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P42 Electrolysis issue... where to start?

Jan 1, 2014
149
Hunter 42 Upper Chesapeake
Looks like my 91 P42 had some electrolysis issues the past season.

looking for suggestions on what to check first. I looked at a couple of boats that were on the same dock and power pedestal and they did not show any issues so I am ruling out marina power problem and neighboring boat(s) as potential causes
 
Dec 25, 2000
4,830
Hunter Passage 42 Shelter Bay, WA
Hi Keith, no apparent electrolysis issues here. Unclear from your post, but our fixed three blade bronze prop will discolor over time, but no pitting or visible erosion; just a barnacle or two. It cleans up nicely with some elbow grease when I redo the hull every seven years. Always place two heavy shaft zincs, which last one year, with some residue left over. Our bronze through hull valves, like yours, have turned green in color, which I consider normal salt water wear over time. If conditions worsen, perhaps then you could have someone run some tests for you to see whether your marina has a serious electrical leakage issue.

Now, if your shaft zincs only last a month or two, that might be cause for concern, and a test might be worth the effort. Please let us know what you find out.
 
  • Like
Likes: Will Gilmore
Jan 1, 2014
149
Hunter 42 Upper Chesapeake
Hi Keith, no apparent electrolysis issues here. Unclear from your post, but our fixed three blade bronze prop will discolor over time, but no pitting or visible erosion; just a barnacle or two. It cleans up nicely with some elbow grease when I redo the hull every seven years. Always place two heavy shaft zincs, which last one year, with some residue left over. Our bronze through hull valves, like yours, have turned green in color, which I consider normal salt water wear over time. If conditions worsen, perhaps then you could have someone run some tests for you to see whether your marina has a serious electrical leakage issue.

Now, if your shaft zincs only last a month or two, that might be cause for concern, and a test might be worth the effort. Please let us know what you find out.
Normally I wouldn’t have been concerned but I have used a paint on the prop the last few years and this year it’s missing and I have never had the prop turn this color.
Hi Keith, no apparent electrolysis issues here. Unclear from your post, but our fixed three blade bronze prop will discolor over time, but no pitting or visible erosion; just a barnacle or two. It cleans up nicely with some elbow grease when I redo the hull every seven years. Always place two heavy shaft zincs, which last one year, with some residue left over. Our bronze through hull valves, like yours, have turned green in color, which I consider normal salt water wear over time. If conditions worsen, perhaps then you could have someone run some tests for you to see whether your marina has a serious electrical leakage issue.

Now, if your shaft zincs only last a month or two, that might be cause for concern, and a test might be worth the effort. Please let us know what you find out.
will get a pic of it an post next time I am at the boat
 

RoyS

.
Jun 3, 2012
942
Hunter 33 Steamboat Wharf, Hull, MA
Is the circuit breaker at your dock pedestal a ground fault type?
 
Sep 25, 2008
6,047
Alden 50 Sarasota, Florida
Discolor of prop - no pitting etc. the end of prop zinc mostly gone. Shaft zinc may 1/2 gone. Some green color on the thru hulls near the engine. I have 4 there 1 - eng, 1 - gen, 2 - cockpit
“Zinc mostly gone” - over what period of time?

It’s hard to tell from your description what if any problem you may have. All of that is normal over a few month period.
 
Aug 26, 2007
236
Hunter 41DS Ventura, California
The fact that the zinc(s) is depleted means that it is doing it's (sacrificial annode) job. IMO, the rest of the "issues" as described seem to be normal. I had an electrolysis problem and my zincs didn't work- my prop was destroyed. There is quite a bit of info here:

Galvanic Corrosion

I would highly recommend buying a tester. I now test my boat on a regular basis to detect problems. Good luck
 
  • Like
Likes: Will Gilmore
Oct 19, 2017
6,690
O'Day 19 Littleton, NH
Normally I wouldn’t have been concerned but I have used a paint on the prop the last few years and this year it’s missing
Same paint, same color, same primer?

Could you have a bearing problem and be generating excessive heat under way?

How much sailing and where to, have you been doing, compared to previous years?

