Anode Studs - Stainless or Galvanised?

[gandy]

Hi,

I need to replace the hull anode, it's a standard pear shaped bolt-on, on a GRP hull. As usual by the time the anode needs replacing, the ends of the studs and particularly the mounting nuts are pretty corroded. Thinking about it I suppose the galvanising would have eroded in the same way that the anode, so would have disappeared pretty quickly.

What are the thoughts on using stainless instead? Any benefit, or would it screw up something?

Thanks, Tony S

 

[macd]

What are the thoughts on using stainless instead? Any benefit, or would it screw up something?

Stainless (316/A4) is perfectly OK.
See: https://mgduff.co.uk/support/knowle...rp-hull-or-should-i-use-the-zinc-plated-bolts

Although galvanised bolts may lose their zinc coating, they are substantially protected by the anode they're holding in place.

 

[VicS]

Hi,

I need to replace the hull anode, it's a standard pear shaped bolt-on, on a GRP hull. As usual by the time the anode needs replacing, the ends of the studs and particularly the mounting nuts are pretty corroded. Thinking about it I suppose the galvanising would have eroded in the same way that the anode, so would have disappeared pretty quickly.

What are the thoughts on using stainless instead? Any benefit, or would it screw up something?

Thanks, Tony S

Both are available ( although they are BZP rather than galvanized ITYWF)

Stainless look flashier and are popular with owners of flashy mobos. I expect they cost more?

They topic was raised on here very recently. An advanced Goggle search of the forum should find what was said then and on numerous occasions in the less recent past.

Your choice at the end of the day

 

[RichardS]

What are the thoughts on using stainless instead? Any benefit, or would it screw up something?

Thanks, Tony S

My saildrive anodes are secured with stainless steel bolts direct from Yanmar. The combination of zinc and stainless seems to work very well.

Richard

 

[forelle541]

ASAP sell the stainless ones.

 

[rogerthebodger]

I used stainless A4 studs to fix all anodes onto my steel hull.

 

[VicS]

Teaching eggs to suck grannies perhaps but:

When stainless steel and zinc are coupled in seawater, because the stainless is cathodic relative to zinc, it will tend to loose its protective oxide film but the zinc will protect it in much the same way that it protects mild steel.

Once out of the water the st.st reforms its oxide film.

This is why some galvanic series charts show two different electrode voltages for stainless steels. One when in the "passive" condition with its oxide film and the other in the "active" condition without the oxide film.

 

[PCUK]

If your nuts and bolts are corroding your anodes are not working correctly.

 

[vyv_cox]

The steel ones are protected under water but not in air, which is where most of the corrosion takes place. Stainless ones will not rust in air.

 

[gandy]

If your nuts and bolts are corroding your anodes are not working correctly.

I did wonder about that, but in all the time we've had the boat we've not seen any corrosion on the non-ferrous underwater parts. Setting aside the fact that all this galvanic stuff seems to be a black art, my reasoning was that since zinc is eroding off the anode, why would it not erode at the same rate from the galvanised fixings?

In terms of the immediate work, I've discovered that I already have a couple of spare galvanised (or BZP) studs. So if it looks like they could do with changing I will use them this time. Maybe look to getting stainless next time the anode needs changing.