A lot depends on the coverage you are looking for and where you are keeping/using your boat. Liability only? Hull coverage? Comprehensive coverage on a mortgaged boat? FOr local waters only or are you going cruising and will be changing countries left and right?
You'll need to give a few more specifics to get the most helpful responses.
As an example of what I consider "not good", I just called Progressive, got through to the end and was almost ready to go for it, and asked what they covered if a thru-hull failed and the boat sank. The rep said nothing, they don't cover equipment failures.
hahahaha....actually I had an insured that had a boat that sank because the thru hull failed. The adjuster from Progressive gave the go ahead to refloat the boat and pickle the motor before he ever got on site. They determined that a thru hull had failed and paid the claim in full. The boat had replacement cost on the personal items and they paid that as well. You're going to have a problem with the comp due to the age of the boat though. I have access to Markel as well as Progressive in my agency. The best thing about Progressive is that in most instances they don't require a haul out and survey to cover your boat. For inland water ways my experience is that they can't be beat. If your headed "out" then you should look other places as their coverage is limited to 75 miles off shore. However, I believe that recently they added the Bahamas and Mexico to their coverage area.
The quote I got on my boat (30 Islander Bahama) was quite a bit higher through Markel and Boat US so I've got a Progressive policy on my boat.