I think I'd start with the idea that under the definition an obstruction is existentially an obstruction by its nature, not defined by the relative position of the boats to it or the courses they're sailing. Obstructions are always obstructions, so it makes sense that continuing obstructions are always continuing obstructions. An obstruction doesn't come into being when rule 19 turns on and evaporate when it turns off.

Since the rules don't define "continuous" I believe the relevant dictionary definition would be "without a break in continuity; ongoing." 

So I'd say a shoreline is always a continuing obstruction.

It's always a good idea to start with the official interpretations including definitions and cases.  Tim, I think you've identified the reason why there is so much confusion over this question as I'm not sure the rules have incorporated a logical distinction between the existence of an object and its relative position to a boat.  But take a look at the definition of an obstruction and US Appeal as a start.

I would say that Rule 19.2(c) starts to apply as soon as the boat closest to the obstruction (Yellow in above scenario) starts fearing it will hit it (or the shallow bottom near it). Yellow can hail for space to avoid the obstruction. 

Also keep in mind that this rule exists for safety of the crews and equipment - it's spirit is to avoid colliding with the obstruction. (yes, this fact can be used tactically)

Years ago I was pushed aground by a skipper that did not know that the beach was very shallow even 200m away from the visible coast ... completely his fault! He should have responded to my hail, and protest me later if he felt I was not hailing for safety... (this was on 1.8m deep keelboat)

Looking at case 33, would you say that that RRS 19.2(c) could theoretically apply?  They are fixed piers.  It's pretty difficult to say they are not continuing obstructions if boats were traveling along next to them.  The issue I'm trying to get to here is when might 19.2(c) be called into question for obstructions that could be continuing.   What makes them continuing?  What makes it not continuing?

Case 33, Answer 1, clearly explains that the other boat needs to respond to the hail by tacking.
Case 33, Answer 2, clearly explains that the other boat needs to respond to the hail by bearing off.
Case 33 is not about 19.2(c), thought. I did not find a case explaining what happens when the overlap is gained by a clear astern boat that had to keep clear, as 19.2(c) defines.

On your question about what makes an obstruction "continuing" -  I agree it's a problem that the rules do not provide a clear definition. I tend to agree with Tim above, specially in the use of the work "ongoing". Maybe you can say an continuing obstruction is an obstruction that goes on (=ongoing) for a relevant length, something that your boat does not pass quickly. I may even risk to say that this may be defined as something of "X boats lengths or more". (with X maybe 3?)

Why isn't Case 33 about 19.2(c)?  That's my question.  Given your response to my question about what makes an obstruction continuing, I think you answered the first question.  But how far or long is ongoing?  And how is that applied.  Given the examples in the second illustration, which might be considered a 19.2(c) situation?  Dave Perry has a bit of a squishy answer to this question, but his is the best I've seen so far.

What does Dave say?

For me there is an element of geometry and shape and angle of approach which is crucial in determining whether an obstruction is 'continuing' or not.

Curios about Daves answer too....  Suggestion: Maybe helpful to start with the opposite. What it is not continuous? "Something that is so short/sharp that a boat passing would change course immediately to the next mark without being restricted by the obstruction. The boat never "follows" the obstruction." Then let every other obstruction be continuous. This would make all Pauls examples continouos. 

About the question if this is a continuing obstruction, also recent YNZ Appeal No 77 mentions that “the nautical or general meaning of the words "continuing obstruction" imply that it must be something that abstracts a boat’s course in a continuing manner. That is reinforced by RRS 19.2(c), as otherwise that paragraph would make little sense. Therefore, an object that the boats pass momentarily is not, even if it is a part of a larger structure”. 

So, based on all the Cases that give examples of continuing obstructions, on relevant appeals, as well as on the nautical and general meaning of those words, i believe that there is no doubt that the land in the diagram is a continuing obstruction.

According to RRS 19.2(c), that paragraph applies between two boats at an obstruction but only if the overlap is established while the boats are passing the continuing obstruction and only if the boat that was clear astern and required to keep clear becomes overlapped between the other boat and the obstruction and at the moment the overlap begins, there is not room for her to pass between them.

