.223 is not indicated for this mission. Wind blows it around at long range, worse, it will deflect off of almost anything, like the hull of a fiberglass boat. The .308 and up will punch through, turning cover for 223 into concealment for 308.
As always, the biggest problem is platform stability. It's VERY hard to shoot accurately from a boat. Even from a ship, you can't get a steady rest. It's up and down and side to side all the time. A semi auto Barret 50 would be perfect.
Actually a Phallenx(sp?) weapon system would do the trick...
"Burrrrrrrrrrppp....Where'd they go?"
MK-19 All the way!
Or a fiddy will do