They say never to have an insurance company that insures (almost) anything without question. Progressive will insure (almost) anything without question. They bet that if they insure enough things, that gives them a larger demographic of customers with other needs, and they'll have enough money upon their policies to insure more random things. But believe me they will hold on to that money as tight as possible.
Sidenote: I think it's wise to always be skeptical about companies with such an abundant amount of money that they can feed new advertisements every week on every channel during every commercial break. It shows that they are not doing all that they can to improve their product/service or provide customers with lower prices. They're keeping that policy premium money as best as they can. It's an automobile insurance company, after-all. By expanding to RV's and ATV's and Motorcycles and then Boats, the reality is those are particular and different vehicles than common automobiles that have regular accidents on familiar roads with witnesses and street signs. Boating is a very particular market, and in my opinion it takes a particular company to focus well enough (and have enough knowledge) on it to do it well.
A google search will provide an overwhelming number of complaints that progressive will not pay claims. Of course, every customer complains through a bad experience so it is to be expected, and you would be able to find complaints about BoatUS and others - but Progressive is by very very far, the worst sounding out there.
Sounds like you have a nice boat and are a serious sailor, and if you admit to the insurance company that you race (which you better, if you have an accident during a race) then I think you should go with a specialty company that handles that well. If you tell BoatUS "racing" is a reason that you have the boat, and they deny you. Then that's a good thing, because you may otherwise be stuck in the future after a racing accident or injury and they will tell you that you were never supposed to be doing that, and they are not responsible to pay your damages. That's not a risk I would be willing to take.
Pop your head into a sailboat racing magazine or website and see which insurance companies are placing ads in there.
BoatUS is a great big generic insurer, but they are HUGE, and to mitigate risks they may not insure your race sailboat unless you want to have a very expensive rate. Their customer service is excellent throughout signing up and any questions you have along the way, I have not had a claim, though. However they are right there when you call them, no recordings, and they have so far been on top of their game with my paperwork and changes to my policy. I have confidence in BoatUS.
I think that you should give BoatUS a shot, they have some perks. But ask one of their specialists about certain concerns you have before you sign with them. Like, exact scenarios you are concerned about coming across on your boat in an area doing something.
Otherwise, a more expensive specialized insurer might be a good choice.
One more thing: I'm not trying to bash Progressive, I can see Progressive as being a fine choice for people who sail/fish/ski on quiet lakes, but due to the size of their boat they are required to carry insurance. But when you're on the ocean in a sailboat which the insurer has never heard of, with a dozen variables affecting your decision making and the conditions you sail in, then a more specifically-focused, true "boat insurance" company is a safer bet.