hull anodes & mixed metals

[EuanMcKenzie]

My yacht, a Hallberg Rassy Rasmus, has no external hull anode and I don't believe it ever has but I am now concerned as I am replacing sea cocks with stainless ball valves onto hull fittings that are bronze. Is this ok or a bit of a no no.

Shops don't seem to sell PBronze ball valves and lifting stainless ones from site is easier anyway.

Also, I have replaced the rudder shaft and pins with a stainless shaft but some of the rudder pintels are still phosphor bronze as they are buried in the keel.

Should I:

Ignore the problem and hope it takes a long time to bother me (the prop seems ok) or start buying anodes and bonding the whole lot together just in case.

So far i have added an anode to the the main rudder pintel just in case

The engine, an MD21A has anodes in the heat exchanger and these seem to have done a good job over the years. It is not linked to the outside via a permanent anode. I have the heat exchanger in bits for cleaning and it is ok.

The prop shaft is stainless and the prop phosphor bronze. No anode again nor space to fit one. no apparent issues either

Is my Rasmus normal, do others have lots of anodes?

What is the general view on this one. I have a 35 year old engine that is in good running order so something must be right.

we're not very gizmoed, the boat lives on a swinging mooring for the summer and is rarely plugged into shore power.

DIY solutions only of course. Your thoughts and advice would be apreciated on this one

Cabatach

 

[VicS]

Stainless steel and bronze are fairly close in the galvanic series and are therefore compatible with each other and neither should need anodes to protect them.

Whether stainless steel is a good choice for seacocks might be a bit debatable. ASAP supplies market the range of Vetus bronze ball valves

The anodes in the heat exchanger are the correct way of protecting that. An exterior hull anode will do no good whatsoever.

Should you ever move to a marina and want to leave a shorepower connection plugged in (not necessarily in use ) then fitting a galvanic isolator if you do not have one would be wise.

 

[alan006]

Re: hull anodes & mixed metals

With regards to the stainless shaft and the bronze prop, if you choose not to protect it with anodes then you risk shortening the life of the prop. This could be to some extent be balanced by regular inspection to hopefully detect early signs of problems (if indeed they do develope).
What would concern me about the stainless valves ( apart from galvonic action with the bronze skin fittings, which would hopefully be detected by discolouration of the skin fittings) is the possibility of the stainless valves suffering from crevice corrosion. If this was severe (and it would be invisable from the outside) then this could cause major problems, perhaps someone else knows more about this.

 

[VicS]

Re: hull anodes & mixed metals

[ QUOTE ]
if you choose not to protect it with anodes then you risk shortening the life of the prop.

[/ QUOTE ] A good bronze ( copper/tin alloy) prop should be perfectly OK. It's brass or manganese bronze that can dezincify ( Manganese bronze actually being a high tesile brass (copper/zinc) containing a small %age of manganese (CZ114)

 

[boatmike]

While Bronze or DZB would arguably be better for ball valves, stainless should not be a problem. If your external fittings are genuine bronze they should be OK. You should watch your prop and shaft carefully if you have recently replaced them. Especially watch the shaft inside bearings, and anywhere where water (oxygen) does not circulate freely which can cause crevice corrosion, but I think the old adage, "If it aint broke don't mend it" applies otherwise.

 

[boatmike]

Re: hull anodes & mixed metals

I think you will find that most props are indeed cast manganese bronze Vic. Otherwise I agree entirely.

 

[alan006]

Re: hull anodes & mixed metals

Thats what I thought, as far as I know phosphor bronze is normally used for bearings, not propellors.

 

[boatmike]

Re: hull anodes & mixed metals

"Gunmetal" is also used to cast small parts and skin fittings. Props used to be gunmetal bronze but its rare now due to cost and the difficulty of casting larger parts like props without flaws.

 

[bennyd10]

Hi, A bit off the subject, but I noticed you had replaced the rudder shaft on your Rasmus. I am considering making an offer on a 1973 Rasmus, and noticed some slop in the steering, and a flex of the rudder shaft at the hull when turning the rudder. The Key looks to be quite corroded, and could be a large part of the steering slop, but the rudder shaft has me a bit scared. How large of a jub was this for you? Any other things you might recommend I check out before making an offer? Thanks!