of its fairing and it is slow. We fixed a J70 keel that had damage from trailering. It required repairing the trailing edge which required resurfacing the back half of the blade. We found several "shrinkage" areas where the layup shrunk while it cured. Those shrink spots caused depressions which I believe are worse than humps. The owner was astounded as he said the low frequency moan was no longer there. That boat went from mid fleet to upper 3rd in a heartbeat, same crew, same driver, same sails, better blades.
When it is hanging in the air, can you wiggle the keel side to side? Best way to do that is quick back and forth with your hand at the tip, actually a few fingers will do the trick if it is real soft. It will even continue "wiggling" after you stop inducing motion for several cycles.
Great post...
Dale
 
Just spent my first season sailing a J24! I bought a 2003 boat built in Argentina and we had a blast this summer on Lake Tahoe!

One issue I had that I'd like some advice on is the rudder had a distinct wobble at speed. The "wobble" was not a vibration. The tiller would move 2 to 3 inches back and forth approx. 3 or 4 times per second. This would only happen off the wind at or about hull speed. I checked the gudgeon straps and pins and there is no play whatsoever. I looked closely at both foils and could not see/feel any anomalies. I do not have class templates so the foils could be out of spec, but if they are, it would be so minor that I don't think it would cause the problem.

I faired a rudder on a Santana 35 once and did encounter a cavitation/vibration at the trailing edge. A pro told me to bevel one side of the trailing edge and that cured the problem. The J24 rudder trailing edge is so narrow that I don't think that is the issue either.

So as you can see, I'm at a loss as to the problem and solution. What I do know is this problem will become a much bigger problem if I don't figure out how to fix it. Any thoughts/advice would be much appreciated. Thanks...........
there are a few other possibilities that you may want to consider:

Rudder alignment: Check to make sure that the rudder is properly aligned with the keel. If the rudder is not aligned properly, it could cause the wobbling that you are experiencing. You can check the alignment by measuring the distance between the rudder and keel at several points along their length.

Balance: Make sure that the rudder is properly balanced. If the weight distribution is off, it could cause the rudder to wobble at speed. You can check the balance by suspending the rudder from its pivot point and seeing if it hangs straight.

Surface finish: Check the surface finish of the rudder blade. If it's not smooth and free of imperfections, it could cause the water flow to be disrupted and lead to the wobbling you're experiencing.

Hydrodynamics: Consider the hydrodynamics of the rudder blade. It's possible that the shape or size of the rudder blade is causing the wobbling. You may want to consult with a naval architect or experienced sailor to evaluate the rudder's design.
 
Hey guys, Thanks for the advice. I'm launching the boat on Monday so I will check the movement in the keel, rudder alignment and balance. I do have a strong background in fairing foils and feel confident that my foils are properly faired and not the cause of this problem.

I did talk to a world class J24 skipper who works at North Sails and his recommendation was that the gudgeons and pinions might have worn down enough to cause the problem. He told me that the fit should be so tight that you have to put significant pressure on the rudder to get the pins pushed in properly. My rudder pins slip in without any effort so I'm guessing that might be the problem. A new set of hardware costs around $600+ so I plan to sail the boat as is this summer and change the hardware next winter.

Thanks again for all your advice and have a great summer!
 
there are a few other possibilities that you may want to consider:

Rudder alignment: Check to make sure that the rudder is properly aligned with the keel. If the rudder is not aligned properly, it could cause the wobbling that you are experiencing. You can check the alignment by measuring the distance between the rudder and keel at several points along their length.

Balance: Make sure that the rudder is properly balanced. If the weight distribution is off, it could cause the rudder to wobble at speed. You can check the balance by suspending the rudder from its pivot point and seeing if it hangs straight.

Surface finish: Check the surface finish of the rudder blade. If it's not smooth and free of imperfections, it could cause the water flow to be disrupted and lead to the wobbling you're experiencing.

Hydrodynamics: Consider the hydrodynamics of the rudder blade. It's possible that the shape or size of the rudder blade is causing the wobbling. You may want to consult with a naval architect or experienced sailor to evaluate the rudder's design.
Rudder alignment - The distance and rake of the rudder blade with the respect of the trailing edge of the keel has no relationship to anything. The rake of the rudder about the gudgeon centerline will change the amount of rudder weather helm or lee helm that is felt in the tiller.

Balance - "Suspending" the rudder from the pivot point will guarantee that the rudder will hang blade down. What else could it possibly do? The weight is all to one side of the pivot. Weight distribution in a rudder is not an item to even consider, it is not rotating, it stationary.

Hydrodynamics - You think? Why consult a navel architect or experienced sailor to evaluate the rudders design? With over 5000 24's built one would think they got it right by now. Borrow a blade off of a buddies boat and see what happens.

Dale
 
You say " A new set of hardware costs around $600+..." You ain't kiddin'. Frightfully expensive. Makes all this J/24 stuff tough, since the boats are cheap, but the hardware has gotten pricey. I priced that stuff out recently and thought it's over $700. I think it was about $250 in 1996. Fixing my boat was a life experience, so I remember it like it was yesterday, but I guess it's been a while :).

One thing: A half-inch bolt will suffice for the pin, which otherwise sells for $85+

Vela wants $250 for one complete gudgeon and pin assembly. You need two of those plus the hardware on the rudder itself. Crikey!
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