A guy in my area had a pair of sweeps, long heavy oars, that he set up in the cockpit. He could steer with the tiller between his knees, facing forward of course, while he slowly worked the sweeps to manuever in and out of the basin after dropping his sails in a more open area. Never really talked to him so I can't tell you if he used the sweeps for anything more than that. The boat was about 30 ft. long. As far as the oar size, the ones he used were at least 10 ft. long and heavy, solid wood. So I'm not sure how a super light SUP paddle would fare moving a keel boat.
The Royal Navy normally carried sweeps as aux power on smaller 5th rates (frigates) , 6th rates, sloops, and unrated ships of war.
Good luck. I think I'd just save my money and get a small 2-3 hp kicker to get me out to the big water.
