Let me elaborate a little more. First, where are you going to keep the boat?
Secondly, you need to look at coverages actually offered before buying a policy. For instance, my boat is in Florida, so hurricane coverage is necessary. Allstate has a 5% limit of the boat's worth for salvage. This means that if your $100,000 boat sinks due to a storm, they will pay $5k to salvage it. That's not nearly enough. If your boat sinks and is totaled, you will pay a significant amount of your settlement just to have it raised and hauled away. When shopping for insurance, I called an international marine salvage company and asked for advice. They told me that they wouldn't even answer a call to an insurer that had State Farm because State Farm would not pay directly to a salvage company, they pay only to the owner an amount they think fair. I don't know if this is correct, but that's what they told me. My salvage coverage From GEICO/Boats US is $500,000.
My coverage with GEICO/Boats US is $2500/year for Florida Gulf Coast. My boat was damaged during Hurricane Sally and from the time I filed the claim till payment was 3 weeks. They covered $50k in damage with no problem. I also have a depreciation rider on my policy. If you go 3 years with no claims, they reduce your premium. I also have an "Agreed Value" on my policy based upon a survey that I provided to them. That means they will pay the value of the boat upon total loss.
So my advice is to be very wary of "cut rate" insurance policies. Make sure you know exactly what coverage you are getting. As of this date, I can't recommend GEICO/Boats US more highly. I don't know what the future of my policy will be, based upon this claim but so far, they have taken really good care of me.
For what it matters, I've done some shopping around for policies at various boat shows and I've been told every time by different companies that they can't touch my rates for the coverage I'm getting.