White Chalky Buildup on Prop and Shaft

[Natedogg]

Hey all, reaching out to try and get some input after finding little info from the rest of the Internet on this issue. My wife and I bought our O'Day 34 on the gulf side of Florida and moved it over to Miami where we keep it in a slip at a local marina. When we bought the boat there were lots of fouling organisms we had to clean off, but the shaft and prop were relatively clean. Now the shaft and prop (and newly attached zinc collar) are getting a thick white chalky buildup about 1/8" thick covering all surfaces. After noticing this the first time I cleaned the prop and shaft thoroughly with a brush and a plastic scraper, and was able to break and scrub the calcium-like buildup off completely. 1.5 months later it's back and just as thick, though not quite the full coverage from before. Now I'm confident it's not any sort of marine fauna buildup or remnant, but could the addition of the zinc have caused this? Or is it indicative of some stray current or other electrical issue somehow causing this scaling on the bronze prop and steel shaft? Any input you have is appreciated, so far it's been a mystery!

[seahag]

You might try reading a multimeter on the propshaft if you suspect an electrical charge. I've never tried that but others here have suggested that the propshaft is where many boats build an electric charge and it can introduce that into the adjacent water. I've also had people tell me they can read a charge in the water itself; again I haven't tried that.

[Calliste6]

Ahoy Natedogg , I too have that scale build-up problem on my Aquamet 22 SS prop shaft . What you can see and clean from the outside doesn't bother me as much, as what accumulates between the grooves on the cutless bearing , just inside the deadwood . This calcium deposit destroy's the cutless bearing rubber, when I put the motor in gear either forward or reverse . I would like to replace that rubber cutless bearing with a long life plastic one ( Vesconite Hilube ) ,,,, are there other readers out there that have a remedy for this problem, other than use the boat more often , or store the boat on hardstand ?

Many thanks Bil , for this thread notice .

[GordMay]

Greetings and welcome aboard the CF, Calliste.

[JOHNMARDALL]

Hello Nate,

I've seen that kind of scaling on shafts and props when another underwater component had current leaking to it, usually through a short circuit from a wire with abraded insulation, so the shaft and prop became the other end of the galvanic circuit and were being plated with gray slag. Is there anything on the underwater hull, such as a thruster drive leg or even through-hull, which is corroded and is acting as an anode?

Best Regards
John Mardall
Vetus Maxwell Group

[Wulf]

We had the same thing on our boat. I discovered that 12volt negative wire from battery charger was tied to bonding system and charger's bonding wire hooked up to the negative side of the 12 volt system. Switched wires and all settled down.

[buzzstar]

Sounds like it must be electrical (galvanic). Possibly relate to the marina, but how is your zinc itself doing. Try the suggested remedies, and if it comes down to it, maybe a different marina, perhaps with fewer stray currents, could make a difference -particularly if you can compare build up between marinas over a given length of time (preferably short if you can just be a visitor at one).

[Natedogg]

A guy couldn't ask for faster responses, thanks everyone! So I tried to check what I could after work after reading your comments.
Seahag, I jumped in the engine room with my new multimeter (birthday present last week!) and took a voltage reading on the drive shaft and got a reading of about 34. This seems like a lot for the shaft to have (does metal carry a readable charge on its own? Sorry, like I said it's a new tool for me), maybe indicative of the problem?
Calliste, we're hauling out in a month, we were planning on replacing the cutlass bearing so I'll take a good look at the current one and see how it's fared w/ this issue.
John, I jumped in to take a look again at everything around the prop and didn't see major pitting/corrosion on any metal bits. Once I knocked a layer of the growth off the zinc it looked pretty normal. Not sure what the rate of corrosion on it should be but it's been in place for 3-4 months and doesn't seem too beat up yet. During the bottom clean last weekend the thru hills looked normal too. The strut isn't getting the same buildup, but maybe that's because it's separated from the issue by the cutlass bearing? The strut seemed normal, no pitting. I actually took some u/w pictures and will post tomorrow when I get my laptop to some internet.
Wulf, I'm new to electrical work but I'll do some research on the bonding system and see if that looks promising (this may be where I play it safe and get a marine electrician to show me what's up, try learning from that instead of the classic trial by error
Buzzstar, after the 10 month waiting list for a slip I'm hoping it won't come to switching marinas. My neighbors haven't had the same issue so I'm thinking it's probably something going wrong onboard, but we'll see.

