Prop nut anode

JokersWild

JokersWild

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Hi. Boat (Beneteau 331) lifted out for a few weeks ashore yesterday. Generally looking very good underneath, but prop nut anode completely disolved. New prop nut anode was only fitted at the start of July, so this means it's lasted 6 months. Yes, I'm in a marina, and yes, I'm normally on shore power, but 6 months sounds like a pretty short time? At that rate, if she goes back in at the start of March, she's going to need another new one by the end of August, when I would have no plans to hoist out again anytime near then.

Does 6 months seem very short to you?

Any other thoughts on how to avoid this happening so fast. BTW hull anode barely corroded (and connection was checked last time she was out).

:confused:
 
Sounds like you need a galvanic isolator. Check that the hull anode is actually bonded to the stern gear as well, not just to the engine - it needs to be bonded to the shaft to protect the prop by a bridge across the coupling unless it is a solid coupling.
 
JokersWild said:
Hi. Boat (Beneteau 331) lifted out for a few weeks ashore yesterday. Generally looking very good underneath, but prop nut anode completely disolved. New prop nut anode was only fitted at the start of July, so this means it's lasted 6 months. Yes, I'm in a marina, and yes, I'm normally on shore power, but 6 months sounds like a pretty short time? At that rate, if she goes back in at the start of March, she's going to need another new one by the end of August, when I would have no plans to hoist out again anytime near then.

Does 6 months seem very short to you?

Any other thoughts on how to avoid this happening so fast. BTW hull anode barely corroded (and connection was checked last time she was out).

:confused:
Click to expand...
My Bene 351, same thing used to happen, I was on a pile mooring, so nowt to do with the marina. I found that a good trick wat to tihten the screw up tight on the new one and then fill the hole up with silicon. When the anode starts to wear, the screw comes loose and away goes the anode. The silicon stopped the screw disappearing and the anode stayed on till it was all eaten up.
Stu
 
Sounds like I can combine these two solutions. Tranona, presumably I can check this bonding by crawling around internally and looking at where the wires are bonded visually. No point in attaching a meter thingy? (you can tell how techy I am, I suspect!)
 
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Tranona said:
Sounds like you need a galvanic isolator. Check that the hull anode is actually bonded to the stern gear as well, not just to the engine - it needs to be bonded to the shaft to protect the prop by a bridge across the coupling unless it is a solid coupling.
Click to expand...
Stewart
For some reason the VP installation on my 351 had an isolated transmission with warning signs not to bond the transmission to the engine (to do with bearings conducting electricity?) I presume it is the same on this one?
Stu
 
I contacted Fox's about the prop anodes, they reckoned they lasted 3 months, so if you got 6, did well by their account.
I have a shaft anode fitted as well, just enough space to get a shaft anode on between the prop and the cutless bearing.
The boat I have was retrofitted with a hull anode by the PO, which is bonded to the engine block, With engine stopped, I have continuity between the block and the shaft, but I think that this could be lost with the shaft turning.
Im in the process of fitting an "electro eliiminator" (I think thats the right name) at the moment.
You should fit a galvanic isolator or transformer as suggested
 
I was having same problem, fitted galvanic isolator which seems to have done the trick (boat is in marina on shore power).
 
Ah, good, have plenty of space in big cockpit locker, next to all the electrickery gadgetry that I half understand. Fitting might be a job for a proper marine elec firm I suspect!
 
skipper_stu said:
Stewart
For some reason the VP installation on my 351 had an isolated transmission with warning signs not to bond the transmission to the engine (to do with bearings conducting electricity?) I presume it is the same on this one?
Stu
Click to expand...

Not sure why that would be. In the saildrive application the engine is isolated electrically from the drive so if you are going to fit an additional anode it needs to be bonded to the drive casing inside the boat. On a shaft drive, bond to the gearbox casing with a bridge over the coupling seems to be the normal method.
 
Puzzled ..

Was going through old boat papers yesterday, and previous owner had ordered a galvanic isolator! So checked the boat today, and there it is in a corner of the cockpit locker (it's a lot smaller than I thought!). It looks to be wired in correctly in the way that the simple diagrams suggest on the sales pages.

So, given that I already have one, should prop nut anode really have dissolved in 6 months?
 
Tranona said:
Sounds like you need a galvanic isolator. Check that the hull anode is actually bonded to the stern gear as well, not just to the engine - it needs to be bonded to the shaft to protect the prop by a bridge across the coupling unless it is a solid coupling.
Click to expand...

I second that, you definitely need a galvanic isolator if you leave the boat on shore power for any time. Prop nut anodes are quite small in comparison to the props they protect, which themselves are much higher on the galvanic scale. On a shaft driven boat some extra protection can be had by means of a shaft anode fairly close to the P bracket. I have always managed to get a year out of a prop anode since fitting the galvanic isolator. I bought mine from this company.
 
JokersWild said:
But I've got a galvanic isolator! Admittedly I only found it today, but it looks professionally installed. Should I get a bigger one?! Or two?!
Click to expand...

No. Think you need to go back to fining out what your hull anode is supposed to do - but does not seem to be doing.
 
nigelmercier said:
I think Stu has hit the nail on the head. It is more likely the anode has dropped off.
Click to expand...

My experience too. My first anode disappeared in about 3 months along with the fixing screw.
After that I used weak Loctite on the screw and filled the hole over the screwhead with stiff grease. Anode then lasted a year.

QUESTION to OP - did your screw disappear as well as the anode, you haven't said?

I repeat someone else's point that if it's a Volvo, on most of them the gearbox is electrically isolated from the engine and they tell you not to bridge it. In this case surely a hull anode has no relevance? You can put a clamp-on one on the shaft though (with Loctite or that may disappear too!)
 
I think that the fixing screw is still there - assuming it has an allen key type end to it? There are tiny fragments of the remaining zinc attched. I wonder if I can do a photo .... ooh yes .... July and now should be below ....
 
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