Insurance is what I do for a living, I can offer a little advice.
First: Someone pays for the marketing expenses of huge companies (insurance and otherwise). Just because you may recoginze the name, it may not be the best deal.
Second: Call an independent agent and ask for some quotes, discuss the uses of your boat and the values, have your serial numbers (boat and engine), values and Horsepower and length ready to discuss.
Third: Liability is of the utmost importance, especially on the water, make sure you are buying enough liability to protect your assets.
Fourth: Each company does things a little differently. Keep this in mind and possible claims senarios when you setup your policy.
Example: Company A may offer coverage for hull, engines and liability for $500/year with a 500 Deductible. Company B: may offer the same hull, engine, and liability coverage PLUS coverage for equipment including electronics and gear. (yes this can include fishing gear), for $600.
Possible Claim Senarios: Someone steals your tackle box $400, rods and reels $350 and damages your boat in the process $1000.
Company A: Boat and hull repair $1000 minus $500 Deductible. For coverage for your gear go to your Homeowners policy. Your homeowner insurance for $750 (gear) less probable $500 deductible. Total loss of $1750, your total coverage after deductibles $750.
Company B: Boat and Hull Repair $1000 minus $500 Deductible, your gear loss $750- deductible already applied because part of same policy. Total reclaimed $1250. This may be worth the difference in the policy premium.
Lastly: Go with a company that can endorse the coverage territory to your needs. The one size fits all approach never works very well, especially with boat insurance.
Parting Thoughts: The company you choose should be AM Best rated A- or better, you should have an agent to help you understand the decisions you make. You may think having an agent involved costs you more money, the studies show this in not the case. Educated buyers make better decisions.
Post up with additional questions or concerns. If you want, I can refer you to someone in my office who is an absolute pro in this niche.