Any recommendations for a *simple* antenna that can be used
on a yacht/boat to receive ~500 kHz, and to receive/transmit
in the HF amateur and marine bands (1.5 MHz ~ 30 MHz)?

Currently I am thinking about a length of wire between the
stern and the top of the mast, fed via an ATU at the stern
end. I can make the wire ~50' long. What is the optimum
wire length? As long as possible?

Thanks,

John