Wasn't able to arrive at cove to Anchor out until 7pm. While rushing to set up the boom tent I realized that I forgot to put the gas can forward. While carry the filled 2.5 gallon plastic can to tie off at the bow I slid on the jib and the can went overboard. By the time I got the boat hook it was too far to reach. It was a cold and getting dark. I was in shock watching the sealed container bouncing along the little waves out to center of the cove. I dove in and had to swim a good 50 feet to retrieve the can.