I make no claims to be an expert in these matters - perhaps Jedi will weigh in. Wifi is a complex, dynamic, adaptable system. The max power output is just that - the maximum. It can be negotiated lower, and the AP will try to use the lowest power levels, in order to minimize interference
with other networks. As I understand it the AP will use the highest power to initiate a connection, then work down (you can see this by watching the received signal strength). With a local wifi and one or two clients this should work great. OTOH in a marina with a badly designed wifi system, with lots of clients and interference, the signal levels can go all over the map trying to adapt, with lost
connections one symptom.
It may be that a strong signal will result in the weaker stations having to wait, which is the normal behavior, but it also results in stomping on the weaker transmissions (not received by the stronger client) resulting in dropped connections and more re-transmissions. In balance it may, or may not, benefit the guy with the amp but guaranteed it will reduce overall performance on a busy AP and basically screw the folks trying to connect directly with their devices' internal radios. It seems appropriate to me that the marina should enforce a good neighbor policy and ban amplifiers - and encourage larger antennae and external radios for better reception
. Ultimately the right way to deal with this is to have several APs each covering a modest area, thus assuring all devices on an AP receive each other, as opposed to trying to cover a large marina with a single
AP. This can be a tough sell to the marina...