Your recourse--and it's somewhat drastic, but it's your only effective recourse--would be to sue your insurer for "breach of contract": for violating their contractual obligations (the insurance policy is a contract) to pay out your claim. In the lawsuit--if it goes to trial; that is, if it does not settle out earlier--you would have to show that you and anyone else they needed information from had provided what the insurer needed in order to move forward, and therefore their failure to resolve the claim was unreasonable and unjustifiable, and also  that the insurer is acting in bad faith. If you have to sue, in addition to seeking the actual amount of the claim (e.g. the replacement cost of the radar, etc.), look also to recover the rental fees on the boat for the period of time you cannot use it due to the insurer's unnecessary delay.