gimmick, all you need is a plate or strut or nut on a wire in contact with the water, preferably going through the water surface to allow the antenna to be grounded. The amount of surface is not that important once you get the RF to the water. It spreads out along the surface so as long as the ground path can carry RF it will work. A thin wire will not work BTW as RF travels along the surface of the conductor not through it. Think braided grounding strap hanging in the water.
I use a mobile stick with base loading ($14 at our ham shack) and a grounding strap 1" wide connected to the grounded end with a large nut to keep it in the water. mount it low as possible to keep the ground strap length out of the water as short as possible.