I have been pondering this matter while preparing Footprints for our offshore trip later this year. You can of course go to a whip antenna but they are quite expensive and you really need to go to a 23' antenna to get the band coverage, unless you use a tuned antenna such as SGC produce. Like Lesley I had heard about the idea of a wire inside a rope core. I found ropeantenna.com in the states and was at the point of purchasing one of their antennas which are evidently manufactured to a high standard. In the end though I had trouble getting them to understand the length of antenna I required and they did not seem to want to sell the antenna without their accompanying ground system.

So in the end I have made my own rope antenna. I bought a 10 metre (+ splicing length) length of polypropylene braided ski tow rope. I spliced each end to a stainless steel ring for mounting purposes and then inserted about 9.5 metres of 4mm square insulated tinned marine electrical cable up the centre of the braid. There is a whipping around the braid at the point where the cable enters and where the cable terminates at the top, which I think I will remove to allow the cable to float more inside the braid.

I have mounted the antenna in the 'chimney' on the starboard side of the mast, the upper end lashed to a saddle at the top of the mast and the lower end lashed to the tow rail. The protruding end of the antenna cable is covered with an extra plastic tube and led through a deck gland directly to the output terminal of the antenna coupler. 

So what I have got is a basic long wire antenna which is as equally good as a back stay antenna. My SSB radio is an older Furuno FS1550. The antenna coupler is an SGC smart tuner. Both antenna coupler and radio are grounded via 2 inch wide copper strap to an external bronze ground plate. Everything seems to tune up OK. The only issue I can see is that the antenna becomes a bit loose as the mast bends slightly to starboard while on the port tack. I have thought that I might insert a short length of heavy shock cord at the lower end of the braided rope to act as a spring and maintain tension on the rope.