Prop vibration

[madhatter1]

Long story short. Bought boat in 2018. 2019 have new (and qualified) mechanic on board. Says I have a bad vibration on port side. Check cutlass. I do. Cutlass bearings needed and all replaced. Much smoother. Seems good to me. FF to this year. Haul out. Recondition props. PM. Splash. Trip home with same mechanic on board. Says the racors are shaking violently (they are). To me same old feeling on the bridge.

Haul out. Send shaft, coupling, and a spare shaft I was given out. Comes back spare machined to mate to coupling labeled as main, original reconditioned but labeled as spare due to wear around log area. Install with new cutlass bearings. Some vibration but need to wait to do new alignment for a week or so to settle. Did alignment and we actually dropped the engine front and rear 1/4”. Alignment to within 4 thousands.

Now you would think we would be good at this point. Still have vibration. I can feel it most standing over the strut in the cockpit. If I run higher RPM the racors stop shaking. Like at that RPM the vibration harmonic is lessened up at the transmission.

Which brings me to this question. Is the prop bad? Running 3 blade 28x25 pitch that started out square. I thought when reconditioned they would be balanced. Is the reduction in pitch from square too far? Am I better off with a new set of 4 blades? I want to fix this.

 

[osprey]

Vibrations suck. I only check / do my engine / shaft alignment in the water after a haul out.

Hope you solve your issue soon.

P

 

[bostonhatteras]

The propeller shop didnt give you a print out of all the findings about the wheels? They should have determined the pitch at three succeeding further out points, at least, on each blade. the radius of each blade too. How old are the wheels, I've been told that old dezincified wheels dont take to recupping too well. As far as I know I never had my wheels balanced when reconditioned, no mention of it on my reports.

 

[SKYCHENEY]

In my experience, if it's mostly at a certain RPM, then its a prop issue.

 

[madhatter1]

Some luck is on my side. The spare props are same diameter and 26 pitch. Got the propscan reports and they were balanced. I think there is an old inherent flaw in the prop and the vibration is due to blade shaping near the hub. I believe the prop is weight balanced but the blade shape (these are originally 28 pitch so at the outer limits of re-pitch. Running in the water vibration starts as turbos spool up and rpm’s increase. Then if I bump up to 1950 I can feel the vibration standing over the strut but things get fairly smooth at the engine and transmission. Spare is off to the shop and will swap next week. We shall see. If this works the flawed prop will still serve well as a spare.

 

[cww]

It's almost certainly the props. I just put new ones on my boat and I thought it was smooth before but wow is it smooth now.

 

[madhatter1]

It's almost certainly the props. I just put new ones on my boat and I thought it was smooth before but wow is it smooth now.

We just sunk a ton of money into the boat. After some time goes by and we hopefully don't spend so much I am going to upgrade to 4 blades. I would now but just tapped out of $ and also out of time to get ready for our Bahamas trip. No time to be tweaking props.

 

[brettportzer]

Hey Madhatter1..!

Unrelated to this thread, I sent you a pm.

Related to this thread, we are also hunting down a vibration and had our props done.

First time for us, curious what difference it might make.

 

[madhatter1]

Brett, the shaft is new, cutlass bearings new, coupling matched. Vibration is most noticeable standing in the cockpit above the strut. To me it has to be the prop. They balance them at 550 RPM but spinning in air, not water. I bet it has something to do with a blade shape as these started out 28" square and are now at the extreme limit of pitch reduction. Props get swapped next Thursday and then I'll run it and see.

 

[brettportzer]

That makes sense. I am starting with the props, if that isn’t it, we’ll have to get into that other stuff.

Good luck with the big trip.

Brett, the shaft is new, cutlass bearings new, coupling matched. Vibration is most noticeable standing in the cockpit above the strut. To me it has to be the prop. They balance them at 550 RPM but spinning in air, not water. I bet it has something to do with a blade shape as these started out 28" square and are now at the extreme limit of pitch reduction. Props get swapped next Thursday and then I'll run it and see.

 

[Captain Ralph]

Brett, the shaft is new, cutlass bearings new, coupling matched. Vibration is most noticeable standing in the cockpit above the strut. To me it has to be the prop. They balance them at 550 RPM but spinning in air, not water. I bet it has something to do with a blade shape as these started out 28" square and are now at the extreme limit of pitch reduction. Props get swapped next Thursday and then I'll run it and see.

Looking so forward to your and Brett's updates.
Sadly, I was a victim of the folks that kept telling me my shafts were good. 3 sets of props latter; I replaced my suspect shaft and all vibrations went aweigh November 2022.
F M
Seems the cold shaft in the air (on the hill) measured real good. Apply some H P to it and it cork-screwed.
Moral,, trust nobody or nothing new or high tech. You feel a vibration, there it is..

https://www.youtube.com/watch?v=fgWLIvGZFGA

 

[cww]

Re: Prop vibrati

We just sunk a ton of money into the boat. After some time goes by and we hopefully don't spend so much I am going to upgrade to 4 blades. I would now but just tapped out of $ and also out of time to get ready for our Bahamas trip. No time to be tweaking props.

Go with the Michigan DQX’s, I couldn’t be happier with them. Sizing is really easy, same diameter you have now but 1” less pitch to account for the extra blade area. The boat will perform better under all conditions and it also reduced vibration on my boat.

 

[madhatter1]

Well it was the prop. Smooth on the bridge where I felt it and zero vibration standing over the strut. But……

I still have the same vibration at the racors that are mounted to the stringer near the transmission mount. Minimal at 1900-1950 RPMS but present. Starboard is perfectly smooth. Allison gears. What on the engine/gear could cause this? Engine was out of alignment for the whole time I have owned the boat. Now everything behind the gear has been serviced or replaced and I have a good alignment.