Vibration

[Franklin]

Every since I've owned this boat (376) I've had vibration. I aligned the shaft last year and that really helped but didn't cure it. This year I had a new engine installed, the boat hauled, the prop reshaped because it was bent, the shaft inspected, cuttlas bearing replaced (so they say) and the engine aligned again. I don't feel much vibration now but there is enough to make the floorboard, which just sits on top of the hull over the shaft rattle.My question is this, is this normal and should I just find a way to stop the floorboard from rattling or should there be absolutely no vibration, even at high RPMs and that I should take it back to the yard and have them redo their work?

 

[Fred Ficarra]

Franklin, one thing I learned from a jet engine

mechanic was that it's impossible to eliminate vibration. It can only be reduced. So, that said, it depends. Sorry. And not being familiar with your boat it's hard to tell you what's best. This summer I re-aligned my shaft again. It's much better. But depending on RPM and other variables on my boat that most others don't deal with, I can still feel some vibration at certain times. Now if you want to free yourself of boatyard maintenance you might consider watching how the work is done and learn from it. I always do my own work, including alignments. In the past I've used pieces of fiberboard strips to gage the coupling to tail shaft alignment. But this last time I was digging in one of my tool boxes and saw my stash of scrapper razorblades. Ah-ha! The sharp edge of the blade would assist in inserting it between the flanges. The flat part would hold it in place and provide an ABSOLUTE dimension (not like fiberboard) and the back brace of the blade would be a perfect stop. Just like a feeler gage but smaller and eaisier to handle. All I had to do is watch out for the sharp part. Most of us can do that with a razor. Me included. It worked great. By the way, I have no noticeable vibration at any cruising RPMs as long as I don't run stuff like the refer or watermaker. Then I have to adjust RPM. I think in your case, it's a skill worth learning.

 

[Franklin]

Actually Fred

I do know how to do it and also checked the alignment and it seems good. If there is too much vibration, which is the part I don't know, then it has to be the bearing or that they didn't get the prop straight which of course I can't tell unless I pull the boat.

 

[Gary Wyngarden]

Franklin

FWIW I struggled with prop/shaft vibration for two years with my boat. After three haulouts, new shaft, cutless bearing, coupling, and a couple of realignments in addition to the ones I did which were damn close, I finally have the problem solved. The problem was bad with a two-blade max prop and only a little better with a two blade fixed pitch. PYI recommended a three blade max prop and gave me a good trade in on my old one. That was done simultaneously with a final adjustment of the steppping of the shaft(done by a new yard). I now have virtually no prop/shaft vibration, but of course there is still engine noise and vibration which both increase with RPM's. Hope this helps.Gary WyngardenS/V Wanderlust h37.5

 

[chuckwayne]

Franklin,you might consider adding a flex coupling (we used one from PYI) between the transmission and shaft-after several years of vibration and cutless wear, we decided to give it a try, and it seems to have helped the vibration-I think Hunter used very soft engine mounts to limit vibration, and the yanmar was whipping the shaft around

 

[Jeff Bacon]

One other item to check.....

... is the tightness of the motor mounts.make sure all of them are tight.Worked wonders for me on my 376Good luck...... Jeff

 

[Fred Ficarra]

The last thing to check is your cutlass bearing.

You don't need a haul out. The yards work can be checked with a dive mask. Jump in and hold the strut and grab the prop. Move it sideways/back and forth. Look for any movement between the rubber bearing and the shaft. There should be little to none.

 

[WayneCam]

"Dynamic" Balance

I have read the posts and can find no reference to Balancing. If your prop was straightened, it must be re-balanced. Did the Prop Shop re-balance? If so did they "Dynamically" balance it. (By spinning it in a machine?) While "Static" balance may cure your problem it may require a real Dynamic Balance. By the way, few Prop Shops have dyanmic balancing machines.Wayne"Sine Wave"Buffalo

 

[Franklin]

Thanks Wayne....did not know that.

.

 

[Cobra]

I don't know....

"Impossible to Eliminate Vibration"? Yes it is possible. I also think the two blade props are crap. Trying to cure my vibration I also did the alignment about 3 or 4 times and installed the PYI drive coupling. Everything I did seemed to make "it" better but just didn't cure it. The second problem I had was I felt my 33.5 didn't have enough prop. After much study I choose a 3 blade fixed Michigan wheel. Then decided to get a new shaft... just to be sure. I verified the shaft runnout and the prop ballance (and made corrections for both). Be Aware, all NEW shafts are NOT Straight. I hauled the boat out and installed the new shaft, prop, cutlass bearing and zincs. (Fred) I have NO vibration so it is possible. Maybe I was just lucky? Lucky beats Good any day of the week. Mike CDestiny IINMB, SC

 

[Fred Ficarra]

Mike, yes you do.

All rotating devices have detectable vibration. Even jet engines. Your level of vibration is just too slight for it to be detected by YOU.

 

[Cobra]

Hummm....

Fred,I think when we're down to engine only vibration that would be considered No Vibration (not meant as if the engine was off). No Vibration to me means No Vibration from the Shaft or Prop while rotating in the water. After I got the shaft to less than .07 mm runnout and ballanced the prop to the shaft, turning it in the lathe at 3,600 rpm produced No Vibration (yes, I know some came from the lathe). Naturnally adding water makes some difference. I expected some vibration, actually more that what I ended up with. In my opinion decreasing the amount of vibration is hit or miss. I've already read where some people have changed shafts and props and still have problems. Thanks for correcting me! Mike C.NMB, SCDestiny II

 

[Terry Goodin]

I have a friend in San Diego with a Hunter Passage 42. He told me he had tremendous vibration until he installed a feathering prop, and the problem went completely away.

 

[Terry Cox]

When we motor sail, the engine on our...

boat does nicely at 1800 to 2000 RPMs, with very little vibration. With its fixed three blade prop we can cruise all day long at seven to eight knots.Terry