Thank you for a reply.
Well, I understand question correctly and the answer remains the same - this antenna will not receive better results, than having at the moment, using this external antenna.
Let me explain why:
I do not know for sure, but I guess, that this cafe at the beach shore, for sharing WiFi for a customer using a simple access point. These devices have up to 6-7 dB antennas and are designed to cover a small areas. Also, they in most case have circular radiation pattern. More information could be found in our wiki.
Having a powerful receiver, you are able to get some fragment of this signal, but this signal is very weak and should provide very low speed. In order to have a better connection, in this case, Cafe should have directional antenna, placed directly to your boat, but again the maximum distance of properly working in ideal conditions, will be around 150-200 meters.
In order to receive WiFi longer than this distance, will need a more complex solution, like point to point antennas.
Hope it helps.