B 35 vibration problem

Harris · Post by **Harris** » Dec 9th, '06, 05:00

I' ve lost my brain with this vibration !!!!!!!
We put out the shafts, we cheked them, we cheked the propellers, we made the engine-shaft alingment, we replaced the couplings with new ones (not flexible), I paid a fortune for that, and we made just nothing !!!!!!!!
After that, Mr "specialist" said to me that the problem is the mountings, because they are not rubber ones. I asked him what we should do, if we change the mountings, however the problem still excists, he said to me that we have to put out the propellers once more for a dynamic diagnosis......!
Any suggestions ?
Thanks

CaptPatrick · Post by **CaptPatrick** » Dec 9th, '06, 06:35

Harris,

If your engines are hard mounted, (no rubber issolaters), then that will certainly be a source of vibration.... Some of the best rubber issolated mounts available are by Barry Controls.

This still does not exclude prop balance... Is the vibration only on one side of the boat or completely through out?

Are these the same engines that you've had or did you re-power to the diesels?

Br,

Patrick

Bruce · Post by **Bruce** » Dec 9th, '06, 07:00

If the shafts and props have been checked professionaly from a reputable shop, theres really no need to check them again.
Now if the shaft was rolled across a parking lot and you looked for high spots, then all bets are off.

As Pat said hard mounting without isolation mounts can pass on any noise.
The other thing that will contribute to the hard mounted engines is any gaps or looseness in the beds to stringers mounting will send the noise thru out the whole boat.

Rubber isolation mounts should be used, but if the engine and driveline are aligned and straight there should be no vibration.

The vibration may be comming from a non firing cylinder in the engine, or some engine condition and not the driveline.

I've seen many boats with solid mounts that have no vibration.

Brewster Minton · Post by **Brewster Minton** » Dec 9th, '06, 08:52

Was the alingment done in the water? If not, it should be. Rubber mounts are best, but if the engine setup was ok without rubber what changed in your setup. Tell us more about what you have done to the boat ie new engines, strut changes, cutlass old or new. Did the vibration start at some point or was it always there. Does it start when put in gear or as you are trolling or jumping up on plain?

Harry Babb · Post by **Harry Babb** » Dec 9th, '06, 08:52

Several years ago one of the local marine mechanics repowered a 31 with new 454's and 3:1 gears. I made new 1-3/8" diameter shafts using Aquamet 22 HS material then fitted and checked the couplings on the bench. As best as I can remember he installed 20"X24" props and reported that the boat ran as smooth as silk.

The owner tied the boat to a pier on the lower end of the bay (really shallow) one summer afternoon and as the tide went out the wave action pounded the propellers on the bay bottom and bent a prop blade.

My mechanic buddy hauled the boat and brought both shafts back to me to be checked and took the props to a reputable prop shop. The shafts were not bent and the prop guy said that he corrected the damaged props.

The mechanic reassembled the boat and went for a sea trial and still had vibration.

After chasing the problem for a day or two the mechanic brought the one vibrating shaft and prop to me for help. I chucked the shaft in a lathe and mounted the prop then tracked the 3 blades. I found that one blade tracked a little more than 1/4" different than the other 2. He took the prop back to the prop shop, showed the guy what we discovered, the prop guy corrected the problem and the vibration problem was solved.

I think that a 20" diameter prop should be mounted on a 1-1/2" shaft and that the entire setup was pushing the limits of the shaft and strut size and the slightest problem would cause vibration.

At any rate...........that is one of my experiences of vibration on a 31 and I hope that it helps. I would look at the props really close again and also check the sister stringers for deterioration allowing side to side engine movment.

Good luck
Harry Babb

Harris · Post by **Harris** » Dec 11th, '06, 01:41

First I would like to thank you all.
The boat powered by Cummins V 555 M, 230 hp each, with MG 502 reverse and we didnt change anything (it was my futhers boat and now mine so I know everything about this boat). The engines are hard mounted both, and they are profecionally maintenanced and runs perfect (690 hours).
I noticed that the vibraition comes from the stbd side but I bellieve, all most shure, that doesnt come from the engine, it appears only when the boat runs and between 2.250 - max rpm, and because when i run the engine in neutral, no viration at all !
Thanks
Harris

thuddddddd · Post by **thuddddddd** » Dec 11th, '06, 07:32

Props.

Brewster Minton · Post by **Brewster Minton** » Dec 11th, '06, 10:06

Props or shaft need work then.

Hueso · Post by **Hueso** » Dec 11th, '06, 18:58

Props, shafts and worst case scenario.......loose struts and/or weak hull.......

Harris · Post by **Harris** » Dec 12th, '06, 13:54

Thanks again

bertram31.com