 Clippers, outrunning the British blockade of Baltimore, came to be recognized as ships built for speed rather than cargo space; while traditional merchant ships were accustomed to average speeds of under 5 knots (9 km/h), clippers aimed at 9 knots (17 km/h) or better.Sometimes these ships could reach 20 knots (37 km/h).Clippers were built for seasonal trades such as tea, where an early cargo was more valuable, or for passenger routes.