Understanding Rule 42

This post is born from hearing sailors frequently misunderstand and misstate the World Sailing rule 42. Unfortunately, rule 42 is complex and has many parts and exceptions and comes with a full set of interpretations. Unlike the simple port/starboard rule 10, rule 42 is not one that you can fully understand without some study and reflection.

This is unfortunate that rule 42 is so difficult, because it absolutely essential as it describes and governs how we sail downwind and it enables the magic of downwind S-turning in boats like the Aero or Laser.


Heard in the Boat Park

On the water, after racing, and on social media, I'm sure we've all heard comments like:

Jim was rocking the boat too much, he's breaking rule 42 and cheating.

Olivia was turning too frequently and it wan't planing conditions ... she broke rule 42.

Theo was rocking and turning more than any other boat ... he's clearly breaking rule 42.

Even experienced sailing commentators seem to regularly get it wrong. In a recent ISAF world cup commentary in a Medal Race, you can hear an experienced commentator confusing the rule on rocking with the rule for pumping.

"Your only allowed to rock once per wave to get the boat planing"

These comments may come from a poor understanding of rule 42 or not understanding the specifics of the rule. Unfortunately, broad generalizations and mischaracterizations of rule 42 confuse rather than clarify how to legally use kinetics when sailing downwind in a small dinghy.

Common Misconceptions

A few of the common erroneous beliefs about rule 42 seem to be:

  • Repeatedly or frequently rocking the boat at all is illegal.

  • Repeatedly turning the boat downwind if planing conditions do not exist is illegal.

  • Rolling the boat downwind if planing conditions do not exist is illegal.

  • Rocking or turning more than other boats is illegal.

  • Trimming the sail after rocking and turning is pumping the mainsheet and is illegal.

These are all WRONG. The sailing rules do permit the use of kinetics including rocking and pumping provided these activities are done according to the strict rules and exceptions specified in rule 42.


Sailing an Aero or Laser using kinetics is fast and is well regulated by rule 42. It is also one of the most fun parts of sailing. It is an art form, like dancing. So whether we like it or not, we need to learn how to do it well, fast and legally.


You can sail directly to the mark, but especially in waves, this is usually slower than reaching or sailing by the lee. Sailing at an angle instead of dead downwind, builds apparent wind and is significantly faster (except perhaps in a gale). When coupled with synchronizing your course to take most advantage of waves as they pass your boat, your speed can be significantly faster than sailing straight to the mark.

The core technique is to:

  • Accelerate by turning the boat to reach up or down by the lee.
  • Turn the boat by rolling rather than by using the rudder.
  • Catch waves and accelerate toward the mark.
  • Repeat.

Rolling the Boat


Turning your boat by using the tiller is very slow as the rudder acts as a break. Turning by heeling the boat is much faster. When heeled, an Aero or Laser will naturally turn due to the shape of the hull. Heel the boat to leeward and the boat will head up. Heel to windward and the boat will bear away. In this manner, the rudder does not need to be used much at all.

You can initiate heeling your boat, by moving your weight or by trimming or easing the mainsheet. For example, you can ease the mainsheet to cause the boat to heel to windward and thus initiate a downturn to sail by the lee.

In this picture, I'm doing a swift downturn by letting the boat heel to weather. Note how straight the tiller is. In fact, I'm using no pressure, the rudder is simply following the water flow.

An additional benefit, is that by rolling the boat during the turn, we move the sail in an arc through the air which increases the apparent wind and lift generated by the sail. This generates more force and will accelerate the boat.

Okay, so this is faster, but how can we do this legally within the rules?

The Rules

I've included a subset copy of rule 42 below at the end of the post and here are the links to the full rules documents. Please read the rule closely in conjunction with this discussion.

Rule 42 Summary

Rule 42 specifies a general intent, a set of prohibitions and a limited set of exceptions. The intent is that we propel the boat using wind and water, not our bodies and unrestricted kinetics. The prohibitions spell out five things you generally cannot do: pump, rock, ooch, scull or repeated tacks/gybes unrelated to wind/waves. Overriding these prohibitions, the rule exceptions and interpretations specify exactly when we can pump and rock the boat.

