No, it's not a ground, it's a dipole antenna and it will be very directional if it works at all.
Dipoles work fantastically if you get them stretched out. You can even string them up vertically for vertical polarization, or horizontally for horizontal polarization. For vertical operation just tie one end to a halyard. Horizontally might be a little more problematic since the idea is to get it level.
The advantage of horizontal over vertical, besides polarization, would be the angle of take-off. A dipole will be affected by the water and cause short skip to be a little stronger than long distance propagation unless you get the antenna way up high out of the influence of the water. The vertical setups work really well for really long distances since the angle of take-off is so low. For that setup try to keep the wire as far from stays as possible.
Yes, a dipole has some directivity, but you can use that to your advantage. Just keep in mind the signals will be stronger when hitting the antenna broadside. (and transmitting). That means, if you have a vertical setup, the weaker part will be straight up. No problem there.