Excerpt from Understanding the Racing Rules of Sailing
by Dave Perry,

Let's look at some common situations when rules 16.1 and 16.2 will come into play.

When a port-tack boat (P) and a starboard-tack boat (S) are converging on a beat:

Situation 1: P will cross S by half a boat-length or so. When about two lengths apart, S hails “Starboard” and makes a medium fast luff toward P. P, who has been watching S, continues for a couple of seconds, realizes she can not cross S safely, and makes a routine tack to starboard tack on S’s lee-bow. S could continue straight-ahead, but decides to tack away to avoid P’s bad air.

Resolution: When the boats are converging, P is required to keep clear under rule 10 (On Opposite Tacks). When S changes her course near P, she is required to give P room to keep clear (rule 16.1). P is able to tack in a seamanlike way to continue keeping clear of S. S is able to sail her course without concern of hitting P. Therefore S gives P the room she needs to keep clear, and P does keep clear. Neither boat breaks a rule.

Situation 2: Same scenario as above but the boats are a bit closer together when S luffs towards P. P tacks immediately in response to S’s luff. P’s tack is a routine tack to starboard tack on S’s lee-bow. S tacks away to clear her air.

Resolution: Note that rule 16.2 does not apply (because P is not passing astern of S), so the fact that P had to “immediately” change course to avoid S is not, in and of itself, proof of a breach of rule 16.1 by S. If in fact P’s tack was “seamanlike,” then P properly kept clear under rule 10, and S properly gave P room to keep clear under rule 16.1. But part of sailing in a “seamanlike way” is looking before changing course. Keeping in mind that P does not need to anticipate the fact that S “might” change course near her, if S gets so close to P before luffing that P will need to tack immediately, typically P will not have time to look over her shoulder to see if she is clear to tack, let alone prepare her crew for the tack, and S will break rule 16.1 if P fails to keep clear. This is particularly true in a fleet race as opposed to a match race where there are no other boats besides P and S.

Situation 3: P will cross S by half a boat-length or so. When about one length apart, S hails “Starboard” and makes a medium fast luff toward P, putting the two boats on a collision course. P holds her course to get across S as quickly as she can (tacking would make matters worse because she would be turning directly in front of S). Just before contact, S bears away and protests.

Resolution: The first job of the protest committee will be to determine if P actually keeps clear. Clearly she doesn’t because S needs to take action to avoid hitting her (see definition Keep Clear). Therefore, P breaks rule 10 (On Opposite Tacks). Their next task is to decide if, when S changes course, she gives P room to keep clear. Clearly she doesn’t because there is nothing P can do to get out of S’s way. Therefore S breaks rule 16.1 and is disqualified; and because it was her “illegal” course change that compelled P to break rule 10, P is exonerated under rule 64.1(b) (Penalties and Exoneration).

NOTE: there does not have to be contact in order for a boat to break rule 16.1. Anytime a right-of-way boat changes course near a give-way boat, rule 16.1 comes into effect. If it is determined that there would have been a collision if the right-of-way boat had not taken subsequent avoiding action, then that establishes that the give-way boat did not keep clear. At that point, either the give-way boat will be disqualified under the appropriate Section A – Right of Way rule, or the right-of-way boat will be disqualified under rule 16.1 (and the give-way boat exonerated under rule 64.1(b)). (See ISAF Case 60.)

Situation 4: P bears away to “duck” (pass astern of) S. When a length and a half away, S bears away towards P and P immediately bears away further to avoid S. S luffs back up to close-hauled and P safely passes close astern of her. P protests.

Resolution: By bearing away, P is keeping clear of S by sailing a course to pass astern of S. When S changes her course, P needs to immediately bear away further to keep clear of S. By causing P to have to immediately change her course to continue keeping clear, S breaks rule 16.2. This is so even though S gives P space to keep clear in a seamanlike way, i.e. S does not break rule 16.1. (See ISAF Case 92.)

BOTTOM LINE: Rule 16.1 is very strict, and S must be very careful with her course changes when near P. Again, course changes when closer than two lengths from the give-way boat are risky.

“I assume from all this that if I get a wind shift on a beat, I can’t follow the shift and hit a port-tack boat that is just crossing my bow?”

That’s absolutely right. Rule 16.1 applies to any course change, regardless of the reason. If you find yourself in the situation where P is crossing you and you get a favorable wind shift and want to head up and pass close astern of P, but you know that P doesn’t have room to tack away after you do head up, simply let P know, with a hail or a wave, that she can continue on across you as you head up to pass close astern of her.

“Do I have to hail before changing my course? And if I do warn the other boat with a hail that I am about to change course toward them, does that count as ‘giving room’ ?”

No and No. First, the rule does not require a hail. Second, the rule is about “changing course,” which means that the test of whether you gave room will begin at the moment you actually change your course. However, a clear hail alerting the give-way boat that you are about to change course is strong evidence that you intend to give her room to keep clear when you do change course, and is therefore strongly recommended.