check your mooring rings

[ex TL systems 63]

I found one of the lines on my pole mooring cut through as if by a knife recently where it had been connected to the stainless steel ring. When I went to replace it I found the once smooth surface of the stainless rod that forms the ring was a series of sharp ridges as if the metal had splintered and it made a very effective saw. I contacted Bruce the council mooring guy and both the pole rings were replaced. It seems it is caused by oxygen depletion? where the rope is tight on the metal and you would need to look closely to spot it . Not sure how old the rings were but at least over 5 years. The lines were connected correctly to the ring .

[ex TL systems 63]

yes i should have taken a photo but didn,t,   Would not think it would have been electrical as it was a composite catamaran with a very simple electric system,which I left disconnected  and lifting outboards so no metal underwater. Will try to remember to have a look at it occasionally from now on.

[ex TL systems 63]

true I did have solar panels and not overly flash wiring, no metal connected to the cleats though,  unless something was coming through the alloy fore beam and the mooring line was touching there.

[wheels 543]

It sounds like it is definitely Electrolysis. Forget the starvation of oxygen thing.That is a red hearing and comes from people that do not understand how SST works, in relation to a microscopic surface.
There can be many different reasons why this can happen and it may not always be your Boat that is at fault, Your Boat could be the other end of the line that connects to the problem so to speak.
But there could be other reasons as well and there may not be a definite answer. This issue has cropped up every now and then with no real cause to be found and I have always had in the back of my mind a possible suspect, but have never tested the theory. And that is that a "battery" may infact be created in the rope/metal connection itself. All it takes is the line to become contaminated right at the connection. Salinity could build up to high levels than if it were submersed and as Salt attracts moisture, it is always damp. Salt (which is a Salt of Sodium, a highly reactive metal) moisture produces the electrolyte and the SST provides the dissimilar metal and the intertface coupled with the line being none conductive then causes current flowing right at the interface of the two materials connecting to one another. Or something along those lines anyway. Iron is another possible contamination. As soon as Rust takes place, then you know have Iron in the form of Oxide and that too can now be a dissimilar metal situation. We have alwasy suspected a current could flow down the line itself, especially when wet. It could be possible, but I also find it harder to believe and I have never been able to measure anything. Yes I have tested. But the current may be far smaller than any meter I have can detect and it most certainly a very very slow process, which means a very very small current flow.
Good practice os to check the ring every now and then and if Rust is showing, give it a clean with some Emergel or similar.