Unlike with a fore-and-aft rig, 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), often pulled to windward to help turn the ship through the eye of the wind. The main (and often mizzen) sails are braced around onto the new tack as the ship approaches the eye of the wind. Once the ship has come about, the remaining sails are adjusted to align properly with the new tack. Because square-rigger masts are more strongly supported 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. Under these conditions, the choice may be to wear ship—to turn the away from the wind and around 240° onto the next tack (60° off the wind). Windsurfer rig – Sailors of windsurfers tack by walking forward of the mast and letting the sail swing into the wind as the board moves through the eye of the wind; once on the opposite tack, the sailor realigns the sail on the new tack. In strong winds on a small board, an option is the 'fast tack', whereby the board is turned into the wind at planing speed as the sailor crosses in front of the flexibly mounted mast and reaches for the boom on the opposite side and continues planing on the new tack. Kitesurfer rig – When changing tack, a kitesurfer rotates the kite end-for-end to align with the new apparent wind direction. Kite boards are designed to be used exclusively while planing; many are double-ended to allow an immediate change of course in the opposite direction. Proa – Double-ended sailing vessels, such as proas, may tack by shunting: turning off the wind, switching the sails and steering mechanism end-for-end and then proceeding on the opposite tack with the former stern functioning as the new bow, and with the outrigger on the windward side as before. Navigating