Maximum gain of your VHF radio antenna

The maximum gain for an antenna that can be used with Garmin VHF radios is 9dB.

NOTE: Generally, the higher the gain, the longer range the radio will be able to communicate. Keep in mind that the higher the gain, the more compressed the beam width of the signal becomes. Narrow beams can fade in rolling seas, smaller vessels should not use a gain above 6dB.