haul down
On a sailboat, to collapse is the operation that consists of descending a sail that was in position to store it. To sail a sail, it is necessary to release the halyard that keeps it hoisted. This operation can be carried out either because the sail is no longer necessary or because, since the wind conditions have changed, it is necessary to hoist a sail with a more suitable weight. The sail may also be partially collapsed to reduce its surface area as a reef grip. If the sail is completely slumped, it can be either simply flattened flat deck or folded over the boom or stored in a sail bag that will be stored in the boat.