Rapid Disintegration of Saildrive Leg
- Thread starter fstbttms
- Start date
You dove on the wrong boat ? Vandalism ? Terrorism ?
Never having had a saildrive, do you know what this part is ? New part, anode ?
A suggestion in future might be to narrate the video, describing what we are seeing rather than just using music. Be a lot more helpful in analyzing just "whahappen "
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Never having had a saildrive, do you know what this part is ? New part, anode ?
A suggestion in future might be to narrate the video, describing what we are seeing rather than just using music. Be a lot more helpful in analyzing just "whahappen "
.It is stray current corrosion. Somewhere in the boat DC current is leaking into the bonding system or on to the engine block. Anodes offer little protection for this.
At the top of the least of usual suspects is bilge pump wiring. Could also be chafe some where else. Scroll down the page for photos and discussion: Unraveling the Corrosion Mystery | Steve D'Antonio Marine Consulting
At the top of the least of usual suspects is bilge pump wiring. Could also be chafe some where else. Scroll down the page for photos and discussion: Unraveling the Corrosion Mystery | Steve D'Antonio Marine Consulting
Surprising that this anode seems to be only mildly corroded compared to the rest of the saildrive body, which I assume is an aluminum casting.
Whatever it was, I suspect it happened very quickly (almost instantaneous). Lightning strike ? ? ?
Beyond that, dunno.
Whatever it was, I suspect it happened very quickly (almost instantaneous). Lightning strike ? ? ?
Beyond that, dunno
.Nope. From the link I listed earlier:Surprising that this anode seems to be only mildly corroded compared to the rest of the saildrive body, which I assume is an aluminum casting.
Whatever it was, I suspect it happened very quickly (almost instantaneous). Lightning strike ? ? ?
Beyond that, dunno
Unlike galvanic corrosion, which occurs comparatively slowly, stray current corrosion moves with startling rapidity, potentially destroying a propeller, shaft, thruster, sail drive or stern drive in a matter of days.
Hmmmmmmmmmm ! I also suspect the impressed current attack is preferential with the most anodic metal going first to most cathodic metal going last. As previously noted, the anode didn't fare to badly in this case. Looks like the aluminum case was harder hit.
I can definitely say "strange", but beyond that, "dunno" without a complete inspection of the boat. And I don't think @fstbttms gets paid for that so unlikely we'll ever know the cause.
Mind you, if that were my boat, I wouldn't be installing a new saildrive until I knew EXACTLY what caused that catastrophe. You know, "once bitten, etc, etc".
Hmmmmmmmmmm ! I also suspect the impressed current attack is preferential with the most anodic metal going first to most cathodic metal going last. As previously noted, the anode didn't fare to badly in this case. Looks like the aluminum case was harder hit.
I can definitely say "strange", but beyond that, "dunno" without a complete inspection of the boat. And I don't think @fstbttms gets paid for that so unlikely we'll ever know the cause.
Mind you, if that were my boat, I wouldn't be installing a new saildrive until I knew EXACTLY what caused that catastrophe. You know, "once bitten, etc, etc".
This is why I'll never own a boat with a sail drive.
Since the port drive is severely corroded and the starboard drive is, it would suggest that something is going on in the port hull. I've heard stories about this kind of stray current corrosion before. None of them with good outcomes.
My last boat had a saildrive volvo penta 110 from 1982 and was in perfect condition ,it looked new( fresh water). When I bought the boat the surveyor had a list that I went thru slowly correcting and replacing. On the list was to bond the A/c and ground with d/c panel as per ABYC. I did this and when I hauled the boat it looked like the saildrive sat in paint stripper. I sanded it primed with zinc cromate and volvo paint same thing next year. Did it again but this time unhooked the bonding ,hauled boat still looked like new . I know a galvanic isolator would have more than likely stopped it and was one of the first items I purchased on my current boat.
If the housing was made of non-metalic materials, any galvanic corrosion would attack the drive shaft, gears and propeller first. Only the prop would be visually inspectible. Serious damage could happen and you would never know until the whole unit was garbage.
I'm watching that video and I see a lot of deposits and possibly oxides, but was there real damage underneath?
-Will (Dragonfly)
I hear what' cha saying, Will, but It seems to me that once the leg is not subject to electrolysis, the other materials could be chosen to be a lot closer together on the electrolysis index. Polymer propellers are getting more common, but in an isolated environment, a naval bronze prop on a stainless (316) shaft would not tend to corrode much.. . The leg downshaft could be easily decoupled electrically from the engine/transmission, isolating the prop shaft .. This stuff is not exotic engineering.. I understand why saildrives are used, I just don't think that the manufacturers have done their homework on reducing maintenance items.. The changes could be made at a very low cost on a per-unit basis..
Not definitively. However, the owner plans to have a galvanic isolator installed.
