Most cruise ships travel about 20-25 knots. A Nautical Mile is about 1.15 stutue miles. However they don't always go that fast. Sometimes when they are going to a port overnight that is not that far...
Container ships truly average 23 kt made good (actual speed). Break bulk/general cargo vessels - 10-12 kt.
Reefer boats (fruit boats) 20-28kt. (credit to for written definition goes to others.)
Depending on the size of the ship and the ships' engine, top speed varies. In general, you can expect top speed around 40 knots, and service speed (the speed that is most commonly used when...