Rounding-up is a phenomenon that occurs in sailing when the helmsman (or tiller-handler) is no longer able to control the direction of the boat and it heads up (or "rounds up") into the wind, causing the boat to slow down or stall out. This occurs when the wind overpowers the ability of the rudder to maintain a straight course.
For example, the sailboat may heel over so far that the rudder no longer engages in the water, or only to such a small extent that it can no longer steer the boat. When this happens is dependent on a number of factors such as the velocity of the wind, design of the sailboat hull and rudder and shape of the sails. While not usually dangerous, the occurrence of rounding up can be startling to the skipper or helmsman of the boat. The boat turns into the eye of the wind with all sails fluttering. However, once the boat has rounded up and lies into the wind, control can be readily regained by steering the boat off the wind to refill the sails with wind and regain the desired course. Rounding-up is in fact a safety design of most sailboats that can help prevent a knock-down and allow the helmsman to regain control of the boat. An occasional round-up may simply be the result of a strong gust of wind. If it occurs regularly, this may be a sign that too much sail is raised and the crew may need to lower one or more sails, change to smaller sails, or reef in the mainsail. In smaller sailboats such as a Sunfish or Laser where the sail cannot be lessened or reefed, frequent round-ups may be a sign that the wind conditions are becoming too strong for the boat, such as anything approaching a Small Craft Exercise Caution condition, and the sailor(s) should immediately proceed to shelter.