What is Prohibited?

The rule 42 BASIC4 interpretation says that any single action of the body that clearly propels the boat is prohibited. This is a very important term. "Clearly propel" means actions that provide an immediately acceleration to the boat, which then quickly dissipates as the boat slows to normal speed. For example: an aggressive roll tack in light air and flat water that gives a short few second burst of speed.

Rule 42.2 says that repeated pumping and rocking are prohibited whether initiated by body movement, sails or steering. Note that the BASIC4 interpretion says that a single boat roll that does not clearly propel the boat is legal. Also background rolling (ROCK3) due to variations of wind and waves is not illegal. The sailor does not need to make efforts to limit background rolling (ROCK4) even if it is beneficial to the boat, provided it does not "clearly propel the boat". On-the-water juries should not penalize unless the sailor is demonstrably causing the rocking.

What is Permitted?

The rule 42.3 Exceptions and part (a) in particular is where the magic happens. This clause coupled with the PUMP2, PUMP4 and the ROCK interpretations provide a set of explicit exceptions where you can use kinetics to sail your boat faster more effectively in waves and changing wind.

The rule 42.3 (a) says

"a boat may be rolled to facilitate steering" and the ROCK6 interpretation says: "Heeling to windward to facilitate bearing away and heeling to leeward to facilitate heading up are permitted. The heeling of the boat has to be consistent with the boat's turn."

This means the rules explicitly permit sailing your boat downwind and repeatedly turning by changing from reaching to by-the-lee. You can roll your boat, provided you turn the boat at the same time according to the pattern of the waves. There is no limit here on turning your boat as much as you like (see ROCK7 below), but your heel must match the turn. This matching should be in turn direction, rate and magnitude. i.e. a small change in course would have a small roll and a bigger change can have a bigger, more aggressive roll.

You can also suddenly ease the mainsheet on your downturn to go by the lee and this will give a nice leach flick (PUMP4). Similarly, you can quickly trim in during your up turn to a broad reach (PUMP2).

Waves Required

The ROCK7 interpretation limits the conditions when we can use this technique:

"Repeated rolling not linked to wave patterns is rocking prohibited by rule 42.2(b), even if the boat changes course with each roll."

This restricts repeated turning with rolling to conditions with waves. Given such suitable conditions, it is perfectly legal to let the boat roll to leeward, turn up and then flatten the boat and trim in the mainsheet to match the new course. Similarly, you can ease the mainsheet, let the boat heel to windward, bear away, then flatten the boat. Further, you can do this repeatedly, provided you are doing so according to the pattern of the waves.

In practice this means there must be waves of sufficient size and that your turning must match the waves at that time. The waves may be quite small, but must be sufficient to accelerate your boat and justify the change in course. In practical measures, waves as small as 15cm can easily accelerate a light boat like an Aero and wind conditions of as little as 7-10 knots are applicable.

You should not have a "clock-like" pattern to your turning, because waves are never consistent, and if you are like a metronome, then you are not matching the waves.

Note: there is nothing about surfing or plaining in this rule. This means it is perfectly legal to use this technique in small waves when there is no possibility of planing. Many sailors think that planing conditions must exist before you can use this technique. They are WRONG. They are mixing up the rules for rocking 42.3 (a) and pumping 42.3 (c).

A frequent cause of sailors receiving a rule 42 penalty is rolling the boat while keeping a (relatively) steady straight course. i.e. not turning sufficiently to match the role. On videos, commentators sometimes remark the penalty was for rocking to aggressively. That is incorrect, the violation is typically for repeatedly not turning sufficiently to justify the roll.

Lastly, remember, the goal is to catch waves and leverage the rules, not the other way round.

Note on Flat water

In relatively flat water and steady wind, where there are no meaningful waves, you cannot repeatedly roll and turn the boat downwind. But this does not mean you need to be static either. The wind will vary and while you cannot repeatedly roll, when you do want to change direction to transition from reach to by the lee or vice-versa, use the same heel to turn technique. You can turn, but your cadence must match the wind or tactical changes. i.e. it generally will be much slower.

