Aluminum keel bolt backing plates

[kirlos]

Hi all,

My 1985 Pearson 34 has aluminum keel bolt backing plates that are in rough shape and quite corroded. I am planning to replace them this fall when the boat comes out of the water. I was going to replace them with some 316 stainless stock but started questioning whether aluminum might actually be the better material, acting as an anode and providing some protection to the SS keel bolts. Any thoughts?

 

[Allan12210]

If bonded (a wire attached to one of the backing plates) to the engine block, the sacrificial zinc will be your protection. I would go with the stainless steel plate. Over time the aluminum can deform under constant pressure and the nuts would need retorquing. 304 stainless would be acceptable and cheaper than 316 unless you have a source at a really good price. Deformation under load is less by far.

 

[Maine Sail]

The aluminum won't stop crevice or pitting corrosion of the SS bolts or galvanic issue between the aluminum & stainless. The aluminum can also waste away, as you've seen, being the weaker metal galvanically. This could leave you with a loose keel if it gets bad enough. I would use 1/4" SS or 3/8" + Garolite G-10. You can order stock from McMaster Carr of either or just have a machine shop make them to your dimensions. Simple stuff and should be quite inexpensive in the whole scheme of boating..

 

[finding41]

In Canada (Ontario) there was this great idea of using aluminum wiring in houses back in the late 70's early 80's. (Well not such a great idea I guess as the practice is now banned.)
Anayway because it is a big pain in the a.. to remove all this aluminium wire in a house there is a antioxidant grease that one puts on the connection between the new copper wire and the old aluminum. This antioxidant grease is supposed to stop the galvanic problem.
Is there such a thing for sailboats? I mean other than the zinks one uses now. Or is are the properties of aluminum and stainless different in a way one couldn't use this type of treatment.

 

[kirlos]

In Canada (Ontario) there was this great idea of using aluminum wiring in houses back in the late 70's early 80's. (Well not such a great idea I guess as the practice is now banned.)
Anayway because it is a big pain in the a.. to remove all this aluminium wire in a house there is a antioxidant grease that one puts on the connection between the new copper wire and the old aluminum. This antioxidant grease is supposed to stop the galvanic problem.
Is there such a thing for sailboats? I mean other than the zinks one uses now. Or is are the properties of aluminum and stainless different in a way one couldn't use this type of treatment.

There is a similar thing, it is called Tef-Gel. You would normally use it to prevent galvanic corrosion between stainless steel fittings and hardware from those made of aluminum, such as stainless hardware used on your aluminum mast.