Freshly painted and shipshape, batteries charged and gas cylinders ready to flash warnings through another April-to-November shipping season, the sentinels of the St. Lawrence Seaway are taking their positions for 1962. Studded along 150 zigzagging miles of seaway from Beauharnois, 20 miles upstream from Montreal, to Kingston at the eastern end of Lake Ontario, are 240 Canadian-operated navigational buoys. These steel signposts guide mariners from the seven seas along the narrow channels hidden beneath the water's surface. They warn against wrong turns and wanderings off that would leave fine-looking ships helplessly beached on the river's shoals and banks. Every year when the last ships pass by (nearly 7,000 transits in 1961) the buoys are lifted from the water, their positions marked by wooden spar buoys which duck under winter ice floes with little damage, and taken ashore for overhaul. Light-flashing devices are cleaned, repaired, put in shape for the next year -- ready to guide another 23 million ship-borne tons of cargo along the nation's inland trade artery.