Food, luxuries, goods, spices, or sugar can keep a crew happy, but it is difficult to keep a good amount of them on hand. Get a good ship upgraded then get a treasure ship. You will hear about treasure ships from bar maids or can find them randomly. They carry a lot of cargo. Keep two ships permanently. Sell the others. Keep a battle/fun ship and your big ship to carry supplies for long voyages. Certain special items decrease the unhappiness of your shipmates. Items such as musical instruments are invaluable for long sea voyages. Obtain these items from the Mysterious Traveler at the pub or from Governor's daughters. Recruit mates with specialties. There are many person(s) in the Caribbean which will decrease the unhappiness of your shipmates. Among others, the cook will provide better meals, the quartermaster will enforce discipline, etc. To obtain these special mates, ask the local barmaid for further information on the ship carrying them and try to capture those ships. Just because they are unhappy does not mean you have to retire soon. You can push the crew to the limit even though their status is "unhappy". However when they are "mutinous" you will be in trouble. Always balance your cash reserves with your crew size. By doing this, you can sail for more than two or three years without having to "divide the plunder".