In summary, what can I do?

  • Change course as often as you like.

  • Roll the boat to facilitate turning.

  • Use rolling to facilitate turning provided you are consistent with the turn and match the wave pattern.

  • Allow rolling caused by the waves or wind.

Summary — What is Illegal?

What can I not do?

  • Repeated rolling caused by the sailor without changing direction.

  • Repeated rolling caused by the sailor that does not match the waves.

  • Repeated rolling caused by the sailor that does not match the turn.

  • Kinetics that clearly propels the boat by itself.

Now You Know

With your newfound knowledge of rule 42, you can clarify common misunderstandings such as when a sailor says:

"He was turning too aggressively"

You can respond that rule 42 does not limit turning, only rolling.

"He was rolling more than other boats"

You can respond that this is permitted provided he is turning when rolling and he is matching the turn and the wave pattern.

"He was pumping the main out of every turn, but there was no planing conditions"

You can respond to say that rule 42 permits trimming the main after turning even if no planing conditions exist, provided that the trim did not clearly propel the boat and the trim was appropriate for the new course.

"He was rocking and no planing conditions exist"

You can respond to say that rule 42.3 (a) does not require planing conditions to exist, only waves. They are mixing up parts (a) and (c).


I hope this discussion has helped your understanding of rule 42. To successfully and legally use downwind kinetics in an Aero you need to practice. Club fleets need to understand and support sailors trying to master these techniques and not be overly critical when sailors step over the legal limits. The rules still apply, and turns must be done, but allegations of cheating are not appropriate when learning new techniques.



  • Surfing: Rapid acceleration down a wave.
  • Pump: A single pull on a sail that is unrelated to wind or waves.
  • Roll: A single cycle where the mast goes to leeward and back to windward or vice versa.
  • Rocking: Repeated rolling of the boat.
  • Repeated: More than once on the same area on a leg.

Rule 42

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 athwartship body movement;
  • (b) rocking: repeated rolling of the boat, induced by (1) body movement, (2) repeated adjustment of the sails or centreboard, or (3) steering;
  • (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.

42.2 (a) Pumping Interpretations

  • PUMP 1: Fanning is moving a sail in and out not in response to wind shifts, gusts or waves.
  • PUMP 2: Pulling in and releasing a sail in response to wind shifts, gusts or waves is permitted, even if repeated (see rule 42.1).
  • PUMP 3: Except when permitted under rule 42.3(c), one pump may be prohibited under rule 42.1.
  • PUMP 4: A flick of a sail resulting from the sudden stopping of an eased sheet is permitted.
  • PUMP 5: One flick of a sail due to body pumping, or a pump not permitted by rule 42.3(c), is in the yellow light area. Body movement that does not result in a flick of a sail does not break rule 42.2(a), but may break other parts of rule 42.
  • PUMP 6: Repeated flicks of a sail due to body pumping are prohibited.

42.3 Exceptions

  • (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 World Sailing website or by mail upon request.

42 Interpretations (subset)

  • BASIC 4: Except when permitted under rule 42.3, any single action of the body that clearly propels the boat (in any direction) is prohibited.
  • ROCK 1: A roll of the boat caused by a gust or a lull followed by a corrective body movement to restore proper trim is permitted by rule 42.1.
  • ROCK 2: One roll that does not clearly propel the boat is permitted.
  • ROCK 3: Background rolling is permitted. Boat’s crew is not required to stop this type of rolling.
  • ROCK 4: Adopting any static crew position or any static setting of the sails or centreboard, even when stability is reduced, is permitted by rule 42.1 and is not prohibited by rule 42.2(b).
  • ROCK 5: A single body movement that is immediately followed by repeated rolling of the boat is prohibited
  • ROCK 6: Heeling to windward to facilitate bearing away and heeling to leeward to facilitate heading up are permitted. The heeling of the boat has to be consistent with the boat ’s turn.
  • ROCK 7: Repeated rolling not linked to wave patterns is rocking prohibited by rule 42.2(b), even if the boat changes course with each roll.


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