Preventing Corrosion on bolts and Aluminium

[davidmh]

I need to isolate a stainless bolt from an aluminium casting. It is on deck .not underwater. Bolts are 10mm dia and the casting has a clearance hole. I was thinking of wrapping the bolt with amalgamating tape so it is push fit in the hole. If the clearance is not enough would a heavy grease or Lanocote work to prevent corrosion. the length of contact is 30mm,
David MH

 

[Roberto]

Lanocote or even simple lanolin works well, I use them on a wind steering system made of aluminium components held together by stainless steel bolts and no one has ever seized, even those frequently underwater . For a permanent fitting you could also use duralac, mastinox, etc.

 

[rogerthebodger]

I used Duralac on all my mast stainless steel fittings

 

[Poignard]

You could use heat shrink sleeving on the threads and plastic washers under the bolt heads

 

[Laser310]

I was wondering about this recently.

I have, over the years, attached various stainless fittings, with stainless fasteners to aluminum masts using Tef-Gel on the screws, and a bit of plastic or something between the actual fitting and the mast.

It seems to work okay, but I always wonder if every so often i should take the fitting off and re-apply the Tef-Gel.

Now, I have been looking at an aluminum boat for sale.

My first thought was that it needed a few more padeyes on the deck- i like to play with the sheeting angles on sails by setting up tweakers

I was thinking that the same procedure could be followed; rubber or something under the padeye, and isolating gel or whatever.

But I was wondering if some other procedure for isolation might be followed because an aluminum deck is relatively thick compared with a mast, and also, whereas on the mast the screws are tapped into the mast, with the aluminum deck I would be using bolts and maybe the gel wouldn't do as well in that application because it is generally a looser contact.. Also, I guess, the nuts and washers would need to be isolated too, but maybe a G10 backing plate would do.

So that situation is more like the one described by davidmh - is there any specific guidance for non-threaded contact areas?

 

[davidmh]

Thanks for the comments, this application is for the a through bolted fitting, the threads and nuts are below deck so there is no stainless aluminium thread contact.
David MH

 

[Roberto]

Thanks for the comments, this application is for the a through bolted fitting, the threads and nuts are below deck so there is no stainless aluminium thread contact.
David MH

These are the mechanical components used by good light alloy hull boatyards for through deck bolts. 1-4 steel washers, 2-3 nylon/pvc washers, 5 pvc sleeve around non threaded part of bolt, "Isolant" is plastic material between stainless fitting and Al deck plate. Other compounds/pastes added if necessary.

 

[madabouttheboat]

I use Tef-gel in any stainless/aluminium connection.

 

[BobnLesley]

Having been introduced to it in the USA, We used Permatex aluminium (I suppose it was aluminum?) anti-seize grease on pretty much every nut and bolt on the boat; I would assume it's available in the UK.

 

[rogerthebodger]

Having been introduced to it in the USA, We used Permatex aluminium (I suppose it was aluminum?) anti-seize grease on pretty much every nut and bolt on the boat; I would assume it's available in the UK.

Permatex is advertised as on anti-galling compound rather than an anti-corrosion compound.

I used anhydrous lanolin (wool fat) as a Anti galling compound of all my stainless fitting and Duralac on all stainless steel to aluminum fittings

 

[geem]

I need to isolate a stainless bolt from an aluminium casting. It is on deck .not underwater. Bolts are 10mm dia and the casting has a clearance hole. I was thinking of wrapping the bolt with amalgamating tape so it is push fit in the hole. If the clearance is not enough would a heavy grease or Lanocote work to prevent corrosion. the length of contact is 30mm,
David MH

I have a similar problem with my aluminium pedestal base. I swapped out the A4 stainless 10mm bolts for custom made 7075 aircraft grade aluminum bolts

 

[Ian_Edwards]

You can buy plastic Top Hat Bushes, which will insulate a SS bolt from aluminum -
Nylon Plastic Top Hat Flanged Bushes Insulation Sleeve | BPF or similar.
I find these better than wrapping tape around the bolt, they are also reusable.
For SS bolts into tapped aluminum I'd use Duralac.
I also spread Duralac around any bit of SS which will be in contact with aluminum. It's a bit messy but cleans up easily with white spirit. A tin of it will last a lifetime. Wear gloves when using Duaralac, it gets everwhere.

 

[Tranona]

I need to isolate a stainless bolt from an aluminium casting. It is on deck .not underwater. Bolts are 10mm dia and the casting has a clearance hole. I was thinking of wrapping the bolt with amalgamating tape so it is push fit in the hole. If the clearance is not enough would a heavy grease or Lanocote work to prevent corrosion. the length of contact is 30mm,
David MH

Presumably this is some sort of deck fitting like a cleat that will be permanently fitted and sealed to the deck. In which case line the hole in the fitting with the same sealant and make sure it is also under the head.