Robert, I think I would get my hands on another militart type
(aerodynamic) vhf aircraft antenna and then have my aircraft
electronics shop cut it down for your frequence and then install it.

You know from your air-to-ground VHF communications what to expect
from it. I don't think you can do much better than that. Over water,
at any altitude above a few hundred feet MSL, I would think it would
cover your area of interest.

Win, w0lz