A VHF,UHF,AM,FM all face similar challanges. The sine waves are absorbed by water. Therefore, a secondary ground plane will replace a bit of ground plane otherwise provided by earth. Whereas the above suggested solution attachs to railing, railing serves some ground plane duty....Beyond or in addition to railing, a Stainless Steel or aluminum plate (larger will increase the target area for the sine waves) may be mounted about anywhere and 50/75 ohm co-ax connected to your TX/RX. Increased performance may require a powered circuit amplifier. Subject to specifying a TV, additional antennas will be needed. The TV antenna is designed to be more independant, but still suffers from water absorbtion.