If located under dock I would not, if above tough call, if it was my dock and not a customers, I would induce epoxy overnight and do 4 coats and call it a day.
As a slight gamble as could be good for 3 years or 10, just cant say for sure.
Here is the part that scares me about painting above the water line, The only paint in automotive market that is air tight or waterproof is epoxy, now no problem if the part will come up for air say every 3-4 months or the water line goes down, say every winter when the lower lake level.
Most auto types paints will last 5-8 months with no air under water before bubbling.