 Early keels were propelled with a single large oar, handled by all the crew except the skipper; they had no rudder, and were steered by a second oar or "swape" over the stern.The crew worked with the flow of the river tides where practicable.Later the oars were supplemented by a single mast with a square sail attached to a yardarm, and latterly with a large spritsail and staysail, though the oars were still used to row when the wind was not favourable.