Why is Ralph so angry with Jack after spotting a ship in Lord of the Flies?

Ralph said right from the start of the book that he had two priorities, to be rescued and to have fun while in the meantime. Jack had told him that his hunters would be responsible for keeping the fire lit. When Ralph spots a ship on the horizon he also notices that the signal fire isn't lit. It turns out that Jack had taken the fire watchers on a hunt. Ralph was angry that just because Jack wanted extra help to hunt a pig the chance of them all being rescued had been missed