Strange white deposit on grounding plate

[Joe Myerson]

When Creme Brulee was hauled and pressure-washed, as usual, at the end of last season, I noticed a stranger deposit on the grounding plate. I ignored it at the time, since I usually clean the plate in the spring, using a screwdriver to chip off barnacles and a brass wire brush to scrub the rest.

This spring my grounding plate looked like this:



With no barnacles and a hard white deposit. It does not come off easily, and I'm wondering if it's something other than critter/algae growth. Could it be the result of some kind of galvanic action or corrosion? Is it safe to chip it off?

NOTE: My prop-shaft zinc shows the normal low level of galvanic corrosion (almost none, but I replace it annually).

--Joe

[Jim Walsh]

I have seen a similar deposit on my ground plate but to a much lesser extent than exhibited here. I just used a wire wheel to polish it off. The sintered bronze plate was intact underneath. I don't think it's anything unusual or abnormal but the concentration of whatever little denizen of the deep which causes it is high in your area.

I cropped this photo out of a much larger image so it's a bit blurry but it shows the same deposits I had last fall. I had already cleaned them up with a putty knife and a wire brush.

[Carl Thunberg]

It's very difficult to tell from a photograph, but you should at least look into the possibility of electrolysis from stray current. Have you checked your zinc anode(s) lately? This may be more than a simple calcium deposit. Hopefully those with expertise in this area will speak up. Zinc should sacrifice before bronze, so hopefully I'm being overly cautious.

There is one quick test you can do. Get some muriatic acid from the hardware store, and place a couple drops on the deposit. If it fizzes, it's calcium.

[Joe Myerson]

Thanks Jim and Carl. I think I'll do the muriatic acid test, just to be sure.

The water in my anchorage reached unheard-of temperatures last summer, and there were all sorts of algae blooms, so I'm hoping it's just some climate-change-related new organism. But it's best to make sure.

--Joe

[Sea Hunt Video]

Joe:

I am little under the weather today so my questions/thoughts may not be very coherent (and yes I know my thoughts are generally not very coherent to start with ) . I also know very little about algae, coral growth, etc. in your area.

When pressure washed in October 2015 did the growth come off or did it stay on the dynaplate even after pressure wash

It is possible (coming from someone who knows less than nothing about electrical issues) some type of electrolysis may have taken place - as suggested by other posters. Given that the dynaplate is bronze, is there any possibility that someone painted the dynaplate with some material before launch in April 2015

Several years ago, a well meaning dock staffer painted the shaft zinc donut with prop paint to prevent corrosion. Fortunately, I noticed what he had done and corrected the issue. I am not sure what the sacrificial zinc would have looked like after immersion in salt water and the chemical reaction between the zinc and the paint chemicals.

Here in South Florida over the past 10-15 years we have been experiencing the sad destruction of our coral reefs by what is called "coral whitening" or "coral bleaching". It looks a lot like your dynaplate The cause in our area is attributed to various sources (including rising sea temps) - all man-made (man-caused). I will try to attach a photo of the coral bleaching. You mentioned that your sailing waters were very hot this past summer. Maybe a clue

You may want to take a sample of the material on your dynaplate to a local University biochem lab or even Woods Hole. The students may have some interest in a qualitative analysis of what the material is on the dynaplate.

[Joe Myerson]

When pressure washed in October 2015 did the growth come off or did it stay on the dynaplate even after pressure wash

It is possible (coming from someone who knows less than nothing about electrical issues) some type of electrolysis may have taken place - as suggested by other posters. Given that the dynaplate is bronze, is there any possibility that someone painted the dynaplate with some material before launch in April 2015

Thanks, Roberto.
I honestly don't know whether the yard painted over the Dynaplate, because I wasn't present when she was splashed. Certainly, it's possible, though unlikely. But I was there when she was hauled and pressure washed, and I recall that whatever was on the plate did not come off in the stream of water. I think it was kind of greenish at the time. I don't think I'll have to take it to WHOI, although they're nearby. But I will do the acid test that Carl suggests.

Joe

[Markst95]

Robert- Look at you posting photos. I'm impressed! When can we Expect a youtube channel or sailing blog?

[Sea Hunt Video]

Robert- Look at you posting photos. I'm impressed! When can we Expect a youtube channel or sailing blog?

Mark:

It took my goddaughter (mia figlioccia) three (3) hours to teach me how to post a photo from a photo that is already on my computer. She also taught me how to save to my computer some, but not all, photos that I see on various websites - like the one with the disparate coral viewings. I have it all written down on paper in detail.

When I asked about possibly learning how to post photos to/from one of the photo websites - Picassa, Photobucket, etc., she just laughed and said "Roberto, baby steps, just take baby steps for now".

In exchange for the above I am taking her scuba diving.

[JWSutcliffe]

Joe:

Looks like electrolysis. I saw that a few times, nothing since I have started hanging a zinc "grouper" off the transom grounded to the aft stay fitting. Not a real issue to worry about, easily handled.

[Joe Myerson]

Joe:

Looks like electrolysis. I saw that a few times, nothing since I have started hanging a zinc "grouper" off the transom grounded to the aft stay fitting. Not a real issue to worry about, easily handled.

Skip,
The extra zinc is easy, but how can I find the source of the current?
If it's from my boat, do I pose a danger to swimmers nearby?

--Joe

[Sea Hunt Video]

Joe:

Looks like electrolysis. I saw that a few times, nothing since I have started hanging a zinc "grouper" off the transom grounded to the aft stay fitting. Not a real issue to worry about, easily handled.

Skip,
The extra zinc is easy, but how can I find the source of the current?
If it's from my boat, do I pose a danger to swimmers nearby?

--Joe

Joe:

Here is a good article on the electrical current/voltage issue:

http://www.boatus.com/seaworthy/magazin ... lained.asp

Bottom line is that in salt water there is little chance of electric shock death/drowning. Also, DC generally does not create electrical current/voltage sufficient to cause electric shock death/drowning. It's the AC voltage that gets you.

[Joe Myerson]

Thanks, Roberto.
I keep my boat on a mooring and do not have any shore-power capability. (When I bought Creme Brûlée she had a really sloppily installed shore power hookup, but my surveyor recommended that I remove it because none of the components were up to code.)

Joe