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Dudes and Dudettes,

I need a bit o' advice. I have a Pearson-O'day 290 with a Westerbeke diesel. Not that that matters really. I installed a single shaft zinc in 2018 only to find it missing at haul out. So, belt AND suspenders, I installed 2 in the spring of 2019. If I hypothetically had to dive on my prop because the neighbors' dog backed over my painter in the middle of Penobscot Bay with a building south westerly, only to discover A) 10 feet of painter and 20 feet of pot warp wrapped around my shaft and B) no shaft zincs to be found (and a 25 foot great white sighted and filmed by the coast guard not 5 miles away while I was in the water wearing my finest harbor seal costume) . . .where was I going with this diatribe? Oh, yeah, anybody have a good way to keep those beasties on the shaft so I don't have to entice sharks!

Delectable in Maine
 

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Could any steel have arrived in the water near where you keep the boat since this problem began? I assume you didn't have it before?
An engine block, steel boat or a bunch of old concrete rubble with rebar used as a breakwater? Those are common culprits in this scenario.
Also a bad ground on your shore power if you have it.
 

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Dudes and Dudettes,

I need a bit o' advice. I have a Pearson-O'day 290 with a Westerbeke diesel. Not that that matters really. I installed a single shaft zinc in 2018 only to find it missing at haul out. So, belt AND suspenders, I installed 2 in the spring of 2019. If I hypothetically had to dive on my prop because the neighbors' dog backed over my painter in the middle of Penobscot Bay with a building south westerly, only to discover A) 10 feet of painter and 20 feet of pot warp wrapped around my shaft and B) no shaft zincs to be found (and a 25 foot great white sighted and filmed by the coast guard not 5 miles away while I was in the water wearing my finest harbor seal costume) . . .where was I going with this diatribe? Oh, yeah, anybody have a good way to keep those beasties on the shaft so I don't have to entice sharks!

Delectable in Maine
Are you in a slip ? Do you have shorepower connected ? Is this a new problem ? How long did zincs last before this problem began ? Have you seen any other corrosion on prop blade tips, shaft or any other under water metals.

Any response would be a WAG without at least some of above information.
 

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While something seems wrong, keep in mind the goal is not to save money on zincs. I roll my eyes when I hear the opposite. Bragging that zincs last for multiple seasons. They're probably not working, if they do. So bright side, yours are doing their job.

The two most common things that cause premature corrosion are a shore power fault (yours or a neighbors or the marina) or a DC ground problem aboard your own boat. Both very difficult to find, but as BP said, a bit more detail would help.
 

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Ok Don - as the others have said, you definitely have some ‘splaining to do...

1.) were the zincs gone as in gone, stolen, disappeared without a trace, nuts and bolts and washers and all, or gone as in mostly or majorly eaten away?

2.) how much rum did it take for you or your neighbor’s dog to be in the boat on the water backing down on painters in Maine in January!
 
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I’ve had the same problem, shaft throws the zincs. They are NOT getting eaten, they get thrown off. Also I have a very short shaft exposed so there is really interesting one type that fits.

Plan B was to paint my prop with Pettit RusLoc Paint, a bunch of coats. The paint is a one part urethane with about 90% aluminum solids. Aluminum is not zinc, but pretty close and it seems to be doing the trick. If it’s worn I just sand it down and put on some more coats.

I e been told by a reputable surveyor that he has seen others do this and at least one cat charter company in Florida does.

I have a steel boat and am seldom at a dock and almost never connect to shore power.
 

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If I'm following, you're saying the aluminum paint acts as an anode? I'm pretty surprised and wonder how one would know, if the bronze is so covered, you couldn't detect the telltale pink leaching. Any chance your metal boat has other zincs that may be taking up the cause?

In any event, some brands of zincs have brackets molded inside, so I'm surprised that could be tossed off, if not worn down to nothing. Are you thinking your zincs split?
 

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Dudes and Dudettes,

I need a bit o' advice. I have a Pearson-O'day 290 with a Westerbeke diesel. Not that that matters really. I installed a single shaft zinc in 2018 only to find it missing at haul out. So, belt AND suspenders, I installed 2 in the spring of 2019. If I hypothetically had to dive on my prop because the neighbors' dog backed over my painter in the middle of Penobscot Bay with a building south westerly, only to discover A) 10 feet of painter and 20 feet of pot warp wrapped around my shaft and B) no shaft zincs to be found (and a 25 foot great white sighted and filmed by the coast guard not 5 miles away while I was in the water wearing my finest harbor seal costume) . . .where was I going with this diatribe? Oh, yeah, anybody have a good way to keep those beasties on the shaft so I don't have to entice sharks!

Delectable in Maine
Don - if your problem is the zincs going walkabout and not being eaten, try seating them with a brass hammer or small sledge as you tighten the screws.....tap the zinc lightly on each side after you tighten the screws until it seats fully and you can’t get any more bite on the screws.

Mainesail has a good article about the whole process on his website:

https://marinehowto.com/anode-installation-best-practices/
 
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I'm going to recommend against swimming in shark infested waters wearing your finest harbor seal costume, or even a shabby one...
 

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You say you replaced your zinc in 2018? You know it is 2020 now right? If you are in a marina you cant expect multi years life. At our club every boat is tested for voltage leaks annually, and I still have to replace my zincs every year. If you leave them too long they will eventually fall off because the material is much thinner at the bolt holes, so the bolts could fall off before the bulkier parts of the zinc are completely dissolved.

If they are just falling off prematurely then you are either not tightening them enough, or you are not using lock washers or nyloc nuts on them.



Sent from my SM-G960W using Tapatalk
 

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For what it’s worth, I can just barely squeak out a full 7 month in water season. The prop zinc really can’t make it that long. The shaft is at minimums. I usually do a change half way through, but sometimes stretch.
 

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I have posted a couple of threads on my issue with sacrificial anodes. I was loosing two after 6 weeks! (see https://www.sailnet.com/forums/electrical-systems/301153-six-weeks-zincs-toast.html)

After breaking down and spending ~$200 on a silver nitrate half-cell, and then spending about an hour testing each circuit with my DVM and the reference cell I found the problem. I discovered that the electric fuel/lift pump to my Universal/Westerbeak M25 was tied to the bonding circuit via the fuel tank. Every time that I turned the key to "ON" the anodes would start fizzing away. I am blaming @Don L. I could never have found this without the half-cell.

This year the anodes were only about 15% depleted after about 4 months of use.
 
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while anchored in barra de navidad i had a zinc last me a year once.. yes ONCE. usually they are well consumed in about 5 months.... in some marinas 3 months..once was 2 months.. i had my electrical system checked that month...san diego mine only lasted 3 months , regularly. on a mooring...
might want to check your zincs more frequently than once every 3 years as they donot last long under normal marina conditions
 

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Discussion Starter #14
Hey Guys,

Thanks for all the info. My assumption is that the zincs are being thrown somehow. I think what I'll do is seat them with a hammer as suggested this year and grit my teeth, prep for shrinkage and dive every few weeks to get a handle on what's really happening. If they really are corroding at warp speed then I do have a REAL problem. If not, then it's a mounting issue. Up here we hit a lot of sea weed and flotsom, not to mention wrapping the occasional pot warp. I'm guessing that's not easy on those tiny #8 machine screws that are supplied.
 

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Mine always flew off.
If you are worried about it,run an external wired zinc fish and lay it over the side into the water.
Unclip it from the shaft before you start the motor !
 
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