the Jester
Legend
I've lazily not even read the rest of the thread yet, so this might have been mentioned by someone else, but the Savage Tide AP (the last one in the paper Dungeon Magazine) has some perfect stuff in it for you. There's one in particular, probably the 4th or 5th one in the series, that's either mostly or entirely set at sea, and it is awesome. It also ties in with the Isle of Dread, which also deserves mad kudos.
U3 is largely set underwater, and it definitely is a great classic adventure featuring sahuagin. There was a 2e trilogy of sahuagin-focused adventures, but I've only ever seen the second one, and it was a bit dull.
If you can find it, the 2e supplement Of Ships and the Sea- one of the "blue books"- is absolutely fantastic, though you'd have to adapt the mechanics. But it's got a ton of good stuff on ships, the undersea environment, etc. A bunch of cool spells, too.
U3 is largely set underwater, and it definitely is a great classic adventure featuring sahuagin. There was a 2e trilogy of sahuagin-focused adventures, but I've only ever seen the second one, and it was a bit dull.
If you can find it, the 2e supplement Of Ships and the Sea- one of the "blue books"- is absolutely fantastic, though you'd have to adapt the mechanics. But it's got a ton of good stuff on ships, the undersea environment, etc. A bunch of cool spells, too.