The advice from Bruce about the RF ground is 100% accurate. When I
first connected up my insulated backstay (yup, it keeps the mast up!) I
couldn't get the antenna to load up very well, and my transmitted
signal was pitiful. A day or so working with copper foil and bronze
screen made all the difference. Lots of area is the key.
I've also sailed on a boat where the owner just had a SS wire from the
masthead to the stern quarter- tensioned with shock cord. Worked fine
as antenna, and was a lot cheaper than a couple of backstay insulators,
too. He had a good RF ground system as well.
John