Is it OK to have monel fastners below the waterline?

[old man]

I know silicon bronze is the metal of choice but is it Ok to have monel as fastners for planks on the hull? I have a 27 year old chesapeake bay workboat. My skeg bolts are 1/2" galvanized, shaft stainless, strut and thruhull fittings bronze, and all the wood fastners on the boat are monel. I know they keep stressing keep all underwater metal the same having a stainless shaft and bronze rudder almost seems the norm these days.

[USCGRET/E8]

check this out:
http://www.coastalfasteners.co.nz/galvanic_action.htm

[hansp77]

Hello old man,
I have a 45 yr old (marine ply) boat originally fastened with monel- and with some bronze fastening as repairs, with a stainless prop shaft and bronze prop and rudder post. I had to replace my deck last year so got to check out some of the above water fastening. The bronze was totally stuffed, looked ok from the outside but was brittle and discoloured insided. The monel didn't look too good, was green etc, but was totally fine. I have kept most of the screws nails I pulled as they just looked too good to throw out.
I don't know what it is happening under the water, but from what I have been able to learn Monel is pretty damn good.
My boat has been in the water its whole life, and during that time has never (apparantly) needed sacrificial anodes (the old owner said the only time there was an issue was when a steel boat was in the pen next to him).

But I really don't know,
Someone like PAR may just come along soon and share their knowledge.

[PAR]

Monel is easily the best fastener material for the marine environment. Most of the bronzes are a good second.

[chandler]

Monel is the best and most expensive. In combination with other metals in salt water you need to check a table of galvanic reactions.

[charmc]

Monel 400 is a nickel/copper alloy (61.5%/31.5%), while bronze is mostly copper, with a small amount of tin or silicon. The high nickel content in monel makes it one of the best materials in resistance to seawater corrosion. Bronze also has good resistance in seawater.

The nickel content makes monel more costly, which might be why bronze fasteners are more common.

The one limitation for monel fasteners is on steel hulls. That particular combination can induce hydrogen charging, which makes the monel brittle. On wood planking, monel is one of the best.