“Zinc mostly gone” - over what period of time?
:plus:

-Will (Dragonfly)
 
Dec 25, 2000
4,830
Hunter Passage 42 Shelter Bay, WA
Never painted our prop, but do apply a liberal coat of zinc oxide to the prop, which helps for a season or two. Each year a diver checks all underwater gear. The prop does turn dark, but cleans up each time I haul the boat. Again, no apparent damage to the bright work below the waterline.
 

eianm

.
Jul 7, 2010
492
Hunter 42 Sydney
OK, had a very similar problem that some of you may recall I posted about.I was burning through shafts anodes in about 8 weeks , where for the previous 10 years of ownership I got around 18 months! I eventually , after months a searching found the main earth point at the engine block was high resistance- pulled it down and cleaned very thoroughly all lugs , bolt, nut and face surface- problem fixed!
My boat is a 1991 model, so at 30 years, i guess one should expect this sort of issue , even on the best maintained vessel!
Let me know if this fixes your problem.
 
Dec 25, 2000
4,830
Hunter Passage 42 Shelter Bay, WA
after months a searching found the main earth point at the engine block
Hi Eian, was going to suggest that in an earlier post, but glad you did. Where is that main earth point mounted on the engine?
 

eianm

.
Jul 7, 2010
492
Hunter 42 Sydney
below the starter motor- i am going to my boat tomorrow- will take a pic and post
 
Dec 25, 2000
4,830
Hunter Passage 42 Shelter Bay, WA
Thanks, Eian. Which access is the best way to see that wire, through the main door hanging over the engine? Back when I installed the Link 1000 shunt, I followed the main ground into a stringer, but could never find where it came out or where it connected. I figured it had to be on the engine somewhere, but...

I hope my Axiom post helps you out. Please let me know the outcome of what you learn.
 

eianm

.
Jul 7, 2010
492
Hunter 42 Sydney
Terry- was intending to go to boat today , but have to delay- will post image asap- the earth point to which i refer is right inside main engine room door- bottom rhs- but will post a photo
 
Jan 1, 2014
149
Hunter 42 Upper Chesapeake
Puesta del sol- what did you find?
So far I have been working on a water flow search and have not started looking at grounding issues. The water flow has me perplexed. Have not found any blockage so far. The engine overheats at around 1800. Couple of pictures of my prop and shaft. From 2011-2018 I used to lose the zinc on the end of the prop and about 1/2 the shaft. Upper Chesapeake bay .. in the water from April - mid -Dec. last year the lost very little of the zincs. This year. The zincs look more like 2011-2018. The weird prop discoloration and loss of the petit prop paint is concerning.
 

Attachments

Jan 1, 2014
149
Hunter 42 Upper Chesapeake
OK, had a very similar problem that some of you may recall I posted about.I was burning through shafts anodes in about 8 weeks , where for the previous 10 years of ownership I got around 18 months! I eventually , after months a searching found the main earth point at the engine block was high resistance- pulled it down and cleaned very thoroughly all lugs , bolt, nut and face surface- problem fixed!
My boat is a 1991 model, so at 30 years, i guess one should expect this sort of issue , even on the best maintained vessel!
Let me know if this fixes your problem.
Which lugs, bolts etc do you mean?
 
Jan 1, 2014
149
Hunter 42 Upper Chesapeake
Same paint, same color, same primer?

Could you have a bearing problem and be generating excessive heat under way?

How much sailing and where to, have you been doing, compared to previous years?


:plus:

-Will (Dragonfly)
Similar amount of sailing. Have been having engine overheating issues.. pretty sure this is a water flow issue

same paint for years
 

RoyS

.
Jun 3, 2012
942
Hunter 33 Steamboat Wharf, Hull, MA
This will not solve your problem but may be helpful in preserving you prop zinc. Paint a stripe on the zinc just outside of each of the prop zinc fasteners. In your photos you will see that that area on the prop zinc is considerably corroded exposing the sides of the fasteners and there is a risk of the zinc coming loose. With the painted stripes your prop zinc will then dissolve more evenly and last much longer. I also put two new shaft zincs on every spring because they are cheap and not because they are completely dissolved. I probably get three or four years out of my max prop zincs with the stripes. My zincs are not dissolving as fast as yours. Suggest also that you test your galvanic isolator.