Steve
At the risk of upsetting the ACOMS Faithful (again), this radio is a budget one and was designed primarily for R/C cars, which don't require a long range. If you want more range then you'll need to go upmarket a bit for a radio which was intended more for model aircraft. There are any number out there, and all have their devotees.
The cheap Chinese 2.4GHz radios are popular, although there are a few quality issues with some of the sets and, of course, after-sales support is generally nil. Above that there's the Spektrum 2.4GHz sets (still a few quirks but they do have a UK distributor with a good customer ethos) and then the 'proper' ones i.e. Futaba, Hitec, JR, Sanwa etc. Like most things, you tend to get what you pay for.
If there are no problems with the availability of frequencies where you sail then I would still advocate a 40MHz FM radio as the best current option. I use Hitec myself.
FLJ