Regardless of the company, some won't cover boats that go over 45mph or have an outboard over a certain horsepower. You need to get those questions settled immediately if you have a full-sized bass boat (or other fast fiberglass).
You need to ask if you're covered on the Great Lakes. Some policies exclude coastal waters including the Great Lakes.
If you do tournaments, some may consider that business use and you could have no coverage during a tournament event unless you buy business coverage.
Many boat insurances don't cover very much of what you carry IN your boat. They may or may not consider attached things (trolling motor, graphs, etc) part of the boat. You may need to ask about riders covering additional equipment. Some will say what you carry is still covered under your home insurance, but be very careful to get this made very clear.