PART 2


This case is worthy of close study. Blue must give room for Yellow to pass Green, because Green, ahead, is an obstruction – yet as soon as Yellow is actually passing Green, Green is no longer an obstruction! Instead Blue is now the obstruction. This is known as the ‘paradox of the disappearing obstruction’. It arises only when the obstruction to two overlapped boats is another boat that is racing, and then only when a leeward overtaker like Blue chooses to pass to leeward of the boat ahead. For Green, it does not matter whether she is being passed to leeward by one, two or ten boats – as soon as there is a leeward overlap, Green loses her right of way, and may now need to act to keep clear. The important implication appears to be that, as soon as the three boats are overlapped, Blue can start to luff, as long as she complies with rule 15 and then rule 16.1. The whole scenario is somewhat unlikely in a reaching situation, but very real when sailing downwind. It can also occur when boats are trying to secure a place in a busy starting line-up, as shown in WS 117.


The right to room is subject to the outside boat’s ability to give it, relative to the time the overlap began. If the overlap begins close to the obstruction, the right-of-way boat may not be able to give room: if so, she does not have to. Suppose that an obstruction can be passed on either side. If a boat just clear ahead and sailing a course to windward of a boat clear astern chooses to pass an obstruction to leeward, and bears away to do so, her course change may make the other boat overlapped to leeward, and therefore now the right-of-way boat. The right to choose which side to pass the obstruction passes to the leeward boat. If the leeward boat now decides that she wishes to pass to windward of the obstruction, she may do so provided that the other boat can now luff to give her room to do so1


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When the ‘disappearing obstruction’ paradox changes a right-of-way boat to a keep-clear boat that must also give room to a leeward boat, WS 117 points out that rule 19.2(b) requires her to do that only if she is able to do so, which may be difficult if she is in turn one boat of many stacked up on a starting line – and an intervening boat is limited by rule 15.


Two further points deserve consideration. Firstly, when an obstruction can be passed on either side by two overlapped boats approaching on the same tack, then if rule 17 applies to the leeward right-of-way boat’s overlap, she can take the windward route past the obstruction only if that does take her above her proper course. Secondly, rule 21, Exoneration applies when passing obstructions, for instance when a windward inside overlapped boat does not keep clear of the leeward right of way boat because the leeward boat is not giving her enough room to avoid the obstruction.


WS 49


A boat is entitled to room even if it was needed only because she created the overlap, for instance by tacking to a leeward overlap2


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When the obstruction to the boat needing room is a right-of-way boat approaching rapidly, WS 49 shows that the boat that has to give that room will normally be presumed to be aware of the situation and to know that she has to give room, even if there is no hail for room, and even if the boat needing room does not try to take the room3


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Because the outside boat is deemed to be aware of all that is happening inside and ahead of her, and to act when needed without being hailed to do so, this is more difficult for the outside boat when there are three overlapped boats approaching an obstruction, and even more difficult when the obstruction is then a right-of-way boat in motion. When approaching an obstruction, just as much when approaching a mark, the room that an outside boat must give a middle boat includes, by definition, room for the middle boat to comply with a Part 2 rule such rule 19, and so give room to a third boat inside her. WS 114 explains this in the context of approaching a mark, but it applies equally when approaching an obstruction. One complication is that the location of a mark will be known to all, whereas a leeward right-of-way boat may not be aware of the obstruction that requires her to give room to windward boats.


There will be more time for compliance with rule 19(b) when the right-of-way boat that is the obstruction is travelling in the same direction of the boats between which room must be given.


1 WS 124 2 WS 33 3 WS 49 is a case published to illuminate protest hearing procedural issues, but which supports these points, partly implicitly. I have again reorientated the World Sailing diagram, which I think gives it a new perspective


RYA The Racing Rules Explained 93


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