Check the link:
http://www.archipelagoraid.com/

From the page....
The Archipelago Raid is an extreme sailing competition where Sport, Nature and Adventure are perfectly associated. Today, the Archipelago Raid is “the largest and most extreme orienteering sailing competition in the world”.

The concept
The concept is simple. Each team sails intensely day and night on a Formula 18 (5,5 m catamaran), along a unique course drawn among 100.000 rocks and islands.
On the way, the competitors have to find 20-25 checkpoints located on islands (pontoons, beaches, boats, lighthouses…) and described in the “Archipelago Raid Book” (latitude, longitude). The teams are free to choose their route between two checkpoints."