Example of Crevice Corrosion

[Brentathon]

Here's a good example of how stainless steel can corrode (significantly) in an environment where there's a lack of oxygen.
This is a screw that was in my transom, for my swim platform supports.
This is why I HATE fasteners used below waterline.
Note how the head of the screw (which is submerged in saltwater) is fine; and how you wouldn't know the condition of the threaded portion that's inside your transom.

 

[Cadwelder]

Re: Example of Crevice Corrosion

I know exactly what you're saying....I've removed plenty in the exact same condition. This is why on my bass boats I only use "shoot thru the hull" transducers and don't mount anything below the water line that can be mounted elsewhere on the craft.

 

[Brentathon]

Re: Example of Crevice Corrosion

And, I'm sure my boat is not the only make/model that uses swim platform supports which extend below the waterline.
I guess a through bolt (with a nut on the inside of the transom) could be another method, but they you still have another possible leak point, and another possible way to get water into your transom.
Ugh.