Corrosion between metals

[saltyrob]

Hi Folks,

The washers on the through deck bolts fixing alloy toe rail/deck to the hull are steel and have rusted. I am proposing to replace them with stainless steel washers. Will this cause any problems with corrosion between dissimilar metals. Can spread a bit of sealant to reduce contact.Boat is 86 vintage.

Many thanks for your advice

Rob the reluctant metallurgist

 

[srp]

I would use Duralac, to prevent corrosion between the aluminium and the stainless washers and (presumably) countersunk head machine screws. Replace anything that you can't verify as being A4.

 

[VicS]

Hi Folks,

The washers on the through deck bolts fixing alloy toe rail/deck to the hull are steel and have rusted. I am proposing to replace them with stainless steel washers. Will this cause any problems with corrosion between dissimilar metals. Can spread a bit of sealant to reduce contact.Boat is 86 vintage.

Many thanks for your advice

Rob the reluctant metallurgist

The bolts are stainless presumably so you already have contact between stainless and aluminum.

Duralac paste or Tef-Gel are the recommended materials to the prevent corrosion of the aluminium but it is important that the bolts are well sealed where they pass through the deck to prevent water ingress leading to crevice corrosion.

Maybe you should stick to just one sealant, using that to seal the bolts and insulate the stainless from the aluminium

 

[Vara]

Isolate, duralac or something similar, the penalty for not getting it right is fairly severe;

Halyard winch clagged onto aluminium base,SS bolts and no isolating medium, it came away in me hand