Recently i've experienced this weird thing with my rudders. The winds have been pretty heavy lately and when I get going close to 16-18 knots or so, upwind or downwind, sometimes the rudders just lock in place. It feels like someone is physically holding the tiller. If I muscle it really hard I can get it to adjust but dang it's a lot of resistance. I keep the blades in decent shape and there aren't any boogers or any imperfections that would cause a problem that I can see.
All I can think of is cavitation coming off the daggers? It's shallow around here so I have them locked at half height a lot which is slightly shorter than the rudder blade. I haven't noticed it happening before when I'm in a distance race but the boards are all the way down then so that's what makes me guess the half height boards. They are smooth and sanded so it shouldn't be related to condition. Maybe the trunk gap that I opened up by raising the boards slightly?
One time when it happened it was downwind and I got hit with a puff and the nose buried so hard the rudders lifted 2/3 of the way out of the water and that really stiff helm feeling happened. But today the back end wasn't out of the water and it did it again. Not sure what to think.
Edited by tamumpower1 on Mar 25, 2017 - 01:12 AM.
Rudder cavitation, or something else?
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Posted: Mar 24, 2017 - 10:23 PM
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Posted: Mar 24, 2017 - 10:52 PM
matt,
does is happen on both starboard and port tack? have you tried to isolate it to one rudder by lifting the windward rudder on each tack?
doesn't seem like dagger cavitation could cause this to me, but the rudder binding at the gudgeons when under load. do you have bushings that might be worn allowing the rudder to shift under load?
j
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Posted: Mar 25, 2017 - 12:23 AM
Well I haven't ever really payed attention to what tack I was on but I can remember on 2 different times that it was starboard tack. I do have nylon bushings on the rudder pins which I made out of stainless last year. It's a pretty simple setup so it's hard to imagine what could make it bind enough that I can't move them without some serious effort. -
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Posted: Mar 25, 2017 - 07:21 PM
Don't know about the H rudder setup , but could it be a rudder
popping out of its locked position only by a inch or so?
On my old P18-2 the rudder sometimes popped out of its position
at high speed, it didn't go up all the way, just a inch or two.
It was impossible to steer then.
Just a suggestion.
Grtz, A
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Posted: Mar 25, 2017 - 10:18 PM
Boat props cavitate and pump impellers cavitate. Sailboat foils do not cavitate - they ventillate and/or stall.
If you're sailing the boat hard with the daggers half way up, that could cause a stall (especially if there are weeds in the water). But that would only happen when sailing upwind, certainly not when sailing offwind, since we always pull the boards up when sailing downwind anyway. Ventillated or stalled rudders really wouldn't cause the rudders to "lock up" though. A stalled rudder is just unresponsive. I've had this happen numerous times on my H17 when pushing the boat hard upwind in a medium breeze- the rudder will just let go and the boat will be going along sideways. You have to sheet out several feet, bear off, and re-establish flow. Then you can sheet back in and get going again. In windsurfing it's referred to as "spinning out."
If you're experiencing a situation in which the tiller physically won't turn under load, then I would look at the rudder mechanisms - lower castings, gudgeons, pins, bushings, and tiller connectors. It sounds like something may be binding up.
You mentioned burying the bow downwind. The 18's bows are so broad and deep that the boat can be quite difficult to steer if they are buried or nearly buried. I still wouldn't describe the rudders as being "locked up" in this condition however. And once the bow pops out, the steering returns to normal.
One thing you didn't mention is what do you have to do to make the "locked up" condition go away?
Also, what type of rudder blades are you running?
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Posted: Mar 25, 2017 - 11:22 PM
The 18 uses a rotating cam with groves in it that a spring loaded plunger locks into when the rudder is all the way down. It is possible that the rudder could kick up a little before disengaging the cam. The speed would depend on the spring pressure being used. I don't think it would be partially kicked up enough to give it the same feeling as when the rudders are straight out but I can definitely look next time it happens to see if that is what is happening.
Interesting. I thought I read before that a dagger or rudder with an unsmooth surface could cause cavitation but I guess a detached flow situation makes more sense.
The rudders are EPOs. One time it came and went away quickly. Maybe the 4th time it happened I really focused on it and it appeared that there was really nothing I could do to fix the rudders being stuck but just wait a second or two for it to go away. The whole time I was yanking on the helm and when it came unstuck it felt more like they came unstuck when they wanted to and not from anything I was trying to do to get them unstuck.
When the rudders are out of the water they rotate very freely. The annoying this is I take them off the boat and clean/grease everything every other month or so. 99% of the time the rudders are great. But when the helm locks up and I have the spin out it freaks me out a bit. -
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Posted: Mar 26, 2017 - 12:09 AM
Matt,
Do you have the updated (post 1987) rudder castings or the originals metal cam ones?
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Posted: Mar 26, 2017 - 12:41 AM
It's the updated ones. The boats sitting out on the beach right now but I think I might go out tomorrow. I'll try and see if there's some way I can get them to jam up mechanically. It really did seem speed dependent though. -
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Posted: Mar 26, 2017 - 02:18 AM
What are you using on the ends of your rudder pins?
Could they be hitting the hull? Back in my 16 days, 20 years ago, I had some small stainless safety pins that I used as a quick pin. Got them from Murray's. They would rotate at speed and cause something similar.
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Posted: Mar 26, 2017 - 02:49 AM
Yea I have safety pins on the top. And I'm gonna guess that yes if they rotated just right they count get caught in the big hull lip an 18 has. I dont see why the rudder wouldnt still be able to rotate on the pin regardless on if the pin gets stopped from rotating though. Might be a good test to take out the pins and see if that fixes it. I have secondary holes lower down the pin that I just put line through anyway. -
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Posted: Mar 27, 2017 - 09:32 AM
no doubt in my mind it is these safety pins your using
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Posted: Mar 27, 2017 - 01:19 PM
Are they original EPO rudders or one of the later sets?
I had a set of EPO II rudders on my boat for a little while and they simply would not balance out right. On one tack, they would go from feeling OK to swapping to lee helm. Sometimes there was weather helm. And they could feel "sticky" at times. The stickiness was probably from the flow separating and then re-connecting. The rudders were just too thin (noticeably thinner in the casting than my original EPOs) making the boat very squirrely and unpleasant to sail. Changing the rake didn't help. If I raked the rudders back, there was too much weather helm. If I brought them forward, the helm would become inconsistent. Just a bad set of rudders. I put a set of original EPOs back on, and the boat felt great again.
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Posted: Mar 27, 2017 - 01:34 PM
What does this mean? 1/2 height?
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Posted: Mar 27, 2017 - 02:46 PM
I believe it means he is running with his dagger boards pulled up to half of their fully inserted depth.
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Posted: Mar 27, 2017 - 03:09 PM
well - that's what i thought too but ...
I owned several hobie cats. they had 2 positions - locked down for proper sailing or not locked down and not locked-down= fighting with the boat - so i can't understand how / what 1/2 way down means -
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Posted: Mar 27, 2017 - 04:16 PM
Huh?
There is a bungee cord attached to the top of the daggerboard and tied off to the boat which applies pressure to hold the board in position. You can set it to whatever height you want from all the way down to all the way up. As long as the bungee cord is in good condition and applying enough tension, the board will stay wherever you put it.
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Posted: Mar 27, 2017 - 04:40 PM
Dagger boards, not rudders -
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Posted: Mar 27, 2017 - 04:45 PM
oops - my bad - got it
