Do your shaft anodes disappear quickly?

[Medskipper]

Year after year I put new zinc shaft anodes on and the following year on lift out there is never a trace of them! I suspect that they fall off after just a few short months leaving me no protection or certainly less as I also use hull and trib tab anodes in a my salt water environment.

Last year I tried a little experiment! I dabbed a little anti foul
on the bolts and thin area where the shaft anode clamps together. This year when my boat was lifted both anodes where still bolted on and the main guts of the anodes, i.e. the thick middle bit had almost gone, so I now know that I can make sure of shaft/prop protection for the whole year just by covering the bolted areas! Maybe you already knew that, but if you didn't try it!

All the best

Barry

 

[homa]

By painting the anode you are reducing its effectiveness.
Try adding a second anode.

I found my single shaft anode didn't last the first season.
Last year I put 2 new anodes on and found one wasted and one half wasted. I am now happy that I have sufficient protection on my boat with 2 anodes for the season.

 

[Skyva_2]

Sounds a good tip Barry. I just replaced my 2 shaft anodes and it was a miracle they were still attached with the amount of erosion that had taken place.

But the huge ring anode and nut anode on the new Gori prop were both as new, which was a surprise. The prop itself is as new, still polished metal after a bit of light scraping, which is even better.

Last year I also fitted a galvanic isolator, which appears to have had no effect on the shaft anode erosion.

 

[michael_w]

Don't forget that a shaft anode doesn't offer any protection to your P-bracket or rudder stock, if the latter is immersed.

Unless the P bracket/rudder is bonded to the shaft.

I've had to remove the engine and the fuel tank on my boat to get to the P bracket so I can bond it to a hull anode. Damn thing was badly corroded but luckily the builders fitted such a huge P bracket there was metal to spare.

 

[VicS]

Shaft anodes being mounted right next to a large area of a copper alloy, namely the propeller, are going to be eaten away quickly. If they aren't then there is probably not proper contact with the shaft. They will do that regardless of whether or not they are actually serving any useful purpose.

 

[wiggy]

I find that if I leave my shaft anode in my garage they last for absolutely ages!!!!

 

[swampthing]

This happened on my tri year after year, I thought they were vibrating loose. So I epoxied the threads and monitored every few weeks with an underwater camera. It was wasting fast. I then bolted one about 60mm dia on hull near prop and problem was solved.

 

[PetiteFleur]

I also now fit two shaft anodes and they are both well waisted by lift out. I do make sure that the bolts are tightened, then knocked with a hammer a couple of times and retightened until you cannot tighten no more.

 

[paulwitney]

I try to extend slipping and anti fouling to the max so tend to scrub the bottom of the boat every fortnight or so after twelve months. (as long as the water is warm enough) Usually get between 15-18 months before I relent to the inevitable and is strange how the anode seems to drop off the shaft a week before going up on the slips. (Honestly it was there last week!!!) Really was though, but has been interesting tightening bolts on anode while gasping for air through the snorkel when anode came loose on the shaft.

 

[shanwick]

During my last 2 lift outs I also found no trace of the shaft anode and only a small amount of prop anode left.

Having left the boat disconnected from shore power over the last 12 months, on lifting out this week both anodes were almost fully intact.

I won't be leaving the boat connected to shore power again!

 

[Phoenix of Hamble]

Would be false economy for me..... saves a few quid on anodes, and leaves your batteries exposed.... I'd rather have a float charge and replace the anodes every season....

 

[VicS]

[ QUOTE ]
I won't be leaving the boat connected to shore power again!

[/ QUOTE ]

You obviously need a galvanic isolator.
Follow the links on this page to read all about the problem and what causes it and how a GI works to solve the problem.
They are available from the electrical specialists and many chandlers.

I you are so inclined and know what you are up to then there are even instructions here for making a basic one.