Something that all of us have to watch out for - but something to consider, especially when running expensive transducers like the LSS2.

These are two of the mounting washers used to attach the LSS2 stainless-steel mounting plate to the transom-bracket. They are (supposingly) made from marine-grade stainless-steel.

They have been installed for just 3 months! on my boat. The boat runs at around 60kph for about an hour and around 3-5kph for around 3hrs every other day.

Checking all the mounting hardware for such cavitation-damage was something I had not even considered until now...

I'm not sure it's caused by cavitation - you need some very high speed components to get cavitation damage (like the prop tip for example). This looks more like galvanic corrosion caused by dissimilar metals. There is something else going on here ! you might also want to look up fretting corrosion, possibly more likely than galvanic - depending on circumstances.

T

I will agree.
Because of the normal Position of the Transducer before the Motor-Prop,
60 km/h (or knots ?) should n make such a damage.
The Prop, where the Cavitation normally occurs is running at a lot of 1000 rpm,
which will result in a very much higher Speed on the outside of the Prop-Wings than 60 km/h.

I cant believe that 60 km/h at the Washers can produce this damage !??

Thank you for the replies guys. I checked, and apparently, Lowrance uses marine-grade steel for the screws, washers and nuts. The mounting plate is also made from it. I thought about galvanic processes as well, but there are no other materials around. The interesting thing is that the damage occurred downstream from the bolts. I honestly have no idea. Interesting stuff...

I've seen a similar kind of 'pitted' corrosion on marine grade (316) stainless equipment - although it was in Indian coastal waters (which I guess has a higher chloride content compared to other parts of the world) and on equipment which had the potential of some electrical current leakage (mounts holding seismic sources and various acoustic / hydrophone equipment). Whilst 316 marine grade SS is usually excellent at minimising thie corrosion, it does happen and we have seen before, that 'marine grade' is not always 316 quality - in which case, corrosion Can be very quick! Guess 1 option is to get replacements which are confirmed as 316 quality and see if you get the same problem. If you do, it must be another factor. I presume you aren't using your boat off India :-) or in a chloride rich lake and there is no chance of any electrical leakage over the transom plate or LSS2 mount.....