First, let me say thanks to Colleen and Ang for your input.

I have for a long time wondered if there is an unavoidable conflict in the rules.

The allowance in the last sentence of RRS 14 and the reality of seamanlike safety.

We have a few concepts and words which need sorting out. 'Needs'.  'Clear'.  'Reasonable'.  'Apprehension'.

I also find that there are a couple of general PC habits.  1.  To jump to the conclusion that Keep Clear is wrong and Right-of-way is right.  2. To use Case 50 as a crutch when the balance of probability is 50-50.

So, this thread is an attempt to investigate those.  I admit though, setting up the question is quite hard.

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My scenario involves two boats with a difference of opinion.  L believes that there may be a collision and acts.  W is all over the situation, watching carefully to the extent that it was never going to be close.  (I deliberately didn't include distances or boat lengths.  Simply, that W was deliberate and cautious on the timing her turn.)  Yet, cautious-L still took action.

Case 26 and Case 123 - I don't think these are directly relevant here.  These cases are based on it being or becoming 'clear' that KC was not keeping clear and whether RoW must act.  In Case 23, P was not keeping a good lookout and did not respond to hails.  Case 123 is about whether P should have acted or not.

In my scenario, it never became 'clear' that W was not keeping clear.  The helm was experienced and watching closely.

Case 88 is probably the strongest case cited.  On the surface it looks close to my scenario.  It makes clear that there is a difference between avoiding contact and 'keeping clear'.  This is true and important.

Then there is a list of factors which along with the definition of Keep Clear led to the appeal decision that KC broke the rule.

1) Collison course
2) Minimal Distance between the boats - Not much distance
3) Minimum time - Not much time
4) Required course change needed - Large course change
5) Manoeuvre times

But 2, 3 and 4 each are based on close quarters of boats in Case 88.  My scenario hasn't said anything about distances (or times or close quarters).  Again, I left this open.  I want the scenario to be based on mixed judgements alone.  Ang has agreed that distances need to be part of the investigation.  I fully agree.  This is what I was hoping someone would point out.

If W was wating until the distance was 3 boat lengths (say 15 seconds) from L and if L thought there was going to be a collision if she didn't react before W was less than 3 boat lengths, then Case 88's relevance is diminished.  Those distances and times cannot normally be said to lead to the decision of rule breach like in Case 88.

Case 50

That leaves us with Case 50.  Both Ang and Colleen suggest that in this Rule 11 situation, the principal of Case 50 (Reasonable Apprehension) is applicable.

My first long-time consideration is whether Case 50 can be transferred to 'all' right-of-way/keep clear situations.  The case doesn't indicate this or specify it can't be used for R11, 12, 13 etc...  But it is a RRS 10 situation (just like Case 26, 87, 88 and 123 incidentally).  Something in the wording tells me 'reasonable apprehension' isn't intended to be a big factor throughout Part 2.

I have seen (and found myself) using Case 50 to decide tough R10 cases.  I teach that it is a useful tool for aspiring judges to commit to memory and pull out of the book, when needed.  But I tend not to let it wonder into other rule decisions.  I'm not sure the intent of the rule writers is for that.

My feeling is that if Case 50 was let loose on all Part 2, we effectively put 'keep clear' safety rules into the realm of 'subjective' and into the minds of RoW at all times.  My feeling is that simply because RoW thought KC broke a rule, it doesn't mean that KC did break a rule.

I do think however, that to practically apply RRS14, a minimal consideration of 'RoWs judgement' is acceptable/required.  But perhaps not prescribed as a weapon for RoW, as in Case 50.
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The last part of R14 is quite clear.  However, as Case 87 shows, sometimes this 'clarity' never comes soon enough.  Case 87 S may have won the appeal, but perhaps lost her boat!!

It has been argued that good seamanship would expect RoW to act anyway before, instead of waiting for a collision regardless of that last sentence.  I tend to agree.  I have done it.  But does that entitled me to a protest win over KC?  This is the question.

If Case 87 S had tacked at Position 2.5 and protested, how would we rule?

Combine the Case 87/R14/Seamanship/Safety tug-of-war and the period between the RoWs reasonable apprehension and unreasonable apprehension and we see the greyness for both boats.

While for R10, case 50 is handed to us on a plate, for other rules I tend to be a little more stricter on establishing 'reasonability' of ROWs supposed apprehension and giving it allowance.  I lean more on the general meaning of the word 'need' in the definition and whether KC was complying.  I don't jump straight from RoWs judgement to a conclusion of KCs rule breach, as I often see.

Good chat.

Thanks.

 Calum, many events use a Whiskey flag to indicate that a boat must return to the starting area. Here is a commonly used instruction:   “If a boat is shown a ‘W’ (Whiskey) flag by an official vessel, it shall return to the starting area. That boat will be scored in its last known position. This changes RRS 28.1, A5.1, and A5.2.”
I recommend avoiding the word “Finish” in your instruction, as it is a definition that may not be changed. 

I would second that for people on a Mac!!

The more I think about this ... the more the reptile-level of my engineering-brain is telling me that the only way that this ILCA gets back to its original position + improved position on the line ... after countering the losses due to wind and water drag forces ... and the initial leeway loss when the sail is initially brought in ... without passing HTW ... is by the input of energy from the body resulting in a fan of the sail. 

Call it just a conservation-of-energy analysis instinct .. I'd have to break it down to each dynamic segment to see if I'm missing something. 

I will return (with trepidation) to my original stance.  In this scenario, unlike on a beam reach for example, I contend that there is only one side that can be chosen by the ROW boat to pass the obstruction and where, therefore, RRS 19 applies.  Blue can chose head up and go behind Yellow.  In this instance, I think we all agree that the obligation is on Green (RRS 19.2b) to give Blue room to pass between her and the obstruction. Blue's obligation (RRS 19.2a) is to give Green room to keep clear as she changes course.
If, however, Blue choses to avoid the obstruction by gybing, she is not passing the obstruction .... indeed, she is not able to pass the obstruction on her port side unless at position 1 she suddenly had a burst of speed and could cross Yellow.  Given that she is unable to pass the obstruction on her port side, she chooses, instead of heading up to pass on her starboard side, to avoid the obstruction by gybing.  Therefore in this instance, RRS 19 does not apply.  Returning to my original post, I believe this is why the language of 'pass' is not used in RRS 20.  

In RRS 20 (sailing close hauled or above), there are things that have to happen for the ROW boat (leeward) to be able to safely maneuver to avoid the obstruction (again, it doesn't say pass).  Should she chose to avoid the obstruction by tacking (rather than passing it astern per RRS 19) she has to follow RRS 20.1 and things unfold from there.

In our scenario, it seems to me that if the intent was that Blue had obligation to give room for Green to gybe between Blue and Yellow (obstruction), there would be another rule entitled ROOM TO GYBE AT AN OBSTRUCTION with a series of hails and responses.  This would be problematic however, for all the reasons that I stated in previous post (broken overlap; uncertain duration of right to room, etc.)  However it seems to me that this is NOT the intent since the ROW boat  going downwind already has the ability to execute the choice to avoid, rather than pass (which they don't going upwind without the protection of RRS 20), and the give-way boat already has the ability to pass the obstruction safely by heading up astern of the obstruction.