Galvanising is typically applied by dipping the steel component in a molten bath of zinc, raising it and allowing the excess to drip off. Thus the coating applied is variable in depth. Zinc is used as a sacrificial anode material to eliminate corrosion on other metals in shipbuilding. Note that, sacrificial!

So while it won't cause problems, it won't last long before it is corroded, and what you are left with is an exposed steel fastener. And rust marks look ugly.

You are much better off with stainless (grade 316 preferably) or silicon bronze. The difference in unit price will be steep, but you are not going to be using heaps, so over the cost of the entire boat, the difference is a pittance, but oh what a difference in appearance.

If you cant find stainless at home depot, go find a specialist industrial nuts and bolts supplier. The devil is in the details.

Ron Deane