Starboard is sailing his proper course which is up and down based on the wind.
I often hear sailors claim "proper course" - usually when it doesn't apply. By my count, the rules only mention "proper course" in three places: RRS 17.1 (which restricts a boat from sailing above her proper course), RRS 17.2 (which restricts a boat from sailing below her proper course), and RRS 18.4 (which restricts a boat to her proper course until she gybes). This situation is not one of these three cases, so "proper course" is irrelevant.
For most of the time period in question he can do what he wants. (he can't be accused of hunting a port tack boat) Port simply has to adjust as best he can.
Near the beginning of the encounter between the two boats, P may be able to react to S's course changes and still keep clear. During that time, P must react to S's actions. Late in the encounter, a change of course by S may render P incapable of keeping clear. During that time, S must hold her course.
Exactly where those obligations change is a judgement call, given that it changes dramatically with the boat type and sailing conditions. S may draw the line in one place; P might draw it in another, and the protest committee could place it somewhere else. You may not appeal the facts found in a protest hearing (only the application of the rules), so behooves you to consider the protest committee's interpretation.
IMO... S's obligation to give room to keep clear comes in the last few seconds... when in this case he dramatically altered course to avoid a collision. What could port EVER SAY in this circumstance.... IMO, His only argument would be... I was clear... the change in course was unnecessary. He would need more evidence to support the claim he was clear and S's change was unnecessary.
S's obligation extends as far as necessary for P to keep clear. Depending on the boats and the weather, that may be more than just a few seconds. If, for example, S changes course enough that P must tack, then S must give P time and space to assess the change and tack - promptly and in a seamanlike manner. How long does it take you to complete a tack (perhaps coming in from the trapeze with crew) - more than a second or two?
In this case, P can (and does) say that S changed course and P reacted, and S changed course again - leaving P unable to keep clear. I don't think we are able to resolve that difference in testimony here, but a protest committee will make a decision one way or another.
With the exception of RRS 18.2(e), the rules do not put a "burden of proof" on any party in a protest. Instead, the protest committee must find the facts and determine whether or not sufficient room was given, and whether or not avoiding action was necessary. ISAF Case 50 speaks to this issue. P and S both need to present and defend their positions.
Regards,
Eric
