What is the distance from your boat
to the marina's access points? Lots of masts around? Do you get better "bars" as you move closer to it (e.g., with your phone
(Unless you're often trying to stream video or something, in which case you're maybe part of the problem...)
Sometimes you can get an inexpensive extender to solve the problem -- sometimes that's as simple as an external WiFi
adapter which has better antennas than your laptop or tablet.
FWIW, we use an o2Air Wifi
Router from Radio
Labs; another advantage is that it then gives us an on-board network so we don't have to log on each of our other devices... You might need some help installing; their printed instructions are completely wrong... but their installation
"wizard" works OK if you have a clue. Or there are similar products from other companies.