making ship character rotate slowly in circle

I am creating a player of a ship image in a tiled map. I am able to rotate it around. But to make it look realistic, i want the ship to move around slowly in circle like a real ship. I do not want the ship to rotate so fast like from up to down immediately. Currently , I could get any codes as how to do it. Can anybody guide with me with some codes?

[358 byte] By [Hanz_05a] at [2007-11-27 8:00:00]