The Case Book published by the International Sailing Federation contains the only authoritative interpretations and explanations of the racing rules that ISAF publishes. ISAF’s Racing Rules Committee reviews new cases each year and those that are approved are published in the Case Book. ISAF approved 10 new cases this year, and some of them contain significant new interpretations of important rules.

Case 126 addresses the question of when two boats are on different legs of the course. The answer is obvious most of the time, but there are unusual circumstances in which the answer isn’t clear, and the answer can be critical to determining whether Rule 24.2 applies. Rule 24.2 states “Except when sailing her proper course, a boat shall not interfere with a boat . . . sailing on another leg.”

Case 126 addresses two situations in which it’s not obvious whether two boats are on the same or different legs.

Assume the race committee set a windward-leeward course with an offset mark near the windward mark. After starting, boats round mark W, mark O, mark L, and then finish between a committee boat and mark W. They round marks W, O, and L to port—in that order. Larry sails a great first leg and is the first to round mark W. However, he forgets to round the offset mark and heads directly for mark L after he rounds W. Further down the leg Wendy overtakes him. When it appears to Larry that Wendy will pass to weather, he luffs her and she protests. Thinking he hasn’t broken any rule, Larry doesn’t take a penalty. In her written protest Wendy alleges that, when Larry luffed, he sailed above hisproper course and interfered with her. In the protest hearing Wendy claims that Larry broke Rule 24.2 because the incident occurred while she was sailing on the leg to mark L, but he was sailing on another leg, the leg to mark O.

Obviously, Wendy is sailing on the leg to mark L when Larry luffs, but what leg is Larry sailing? Case 126 answers this question in stating: “For the purpose of determining whether Rule 24.2 applies to an incident, a boat is sailing on the leg that is consistent with the course she is sailing before the incident and her reasons for sailing that course.” Larry was sailing toward mark L, not mark O, and his reason for doing so was that he was unaware of the requirement to round mark O and, therefore, thought that the next mark for him was mark L. Applying this interpretation, Larry and Wendy were both sailing on the same leg, the leg to mark L, and so Rule 24.2 did not apply when Larry luffed.

Now consider a different scenario. Suppose that, as before, Larry does not round the offset mark. However, after sailing part of the way down the run he recognizes his error, changes course and begins to beat upwind to mark O. While on his way to O he encounters Andy, who has rounded O and is running downwind to L. Larry deviates from his proper course to mark O to interfere with Andy by forcing him to change course. Does Larry break Rule 24.2?

We can apply the principle quoted above from Case 126 to this incident. Clearly, when the boats meet Andy is sailing on the leg to mark L, but Larry is sailing toward mark O and he is doing so because he now knows he is required to round O. Therefore, Larry is sailing on the leg to mark O. Larry departs from his proper course to interfere with a boat on another leg and, therefore, breaks Rule 24.2.

Case 132 answers another question related to sailing the course: “When is a boat on a beat to windward?” Two rules require you to know the answer that question. Under Rule 18.1(a), if two boats are on opposite tacks on a beat to windward Rule 18 doesn’t apply between them, and under Rule 42.3(c), if you are on a beat to windward, you are not permitted to pump to initiate surfing or planing.

Many people confuse the terms “a beat to windward” and “the windward leg.” The case states that, for the purposes of rules 18.1(a) and 42.3(c), “a boat is on a beat to windward when the course she would sail to finish as soon as possible in the absence of all other boats is a close-hauled course or above.” Usually a boat is on a beat to windward when she is sailing on the windward leg. But that is, by no means, always true.

The diagram shows a snapshot of seven boats sailing on a windward leg, but only five of them, Franklin, Lucy, Patty, Sally, and Charlie, are on a beat to windward. At the moment the snapshot is taken, the course each of those five would sail to finish as soon as possible, in the absence of all other boats, is close-hauled. One of the five, Charlie, is shown sailing below close-hauled, but he was only doing so because he is required to keep clear of Sally. If she were not there, Charlie would’ve been sailing close-hauled.

Woodstock and Snoopy are, like the other five, on the windward leg. However, when the snapshot is taken they are overstood and the course that they would sail to finish as soon as possible is below close-hauled. Therefore, they are not on a beat to windward. If either of those two catches a wave or a gust, Rule 42.3(c) permits them to pump once to initiate surfing or planing. The other five may not pump.

There are circumstances, albeit rare, when a boat can be “on a beat to windward” while she is sailing on an offwind leg. Here’s an example. Barb and Bill are on a reach to mark X in light wind with a strong current setting them to leeward. Barb heads just enough above the rhumb line to X to enable her sail to directly over the bottom to X and round it without tacking. Bill, who is not aware of the effect of the current, doesn’t head as high as Barb and ends up down current and downwind of X, in a position from which he must sail close-hauled and tack in order to get back upwind to X. While he is sailing close-hauled and tacking he is “on a beat to windward.”

I am often asked why Rule 18.1(b) is in the rulebook, and why Rule 18.1(a) is not sufficient. Case 132 helps to answer those questions. Rule 18.1(b) states that Rule 18 does not apply “between boats on opposite tacks when the proper course at the mark for one but not both of them is to tack.” Rule 18 is not intended to apply when two boats sailing upwind on opposite tacks meet at a mark. Rule 18.1(a) applies to the majority of such meetings. But Rule 18.1(b) is needed to cover a minority of such meetings. These occur when two boats sailing upwind on opposite tacks meet at a mark while one of them is not on a beat to windward. Here are two examples of situations, which illustrate the need for Rule 18.1(b).

Let’s suppose Barb and Bill arrive at mark X on opposite tacks. Rule 18.1(a) does not apply because only Bill is on a beat to windward. Rule 18.1(b) does apply because the proper course at the mark for Bill, but not for Barb, is to tack. Now look at the diagram again to see a second example of the need for Rule 18.1(b). Suppose that Snoopy and Franklin arrive at the mark on opposite tacks. Rule 18.1(a) doesn’t apply because Snoopy isn’t on a beat to windward. Rule 18.1(b) does apply because the proper course at the mark for Franklin, but not for Snoopy, is to tack. In both examples, we intend that Rule 18 be “switched off” and Rule 18.1(b) is required to make that happen.

There is a second frequently asked question about Rule 18.1(b). Why are the words “but not both” in the rule? Consider Franklin and Lucy, two of the boats shown in the diagram. They are on the same tack, and the proper course for both of them at the mark is to tack. Because both must tack at the mark, Rule 18.1(b) does not apply, and therefore Rule 18 does apply. We intend that Rule 18 apply between those two because, if it did not, Lucy would be under no obligation to give Franklin mark-room and she would be permitted to luff him to the wrong side of the mark. It would be just like Lucy to spring that devious trap on Franklin.