You can get more distance the 2pc set of
$25/pr windsurfer reflectors, about 3mi over the ocean, however the next problem you'll have is battery life. DBSmod can go farther, but costs more and is more bulky to store the RC in the case. Since you're a marine application you should carefully consider the case ramifications for the RC. With Windsurfer you are highly directional, same as DBSmod. You'll have to be careful to ALWAYS face the antenna reflectors toward the craft, IE don't turn around to talk to someone and expect the craft to be happy. Also, I hope you have learned and tested dynamic home point, so the craft doesn't go back to the original launch location. And lastly, make sure you're not using 1.5 firmware over water.