Vhf, ship to ship is basically line of sight, the higher your antenna the greater the distance.
Ship to shore the range is a great deal more as Coastguard have transmitters located on the tops of hills etc.
I am able to speak to Liverpool Coastguard using a five watt hand held from at least ten miles of the west coast of the I.o.M. as the transmitter/reciever is located on top of Snaefell.
In saying that tho' there have been times when I was unable to contact them, thats when fishing right in under the cliffs.
Jack, I use a handheld VHF & I fish in Swansea Bay/Gower & I have had no problems contacting the Coastguard as yet.
Perhaps if you were off the Worm you might struggle, but you can always contact some other boat in line of sight.
If there are no other boats in line of sight, then you shouldn't be down there with just a handheld should you!