[C320-list] Strange coating

[Charles Holbrook]

 Het Chuck and Michael:
I too am a freshwater C320 in Lake Erie.  Annually, I treat the bottom with VC 17.  Sometimes I need to sand a blister here and there but have never treated the bottom with anything but VC 17.  I have had the boat for 7 years and have never done any bottom treatment but VC 17 right over top of the sanded areas. Should I be painting the bottom on the spots I have sanded off?  
Charlie
    On Thursday, January 5, 2023 at 10:58:54 AM EST, Michael Leschisin <mleschisin at imagestudios.com> wrote:  
 
 Hey Chuck,

In doing some research since October I have seen that overprotecting with anodes can cause a ph shift in the water surrounding the protected metals and promote a calcification type of buildup.  Not sure but it sounds like that might be the case if you’re running two anodes, even though aluminum has a lower potential than magnesium.  Everett Collier’s Boat Owners Guide to Corrosion talks in depth about matching volume and potential of anodes to the volume and type of metal being protected - might be a good resource.  

In my case, with a zinc anode on and what seems to be a crazy amount of build up, I’m guessing I must somehow be pushing voltage into the water.  Could be the dock pedestal or the boat’s electronics but I’ll have to do a whole lot of testing once the boat's back in the water next spring.

I’ll keep you in the loop and post to the forum if I’m able to narrow down a cause.


Michael Leschisin

Wild Blue Yonder
C320 995
Menominee, MI



> On Jan 5, 2023, at 7:25 AM, Chuck Mueller <katchu at chartermi.net> wrote:
> 
> 
> 
> 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
> 
> 
> 
> 
> 
> 
> End of C320-list Digest, Vol 4357, Issue 1
> ******************************************
>