I'll post pictures of what the prop, shaft, and zinc are looking like, but if any of this info has given anybody any further idea what could be amiss I appreciate all the help!

[buzzstar]

Thanks for the information in the collected response. I have no answer, but it still sounds electrical, and your boat is receiving the stuff rather than contributing. Sort of like when you plate something. There is a source for the plating. Let us know -it is an interesting problem from the sidelines. Fair winds and proper wiring.

[Natedogg]

Alright, I attached the photos from yesterday showing the prop with the chalky buildup, the strut (with some growth but not too much in the way of corrosion), the zinc and shaft with buildup, and then the zinc and shaft after a quick scraping. If anyone has any new ideas let me know. In the mean time I'm working on some electronic wires inventory to try and identify if everything's connected where it should be!

[seahag]

Nate, if you turn off your shore power and then read it what do you get? The guy who told me about voltage found in the water itself said there are times and places in our harbor that hit much higher voltage than your 34. He said he found 110 once! Divers have gotten badly shocked, even killed by stray current. A lot of people who leave their boats here drop a zinc attached to a wire and then attach that to the shaft or motor. Obviously if you attach to the shaft you'd want to remember to remove it– tape a note to your starter button or key to remind you or have another method that works for you in place. You might ask your neighbors if they will let you check their shaft readings and find some directionality about the current path, i.e. Further from a dockside transformer it reads less, or closer to a problem boat it reads more. Anyway good luck and hope it isn't your own boat but you can figure that out easily.

[Seeking Solace]

34? 34 what? Volts? Was it AC or DC? How are you going about using your meter? What are you using for positive and negative probing?

As others have already said it is very likely an electrical issue. Have you checked between your batteries and equipment to see if it's drawing any current? If everything is off it should be nil. Turn off all breakers and pull the battery terminal and check for current being pulled. Something may not be on a breaker to begin with. Also, remember that shore power may not have a good ground too. Make sure it's disconnected.

Having a qualified marine electrician look at things is a very wise decision if you are not familiar with the basic principles. You can very easily damage your meter, other electronics, and yourself if probing improperly or with improper settings. Batteries and shore power can both produce lethal voltages.

I strongly encourage you to use your new toy and familiarize yourself with it's functions and proper uses, most importantly it's limitations. If you insist on doing it yourself, look for things attached to thru hulls and where they go. You'd be surprised at how something as small as the clock in the radio or the memory power being drawn can do exactly what your boat is doing in a fairly short time.

Good luck! Let us know what you find.

[thinwater]

Originally Posted by Natedogg

Alright, I attached the photos from yesterday showing the prop with the chalky buildup, the strut (with some growth but not too much in the way of corrosion), the zinc and shaft with buildup, and then the zinc and shaft after a quick scraping. If anyone has any new ideas let me know. In the mean time I'm working on some electronic wires inventory to try and identify if everything's connected where it should be!

Nate, am I correct in that someone installed 2 different anode types? I notice there is growth on one and not on the other. That's not normal--anodes should not have growth, not like that. I'd start with ALL fresh anodes. Are the others?

[Natedogg]

Well I've found plenty of shortcuts done w/ our wiring that I intend to fix/get fixed one at a time through this hunt, but for now I think the problem is on hold. The boat came out for dry dock for a bottom job and some other items, and the strut did look a little more worn than I'd previously thought. The most likely culprit seemed to be something to do with the bonding wire given that there was a loose copper bonding wire attached to the engine intake thruhull where the strut bonding wire was also attached. I suspect at one time it had been attached to either the batteries or the engine negative ground (feel free to debate, this was Internet hunting and best guess work). Not sure what the engine negative ground looks like and didn't see anything obvious so I attached the loose wire to the negative peg on the battery and after the last few days on shore power there hasn't been any buildup of my chalky calcium ulcer maker. I'll check again in a week and see how it looks and update the thread if it is still clean/not clean. Fingers crossed! If any of this sounds foolhardy feel free to let me know, I really appreciated all the feedback from this post!

[Blue Crab]

That's a nightmare Cap.