My legal opinion is that the guy is an a$$hole.
When a claim is filed, insurance companies are required to conduct a due dilligence investigation of the occurance and then either pay the insured an amount determined by the terms of the insurance contract, or deny the claim if a coverage exclusion applies. I used the term "insurance contract" because that is how the law views insurance policies. They are a contract between the insurance company and the policy owner. Each party has to honor his duties under the contract.
If the investigation uncovers any evidence that the boat owner intentionally caused, or even allowed his boat to sink, they will deny coverage. If they find that he was only guilty of "ordinary negligence" they would have to cover the loss.
I doubt the marina has any legal obligation to save your boat from slowly sinking at the slip. But if it can be proven that the marina worker was the sole cause of the occurance, then the insurance company might be able to recover some or all of the money from the marina's liability carrier. I say "might" because admiralty law protects those who attempt to save lives and boats. Most marinas require proof of liability insurance which would cover damages to other boats and the marina caused by your actions or inactions.
Peter
1981 32' sedan bridge
twin Chrysler 360 cu. in. 250 hp engines
Raw water cooled
Nimbus II
Home port: New Buffalo, MI