Looking to change Gori 2 blade folding due to extreme vibration

[PPin]

Hi all, I've had my C&C 27 for two summers now and when the engine is on and making way the whole boat shakes to the point where I am afraid things will start falling apart..

Before we go there, I took the pre-launch time this spring to properly align the engine to the shaft, and did it again in the water. the alignment looks really good now. I also replaced the stuffing box cord and hose. the cutless is in very good condition as well.

But the shaking this summer is just as bad. I have come to the conclusion that it has to be the Gori two blade folding prop.

Would people agree with this assessment? why is the prop giving so much vibration? I do the whole "go into reverse and then forward to open the blades" and in fact sometimes I can tell the blades don't open right away. lots of engine noise and no movement.. it is probably close to an original prop and I'm wondering if there is anything I can do to fix it? I see that the three blade has stoppers so that they don't open too wide but not the 2 blade. I guess my first job will be to see if any of the allen screws are loose on the Gori before taking it apart.

I have noticed on this forum a few people mentioning they have experienced vibration with a folding prop.

At this point I want to change the prop in the water. Having looked at instructions I think I can take off the Gori.

But here's the other thing. I don't think the Gori has the proper nuts I will need to install a regular 3 blade prop? the instructions for the Gori call it a nut thread. If I have a 7/8" shaft, can I find the nuts at a regular hardware store?

lots of questions and a long thread but I am beyond frustrated with this problem. I have been doing all kinds of maintenance on the Atomic 4 and it runs so well, and then I put it into gear and the shrouds, cabin top, even the mast start shaking!? and everything else.

thank you for any insight on this problem someone may have.

[Dave Neptune]

If you going into the water I would first check to se if the prop shaft is bent behind the strut. Just leave the engine in neutral and turn the prop if it is bent enough to shake the boat you will see it.

Also be sure the prop is working freely, IE one blade may not be opening all the way.

And yes the shaft should be tapered and use a std prop nut on the end of the shaft. They are nothing special.

Dave Neptune

[indigo]

The standard thread utilized on the aft end of a 7/8" propeller shaft is 5/8"-11 coarse thread.

Tom Stevens

[Al Schober]

Nut should be a 'castle' nut with grooves for a cotter pin. Both obviously stainless.

[PPin]

thank you! Any idea why it would shake so much? Sounds like the Gori should be a step up from the fixed propellers?

[Dave Neptune]

See post #2. Folding props are notorious for shaking if not working properly. A fixed prop is either good or broken if it shakes 90%of the time.

Prop balance in your case is fully unfolded or a bent shaft behind the strut.

Dave Neptune

[PPin]

Gotcha, thanks Dave. much appreciated!

Patrick