Internet hotspots or wireless access (wi-fi)points.
Not necessarily free. Many providers charge for this service, and you sign up in the same way as for an ISP.
Many marinas have already installed this service, and many others are installing it. These are not typically provided by the marina but by one of a few specialist companies.
<hr width=100% size=1>There is no such thing as "fun for the whole family."
I got details of this service for Brighton marina but its certainly not free. It is provided by an outside specialist company, not by the marina. From the comments I heard it is not totally successful but cannot be sure. Very, very expensive by the looks of it. Cannot give more details as I left the brochure on the boat. Just go to your marina office and they will have details if its available that is. If your laptop is not WiFi equiped you need to buy a suitable pcmcia card.
Plymouth Yach Haven have a system installed by SqauerMile. I've signed up and it works a treat!
Pricing is similar to land-based broadband (£30/month). You get a permanent 512K internet connection to use as you please. Mine gives a reliable download speed of between 50 and 56KB/s. Make sure you get a good PCMCIA WiFi card for your laptop - they vary greatly e.g. I have a D-Link card which works fine and my wife's "work laptop" has a 3Com which won't connect at all!
You should check out the YachtSpot service. YachtSpot allows marinas to provide wireless Internet to slips for all personal wifi devices. The marinas and yacht clubs keep 100% of all revenu and it is a very low priced service. The best marina wifi solution.