Lots of them. Many biggie auto insurance
companies will insure boats but usually on the smaller end of things. But a web search should give you hundreds. Each insurance company sells their policies either direct or via brokers. And every company and every broker have different "personalities" and coverage and prices. This is definitely an area you should do some research
on as rates can vary tremendously as can the policies themselves. You might try asking other boaters who have similar boats what they have. I wish I had done a better job in finding the right company with our first boat. Very happy with our coverage and broker now.
I considered BoatUS but they were too expensive for less favorable coverage. We have Chubb Insurance and the broker is Rich Haynie Insurance in Seattle
. (Other than being a customer I have no financial relationship with them otherwise. There are many other brokers who do good jobs too.) A good broker will have multiple insurance lines they carry and they should help you find the right one and help you through the underwriting process. If things don't "smell" right with one, drop them and find another. The business is very competitive.
It can be intimidating the first time. Just take your time and let the process go. You can usually drop a policy with little pain if need be.