Boat US is the official boat insurance provider of USA Waterski. They have cost competitive boat insurance; the medical portion of my boat policy provided a hassle free payout on a ski injury.
You can get a 50% discount ($15) on Boat US membership dues by forming a group co-op with 5 or more members.
Group Co-op Info http://www.boatus.com/membership/group/default.asp
Membership Benefits http://www.boatus.com/membership/
USAWaterski Partnership Press Release http://www.boatus.com/pressroom/release.asp?id=918#.UvD1aNJdXhI