Metal epoxy paint will work, but will require recoating from time to time. Trick here is it has to completely dry before getting wet (4 hours is not enough for painting in place). Sherwin also makes a Polyurea paint just for underwater structures, but be aware that it is pretty expensive. If you do paint, I would recommend dipping all brackets and mounting hardware to ensure 100% coverage, and for touching up after assembly if possible. Another option to consider is design of the dock assembly. Is there a way to remove the brackets for replacement if need be in the future without having to dismantle the dock sturcture? This may aid in recoating. Also, might check with a boat dealer or service center for their thoughts on what type of paint and its durability.

I'll give you Petrobras specification for painting the supporting structural steel of the offshore platforms. Petrobras is the Brazilian state owned oil company.
Take into account that once the platforms structural steel support is submerged at, say, 150 meters deepness (500 feet) , it will never come up again. Although it's possible to repair a weld at that deepness, it's impossible to repair a badly executed paint.
Most Petrobras platforms have been in service in salt water for 20 years now, so the painting specification must be good.
OK, here it is:
1. Sandblast to white metal.
2. Apply zinc chromate epoxy paint up to a thickness of 150 micrometers (you convert to mils) when the film is dry.
If you have any doubt, let me know and I'll give you further details.
Giovanni S. Crisi
Sao Paulo - Brazil

Have you considered galvanizing?

From the conditions you describe (submerged 20 hours /day) I assume the brackets are being used in salt water?
If so, I would not use spray galvanizing, or other zinc rich paints by themselves. Salt water just loves zinc. It is sometimes used under coal tar epoxy so that if the CTE is damaged in small areas, the zinc rapidly corrodes and "plugs" the damaged area with zinc corrosion salts.


Zinc chromate was mentioned which is not the same material as zinc rich paints and I believe it could work well for you.

Coal tar epoxy is an excellent immersion coating that is commonly used by itself for dam gates, pilings, and etc. It is ugly, comes in black and 'not-so-black' colors (red tint) and will chalk turn gray in sunlight, but the stuff will last a long time.

Other epoxies could work but they aren't always the best water barriers by themselves.

Chet Guilford