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Post by davideso37 on May 30, 2010 11:01:13 GMT
I have noticed a humming noise from the rear of our SO37P when travelling above 9 kts. Last Wednesday broad reaching in 25kts plus wind and the yacht hitting over 10kts on the log the noise was quite loud and concerning the crew. It is not propellor rotation because the gear was set to reverse to stop the feathering prop turning the shaft. And yes I did go below to check. I have experienced centreboard hum on small boats at planing speeds but do other displacement yacht have vibration from the rudder at speed? Any other suggestions for the noise? Should I be worried? Regards David
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Post by offshore on May 31, 2010 2:46:13 GMT
Hi David
We have exactly the same problem with our 36i. It sarts at about 7 knots and gets louder as we go faster. At our top speed to date of 16.7knots(surfing down waves with a kite up) the noise is so loud you have to yell to be heard over it. The vibration seems to definately be in the rudder as it can be felt in the rudder post. I have checked it all over when the boat was on the slip, but found no obvious reasons. Maybe we need to fair the rudder. I think it can not be good for the rudder bearings and seals. I would love to find a fix as it worries me a lot.
Barry
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Post by davideso37 on May 31, 2010 8:37:42 GMT
Barry, Thanks for that response. Hopefully someone on the forum will have a solution or at least satisfy us that it is not a warning of some pending gear failure.
That top speed is impressive even if down a wave.
Regards
David
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Post by jiipee on Jun 1, 2010 13:02:12 GMT
Hi! There are some articles about keel hum on the internet. I began to read them last summer after launching our new 33i P. We do not feel any vibration at all in the rudder but only a singing/humming from down below, increasing with speed. I talked to some local specialists,e.g sailmakers, and their opinion was that very many industrial boats have the same humming due to round afts of keels. On the internet, check articles about Akilaria (same constructor by the way).
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Post by renegade27 on Jun 1, 2010 23:57:48 GMT
So is the solution to grind a flat on the trailing edge of the keel/ rudder? General practice, not a big deal....
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Post by jiipee on Jun 2, 2010 10:20:42 GMT
Yes, or to continue the keel backwards with epoxy filler and then fair it sharp. There is, by the way, an article in the American J22 association's magazine about the forms and vibrations -try to google it...I do not have the link here at the office.
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Post by Zanshin on Jun 4, 2010 8:29:27 GMT
I have an excellent book on yacht design, "Principles of Yacht Design" by Lars Larsson and Rolf Eliasson, which covers this harmonic vibration at certain speeds and even has charts showing the vibration frequency depending upon trailing edge shape. Grinding the trailing edge of the rudder and/or keel may work, but it depends upon the thickness. I will look up the boat later this weekend and post the relevant chapter and am unsure if I can post a picture of the one chart (it may or may not fall within the "fair use" clause with regards to copyrights).
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Post by davideso37 on Jun 5, 2010 1:06:25 GMT
Zanshin,
Thanks for that. I am sure the problem is the rudder trailing edge because that is where the noise is coming from. Also the keel shape is very fair with a sharp square on the trailing edge. The keel shape on my SO37 is amazing quality for a production yacht but the rudder trailing edge is a bit rounded.
Regards
David
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Post by Zanshin on Jun 6, 2010 7:17:34 GMT
From "Principles of YACHT DESIGN (third edition)" by Lars Larsson & Rolf E. Eliasson, 2007, ISBN-10 0-7136-7855-0, p. 137 "For practical reasons the trailing edge of a keel or rudder cannot be razor-sharp. It is therefore interesting to investigate the effect of various endings of the section. Reference should be made first to figure 6.34, which shows the effect of cutting off part of the tail. For a wing the drag starts increasing immediately, even for very small cut-offs. This is in contrast to the effect on an axisymmetric body, like a torpedo or keel bulb, where relatively large cut-offs are permitted without a drag penalty. Therefore, the cut-off on a wing should be kept to a minimum. The way the cutting is done is also of importance. Fig 6.35 shows some alternatives. An interesting phenomenon is the vibration that occurs for certain shapes. The figure shows the amplitude of the vibrations at resonance for each case relative to those of a square cut-off. It can be seen that if the edge is symmetric and wedge-shaped (cases 2-5), the total wedge angle has to be 30° or smaller. For 90° and 60° much larger vibrations occur than for the square ending. This is also the case if the ending is rounded in some way, which it normally is, if the trailing edge of the keel or rudder is left without attention. An asymmetric cut-off is somewhat more forgiving, and a 45° cut-off is acceptable, provided the corner on the cut-off side is smoothed. The vibrations are not only of academic interest. On the contrary, they may cause severe vibrations and noise in the entire hulls at speeds where resonance occurs. Using the information in Fig 6.35 these problems can be solved." Fig. 6.34 | Fig 6.35 | | |
While I find the book rather technical, it is a worthwhile addition to any library when it comes to design questions and covers all aspects of boat design.
