I have a boathouse on the puget sound in WA. Medium bluff, then house below that on concrete piers. Half the time, it's above a pebbly beach. The other half, it has several feet of saltwater under it. In fact, last winter, between a king tide and storm surge, there was water over the floor/deck. I wasn't there, but a week later, I saw that things had moved around and one paddleboard was gone. Currently, there is a 20A wire from a GFCI breaker at the main panel, 100' to the boathouse. The wire is direct buried (expect where it is exposed!). I'm not even sure it's UF - it may be 12/2 NM. And the path from the main house to the boathouse is down a number (3?) of terraces, so replacing with conduit will mean a number of angles. The GFCI trips pretty much as soon as I turn on the lights. It feeds a number of flood lights inside or outside the boathouse and a number of outlets. The wire is mostly stapled to ceiling joists (with NM staples that are now rusting). But some runs horizontally along walls, and then serves as a "holder" for things stored behind it (!!!). The outlets are normal 15A outlets inside plastic boxes (again, with rust apparent).
I'd like to redo this whole mess to something more safe and code compliant. I'd like to have at least 50A at a subpanel at the boathouse, feeding lights and outlets and possibly a boat lift.
Any feedback on best practices for doing all this in a manner that is more safe, code compliant, and which will live longer in this salty mist filled environment? I know this likely covers a lot of different issues. If I should separate this into separate issues (wire to the boathouse, panel in the boathouse, wiring in the boathouse, outlets in the boathouse), let me know. I just was hoping to avoid replicating the description of the currrent state of affairs.