I live in a coastal area and sometime in the next couple years I may be getting a boat for some cruising.  I was wondering if anybody knows how the black finish on an AR holds up in this environment?

If you mean the black hard anodizing on the upper and lower receivers, rail system handguards, etc, you shouldn't have any problems (unless your rifle has severe abrasions through this coating, and/or you expose it to (submerge in) salt water without rinsing)

The manganese phosphate (Parkerizing) found on the other parts is not as forgiving. Pay attention to areas where steel phosphate parts are in contact with aluminum anodized parts, especially in wear areas and those that trap water. Pins and springs on moving parts (around the extractor, and the charging handle latch, for example) might require more maintenance.

You might find yourself giving more than a routine cleaning, and I would use extra helpings of CLP in the above kinds of tight spots.

You might go ahead and get yourself a stainless barrel, and a hard-chromed bolt and carrier assembly. A condom over the muzzle might not be a bad idea, either.

Hope this helps...

Are you bringing it along or storing it on a boat? Questions like that will reveal how much additional care might be needed to fulfill your needs.

Before my daughter was born my wife and I spent a lot of time on our 21' cuddy on the ocean here in NH. One of my Colt HBARs and a handgun or shotgun always went with us whenever we went out. The finish on the ARs held up fine. Any weapon that came aboard was well lubricated due to worries about salt air corrosion.

If you are going to store ammunition on your boat like we did I'd stongly recommend a USGI surplus ammo can, and make sure the rubber gasket is in good shape. If the gasket is a mess you can remove it, clean it up, and then reinstall it.

The boat is still a good bit out in the future.  This was a thought that popped into my head while considering the "important" stuff.  Mostly daysailing I expect, and I'd probably spend about a week on it at the most.

Thanks for your input.

OK, don't yell at me, but I carry a stainless Mini-14 on my boat. I keep it well oiled and in a plasic bag. I don't leave it on the boat for more than a week at a time and have had no problems.