If you have a ham license and you already use Winlink, this will be easy to set up. Best of all, it is free. There are currently about 447 Winlink users who are reporting their positions with this tool.
http://www.winlink.org/userPositions <<< check this out!
If you don't use Winlink for email, I think you can still use this system. [There a few reasons not to use Winlink, mostly having to do with bandwidth. There seem to be regular pileups on the frequncies used. Landlubber hams tend not to be too enamored with it.]
All you need is a computer, someone with a ham license and an HF radio enabled for the ham bands - with a Terminal Node Ccontroller. You also need to tell your computer what your GPS position is. The following site details the requirements and setup far better I am able.
http://www.winlink.org for general info
http://www.winlink.org/node/23 "WL2K For Dummies"
http://www.winlink.org/node/20 how to locate someone
You may also use this site for locating users, but it merely replicates what is on the Winlink site. It's just easier to save as a link when you want to find the same user more than once. Paste it into your browser's address bar and replace the placeholder with the call sign of your favorite sailing ham and see whether they have been connecting.
http://www.findu.com/cgi-bin/winlink.cgi?call=AANAAA (whatever the call sign is)
Happy sails 2u