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Prop Not Turning -- C&C 27

2020 Views 5 Replies 4 Participants Last post by  Faster
The prop on our C&C 27 is not turning.

We documented it in a youtube video: (You have to copy and paste the link because I can't post a link because I'm too new here. I promise it's not spam or anything nefarious.)

It's a folding prop, as you can vaguely tell in the video.

The boat has a very clean and recently serviced Yanmar Diesel engine. The prop previously gave us some trouble in that it wouldn't open right away when we put the boat in gear, but this seems like a different problem. We also had an issue with the stuffing box coming loose and taking on water, but that seems to have been resolved too.

I'd appreciate any insight you could offer on the cause of the problem and, more importantly, the solution.

Thank you.
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No could find video.
Would have posted as a link here for others.

Sounds like maybe a transmission problem.
1st, make sure the linkage for the shifter is moving the shift lever on the engine. Try moving the shift lever on the engine by hand to see if you can engage forward (and/or reverse). If you can engage a gear this way then your linkage may need tweaking.
Either the transmission isn't engaging properly, or your shaft coupling is kaput. Do you have some sort of flexible shaft coupling? That might have sheared and essentially disconnected the engine from the shaft.
Thanks for the replies. Here is some more detail from my boat partner, who is closer to this than I am.

I just bought a 1987 C&C 27.
It's my first inboard engine (Yanmar 1GM 10) and my first folding prop.

I had been having a tough time getting the prop to fold out, and was experiencing intermittent heavy vibration when, I assume, it wasn't folding out properly. I spend the last week or so, shifting back and forth from forward - to reverse, trying to get the thing to spin right.

Then the other day, I was out for a sail, and fired up the engine, and motored for about 20 minutes before I started seeing my knot meter fall to zero.

The engine ceased to provide thrust in forward or reverse.
I could see via the cockpit locker access that the prop shaft is turning a little.
So after sailing back to my mooring, I grabbed a GoPro and made this video

While filming the video, I had the Yanmar running around 1200 RPM. I shifted the engine from neutral into forward, then reverse, then forward again. The prop shaft doesn't seem to be spinning consistently or much at all.

The engine runs well, and the transmission is shifting, but something seems to be broken somewhere between the stuffing box and propshaft.

Thank you for your kind consideration - any advice would be helpful
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Is the shaft spinning where it comes out of the transmission? If it isn't, then the transmission isn't engaging for some reason. If it is, then is the shaft spinning where it goes into the stuffing box/packing gland? If it isn't, then the coupling is probably bad. If it is, then the prop nut(s) isn't/aren't tight or the prop key is broken (if it had one). There isn't much else that could be bad.

If you're certain that the prop shaft is turning properly at the coupling aft of the transmission, then the shaft must be broken - and just 'grabbing' on itself occasionally. Certainly not normal behaviour.

The 'one blade down' position is classic for the vibration you describe - usually a quick burst in reverse will reset the prop and you can go forward after that without problem.

You need to confirm shaft rotation at the transmission output - to say the transmission is 'shifting alright', I suspect, simply means you can move the lever from fwd to reverse OK. Doesn't mean the transmission is actually responding. My guess is that you've lost transmission function, but it could be simply the damper plate too.
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