I use Progressive for my (now sold) F18 and my Hunter 23 monoslug. It was about $300 per year for both boats which included racing coverage, the trailers, trailering (in addition to any automotive policy), and charter boat coverage. They were the only company I called (didn't try the US Sailing program) that actually knew what a Nacra F18 was back in 2004. They also pleasantly surprised me by dropping my deductible 25% for every year I didn't have a claim. I should have no deductible at this point or very soon.
I have heard recently from someone else that recently tried to get a progressive policy that they didn't cover charter boats anymore though. I'm getting ready to work on a policy for my A-cat so would be interested in hearing your experiences.