DV is right. The marina rental owner's policy covers their OWN liability(butt).
If the renter requires or feels the need to protect his OWN ass-ets
, a short-term liability policy CAN be purchased from your agent. Think airline short-term flight insurance.
I can see how a marina rental owner would "hedge" the answer to the liability coverage question. The answer doesn't have anything to do with coverage for the renter.