When tacking, a square-rigged vessel's sails must be presented squarely to the wind and thus impede forward motion as they are swung around via the yardarms through the wind as controlled by the vessel's running rigging, using braces—adjusting the fore and aft angle of each yardarm around the mast—and sheets attached to the clews (bottom corners) of each sail to control the sail's angle to the wind. The procedure is to turn the vessel into the wind with the hind-most fore-and-aft sail (the spanker), pulled to windward to help turn the ship through the eye of the wind. Once the ship has come about, all the sails are adjusted to align properly with the new tack. Because square-rigger masts are more strongly braced from behind than from ahead, tacking is a dangerous procedure in strong winds; the ship may lose forward momentum (become "caught in stays") and the rigging may fail from the wind coming from ahead. The ship may also lose momentum at wind speeds of less than . Under these conditions, the choice may be to "wear ship"—to turn the ship away from the wind and around 240° onto the next tack (60° off the wind).