Your options in FL are a bit limited:

Progressive
State Farm (if you have homeowners with them)
Ace/INAMAR (big boats)
Lloyd's / Atlas (big boats and liveaboards)
Chubb (if your big pimpin' and have 100+ feet of waterline)
Boat US
I think United might still do the occasional boat

and, of course US Sailing if your boat is listed.

There may be one or two more but that's all I can think of off the top of my head. It would seem that Progressive and State Farm, are two of the cheapest for boats under 30 feet.