In article , rickman wrote:

Interesting. Any idea what the specs mean?

Gain 3dBi
"Marine Gain" 6dB

I know what dBi is, but what is Marine Gain? Is there some reference
antenna they use such as the rubber ducky?

That's probably taking into account an assumed 3 dB of additional
gain, due to the fact that the antenna is located a short distance
above the water surface. Salt water is an excellent reflector of RF
energy. At certain angles and distances, the primary wave from the
antenna and the reflected wave from the water surface will be in-phase
with one another, and will reinforce, doubling the strength of the
received signal.

In other places the two signals will largely or entirely cancel out.
There Ain't No Such Thing As A Free Lunch.