The key here is the very last few seconds when "S" started to round up. What did "P" do? If "P" jagged the stick and did an emergency bare away immediately after "S" changed course and a collision was still going to happen then I'd say "S" has fouled. If "P" delays by even a short time and then reacts or only a mild change of course then "P" will clearly have fouled. The devil is in the detail on this one.
Things aren't quite that simple. You cannot put a specific time or distance limit on "room to keep clear". There's far too much variation depending on the boats involved and the sailing conditions. For example, a small catamaran sailing upwind can slow down very effectively by letting the sails out. That's an easy technique for ducking. It's entirely useless for an 8000lb blue-water boat. She would have to act sooner in a cross and turn down to duck. Similarly, a laser can roll-tack in 2 seconds within one hull length. A tornado simply cannot. A port-tack laser traveling at speed but failing to cross 2 boatlengths from contact is still keeping clear. A tornado in the same circumstance is not.
RRS 16.1 states "When a right-of-way boat changes course, she shall give the other boat
room to
keep clear", where
room is defined as "The space a boat needs in the existing conditions while manoeuvring promptly in a seamanlike way", and
keep clear is defined as "One boat keeps clear of another if the other can sail her course with no need to take avoiding action..."
Therefore, each and every time S changes course (and here "course" means compass bearing), she must give P the opportunity to assess the change and respond. P's response must be prompt, but need not be unseamanlike.
Normally, if S and P are involved in a close crossing, then it is reasonable to expect P to watch S throughout. P need not anticipate S's actions, but she must recognize and respond to them without delay. S may change course, but she must give P sufficient time and space to see the change, decide what action to take, and do it -- all in a seamanlike way. Actions that might cause damage or injury are not seamanlike. S cannot force P to capsize, nor crash-tack, nor bear away so hard that she risks losing control. Generally speaking, if P delays responding, or does not exhibit competent seamanship, then P fails to keep clear. If P acts promptly and in a seamanlike manner but cannot keep clear, then S failed to give sufficient room. If P manages to keep clear, but had to perform an emergency or unseamanlike maneuver, then S failed to give room.
ISAF Cases 60 and 92 apply.
Regards,
Eric
