mixing aluminium and stainless steel

[BlueSkyNick]

I know this has probably been asked before and I should know better, but I am short of time !

Aluminium toerail, with aluminium fairlead bolted in it. One bolt got sheared when another boat tied alongside was 'agitated' by wash from another.

I am told by Moody parts service (excellent BTW) to use machine screws available from any chandlers, which will be stainless.

Do I need to use anything between them to prevent corrosion, like that funny looking yellow paste stuff whats name slips my mind right now, or just screw straight in?

 

[Aja]

Nick

I'm pretty sure that you'll find all the bolts in the toe rail are stainless. You could use 'Duralac' but I'm not sure it would be necessary.

Donald

 

[thalassa]

You are looking for zinc chromate paste. Alternatively, you can use Loctite threadlocking fluid, which has insulating properties.

 

[rob2]

If there's room then the ideal would be to use nylon top hat cross section washers. This insulates both the bolt head and shaft from the aluminium.

 

[srevir]

years ago had stainless bolts eat their way through an aluminium traveller in a matter of weeks so definitely would insulate them, preferably with something that is more substantial than a paste

 

[Amari]

See my post of 02/08/2007; ''Something for the weekend, Sir?'' : Many helpful replies /forums/images/graemlins/laugh.gif

 

[Boathook]

Duralac is recommended for mast fittings so must be ok for toe rails.

 

[VicS]

As suggested completely insulating the stainless steel from the aluminium will solve the problem but Duralac paste is commonly used to prevent corrosion of the aluminium and is the stuff you were think of

I dont think I would rely on a threadlocking fluid to electrically insulate the two.

BTW Duralac is barium chromate.

 

[Topcat47]

Monel is the material for Ally, rather than SS, however it is very expensive. I used to have a contact for Aircraft Standard bits & pieces but no longer.

I don't know about "Duralac" but we always used Zinc Chromate when using SS fastenings, even on Carbon Steel. The only time we didn't was in plastic. Mind you I don't bother these days, and I'd not use SS in ally anyway.

 

[wotayottie]

Yopu could always try some of those fancy anodised aluminium fasteners beloved of the weekend wonders who ride Jap sports bikes. Paticularly the pink ones!

I think they even sell titanium fasteners for bikes.

 

[BlueSkyNick]

[ QUOTE ]
Mind you I don't bother these days, and I'd not use SS in ally anyway. [/quote So what would you use, as M6 machine screws, then?

Thanks for all the responses, BTW.

 

[mandlmaunder]

Don't.

 

[comoxlarry]

I made the mistake of using SS screws to mount a fitting on the aluminum mast of my previous boat. Electrolosis rotted away a large area around each screw in less than a year. Sometimes you can get away with it some times disaster. It's worth while going to some trouble to insulate them.

 

[rutten]

Remarkable that no one mentions Lanoline (marketed as Lanocote); see PBO somewhere in the last two years.
Mast makers Proctor of Breskens switched from zinc chromate paste to Lanocote. Expensive (€ 25 for 250 grams) but seems to work ok on my mast & boom.
I have been told that lanoline is also (lot cheaper) available at pharmacists. Do not know if it's the same formula

 

[seedog]

Lanolin used to be extracted in large quantities at some sewage works as well as being extracted from wool as it is a natural part of human excrement. It has a variety of industrial uses and interestingly has a yellow tint which someone said is the colour of Duralac.

I have just bought an aluminium hulled 'Extravert' trailer sailor and I would appreciate any advice on how best to look after her as quite a number of fittings and screws appear to be steel.

 

[extravert]

Hey I used to have one of them - hence the username!

I'll be in touch by pm.

 

[rogerthebodger]

Ronstan do some plastic counter sunk washers that is supplied with their aluminium T track to insulate the stainless steel screws from the aluminium rail.

I have looked for another supplier for a simular washer to fit my aluminium toe rails to my steel deck. The best I found is red fibre washers used to seal pnumatic banjo fittings.

 

[Avocet]

Oddly, there are a variety of stainless (don't know what grade) self-tappers in my ally mast that have been there for over 30 years and don't seem to have caused a problem. I've had them out several times and although it is true that the edges of the holes are starting to go a bit white and furry, they're not at all bad considering the age of the parts! There doesn't appear to be any trace of any kind of insulating coating either and I've certainly never applied any!

Are some grades of stainless and some grades of aluminium very close together in the galvanic table?