Help in diagnosing engine/prop problem please

[Oscarpop]

Hello all,

Bit of a head scratcher and i would love your help in trying to work out what the problem is here.

Two days ago we were motor sailing along when we noticed we had picked up a crab pot. It was attached to a really thin (2mm) polyprop line. We cut the line and then that evening when we were anchored, cut away the excess line from the rope cutter and prop.

We have an ambassador rope stripper and I noticed that one of the plastic washers separating the blases was slightly out of place. (They need replacing at the end of this season.)


So the problem.

Yesterday we were motor sailing along and there was a horrid groaning sound from under the boat. couldn't work out where it was coming from, but put the engine into neutral. problem went away. left it for a few minutes then carried on under engine with no problem.

Went below to check the stuffing box and noticed that it was hot, about 40 degrees c. Some water coming through but not a lot. Anyway, loosened the nuts on the box half a turn and the drip started at about once every 15 seconds.

This morning, sailing along. Checked the stuffing box and still warm.

But the noise from underneath the boat happened again. Boat in neutral, it went away. Boat in drive, the noise came back.

Turned off engine, dropped sails and got into the water to inspect the prop. No sign of problems. All blades ( featherstream) in place and turning fine.
Start engine and put it slowly in gear. prop spins fine, no problem.

Stuffing box still dripping away but is now cool.

Some remnants of blue line still in place around prop shaft.

Anyway, we are now motoring along and (touch wood) everything seems ok.


We have no engine alarms, everything seems to be ok with the engine, but I have no idea what the problem is?

If I had to put money on it, I would say it is something interfering with the prop turning, possibly the blue line in some way. Or failing that the blades of the rope stripper clashing and locking. But these are all guesses.
Any ideas :?

 

[RichardS]

I agree with your diagnosis. I don't have a stripper but I'll bet it's something to do with the stripper being displaced and something rubbing that is not supposed the be rubbing. It may only be evident when he prop is pushing the boat along and everything is forced fully forwards towards the cutlass bearing.

Richard

 

[Oscarpop]

forgot to add that i went below about 5 minutes before the noise started. our aft cabin is over the prop. heard a whistling that i had never heard before, coming from the prop area under the boat.
after the noise started and we put the boat into neutral the whistling went away. sounds normal at present .

 

[Glenlivet]

Could be melted polyprop found its way into a bearing. Did you try a bit of reverse to see if the problem cleared?

 

[sarabande]

Whistling under load is sometimes a sign of cavitation. Is the edge of one of the blades dinged or chipped ?

Can't help with the groaning sound, except perhaps the cutless bearing having been damaged ?

 

[cueball]

What does it do in reverse under load? can you hear the same noise?

 

[Oscarpop]

problem seems to be ok now. however it has happened intermitently 3 times now in the last two days, which puts me on edge. will dive under the boat later and see if there is any signs of damage to the rope cutter.
the fact that the stuffing box is now back to room temperature makes me tjink that some polyprop did get into the stern tube and restrict the water supply.

 

[Neil_Y]

Could be melted polyprop found its way into a bearing. Did you try a bit of reverse to see if the problem cleared?

That's what I'm suspecting, if the rope has prevented water flow then the bearing could have been cooked. depending on the amount of rope and other factors such as speed and engine hp a rope can bend the P bracket or at least move it if you have one. The forces also try to pull the engine back which can (if you have a big enough engine) damage the gearbox. It's unlikely in a small yacht though, we see it more in fishing boats.