Improving wi-fi connection/reception no router or modem being used

I believe my issue is different from all that I've read. I live on a boat in a marina. The marina has towers (transmitters) placed around in various spots. The internet provider is Beacon wi-fi. A big wi-fi provider for marinas around USA, Canada and Bahamas.

So I get my password from the marina and log in. I use a MacBook Pro laptop which has an internal wi-fi antenna. So there is no router or modem on board my boat. My problem is the connection is extremely poor. When I finally get connected the reception is weak. Streaming a hockey or football game is almost impossible. Loading a page of text can be fast as times but usually takes 15 to 90 seconds to load when it's at it's best. A 2 minute utube video can take 30 minutes.

My boat is about 200 feet from the closest tower of transmitters or whatever they might be called. There are several to chose from on my drop down list. I have to constantly keep selecting a different one to get reconnected. The PHY Mode is 802.11G The RSSI: is sometimes as good as -59 but usually around -80 when I'm actually getting as good a reception as possible.

I've tried this trick. I bought an external wi-fi (looks like a memory stick) and a USB extension cord plugged into one of my ports. I then got a large kitchen strainer and poked a hole in it at the bottom and fastened the wi-fi gizmo to it. Then pointed it towards the transmitters on the poles on the wharfs. It did make an improvement but it was minimal and not consistent plus it cost $100 so I returned the USB extension cord and the external wi-fi. Anybody want a free strainer with a hole in it?

I contacted Beacon wi-fi in Dallas and they say everything is good at their end. I've contacted the marina and they say everything is good at their end. Does anyone have any tricks other than what I've tried to improve my internet?