Edited: Many thanks for the help

[a64pilot]

He has an autoprop, and that is my bet on what his issue is.
I’d just as a guess, guess that the seal in cold water has gotten hard and has led to his issue.
He rebuilt it not too long ago, but I’m betting that is the problem
If I were him, much as it sucks, I’d turn around as he states he has to have the engine in the ice.
Unlikely as it is, but if it slung a blade, I don’t think he could continue, even at very low RPM.

Some will say Autoprops sling blades, and the old non greased ones I believe did have issue, but the newer greased ones don’t seem to.

[a64pilot]

The Autoprop due to passing through dead wood at each revolution, varies pitch constantly, even if Boat speed is held constant, or at least I believe they do.
What controls pitch is a balance of induced flow and centripetal forces from rotation, without grease and assuming water has gotten in and there is enough wear to cause a looseness enough to be heard, it’s time to turn around, in my opinion.

I’d throttle back and baby it back to port.

If I’m right, he will not be able to see any problem, it would take holding the blades and feeling for excess play.

I hate to say this as it will ruin the trip, but it’s my best guess

[Seaworthy Lass]

Thanks.
All posts have been emailed to Dockhead.

[estarzinger]

Oh, yea, another common thing to check for - a loose zinc.

[Island Time O25]

Or if installed a loose rope cutter.

Also is there a wobble in the shaft? Could be from a loose or misaligned coupling. Or a misaligned engine mount. Especially since there was recent shaft/cutlass work done those could be off by a minute amount but enough to "clank" the shaft. Don't ask how I know.

[2big2small]

+1 on checking for fouled prop first.

Happened to us with extra vibration and the works. We immediately switched the engine off not knowing what was happening and then had a grueling sail at 2 knots. Arriving at port we thought we’d risk using the engine again at slow revs to get in, only to discover that the problem was gone.

[NYSail]

As he sails or motors slowly he needs to feel the shaft as it spins. Is there a wobble? Water proof GoPro.....

Greg

[RaymondR]

First thing I would do is check the bolts on the prop shaft connecting flange.

[JPA Cate]

Yes, Raymond. Very easy on our boat, anyhow, to check. Hope it is similar on the 54' Moody.

Ann

[Seaworthy Lass]

Thanks everyone. The help is very appreciated.
I have emailed the latest lot of responses.

There has been a reply from Dockhead:


Thank you very much.
These were useful perspectives.

I did also get a response from the engineer who installed the shaft seal. He said that there is nothing whatsoever in the seal (as someone else on CF posted) that can make a knocking sound. He said it must be the rope cutter.

Indeed, I adjusted the position of the ropecutter (an Ambassador Stripper) to leave more space between the static blade and the v-shaped notch which holds it. This on advice from that engineer, who pointed out that there needs to be space for the shaft to move forward under power. I am guessing that I overdid it and the static blade is now turning and banging against that notch bracket thing. That's exactly what it sounds like. If this is the case, then it will wreck my rope cutter but shouldn't hurt anything else, so I think we will carry out. We might try to get a look at it with a GoPro when we're anchored.

We're sailing at 9.5 knots in 16 knots of cold NNE wind.
Thanks to everyone for the help.

[El Pinguino]

SL
Any idea how he got on re the water?

Re his problem.....

#1 on arrival send down the GoPro/SJCam on the end of a boathook.....

#2 don drysuit... dive on it.... sea temp is probably 4*C... no biggy....

[noelex 77]

Originally Posted by estarzinger

Oh, yea, another common thing to check for - a loose zinc.

This (or loose rope cutter) would be my first thought as well.

If you have an underwater camera attaching it to a boat hook will often help show the issue.

If it is a loose propshaft zinc tightening (or removing ) the bolts can be sometimes very difficult when free diving, even in warm water.

A temporary fix is to attach a hose clamp on the shaft just behind the zinc. This stops the zinc sliding backwards and rubbing on the P bracket. It might still rattle a little but at least you know it is not doing any damage. If it is loose zinc on the prop this will not work, but at least these are usually quick to remove.

[Seaworthy Lass]

Originally Posted by El Pinguino

SL
Any idea how he got on re the water?

Re his problem.....

#1 on arrival send down the GoPro/SJCam on the end of a boathook.....

#2 don drysuit... dive on it.... sea temp is probably 4*C... no biggy....

Thanks. I will relay the message.

I haven't heard how he resolved the water container issue.

[Pete7]

I have e mailed Dockhead, before seeing this thread.

My money is on the rope cutter. It could even be the gap between the "striker plate" and the "clamp ring which turns with the shaft" which if like mine makes a ticking noise under sail but under power either can't be heard or the turn shaft holds the "clamp ring" part against one side of the "striker plate". Its actually a very sensitive way of judging sail trim because a slight increase in boat speed under sail alters the ticking noise frequency which is easy to detect without relying on gauges or GPS with a time delay.

He does have dive kit on board, one of those shallow water all in one sets, but hasn't any diver training and I don't think anyone else in the crew has either.

They have a photographer with some snazzy kit so there might be a waterproof camera on board.

Pete

[Pete7]

Originally Posted by Seaworthy Lass

I have done a search of what prop Dockhead has and I think it is a Bruntons. I presume an Autoprop?

Confirmed, I did an anode change for him a couple of years ago.