Securing anode to hull - what metal?

[skyflyer]

About to replace my pear shaped hull zinc anode. This comes on a metal strap with holes at each end

the existing anode is secured by nuts onto two threaded studs that go right through the hull and have double nuts on inside

last time I did this the nuts came off relatively easily but this time they are rusted solid and I think I may have to cut them off and replace the studs
If so do I use stainless or BZP.

I guess BZP was used before and obviously the zinc plating has become part of the anode and been lost, hence the heavy rusting

but I have a vague memory that stainless and zinc have a galvanic reaction

Finally if I do replace studs, what sealant would you recommend to ensure no water ingress through the holes where they pass through hull

many thanks

 

[davidmh]

You can get McDuff anode bolts either stainless or galvanized. I have always used Galvanized. They do tend to corrode the trick is to grease the threads well. I have my boat out each winter and find that there is no problem taking the anode off if you di it as soon as it is ashore, the rusting seems to happen during the winter.

David Mh

 

[VicS]

About to replace my pear shaped hull zinc anode. This comes on a metal strap with holes at each end
the existing anode is secured by nuts onto two threaded studs that go right through the hull and have double nuts on inside
last time I did this the nuts came off relatively easily but this time they are rusted solid and I think I may have to cut them off and replace the studs
If so do I use stainless or BZP.
I guess BZP was used before and obviously the zinc plating has become part of the anode and been lost, hence the heavy rusting
but I have a vague memory that stainless and zinc have a galvanic reaction
Finally if I do replace studs, what sealant would you recommend to ensure no water ingress through the holes where they pass through hull
many thanks

Reasonably good video here ... (They omit to tell you to fit nuts on the inside before attaching the anode to the outside though )

the sealant they recommend ( Arbokol 1000 ) is a polysulphide


BZP or stainless steel studs is your choice. Pros and cons as you have already noted.
There will be a very small amount of galvanic action between st. st and an anode ,
BZP will lose its Zn plating but be protected by the anode. It will rust when the boat is lifted.
The price difference may be the main consideration

 

[Pye_End]

From MGDUFF website: 'You can use either zinc plated or Stainless 316 mounting bolts. The stainless bolts will place more of a demand on the anode but this is not a problem. '

I always understood zinc plated was the preferred choice, but sounds as though this isn't necessarily so.

 

[VicS]

From MGDUFF website: 'You can use either zinc plated or Stainless 316 mounting bolts. The stainless bolts will place more of a demand on the anode but this is not a problem. '

I always understood zinc plated was the preferred choice, but sounds as though this isn't necessarily so.

ITYWF that owners of shiny power boats prefer shiny fittings rather than rusty ones.

Rusty anode studs on a boat that flies like dung off a chromed shovel would not look right would they.

 

[Momac]

ITYWF that owners of shiny power boats prefer shiny fittings rather than rusty ones.

Rusty anode studs on a boat that flies like dung off a chromed shovel would not look right would they.

Bear in mind as the iron oxide develops it expands so can cause damage to the surrounding material.
So not just a cosmetic thing.
From a structural engineering perspective BZP is not considered a suitable protective coating in an exterior environment. Galvanised is better.
But in sea water and for a small number of fixings why not use 316 stainless steel ?