The recognized authority (in the US) on marine insurance and general average is Marine Insurance and General Average in the United States, aka “Buglass.” I have a copy that was the text in my graduate school marine insurance class, and it’s a fixture in every Admiralty law library. However, I was shocked to see how much it sells for, so it’s not something you’ll pick up to satisfy a casual inquiry (a used copy costs more than a 1981 Bowditch…).