you're not going to believe this

[Birdseye]

Boat is 96, in my ownership since 2009 and as far as I am aware the mainsheet track has never been in bits before. But after tossing and turning in bed last night wondering about the problems I was going to have with all those stainless screws into aluminium - ALL 12 CAME UNDONE WITHOUT PROBLEM

Had to tell you. In a long lifetime of boating this has never ever happened to me before.

There is a god!

 

[TOKOLOSHI]

Good job they werent tightened down then? :encouragement:

 

[RichardS]

It sounds like the previous owner or builder did the right thing and put a dab of the right grease on them before assembly. :encouragement:

It's not rocket science but so many people get it wrong.

Richard

 

[Kukri]

Wouldn’t we all like to know what paste was used in the first place!

I once unscrewed a bronze mushroom vent on the counter of a 48 year old wooden boat and found the white lead paste that it had been bedded in still liquid.

 

[GeorgeLlewellin]

The right thing and put a dab of the right grease on them.

In my humble opinion and that of Vyv Cox ("Metals in Boats" Page 38, Chapter 3). Stainless steel galling is a type of welding , therefore the best grease is molybdenum disulphide. But, if I have got this wrong, because of the mix of metals then I hope Vyv will be along soon to correct me.
George.

 

[RichardS]

In my humble opinion and that of Vyv Cox ("Metals in Boats" Page 38, Chapter 3). Stainless steel galling is a type of welding , therefore the best grease is molybdenum disulphide. But, if I have got this wrong, because of the mix of metals then I hope Vyv will be along soon to correct me.
George.

I don't disagree .... but you won't get galling between stainless steel and aluminium.

What you will get, in the presence of any moisture, is electrolytic action and corrosion which will, effectively, "weld" the two together. Anything which is sufficiently viscous, is an insulator, keeps the moisture out and doesn't dry out itself will be suitable.

Richard

 

[mdonnelly]

You’re still sleeping. When you wake up it will all have been a lovely dream

 

[anoccasionalyachtsman]

I had exactly the same with my keelbolts. I've watched others in new boats being tightened down with a scaffold tube extension bar in factories and so went armed with my 3/4" drive stuff - and a scaffold tube.

I put the socket on the first one and I'd swear I saw it move! And actually it had moved, not even finger tight. Same as the other the other eight. They're a bit tighter now.

 

[johnalison]

I don't believe the OP. Either he lives a charmed life or it's a case of the devil looking after his own.

 

[ShinyShoe]

Next week we will all be much more relieved when he reports all the screws cam undone while underway and now he is looking for a replacement...

#Karma

 

[awol]

.... but you won't get galling between stainless steel and aluminium.
Richard

I beg to differ. Dry assembly of SS screws into Al are prone to galling.

 

[rogerthebodger]

I beg to differ. Dry assembly of SS screws into Al are prone to galling.

I agree with Richard. Aluminium is too soft to cause pickup in the stainless steel.

What you can get if seasing due to grip in the joint but even then the aluminium is too soft to prevent the joint seating fully.

 

[RichardS]

I beg to differ. Dry assembly of SS screws into Al are prone to galling.

I do find that surprising as I have plenty of experience with SS to SS galling but none with aluminium alloys. However, the remedy is the same in all cases as described in post #6.

Richard

 

[DownWest]

Having to get the end casting off a near 40 yr old boom, I got a decent driver and braced myself for a fight. All four of the SS screws came out of the ally without trouble. Amazed? You betcha..

 

[Sandyman]

I don't believe the OP. Either he lives a charmed life or it's a case of the devil looking after his own.

Nah he already said it was gods doing but as neither a god or a devil exist that's all bollox as well
Stick water pump grease on everything. Works wonders.

 

[rotrax]

I beg to differ. Dry assembly of SS screws into Al are prone to galling.

No they are not.

My experience of S/S into alloy is extensive. I have never experience galling or cold welding with S/S fastners into all types of aluminium alloys, from Mazac shit metal to high quality hardened and tempered plate used for motorsport.

It does however, suffer from galvanic reaction which can sieze the two metals together as easily as a proper weld.

Moto Guzzi motorcycles were prone to this with the engine mounting bolts-about200mm long and passing right through the crankcases. When the OE Zinc plated ones were changed for S/S owners thought their problems were solved-but they were not unless some sort of insulating paste or grease was used upon assembly.

I have seen engine cases ruined when excess lube was applied to a screw in a blind hole. The hydraulic action would split the casting.

Seen it all, but NEVER dry galling.

 

[Birdseye]

I don't disagree .... but you won't get galling between stainless steel and aluminium.

What you will get, in the presence of any moisture, is electrolytic action and corrosion which will, effectively, "weld" the two together. Anything which is sufficiently viscous, is an insulator, keeps the moisture out and doesn't dry out itself will be suitable.

Richard

Quite right. The way I read it is that the corrosion products that are generated between the stainless and the ally take up more space than the parent metal and so the joint gets ever tighter. To make it worse, the corrosion products are a form of abrasive. So an ever tighter joint lubricated if thats the word by sort of emery