Vibration - Yanmar 20GM in a 1994 29.5

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Bruce Leidal

PYI Expert; I have a 1994 29.5 with an 18hp Yanmar 20GM with a Flex-O-Fold prop. I have a vibration when underway. It gets worse as I increase the RPM. The marina has checked the alignment and it is fine. The vibration begain a few years ago when I put a MarTech folding prop on. I sent the prop back to Martech for rebalancing. The vibration was still there. Based on the stories I have heard regarding vibration problems with Martech, I purchased a Flex-O-Fold and used it this season. The vibration is still there. No change. Suggestions, recommendations?
 
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nick maggio

try two blade

Try putting the original two blade on and see what happens ,if it still vibrates than you know something is wrong .
 
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Frederick Pierce.

Yanmarhelp website

BRUCE. I have 27 HP 3gm30 in my 28 ODAY its great its over powered it came with the boat yanmar has a SUPER TROUBLESHOOTING WEBSITE its WWW.yanmarhelp.com its is very helpful Iused it a few times and grate you can see other peoples problems and answers thats my frist way to go I hope you can answer of your problem FRED PIERCE MY email is ekleinert@yahoo.
 
Dec 2, 1999
15,184
Hunter Vision-36 Rio Vista, CA.
Find a three blade for a real test.

Bruce: If you can find a fixed 3 blade prop, you will have a better test. I do not have any problem with my 2GM20F but other report vibrations. When they put on a three blade they claim that the vibration goes away or diminishes greatly.
 
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Bryce Custer

"normal" vibration

Our '95 29.5 currently has three blade prop. Had severe vibration, realized that engine mount bolt had worked loose. This helped a good bit, but still have what I consider significant vibration between 1700 to 2700 rpm. (significant being lockers chatter) Was told by local Hunter dealer that noise and vibration was nature of the 2GM20F two cylinder. Previous owner had installed two blade folding prop, but removed due to "worse" vibration. Looking forward to seeing other 29.5 comments.
 
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Monty Miller

29.5 Vibes

Our 94 95.5 had a similar problem when we first got the boat in 96. The boat spent two years on a dealer's lot and had seen very little use. I noticed while under power that the port rear motor mount was doing more work than the others and was compressing significantly to the point that the upper and lower plates were almost hitting each other. I rebalanced the engine weight on the mounts by installing washers on the bolts, then carefully realigned the shaft. The problem went away and never returned. We have a two bladed Martec folding prop and have no vibration problems, runs like a fine watch. I contributed this problem to poor manufacturer's assembley and dealer prep. So, observe your motor mounts carefully while under power and at cold idle. You may have the same problem or the mounts are worn out and need to be replaced. Good luck! Monty s/v Lucky Lady Lake Travis, TX
 
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Kevin

Not easy to figure out.

Hello Bruce, Vibration is not an easy thing to pin point in any situation. We often find that one thing compounds many other problems. So removing or eliminating one area may not seem to be helping. I would like to make a statement that all in all folders work to there potential and that in no way am I slamming Matec or Flexofold. Regardless of which kind of folding propeller you have, the system is working on centrifugal force to open and hold the blades into an open position. When you add angle to the propeller shaft the loading of the blades becomes different between the two. If you imagine a clock face, as the 12:00 blade is advancing downward it is increasing in load because it is being presented to the flow of the water being presented to it by the movement of the boat. Just the opposite is taking place with the 6:00 blade, as it raises its loosing or reducing in load. Add this to blades that move independent of each other and one further increases the discrepancy between the blade loadings. The greater the angle the greater the load discrepancies can be. Switch back to a fixed blade and the loads are starting to balance out again. If we add a third blade we then begin to transfer or distribute the difference in loading over greater surface areas, thus helping to reduce the whipping in the shaft. Keep in mind that the new fixed is not any anyway perfect, its just that the supporting items like engine mounts, shaft diameter and cutlass bearing are know able to support the rotating propeller. Perfect world for most sailboats would be to have a parallel running shaft to the water line. In your case you may find that the shaft angle may be 8-10 degrees. Some of the older race boats had 15-18 degrees of angle, this created huge noise problems in the boat. To fix the noise you may have to increase support to the running gear. Worst case you may need to consider a fixed blade style propeller. Hope this helps. Kevin
 
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Monty Miller

Engaging a folding prop

This a question that I've always wanted to ask but never got around to it. Our Martech 2 bladed folding prop will never open fully if the boat is in forward motion or if the water is flowing from bow to stern unless we rev the transmission in reverse past 2500 rpms or so then quickly engage forward gear resulting with a definate cruch from the transmission. It will cause extreme vibrations otherwise. We always back out of our slip and putting the transmission in forward with the prop fully opening without vibration is never a problem, thank God! When ending a sail we like to warm up the engine, put it in forward gear, then take the sails down, dead into the wind. The folding prop will not fully engage unless we slam the transmission from reverse to forward. Often, it takes several cycles to accomplish this. I contacted Martech and they wanted me to send the prop in to be balanced. They said this was necessary every 500 hours. Our boat had at the most 50 hours of engine usage, so I did not. Last year we chartered a brand new Beneteau from Sunsail that had a folding prop. No idea what brand. We had to use the same procedure to engage forward motion. So, my question is, what is the proper procedure to engage a folding prop so that it opens fully without any vibraton? Is this the same problem we are trying to solve? Monty
 

Rick D

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Jun 14, 2008
7,187
Hunter Legend 40.5 Shoreline Marina Long Beach CA
Not Right

with a disclaimer. I don't have one but have been on several that did. Never a problem, but the prop does take revs in reverse to open. Never in forward. Talk to them again and tell them re: 50 hours. Rick D.
 
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