New propeller vibration?

[C&C32]

Hi
I have a 1980 c&c 32. It had a plastic/composite prop on it when I bought it. It had a slight chip in it on one of the blades ( two blade prop). Boat ran great with it. No vibration so I left it. But I hear about the indigo prop and how it is designed specifically for the A4. And was sick of other sailors pointing out my chip when the boat was on the hard for the winter.
So I ordered the Indigo prop and put it on with little trouble. Found the old plastic prop was barely on the shaft. Pulled it off with my hand. So glad I changed it.
Once back in the water i had to re-learn the new prop to gauge the rpm, boat speed and reversing characteristics. Seems it need way more revs and vibrates way more. Causing cups to shake in the cockpit cup holder. And once I drop to neutral the revs are way too high and have to throttle way down to idle in neutral. And at low RPM I can hear a slight resonance squeak.
Is this normal for these 3 blade props?

[roadnsky]

A few things are likely going on...

The vibration could be (and is very likely) your engine is out of alignment to the prop shaft.
There are a number of threads on this site discussing the procedures.
I attached a doc relating to it as well.

The squeal sounds like your stuffing box might need attention.
When was the last time you re-packed or adjusted it?

[C&C32]

Thanks for the reply.
Will have a look at the alignment this weekend. As for the stuffing box, I have not done much to it. Seemed to be working well with a very slight drip underway. So assumed it to be working fine.
Just surprised with the vibration now, having no vibration with the old pro with a chip out of it.


thanks
cheers

[Mo]

Also check your ignition timing. Small things. A dead plug can send a vibration as well. I put an engine in mine last fall. This spring it shifted in rough weather and I got a wicked vibration. Lined up the shaft and engine and still had a small vibration...days of screwing around with that with no joy...then found a dead plug on number 4 cyl...back to normal....smooth as silk. Give everything a good look.

[Al Schober]

Hope you saved the old plastic prop. I had one of those on my Tar 30 for many years (mine was made by CDI) and was quite happy with it.
I raced my T30 so the 2 blade prop was a no brainer. Oriented vertically, the prop sat in the wake of the keel with little added drag but I still got the full 6 sec/mi propeller allowance from PHRF!
My opinion re: 'the squeak' is that it's not the prop but the rubber bearing just fwd of the prop. Do you have a strut? If so, check clearances fwd/aft and see if the strut is aligned to the shaft. Your strut may have taken a hit from a lobster float and need to be reset.

[indigo]

You certainly need to check your engine to prop shaft alignment as a first step. Assuming that a blade(s) of the prop were not damaged during the splashing process, one other thought comes to mind especially when you indicate that the plastic prop was so easy to remove.

The CDI props were all made for a 1" shaft. For smaller shafts, they provided a Nylon? bushing to accommodate the 7/8"shaft you most likely have. If the prop was loose on the shaft, then the torque was being transmitted through the shaft key as opposed to the tapered fit of the prop and shaft. Assuming that was indeed the case, the possibility exists that the key had become somewhat damaged/distorted.

When you go about installing a prop on a tapered shaft with a key, it is of utmost importance to assure that the key does not slide too far forward during the process. The shaft keyway is cut with a rotary cutter such that the forward end of the keyway has a bit of a "ski jump" geometry. If the key is allowed to slide too far forward, it can ride up on the "ski jump" area and thus cause the prop to appear to be fully seated on the shaft. A damaged key would have more of a tendency to slide forward with the prop. In that case, the prop is actually resting on the top of the key and the shaft 180 degrees away from the key. You can actually tighten the nuts fully as though the prop was properly seated on the shaft. The reality is that the prop mass is offset from the shaft centerline some amount (maybe .010-.020") which can cause significant vibration although the prop appeared to be proper installed.

Did you happen to take any pics of the prop at final installation?

Do you happen to recall how far the shoulder on the shaft was up inside the prop bore prior to installing the nuts? It should be about 1/16" depending on the stack up of machining tolerances.

The above information may help us understand if the prop itself is indeed the source of the vibration.

Tom Stevens
Indigo