Since you would be moving from place to place it's almost impossible to tell you what you could expect to receive as far as channels however you may be able to get something in many of your docking locations as long as there are transmitting towers within range. You would pick up different channels in different places depending on several things:
- Distance: from TV towers (usually large cities have more towers nearby)
- Terrain: If you are in the mountains or in a valley there may be no or limited signals. Higher is always better for signal reception.
Metal blocks reception: Your windshield/window is going to be the best place to hang your antenna especially if your boat is made of metal. Also note that if there is metal rigging/rails/brackets between your antenna and the signals it could block them. Even a neighbors boat, if made of metal, could cause issues.
- Motion: If the plan was for someone to watch TV while you are moving that will be difficult to accomplish since the signals are stationary and you would "sail out" of range very quickly.
If you wanted to try an antenna we'd suggest a Leaf 50. This antenna has a 50 mile range BUT you can take the amplifier off and it, in essence, becomes a Leaf 30 with a 30 mile range. Why is that important? Since you are going to be going from place to place you may dock somewhere that the towers are really close to you and you would not need the amplifier because it would overpower your TV's tuner. On the other hand if your destination port was 30+ miles from the towers you could put the amp back on to pull in those signals.
One LAST thing. Water can cause issues with reception sometimes. So if you are trying to pull in signals that are transmitting over a body of water you could have a "scattering" effect. Which is when a signal hits water and is bounced away from the antenna. There is a site called www.tvfool.com that you could check out to see if some of the locations you frequently travel through have good reception. This site will also tell you the best direction to hang your antenna.