42.1 Basic Rule
Except when permitted in rule 42.3 or 45, a boat shall compete by using only the wind and water to increase, maintain or decrease her speed. Her crew may adjust the trim of sails and hull, and perform other acts of seamanship, but shall not otherwise move their bodies to propel the boat.
42.2 Prohibited Actions
Without limiting the application of rule 42.1, these actions are prohibited:
(a) pumping: repeated fanning of any sail either by pulling in and releasing the sail or by vertical or athwartships body movement;
(b) rocking: repeated rolling of the boat, induced by
(1) body movement,
(2) repeated adjustment of the sails or centreboard, or
(c) ooching: sudden forward body movement, stopped abruptly;
(d) sculling: repeated movement of the helm that is either forceful or that propels the boat forward or prevents her from moving astern;
(e) repeated tacks or gybes unrelated to changes in the wind or to tactical considerations.
(a) A boat may be rolled to facilitate steering.
(b) A boat's crew may move their bodies to exaggerate the rolling that facilitates steering the boat through a tack or a gybe, provided that, just after the tack or gybe is completed, the boat's speed is not greater than it would have been in the absence of the tack or gybe.
(c) Except on a beat to windward, when surfing (rapidly accelerating down the front of a wave) or planing is possible, the boat’s crew may pull in any sail in order to initiate surfing or planing, but each sail may be pulled in only once for each wave or gust of wind.
(d) When a boat is above a close-hauled course and either stationary or moving slowly, she may scull to turn to a close-hauled course.
(e) If a batten is inverted, the boat’s crew may pump the sail until the batten is no longer inverted. This action is not permitted if it clearly propels the boat .
(f) A boat may reduce speed by repeatedly moving her helm.
(g) Any means of propulsion may be used to help a person or another vessel in danger.
(h) To get clear after grounding or colliding with a vessel or object, a boat may use force applied by her crew or the crew of the other vessel and any equipment other than a propulsion engine. However, the use of an engine may be permitted by rule 42.3(i ).
(i) Sailing instructions may, in stated circumstances, permit propulsion using an engine or any other method, provided the boat does not gain a significant advantage in the race.
Note: Interpretations of rule 42 are available at the ISAF website or by mail upon request.