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Movement in rudder blade

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samba View Drop Down
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    Posted: 11 February 2009 at 15:22
Hello,
 
I noticed some vibrations in the steering column. When sailing this occurs sometimes and it is just a little vibration. When using the engine I feel it now most of the time when using the engine above 2000 revs.
 
When I dived under the boat to feel the rudder blade, I noticed that there is a little movement in the rudder blade.
 
Has anyone got any suggetion what I can do?
 
I am now looking for a place to get the boat out of the water.
 
Thanks,
 
Michiel
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Gregor View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gregor Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2009 at 15:32
Hello Michiel,

I assume you have a steering wheel.

Is it the blade you feel, or the rudder stock that is moving?

There is a topic about the rudder (called Emilia's rudder) that might be of help. It tells you much about bearings. A company called Jefa also posts on this form. They have in depth knowledge on rudders. If you can not figure out what's on, maybe they can be of any help.

Gregor
Uisge Beatha

Currently sailing Dehler 36 JV (2002)
Previous boat: Hanse 311 #80

http://www.uisge-beatha.eu
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samba View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote samba Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2009 at 21:30
We do have a steering wheel.
 
I can't move the rudder stock when in the aft locker.
 
When I dive under the boat I can move the rudder blade when I try this at the very bottum end of the blade. I am not quit sure if this is the blade or the stock. I will check to see if I can find out.
 
Cheers,
 
Michiel
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panos View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote panos Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2009 at 21:39
Hi,

Some vibration during very fast sailing (planning in the face of a wave for example) is normal.Strong vibrations during fast motoring  ,specially during acceleration are also normal. The first are caused by turbulence on the trailing edge of the rudder blade, when the flow reaches a critical speed and can be reduced by fairing the blade. The second are caused by cavitation (steam bubbles in the water) caused by overloading the propeller. If the blade or propeller surface is "dirty" the vibrations appear earlier.

 I suggest though to be on the safe side to check it the first time the boat is out of the water. If the rudder moves relative to the shaft then this could be dangerous and IMHO should  be corrected. If the shaft has a little clearance in the bearings then this is normal wear.In my boat I would tolerate a movement of the tip of the rudder of 15 to 20mm.
Panos

Hanse 630e - selling her -
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samba View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote samba Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2009 at 22:01
Hi Panos,
 
I get the vibrations when motoring above 2000 revs. So no real high revs in my opinion.
 
You do give (as always) a very good tip: The blades of the propellor are very dirty. I will clean them tomorrow. In the past the vibrations came above 2400 revs.
 
I did change the standard propellor for a 3 blade max prop propellor.
 
The tip of the blade does not move more then the 15-20 mm, so I presume that is normal then.
 
Thanks,
 
Michiel


Edited by samba - 12 February 2009 at 15:24
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samba View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote samba Quote  Post ReplyReply Direct Link To This Post Posted: 17 February 2009 at 02:49
Hi Panos,
 
I cleaned up the propellor and although the fish liked it very much, it made no real difference. The next port where I canhaul out the boat, I will do so since there is nothing I can see / do right now.
 
Cheers,
 
Michiel
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samba View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote samba Quote  Post ReplyReply Direct Link To This Post Posted: 05 April 2009 at 03:38
Hi All,
 
I have put the orginal propellor back on the boat. However the problem still exists but it is less since the fixed two blade has I presume less turbulence.
 
The yard also checked the rudder from the outside but there was just a little bit of movement. I also had some riggers check the kwadrant and this was all tensioned properly.
 
One thing that I did find out is that the engine can now run at higher revs  (3200 revs). With the maxprop it could just about reach 3000.
 
When back in Holland I will put the maxprop back on and change the pitch of the prop. I will also remove the rudder to check the bearings. I don't want to do that now since I know of one other boat that had big problem after they worked on his rudder in Las Palmas.
 
Cheers,
 
Michiel
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gshannon Quote  Post ReplyReply Direct Link To This Post Posted: 06 April 2009 at 03:25
Turbulence from the prop is one possible cause of vibration in the rudder, however Hanse rudders are usually quite far from the prop which reduces the effect.

Does it happen under sail? If so it could be the trailing edge of the rudder. The worst shape is a rounded back edge. Better is a sharp edge but subject to damage. Even better is a squared off flat of 3 to 6mm. Best of all (I know this from tank testing) is the least likely shape you would think of, which is a flat with one edge radiused off, the other sharp.

The explanatory theory is  complex, but it works. It doesn't matter which side is which.
Grahame

Tangleberry 371-092

aviadesign.com
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panos View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote panos Quote  Post ReplyReply Direct Link To This Post Posted: 06 April 2009 at 12:23
Originally posted by gshannon gshannon wrote:



The explanatory theory is  complex, but it works. It doesn't matter which side is which.


Hi,
When I was racing seriously, we followed your suggestion. But we always selected one side. It depends if the boat races in the Northern or Southern hemisphere. Obviously Coriolis forces make a small difference in the flow of water around the two sides of the rudder, so you want the faster side to be straight. The difference though could be so small that only Grand Prix boats (TP52,AC etc) are affected. But of course the subject caused long discussions in the club evenings and everybody followed the champions.

All this just to pass the time, of course, since no Hanse boat will gain any advantage following my theories.
Panos

Hanse 630e - selling her -
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gshannon Quote  Post ReplyReply Direct Link To This Post Posted: 06 April 2009 at 15:34
Hi Panos,

That is amusing, and reminds me of an old story told me by Ted Brewer. He and Bill Luders entered a boat of their own design in the 5.5 Meter World's. That class has a minimum beam requirement, and when the boat was measured it fell short of the minimum by a few millimeters. Ted and Bill used putty to put bumps at the measurement points in order to not be disqualified.

It would have ended then, had it not been that they WON the World Championship. The next year ALL the top boats had bumps, although nobody except Bill and Ted knew their purpose!


Edited by gshannon - 06 April 2009 at 15:34
Grahame

Tangleberry 371-092

aviadesign.com
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