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.