I like to read threads such as this, as I am an attorney and I hate to see so much misinformation being thrown around.
First off almost all liability issues are governed by state law, that law that varies from state, there are basic legal principles but even these can be affected by the nuances of state law.
As a basic principle unless you are engaged in an inherently dangerous activity if you or your property causes damage the injured party must prove negligence (i.e. you didn't act a reasonable and prudent manner) if you fail to show the other party was negligent then you will NOT recover no matter what your damages are.
Inherently dangerous activities are things such as blasting, pile driving et al if you cause damage you will have to pay no matter the amount of care you took.
Many states have no-fault laws for automobiles accidents but those law are generally limited to autos and may or may not cover all damages. Never heard of no fault boating laws
Depending upon the state you may or may not be able to proceed directly against the insurance company for alleged at fault party, this is called a direct right of action. Sure companies may deal with you as it more expeditious (cut out the middle man) but in a state that does not have a direct right of action you can not sue the insurance company you can only sue the party you think is at fault. In any event the policyholder must be liable to you under some legal theory before the company will be obligated to pay you, general speaking negligence
Trees are generally governed by these same legal principles. Never a particularly good idea to rely on on insurance companies for legal advise, in my experience it is often wrong. A boat crashing into yours is NOT an act of god. Acts of god are things like volcanos and the storm itself.
Sorry for the long non boating post but these questions seem to reoccur with all the same type of comments some of which are correct and some of which are wrong and some fail to address variances in state law. Finally if you can not eat a total loss and buy yourself anther boat don't buy just liability insurance.