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Post by MartyB on Jun 6, 2010 15:41:04 GMT
I'm recalling over the last 3 or 4 months, Bob Perry talking about some of this in "Good Old Boat". e has started writing a why it is designed that way for lack of better way to put it, column with hull design, then keel, July/Aug issue is about rudders. www.goodoldboat.com/newsletter/10_junnews72.php click what is coming in July, and it shows he has an article on rudders. Marty
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Post by gjwilliams on Dec 8, 2010 10:36:50 GMT
We have just taken delivery of a new 36i Performance and from the very first sail have experienced a vibration in the hull when sailing at low speed. The prop is not spinning and no vibration felt on the shaft. The vibration can be felt thru the rudder stock when accessed thru the inspection hatch from the life raft storage area. This makes me think the vibration is coming from the rudder. Has anyone else had this experience?? There is no suggestion of the vibration in the mast or rigging. The noise of the vibration is quite noticeable when the engine cover is opened suggesting the noise is coming from the stern of the boat.
Postscript: I have now heard back from the broker from whom we purchased the boat. He has communicated with the Jeanneau factory and the possible explanation is the fairing on the trailing edge of the rudder. The factory are to provide details of required modification. I will report further once the work has been done.
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Deleted
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Post by Deleted on Dec 8, 2010 22:47:40 GMT
New SO36i (standard keel, fixed prop, stopped) - acceptance sea trials today - no significant vibration as such, but standing at the helm there was a high frequency 'tremor' felt through the feet. No vibration felt on the rudder shaft; no noise or vibration found on (internal) inspection of the aft hull - just this 'tremor' through the feet.
gjwilliams - many thanks for the info from Jeanneau; looking forward to your report of the fix.
What a lovely yacht this is - looks well engineered, beautifully balanced, responsive, easy sailing at 7.5kt; and a very helpful forum to learn about the marque - thanks all.
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Post by mkremedy on Dec 14, 2010 4:15:33 GMT
I have a 2007 36i performance with a 6-4" deep keel. I haven't felt or heard any humming or vibration. I also have a Flex-o-fold 3 blade prop. I guess I am lucky. Happy Sailing, Martin Kohn
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Post by gjwilliams on Sept 14, 2011 3:43:51 GMT
Reporting back after modification to trailing edge of rudder by shipwright using info provided by Jeanneau. The change was to grind a small amount at an angle off the edge so that water travelling over each side of the rudder travels a different distance. This is consistent with the articles on keel/rudder design shape. I can not feel any sensation of vibration now.
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Post by ianqv on Sept 26, 2011 6:26:06 GMT
HiGjwilliams
Did you take any pictures of the mod??
Regards
Ian
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Post by j on Sept 28, 2011 2:43:01 GMT
If he didn't, I did when I had a look at his rudder out of the water. I've attached a photo It's a bit hard to photograph as it's so minor, but hopefully the red lines help highlight the angled trailing edge. I don't have a photo for comparison, but our rudder edge is symmetrical and slightly rounded. We get some very minor vibrations (36ip). If we do the modification I'll take some pics. The white outline is to give you an idea of the edge profile, it's the same as shape #6 in figure 6.35 posted by Zanshin a few posts ago. ( www.sv-zanshin.com/images/big/principlesofyachtdesign6.35.jpg) I think it was about 6mm difference from one side to the other. -James
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bking
New Member
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Post by bking on Apr 17, 2013 20:45:47 GMT
I have a 2008 42iPerformance with exactly the same problem. Vibration/hum comes in at different speeds and wind conditions. We went for months without hearing/feeling it, then it was back. Held my ear to the compression post down below, crawled into the aft cabin and forpeak, but could not pinpoint where it was coming from. You can feel it when holding the wheel. I will look into the keel fairing issue.
