I've been in marinas in Maine where at high-tide, you get a great signal -- but as the tide goes out, you get blocked.

Our marina in Annapolis started out with a single antenna that we would 'see' until big power boats blocked it.

Generally, there are a number of USB antennas which you can get a extension USB cord for, then take up from "below through a hatch or the companionway. You can put it in a plastic bag if it's raining a bit -- but don't "submerge" it in a drenching rain on a deck.

These USB antennas can conflict sometimes with your internal wifi-fi. you can try 'turning off' the internal wifi with the switch on the laptop.

There are some external antennas which can be connected with various degrees of sophistication. Those would involve several hundred dollars of equipment and some time to install on a spreader or whatever.