R-27 Outboard: Weeping rust on bow thruster nut

[BB marine]

I have a hard time believing a marine thruster manufacturer designed a composite housing thruster that requires nut and washers to be replaced like and anode.It sounds like they did. I would suggest making sure the washer and nut are 316 stainless. I'm sure they are. There is no way a thruster manufacturer would use 304 fasteners for below the water line hardware. I still have the opinion a physical disconnect of positive and ground leads at the thruster would reduce the corrosion. The other question/sugggetion I would have is what would be wrong with using a brass nylon insert lock nut and washer in place of the stainless fasteners?

 

[baz]

Just had the washer/nut/prop replaced by my diver service today. Some good news...

1) The prop, washer/nut were replaced without issues. the weeping rust was definitely evident on just the washer & nut. The rest of the bow thruster was in pristine shape. 😀

2) The other underwater anodes looked good and were hardly eroded at all. Last replacement for the trim tabs and engine bracket anode was in early March this year; thus some 4 months ago. Normally after 4 months my anodes are a good 50% gone. I have been connecting shore power since March for just 24 hrs per week, so I think this is a credible reason for extending the under water anode's life span for me. 😀

BTW... I keep the boat in salt water 100% of the time.

 

[baz]

I had the chance today to inspect the washer/nut and prop that the diver service removed yesterday. There were actually two washers removed; one small and the other larger. The small one is for seating the nut but I'm unsure what the larger washer was used for, other than maybe the backside of the prop.

The washers and the nut appear to be in very good condition with little to no rust showing. However, the prop does show brown 'weeping' rust residue which must somehow result from the washer/nut casting off something as part of a chemical reaction. :?

No matter, it appears there's really no concern here as washer/nut are in good condition after some 9 months in salt water. I will replace them periodically however just so that any rust buildup does not cause issues wanting to remove them later when necessary.

Album
http://www.tugnuts.com/gallery2.php?g2_itemId=53196

Photos

 

[baz]

[EDIT]
I've forwarded the above information to Andrew Custis and it was agreed that there's no real concern here. The visible brown rust-like residue is a normal bleeding out of SS and is similar in nature to other SS hardware having this issue when not rinsed off or in a salt water environment.

Of course, I now have a gratuitous spare bow thruster prop, washer(s) and nut onboard... thanks to Lewmar & RT customer service. 😀

As an aside... the bow thruster prop is made from a composite material, is very hard and stiff with little to no vane bending when I applied pressure to them.... a very sturdy prop in other words.