CD31 Vibration

[gca]

I am looking for help in resolving a vibration problem with my CD31. I repowered last winter with a 3 cylinder Beta 25, with a 2:1 gear ratio, new shaft and cutlass bearing. I am getting a vibration or rumble that becomes noticeable around 2,000 rpm and gets increasingly worse as rpm is increased. The engine is rated to 3600 rpm but the vibration is so bad I haven’t run extensively above 2500 rpm. It appears to come from the rear (shaft log area) and can be felt in the cockpit floor and even more so by putting a foot on the hull inside the cockpit locker. At high rpm (2500-3500) the rudder will also start to wag slightly. The wheel will rotate side to side an inch or so. I had a vibration similar to this with the old engine (3 cylinder Universal 25 with a 2:1 gear ratio) but it seems worse now. I never ran that engine much above 2200 rpm so maybe it is worse only because I am tying to run at higher rpm. After initial launch I had the boat hauled and got the 3-blade prop re-pitched from 13/13 to a 13/11 to be able to get max rpm out of the engine with the hope that it would fix the vibration problem as well but no luck.
The alignment out of the water is within .003 but an alignment was not done in the water because when the flexible coupling was removed the shaft was too short to bring the shaft and transmission flanges together. The alignment done on the hard was done without the prop on. The 1-inch shaft length was sized so the overhang would be 1 inch. The new cutlass bearing/shaft combination had a .006 clearance that my yard mechanic says meets spec although I don’t like it. The yard ordered another cutlass bearing for comparison and it has the same clearance on a 1-inch shaft. I’m told, “This is the way they come through these days”.
Turing to starboard the vibration gets worse and turning to port it stays the same or is a little bit better. In reverse at 2500 rpm there is no vibration what so ever.
I don’t know that I always had the vibration with the old engine but have no idea when it first started. A number of years ago the shaft was shortened, moving it closer to the keel, because it over hung more than 1” beyond the cutlass bearing. I don’t recall how much it was shortened.
Does anyone out there have any ideas or similar experiences with vibrations? I am about to haul out for the winter and would like to do anything before hauling that might help solve the problem.

[Zeida]

This does not sound good! Do not accept "things just come that way" from anyone... The installation of the new Beta looks like it needs revisiting. Contact the Beta people themselves and research thoroughly this issue before you ruin the tranny, new cutless, etc. the way the shaft was routed from the outside into the boat to meet the tranny may be the problem, and when the prop was added, the problem compounded. If you continue to sail the boat with that horrible vibration you describe, you may end up out there stalled, after the tranny says "enough" and quits on you unexpectedly. Make sure you have tow insurance, and by all means get a mechanic who REALLY knows how to deal with a new engine install. That's just my opinion. I hope I am wrong.

zeida
s/v Bandolera II

[tmsc]

Really sounds like an alignment issue to me. Are you sure the shaft and coupler are true? Also, you have to do the final alignment once the boat has been back in the water a few days (I like a week myself). There is just no way that I am aware of to get around that. Can the prop be removed so the couplers will mate up? If not I would have a machine shop machine a disc faced on both ends the thickness of the drive saver that could be used for alignment purposes.

[gca]

Thanks Lee, but wouldn't I also get the vibration in reverse if it was an alignment problem? My plan is to have a longer shaft made up over the winter so the alignment can be done in the water. I am also contimplating having the shaft slightly over sized at the cutlass bearing to take out the .006 clarance. This will also move the prop a bit further aft more like it was originally.

[Bill Goldsmith]

Zeida is correct, if you had someone do the installation for you, I think they need to revisit the installation and correct the problem. If you did it yourself, then now is the time to get some advice from a good mechanic.

Other ideas that come to mind:

--Have you checked all the engine mounts? If one engine mount is loose, that could result in the banging around in one direction, but not the other.
--Was the propeller balanced after it was re-pitched before installation?
--Is there plenty of room for water to get into the cutless bearing? If access is restricted, it could be running hot and drying out.

[tmsc]

Just reread your post. I still maintain it needs to be aligned in the water but Bill brought up some good suggestions that you should definitely check first. You do need to make sure there is enough clearance for the cutlass bearing to get water. Do you have a spare prop you could just install to see if there is a difference?

[moctrams]

I guess there is no vibreation in neutral.

[Klem]

As moctrams suggests, try to rule out the easy stuff like whether it happens in neutral. If it happens in neutral, it isn't related to the shaft but if it doesn't, then it is likely related to it.

Also, you can do an alignment with your current setup, it is just harder. You need a dial indicator and a clamp arm. You attach the clamp to your transmission output shaft and put the dial on the propeller shaft. By spinning the transmission output shaft and watching the indicator, you can see high and low points. Center the shaft, then check a different point on it. If it is not also centered, then you are out of alignment. Figuring out how to get back into alignment this way is a bit of a mind bender but it works. Beware, this method is frustrating and can take some time but it might be the fix for the rest of the season.

[Larry DeMers]

One thing that you mentioned that caught my attention, was that the rudder moved back and forth while this vibration was in effect.

This seems to be improbable to me, as the mass of the rudder should prevent any oscillation like that...unless the pintle/gudgeon on the rudder base is worn, and moves when water is being thrust against it, under power.

This would explain the loss of vibration when reversing..no water flow over the rudder! It also explains the vibration and the rudder movement. The water flow under power causes strong forces to move the rudder, which would vibrate in the bronze bearing at the bottom of the rudder, assuming a worn bearing. The fix is pretty straight forward, if that is the cause.

