Power output is often thought to increase range, but really, the difference in range between a 25-watt fixed marine VHF radio and a 5-watt handheld is due to the fixed mount's antenna being taller, and therefore it can "see" farther. More power will allow you to punch through static and other radio traffic better, but only within the range dictated by antenna height. Marine VHF radios work on a line-of-sight basis. That is, they can transmit and receive to and from another antenna as long as that antenna is above the horizon. How far is that? Standing in the cockpit of a boat, the distance to the horizon for most adults is about three miles.