Shortly after the United States gained independence in 1783 trade was instituted from East Coast ports with the West Coast to gather furs in the Maritime Fur Trade to trade with China for porcelain, silk, spices etc.. British Royal Navy commander George Vancouver sailed up the west coast past the mouth of the Columbia River and in April 1792 and observed a change in the water's color, which implied there may be a major river emptying into the Pacific. Later that month, Vancouver encountered the American captain Robert Gray at Grays Harbor—later named that in his honor. Gray also reported that he had seen the possible entrance to the Columbia a few years earlier and had spent nine days trying but failing to enter the river over its extensive sand bars and turbulent waves; but bad weather forced him to give up. Gray returned to the river mouth a second time in May 1792. This time he ordered a small sailboat launched to attempt to find a safe passage across the sand bars and turbulent waves by sounding (measuring the depth with a weight attached to a line of known length) the water depth to find a channel deep enough for his ship. Finally in the evening of 11 May 1792, Gray's men found a safe channel and he and his crew sailed their ship "Columbia" into the estuary of what he named the Columbia River after his ship.