I would watch the movement of the rudder, and definitely associate it with the vibration. Try testing while turning going forward. Do strong turns, easy turns. Any difference?

When you pull the boat, test that bottom bearing by putting decent pressure against the rudder bottCd at that bearing site, on both sides, and note any movement.

Also, check your cutlass nearing again. Push and pull on it hard to detect any movement over specified shaft clearances. You can tell if it is too sloppy by simple feel here. Changing it out is pretty simple.

Something, either in the drive train or within the water flow is causing this vibration. Fixing it is essential of course. So, let us know what you find it was. Another learning experience.

Cheers,

Larry DeMers
s/v DeLaMer
CD30 Sailing Lake Superior

[JWSutcliffe]

I assume that the transmission on the Beta is similar to that on the Universal M25, which a 2:1 reduction in reverse. That would explain the lack of vibration in reverse - the prop is only turning half as fast. The rudder shaking is more likely due to flow disturbance than the vibration of the prop and shaft. On my M25 I only turn 2200 rpm max, and above that (even with a balanced prop, new shaft, new engine mounts, near perfect alignment and cutlass bearing) get a fair amount of vibration above 2200 rpm. I tend to think that your vibration is a combination of the very short prop shaft and inherent vibration in a 3 cylinder diesel. I have certain speed ranges where the vibration is so high that it shakes the oven racks and bowsprit mounted CQR anchor loudly. Look closely at the spacing of the 3 bladed prop in the rudder aperture, and rebalance the prop.

[moctrams]

Have you tried to run the engine "withou" the prop? It sure sounds like more of a problem with the prop.

[moctrams]

I found this calculator on line. Could it be you have too much prop?

http://www.vicprop.com/displacement_siz ... =calculate

[gca]

Skip, I find it interesting that you are the only CD31 owner to respond so far and you have a vibration as well and don't run above 2200 rpm. Do you supose there is something inherernt in the CD31 that is causing the vibration? I also never ran above 2200 rpm with my M25 and did have vibration although I am not sure I always had it. Does your vibration get continually worse with increasing rpm or is it worse at a certian rpm? How far is you prop located behind the cutlass bearing? The TMC40 transmission on the Beta25 has a 2:1 gear reduction in forward and I though it was the same in reverse. I will check on that with the guys at Beta. The Hurth on my M25 was also a 2:1 in forwad.

Again I thank you all for your comments and suggestions.
The engine was installed by a yard and I am working with them to resolve the issue but they have run out of ideas. We all reconize that the alingment has to be done in the water and next season with the longer shaft we can but that to bed.
The engine mounts are tight and the prop was balance when it was re-pitched. I do not have a spare prop. I get no vibration in netural. I have not tried running without the prop. Not sure how I would get the prop removed while in the water I have very carefully put a finger on the shaft while running and feel almost no vibration.
I have a dripless stuffing box and am pumping cold Maine water through the cutlass so I don't think it is over heating and drying out.
The rudder movement I am getting only happens above 3,000 rmp and it is not uniform. It is kinda like a wiggle - short pause - wiggle - short pause.
I could not get the prop calc to work but I have had prop cals done by several different people and they all come out about the same. After re-pitching I was able to reach 3,500 rpm. Not qiuite the 3,600 rated but Beta considered that close enough. I may be slightly over pitched but not much.
The boat will be hauled for the season tomorrow so nothing needs to be done for this season.

[JWSutcliffe]

I attribute my vibration issues to the poor dynamic balancing of a 3 cylinder engine and the very short driveshaft. In the past year I have replaced everything in the driveline between the prop and transmission, as well as the engine mounts. I aligned the shaft dry and again in the water. In my case the need was driven by a failed engine mount and cutless bearing, and exacerbated by finding that the stern tube was grossly inadequately laminated into the hull. I will admit that I was rather disappointed that none of this improved the vibration issues, but with the original M25 and a new heat exchanger I am happy to be able to run all day at 2200 rpm with acceptable vibration and no overheating. I have seen the rudder shaking at higher prop speeds, and attribute that to the relatively large 3 bladed prop operating close to the rudder in a small aperture causing flow dynamics issues. I do see increasing vibration at speeds higher than 2200 rpm, but I also have very significant resonances in the entire hull structure as low as idle. When I am idling into the marina slip area with my oven racks buzzing and anchor shaking I always feel a bit conspicuous. My attitude is to simply avoid the low speed resonances with use of neutral and avoidance of the bad rpm ranges. In addition, above 2200 rpm I do not see much improvement in speed through the water anyway, so the higher speed vibration ranges are meaningless.

What helped me to stop worrying about the vibration was the finding that I had nearly as much vibration at those rpm ranges even if I shifted into neutral. You have to remember that the Universal M25 and Beta 25 are both based on the 3 cylinder Kubota tractor engine. My experiences with Kubota and John Deere 3 cylinder diesels in construction and farm equipment has shown them to be very rough running. Even my 4 cylinder John Deere 4.9L tractor engine shakes throughout the entire operating range.

I can't say with certainty that your issues are the same. Try realigning with the boat in the water and also balance the prop.

[Phil Shedd]

Hi

My 31 runs very well with no vibration. I have a three blade prop that will push me along a 5 to 6 knots.

I would look to see if the flange bolts may be loose if not you could loosen them and check with a feeler gauge to see if there is any space between side to side and top and bottem. Also check the engine mounts to make sure they are tight . They may have backed off after the engine was installed. Try that

Phil

PS if you can get a dial indicator dial the shaft to see what you get . This will tell you if the shaft is true