Mild steel corrosion in sea water.?

Question

I have a fibre glass boat with mild steel bilge keels through bolted with mild steel bolts onto the outside of the hull, regularly anti fouled over the keels and the bolt heads.Would it be benificial to replace the bolts with A4 stainless steel even though this would now be 2 dissimilar metals not a good idea from a corrosion point of view or better to stay with 2 similar metals even though they are mild steel.

Answer 1

Would not sacrificial anodes be better. They bolt and come i all shapes and sizes.  I have them on my cabin cruiser and they corrode away and the out drives are not affected at all.

Answer 2

Stainless steel is not dissimilar to ordinary steel, however if you keep the paint in order then this action should not be necessary and you can always change the bolts if they look suspect. Just remember that stainless steel is more brittle than mild steel.

Answer 3

It wouldn't change much changing them other wise then not gathering rust.

Answer 4

Will not do any harm in changing them.

Answer 5

The best performance re galvanic corrosion can be had from using 316 grade stainless bolts.  Very pricey though.  You might find fitting a zinc anode or two beneficial.

Downside of zinc is it will leave your boat unprotected in freshwater.