thanks for the info. At least I know I'm not hearing things now.
bking
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Post by Zanshin on Apr 17, 2013 23:56:02 GMT
I dove on my boat yesterday to remove growth and when I was cleaning my rudder I first thought I had a construction error when I noticed that the trailing edge was asymmetrically ground, then remembered the article and pictures that I'd posted from the book; so I had to post this revived thread that on the Jeanneau 57 they did indeed use an angled trailing edge to reduce or remove vibration at speed.
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Post by kordakiskostas on May 11, 2013 12:16:33 GMT
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Post by sehulfb on Jun 15, 2013 20:19:30 GMT
I have noticed a humming noise from the rear of our SO37P when travelling above 9 kts. Last Wednesday broad reaching in 25kts plus wind and the yacht hitting over 10kts on the log the noise was quite loud and concerning the crew. It is not propellor rotation because the gear was set to reverse to stop the feathering prop turning the shaft. And yes I did go below to check. I have experienced centreboard hum on small boats at planing speeds but do other displacement yacht have vibration from the rudder at speed? Any other suggestions for the noise? Should I be worried? Regards David
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Post by sehulfb on Jun 15, 2013 20:22:21 GMT
Hi
Most probably the "humming" haved been adressed by now.. I have had the same sound at speeds exceeding 7,5 knot, the solution was to compare the two halfs of the rudder and one one the halfs was slightly less convex the other half. So a shipyard added epoxi to the one side and the humming stopped.
Hope it helps BR Ulf Berggren
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Post by Anwen (Deep Joy) on Jun 16, 2013 6:23:09 GMT
This thread makes very interesting reading for me, as one of my other hobbies is building and flying radio controlled model aircraft. One of the problems you can get is flutter of the control surfaces, and most modellers know not to round off the aft edges of the elevators and ailerons, as this is a sure fire way to get flutter. You have to have either a razor sharp or square trailing edge. My slower flying models are fine with square edges, but the faster models always have trailing edges as sharp as I can get. I'm interested to try the asymmetric design which Jeanneau have recommended, and will bear this in mind for the next build.
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Post by Zanshin on Jun 16, 2013 14:24:17 GMT
If you think flutter is bad on models, it is much worse on actual airplanes. I did aerobatics in gliders and you'd often be close to Vne during maneuvers and the dangers of flutter or a high-speed stall are ever-present. But most of the flutter danger potential in full-sized aircraft is caused by loose linkages rather than incorrect fairing.
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Post by loredo on Dec 20, 2013 9:19:01 GMT
Hello, this is my first MSG here. My boat is a 2006 SO49. I did find this forum because I'm searching for a solution for... yep rudder vibration at speed. My boat does exactly the same thing the OP is telling us. At any speed above 7.5K I get what I can best describe as a "rumble". You can welcome me in the rudder vibration club. Then higher the speed then louder it becomes. I have already ruled out any other causes, this rumble comes from the rudder!
If the fix is as "simple" as reshaping the trailing edge of the rudder, would be great! Still, one would think that a company as big as Jeanneau would address such problem during the engineering stages, don't you think?
Yet, having seen several other threads on here about the rudder bearings and the related problems I think I'll need to investigate rudder as a whole and drop the rudder once the boat is on the hard. Same thing here, Jeanneau builds ( has build???) their boats with a flawed rudder bearing / bushing design. To us, the owners, to find out once we did spend our money on their boats.
Please don't get me wrong! I love my Jeanneau! It's just that I did not expect to have to deal with problems caused by the MFR's cheap design.
Thanks for listening!
Loredo
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Post by Zanshin on Dec 20, 2013 14:45:02 GMT
Welcome to the forum, loredo!
The solution can really be as simple as changing the angle on your rudder's trailing edge; did you see the images posted on the first page of this thread?
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