Case 33 does not deal with a situation described in this paragraph, this is why it is not about RRS 19.2(c), but about RRS 19.2(b) and 20.

In the diagram above, in order to answer whether RRS 19.2(c) applies, we need to know if the overlap was establish while both boats were passing the land. 

If yes,19.2(c) applies while the boats remain overlapped. If not, RRS 19.2(b) applies. 

I also have to mention that since the land seems to be inside the zone of the mark, RRS 18 will not apply when one of the boats reaches the zone, since according RRS 19.1, at a continuing obstruction RRS 19 always applies and RRS 18 does not.

"and at the moment the overlap begins, there is not room for her to pass between them."
Given the courses as drawn for the boat initially clear ahead, for all but course A, there is room for an overtaking inside boat to claim room right up to a point past the last house on Portofino Lane.
In the first drawing, interpolating where the overlap began, Yellow established leeward overlap ROW when there was space to do so, whether continuous or not.

I suggest the solution to these problems lies not in the definition of continuing obstruction, but rather, in the method of applying rule 19.2(c).

 

As far as defining continuing obstruction goes, examples of a continuing obstruction are:

·         An obstruction not surrounded by navigable water;  and

·         An obstruction which, once a boat is passing it on one side, the proper course of the boat is not to pass it on the other side.

I’m less than delighted with the wording of the second example, and would welcome discussion or suggested improvements.

 

Whether an object is a continuing obstruction or not does not depend on the direction from which it is approached (but the application of rule 19.2(c) does).

 

Let us consider the application of rule 19.2(c).

 

Around the edge of a continuing obstruction there will be a depth contour, depending on the draft of the boats concerned, inside which it is not safe to sail.  This is shown in dark blue in the diagram.  Where the obstruction is steep to, such as a cliff, or a wharf, this depth contour may coincide with the edge of the obstruction, as shown at the protruding wharf towards the right of the diagram.

 

Around this depth contour, there will be a further envelope, of width depending on the boats and the existing conditions, which represents the room needed by an inside boat to pass between an outside boat and the depth contour in a safe and seamanlike way.  This is shown in yellow in the diagram.

 

Note the depth contour and the ‘room envelope’ don’t stop short at the ends of the coloured areas marked:  they extend along the obstruction in both directions.

 

We may find it helpful to remember that the usual effect of rule 19.2(c) is to protect the tactical advantage of a boat hugging a shoreline, for example to avoid adverse current.

 

Applying the ‘freezing’ or ‘snapshot’ approach explained in RYA Case RYA2014-04, we can see that if a boat, initially clear ahead (A) reaches the outer boundary of the ‘room envelope’ (yellow in the diagram), before a boat behind her (B) becomes overlapped inside her, there is not room for B to pass between A and the obstruction, and, according to rule 19.2(c) B is not entitled to room and must keep clear.

 

Conversely, if B is overlapped inside A when A reaches the outer boundary, there is, at the moment the overlap began, room for B to pass between A and the obstruction and rule 19.2(c) does not apply and A is required to give B room in accordance with rule 19.2(b).

 

Turning now to the Examples A, B, C, and D.

 

 

In Example A the course lies parallel and as near as possible to the shoreline.  All the time it is inside the outer boundary of the ‘room envelope’.  At no time is there room between a boat sailing this course and the obstruction for another boat to pass inside.  This is the archtypical application of rule 19.2(c).  Rule 19.2(c) applies and any boat becoming overlapped inside from clear astern is not entitled to room and must keep clear.

 

 

In Example B the course converges on the line of the shore.  It (by drafting accident) reaches the outer edge of the ‘room envelope’, just where the yellow area in the diagram begins):

 

 

In Examples C, D and E, the analysis is the same as for Example B, except that the courses reach the outer edge of the ‘room envelope’ at points successively further along the boundary.  In each example:

 

 

In Example F the course never comes within the ‘room envelope’.  A boat sailing this course will always be giving room and rule 19.2(c) will never apply.