Re: [Amel Yacht Owners] Re: Engine and Service Battery circuits Isolated
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The corrosion/electrolytic? damage was primarily under the "wearing out bearing" aft of the inner Oring. That is an area that has free flow of sea water between the bearing and the shaft, so maybe not a hypoxic environment There is a hole about 2mm in diameter and depth that is aft of the bearing, and there is discoloration and loss of sheen to the shaft forward of the Oring still under the bearing.
I will inspect for any evidence of voltage leak, which I think I may find related to the installation of three new chargers about a year ago.
Amel believes that you can "overzinc" which may cause problems as well. They believe that on our SM's the two zincs on the rudder
"balance" the system appropriately. I didn't have a prop zinc when I bought the boat, and instead had the red plastic cap that was supplied with the AutoProp. When I switched to the MaxProp it was supplied with a zinc, so I used it. I've seen that prop zinc disappear about twice as fast as the rudder zincs, so I think it's doing something...?something good?...I don't know now.
I'm still reading about bonding systems and haven't found anything yet that makes it perfectly clear to me. If I run across anything that makes it easier to understand I will post it here. It seems to be a complicated subject that doesn't have absolutely clear answers...there seems to be an "art" to it as well as the science. Henri was as much an "artiste" as anyone when it comes to building boats, so I'm leaving things the way he designed them.
Kent ( you can call me "Rusty")
On the hard in Fernandina Beach, FL
Sent: Thursday, April 24, 2014 6:50 AM
Subject: RE: [Amel Yacht Owners] Re: Engine and Service Battery circuits Isolated
You could be right...the voltage potential is just so overwhelming everything goes....
I can't find a lot of logic in most of this....
I've just antifouled and refurbished the Autoprop with new bearings...and after seeing the shaft corrosion on (your?) shafts, I've installed the prop zinc that comes with the bearing kit... I see the 54s have it whereas our SM53s don't ...why ??
Also I showed those pics to an engineer here and he thinks it is crevice corrosion caused by Stainless steel operating in an oxygen deprived environment...which could be the case if the outer seals failed, but the inners didn't....more food for thought.......
SV Elyse SM437
Gulf Harbour NZ ...currently