Dissimilar metals - rudder fitting

[weaver_fish]

Pintles and gudgeons are phos. Bronze. Where they are a little worn they rattle as the boat rocks on the mooring. Trouble is that its only 1mm of play... so not enough to make a bush and both fittings are glassed in so I cant turn the pintle down or widen the gudgeon.

The previous owner had sleeved the pintles with copper pipe to take up the slack.

I am wondering if that is wise, with bronze fittings, copper sleeve and the stainless prop shaft all next to each other.

Will this cause major electrolysis?

Cheers

 

[Evadne]

I wouldn't have thought so, personally. 316 stainless and most bronzes are compatible, copper is actually the least noble of the set, but not by much. I'd have thought that physical wear on the relatively soft copper would outstrip electrolysis, but that is a conjecture rather than an observation. If it's been like that a few years and the copper hasn't fizzed away, then there's your answer. You could always try and fit an anode if you're worried. Personally, if all I had was 1mm of play on the rudder I'd be quite happy!
This is a useful quick-look article.

 

[VicS]

Copper and bronze are fairly close to each other galvanically so there should be no problem there from the galvanic corrosion point of view. If anything it will be the copper that corrodes rather than the bronze but being so soft it will wear away more quickly than it corrodes I would think.

Stainless steels are either in a similar position in the galvanic series to the copper alloys or are more noble than them depending on the stainless steel in question. So there is no problem there either. I expect you've got a bronze prop on the shaft anyway, but since you presumably do not have any electrical bonding between the prop shaft and the rudder fittings there is no question of any interaction between them.

The only area of concern will be the prop if it is manganese bronze, a common alloy I understand for props, but actually a high tensile brass not a true bronze at all. This is quite independent of your rudder fittings. It would be wise to keep an eye on the prop and take action to protect it by means of a shaft anode, or a hull anode and an "Electro eliminator" brush assembly to bond it to the shaft, if there is any sign of dezincification.

 

[vyv_cox]

This suggestion may be close to blasphemy to traditional boating types, but why not replace the copper with plastic? Cut some rectangles out of a plastic bottle and wrap them around the pintle. Better perhaps, you may find some tubing to fit. Reasonable wear resistance and absolutely no galvanic corrosion. Cheap, too.

 

[weaver_fish]

sometimes the solution is so obvious that you need someone to point it out! plastic bottle sides!!! Nice one, thanks?

Does it matter whether it is diet or regular lemonade? /forums/images/graemlins/cool.gif

 

[Strathglass]

MUST be Diet /forums/images/graemlins/laugh.gif

 

[nancy143]

hi
this is very new for me and most of the comments are related to the material like copper bronze etc.Copper and bronze are fairly close to each other galvanically so there should be no problem there from the galvanic corrosion point of view. If anything it will be the copper that corrodes rather than the bronze but being so soft it will wear away more quickly than it corrodes I would think.
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nancy143

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