[C320-list] Strange coating

[Michael Leschisin]

I’m starting to make headway or at least have some theories on how stray current might have caused the coating on my prop that I posted to the list last week.  

It will take some testing when the boats are in the water this spring to really confirm what’s going on but I think I have some good starting points.  One of the mysteries to me was why my prop was coated and a dock neighbor on the other side of the boat with suspected electrical issue was spot less.  I talked to the owner of that boat and he said that his underwater metals are actually separated from the boat's bonding system (and therefore grounding) via a plastic DriveSaver coupler on the prop shaft.  Although the primary design of the DriveSaver is to break away in a catastrophic prop strike, I found that it could be an interesting solution to avoiding any future stray current issues.  Does anyone run a DriveSaver or similar coupler on their boat?  Any pluses, minuses or opinions on their use?  If anyone is running one and has had good luck do you know what model number that fits a C320 with the Yanmar 3GM30F with the KM2P transition?  They seem pretty straight forward to install….


Michael Leschisin

Wild Blue Yonder
C320 995
Menominee, MI




> On Jan 5, 2023, at 7:25 AM, Chuck Mueller <katchu at chartermi.net> wrote:
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> Michael
> 
> My boat is also in fresh water in Holland Michigan.  I replaced my shaft with SS and installed a new Flex-o-fold prop for the 2020 season.  Installed magnesium anodes on both the shaft and prop.  When I pulled the boat in the Fall it looked like I had electrolysis at the top of the rudder.  However, like your case, it sanded off.  I thought that maybe two anodes was overkill, so backed off to aluminum.  It’s better, but I’m still getting the same thing at the top of the rudder.  My case is not as bad as yours, but still very curious.  By the way, using VC-17 bottom paint.
> 
> A few years ago, someone on this forum talked about a loose wire in the binnacle causing the rudder shaft to get a positive charge which corroded the rudder.  Could something like that be happening? In any case, I’m interested in hearing any solutions.
> 
> Chuck Mueller
> Northwind #676
> Holland, MI
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Wed, 4 Jan 2023 14:02:08 -0600
> From: Michael Leschisin <mleschisin at imagestudios.com>
> To: C320-List at catalina320.com
> Subject: [C320-list] Strange Coating on Prop and Shaft
> Message-ID: <0199538E-E638-425B-89EB-A590753B0DDF at imagestudios.com>
> Content-Type: text/plain;	charset=utf-8
> 
> This past October, when we hauled the boat out for the season, there was a thick hard coating, mostly on the bronze prop, but also heavily on the stainless shaft tip and speckled across the zinc anode, the stainless shaft and bronze strut.  My first reaction was, ?Oh crap I just cooked a thousand dollar prop with galvanic corrosion? but on closer inspection it seemed to be some sort of yellowish/ off-white coating on the underwater drivetrain.  Some areas of the prop were up to an eighth inch thick but after an aggressive power washing and scraping with a metal putty knife I was able to remove the hard crusty substance.  I?m guessing it was calcium carbonate or something similar, but I found there was no pitting or metal lost at all.  In fact the narrow threads of the stainless shaft were untouched, even the cotter pin was 100% intact and the bronze prop showed no loss of metal.  (I can email before and after photos if anyone has any thoughts on assessing the issue).  The drivetrain 
> was clean as a whistle when the boat was splashed in May of 2022, so the buildup occurred after just one season in the water.  There was never any buildup or anything odd in any previous season and nothing has really changed on the boat other than the installation of a new fail safe isolator in 2020 (no buildup following installing it in 2020 or 2021).  In 2018, after I had first purchased the boat, I put a fresh zinc anode on the shaft, come to find out I should be running a magnesium one in fresh water (rookie mistake), but again no buildup in any of the previous years.
> 
> Here?s the weird part; the boat is slipped in Menominee, MI. (Great Lakes, fresh water) and after talking with the two boatyards that service our marina, out of the couple of hundred boat that they pulled, mine was the only one with this odd coating on the drivetrain.  I?m wondering if anyone has experienced anything similar or has any thoughts on how to start chasing down the source of the issue.  
> 
> I did some research online and I?m guessing I have cathodic coating happening, which is sort of the opposite of galvanic corrosion.  Rather than your drivetrain acting as the negative pole for the stray current coming off of someone else?s boat and giving up its metal, I think I?m pushing a positive stray current into the water and attracting minerals out of the water.  I?m not sure if this assessment is correct, if my isolator would allow a stray current from the dock to be passed onto the boat via the ground or how and where to start to digging for the source of a stray current on my boat.
> 
> Any thoughts or ideas would be much appreciated,
> 
> 
> 
> Michael Leschisin
> 
> Wild Blue Yonder
> C320 995
> Menominee, MI
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> End of C320-list Digest, Vol 4357, Issue 1
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