Two boats, W and L, are sailing downwind on the same tack in conditions where they would normally use spinnakers in place of headsails to finish as soon as possible. The next mark is directly downwind from their current positions.
 
 W has a problem hoisting her spinnaker and L, sailing faster, establishes a leeward overlap from clear astern and is subject to rule 17. In order to gain a tactical advantage over W, L decides to continue sailing with her headsail and to delay hoisting her spinnaker.
 
 L then sails the course that results in the best VMG (‘velocity made good’, velocity towards the next mark) for a boat sailing downwind with a headsail. That course is above the course that would result in her best VMG if she were using her spinnaker.
 
 W protests L alleging that, by not hoisting her spinnaker and sailing a lower, faster course in order to finish as soon as possible, L breaks rule 17. In the hearing L’s representative stated that, to finish as soon as possible in the absence of W, L would have hoisted her spinnaker and sailed a faster and lower course.

Question
When L delayed hoisting her spinnaker and instead sailed the course that resulted in the best VMG for a boat sailing downwind with a headsail, did she break rule 17 by sailing above her proper course?

Answer
No. A boat’s proper course at any moment depends on the existing conditions. Some of those conditions are the wind strength and direction, the pattern of gusts and lulls in the wind, the waves, the current, and the physical characteristics of her hull and equipment. The sails that she has set are part of her equipment and, therefore, one of the conditions on which her proper course depends. While L was sailing with her headsail, her proper course was the course that gave her the best VMG with her headsail, and not her spinnaker, set. L did not sail above that course so she did not break rule 17.

There is no requirement in the racing rules for a boat to hoist her spinnaker at any particular time or for her to finish as soon as possible. There could be a variety of reasons, including tactical considerations, why a boat would not use a spinnaker. Therefore, even though L stated that in the absence of W she would have hoisted her spinnaker and sailed a lower course, L broke no rule by continuing to sail with her headsail instead of her spinnaker. (See Case 78 for a discussion of tactics that interfere with or hinder another boat’s progress.)

World Sailing 2014