Getting your boat insured is a have to, too many expensive things can go wrong to avoid it and most states require some form of boat insurance.   

There are 2 main types of boat insurance: Actual Cash Value & Agreed Amount Value.

Actual Cash value covers pays out replacement costs minus depreciation and the deductible. Which means you only get back the estimated value of your used equipment/boat from right before the accident.  Usually that amount doesn't cover the cost of replacing your boat or equipment unless you find a used deal.

 Agreed Amount Value is straightforward,  you and your insurance provider agree on the value of your boat at the get go, and in the event of a total loss you get that amount back. 
 

Coverage:

You may be thinking about using your general insurance provider to insure your boat, and while you may get a better rate this way, you will most likely pay in a smaller amount of coverage.    Many things can happen to your boat making boat insurance much more complicated, using a provider who specializes in boat insurance helps in two ways.  First you getting coverage geared towards boats, which brings with it the experience of what you need for your boat insurance.  Secondly boat insurance providers have lots of technical knowledge about boats and can you help find out exactly what coverage you need.

Coverage Details:

When shopping for marine insurance here are some details you want to ask about:

Physical Damage Coverage-  this is the bread and butter of your coverage but you want to make sure it covers your hull, engine, and trailor.  It protects against vandalism, theft, lightning, windstorms, and collision

Personal Effects Coverage- This covers all your personal property on your boat such as a TV, cell phone, cameras, radios.  You won't usually find this coverage for a general insurance provider. 

 Boat Liability-  This is coverage you have to have, its required if you financed your boat, and most states require it.  This covers any damage you do to someone or their boat.

Uninsured boat owners coverage protects you from damages received from a hit and run or uninsured operator.

Medical liability coverage ambulance and hospital costs if someone injures themselves in, on, or boarding/leaving your boat

Commercial Towing coverage reimburses you if your boat stalls and needs to be towed in to port.  Additionally you can get coverage for towing if your boat becomes grounded ashore. 

Salvage Coverage will cover the cost of salvaging a sunken vessel, which is required on most lakes/rivers

Spillage Coverage covers clean-up costs for oil/fuel spills in the water.

As you can see there are many types of coverage you have to look into before you get boat insurance.