Loud grinding sound when in both forward/reverse

[Challengerjr]

I have a Catalina 30 with a Universal diesel in the Chesapeake Bay. Between COVID and health issues we haven’t been out much in the last 3 years. At summer’23’s end I was preparing for perhaps my only sail of the season. When I placed her in gear there was a very loud grating sound. The transmission oil is full. By myself, I couldn’t tell if the sound was coming from the gear box, stuffing box, or from outside the hull. I pulled her out of gear quickly and only made a few more brief attempts, all with the same painful sound. Any similar experiences or suggestions?

[ChrisJHC]

Some questions to narrow down the likely causes:

Does the grating sound only come when you’re engaging gear from neutral or does it continue while in gear?

Does the sound change with different engine revs?

Does the gearbox engage and drive the boat forwards or backwards (while tied up alongside)?

Definitely worth having a quick look underneath to make sure there’s nothing stuck or growing under there. Either jump in or rig up a Go Pro on the end of a boat hook.

[Cheechako]

With the boat sitting, is the prop or shaft all crudded up with barnacles maybe?
Or something like a plastic bag stuck on the prop?
Stuff can grow inside the cutlass bearing also gouging it badly when first used.
Stored boats often get bad corrosion on the shaft inside the stuffing box. Water trapped in there eats the Stainless Steel due to low oxygen environment. Years ago I had one that looked like a worm ate away at it!

[capt jgw]

Assuming the Universal still has the original Hurth transmission. It has separate clutches for forward and reverse so it's unlikely it would make bad noises in both gears. "Transmission oil is full". Does that mean really full or up to the mark on the dipstick? The full mark is only about 3/4" from the bottom of the stick. There's only supposed to be about 4 ounces in there. I don't know what overfilling would do, but I doubt it would be loud noises. I would most suspect growth like barnacles on the shaft, strut and prop. That would go away after a while but as Chris said you should get a look at the underwater gear before running it.

[MicHughV]

not sure that the transmission case should be "full", which might indicate water in the oil.

I'm not sure of the Universal engine, but some marine diesels have a cooling tube run thru' the transmission, which could lead to water mixing with the oil.

Usually seen as a milky color.

Just adding some ideas to what has been said above..

[capt jgw]

Again assuming it's the original Hurth gear. They don't come standard with a cooler but there is an add on one, it's just a plate with water flowing through it that bolts to the side of the transmission. It cools by conduction through the aluminum housing. No possibility of mixing water with the oil.
The Hurth manual recommends filling the housing to the top with oil (actually ATF) for winter storage. If you do that you have to remember to drain it back down in the spring. I don't know if anyone actually does that, I didn't when I owned two of them, but that's what the book says.

[Calif.Ted]

I believe if you turn the shaft by hand at the coupler you should be able to distinguish if the noise is from gearbox (transmission) or running gear. Engine off, in neutral, does it turn easily and quiet or hard with a grind?

[DirtPete]

Originally Posted by Calif.Ted

I believe if you turn the shaft by hand at the coupler you should be able to distinguish if the noise is from gearbox (transmission) or running gear. Engine off, in neutral, does it turn easily and quiet or hard with a grind?

Ted is on the right track. Seems like the boat was able to maneuver..or not. But until you get eyes on the entirety of the running gear not much to know. Could be sheared key, could be growth in the cutlass, could be a failing shift cable etc.

[skipperpete]

Its my favourite nasty noise, some countries marinas are worse than others but usually this is a calcium buildup on the propshaft, not a regular even layer though, no buildup where the bearing flutes are in contact with the shaft, just in straight lines along the valleys hence the juddering noise. Calif ted knows his stuff, rotating the shaft by hand immediately identifies this really common and very destructive problem. Its easy to fix, just open the coupling at the gearbox, slide the shaft back 5 or 6” and scrape the layer off, it can be very hard but its also brittle so tapping it with a small hammer often shatters it to speed up the removal.

[Challengerjr]

A gracious thank you for the responses to my question. I will be traveling for work for the next several weeks. I look forward to returning so I can apply all this new knowledge. Thank you all.
Chip