Prop Vibration

[awesome34]

I just got out of the boatyard with a new PSS dripless shaft seal and a new flex-o-fold two bladed (15x10) prop.  I expected a little more vibration because my previous prop was a fixed 3 blade 15x9.  While it is nothing drastic that would stop me from using the boat in the short term, when motoring I feel like I get a lot more vibration, especially in the cockpit and sometimes the backstay, now than I did before. My crew has noticed it as well.  Any suggestions of what can be done to reduce the vibration and how I might be able to tell if it is a real long term problem or just normal with a two bladed prop? 

The new prop is delivering propulsion just fine and is definitely reducing drag when under sail.  Right now, I plan to go back to the folks that did the work at the boatyard and see if they will ride along and give me their opinion, but I thought I would see if any other c34 owners have had experience with this. 

Thanks,
Eric

[Noah]

Eric- Sorry i don't have a solution for you, but I do have some questions: I am hauling soon for bottom paint and to install a 3-blade Flex-o-fold 15x10 on my boat. What made you select the 2-blade over the 3-blade? I also am considering replacing my bronze shaft with a stainless one and installing a PSS dripless box as well. Who did the PSS work for you and do you have a stainless shaft?
Thx
Noah

[Ron Hill]

Eric : The first thing that I'd check is the engine alignment.
It is more apt to be out of alignment than a new prop out of balance!!

A thought

[awesome34]

Thanks Ron.  Are you are talking about the shaft alignment or something else in the engine?

Hello fellow San Diegan, Noah.  I went to the shelter island boatyard and basically did what you are about to do.  I still have a bronze shaft.  I chose the two bladed prop because I race more than I cruise so minimum drag was the most important thing to me, plus 2 bladed props are less expensive.  I rarely have to fight through waves or any of the types of things that I have read 3 bladed props are better for.  My PSS was installed by Hoffman Yacht, one of the businesses in the yard.  I like my PSS, but the manufacturer recommends drilling an additional thru-hull for it, which I reluctantly agreed to. There is another way involving a tube that is two feet above the water line all the time even when heeled over which can be difficult to do in a c34.  The older PSS design didn't have either and I think some folks on the c34 board have gotten by with less tube and a reservoir.   Anyway I recommend thinking about that ahead of time.  Initially the new thru-hull leaked, so I had to get that addressed after I left the boatyard, but they fixed it. Now that everything is squared away, my bilge was bone dry until it rained.  If you have any questions about my boatyard experience feel free to send me a message, Noah.

[Noah]

Thx for the quick reply. Interesting info on PSS. Wasn't aware of the need for tubes or through hull. I need to do some additional research, apparently. If either of those prove to be necessary I will stick with the old stuffing box, although probably still change my bronze shaft to SS, but maybe not?

[Ron Hill]

Thanks Ron.  Are you are talking about the shaft alignment or something else in the engine?

Eric : Yes, I mean engine / shaft alignment!!

[awesome34]

Noah, I just went for a ride along with the mechanic from the boatyard.  He felt like the increased vibration was likely due to the increased bite in the new prop and because I have a brass shaft so that it has more bend and thus more vibration than a stainless steel shaft would.  He looked at the shaft while we were going and didn't think the vibration was that serious an issue though.  I don't plan to do too much about it in the short term since I just got out of the boatyard, but he felt that putting a stainless steel shaft in would likely reduce the vibration, so maybe it is a good idea for you to do that.  Also, he said that at some point a bronze shaft will break, it could be a very long time, but stainless steel is much stronger. 

[Mike and Joanne Stimmler]

Awesome,
I don't recall ever reading about anyone on our board actually having a shaft "BREAK" but I would suspect that it could be bent. I think you should take Ron's advice and check the engine and shaft alignment first before going to the expense of a new shaft. You can usually tell if the shaft is bent while checking the alignment by seeing if the alignment changes as you rotate the shaft.

Mike

[awesome34]

Mike,

I haven't ruled out the suggestion that engine alignment is a potential cause of the vibration. The people on this board have a lot more experience than I do and are very wise.  I just wanted to give Noah, who is going into the boatyard soon, the opinion of my mechanic that the shaft could also be contributing since he is thinking of replacing his shaft while he is in there.  I don't plan to replace my shaft anytime soon, and I think a broken shaft is extremely unlikely, but I am sure my boat mechanic has seen it somewhere, even if not on a c34.  I may consider replacing my shaft the next time I have work done if I haven't found other ways to reduce the vibrations by then though.   

-Eric

[Clay Greene]

This is from the Flexofold salesperson when I was comparing the two-blade to the three-blade props:

One would choose a 2-blade because, in flat water, it will reach a higher speed for any given RPM.  It will also have lower drag under sail and will cost less.  The 3-blade Flexofold will perform better in maneuvers around the docks, in forward and reverse, will attain a higher average speed against a head sea, and will stop the boat quicker.  The 3-blade may also be a little smoother running if there is a problem with vibration. The choice of 2-blade vs. 3 blade is really up to your personal preferences.

We bought the three-blade prop and have not had any issue with two boats.  However, I also have a friend who bought the two-blade and there is no issue.  It may be that the two-blade heightens a pre-existing vibration issue to the point that it is noticeable.  The hubs also are a lot heavier than a standard fixed prop so that could pull things out of balance as well.  I would check to make sure the prop shaft is properly aligned in the transmission.

[Ron Hill]

Eric : You shouldn't get prop vibration if your prop hub is about 1 inch aft of the strut. 

Further than one shaft diameter and you might get vibration and added wear on the cutless bearing.

A thought

[awesome34]

Thanks Ron.  I have tried to attach a photo of the prop from when it was installed in the yard.  It does look like there is more than an inch between the hub and the strut.  That could be an issue.

[attachthumb=#]

[Jon W]

Hi Awesome,
     I used Morton Marine at Shelter Island Boatyard for a host of upgrades (excellent work and would use them again). When they installed a new Pedro hose they pulled the original bronze prop shaft back. I've attached a picture of what we found on the old shaft. The burnished shiny black area is slightly smaller in diameter than the shaft should be. It is actually a built up epoxy repair where the shaft passed through the cutlass bearing. Don't know the history, or why one of the previous PO's chose this route. No one at SIBY had ever seen such a repair on a prop shaft, but it could have failed in the future. I now have a new SST shaft and cutlass bearing. Don't want to imply anything, just passing on what happened to me.
Jon W.

[Noah]

Thx for sharing guys. My thoughts are, as much as I enjoy "classic materials" my 1990 bronze shaft is probably ready to retire. And after forking over $1,900 on a new Flex-o-fold 3-blade, I am better off replacing the orignial bronze shaft with a strong alloy SS shaft, properly faced and fitted to the engine/transmission/drive train. The switch to PSS dripless will take more investigating.
Thx
Noah

[Robert Mann]

Noah,
My C34 was fitted with a 2 blade folding prop and PSS dripless at the time of new purchase by the previous owner.  There were initial problems with the original bronze shaft bending.  This created a lot of conversation with Catalina.  Bottom line is; mine was refitted with a stainless steel shaft, which is in great shape 13 years on.  I will say the folding prop is noisy during direction change from forward to astern and I would never feel completely at ease making fast changes.  I always allow the engine to slow to idle and then reverse the gearbox, still there is a major clunk as the prop opens.  This makes it challenging to maneuver in tight spaces, where I feel a fixed blade would be better.