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Old 14-10-2017, 13:17   #376
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by ramblinrod View Post
First of all, it is Rod.

SNIP
.
Sorry about the name typo Rod.
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Old 14-10-2017, 13:19   #377
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

RR,

You're doing a great job! I'm still with you bro.

Some just seem to be way more anal about stuff with a very tight "pucker factor." Others like us... are just out enjoying a worry-free day in the sun. Honestly, I can't be troubled by ships still cresting the horizon, we just wait a bit longer to figure stuff out.

We've only needed to use the VHF twice in six years to contact a large ship, once in terrible weather at night just to make sure we were seen, and another time to alert the ship we were dead in the water without a working engine and without wind.
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Old 14-10-2017, 13:35   #378
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Again, I'm coming at this with more book knowledge than experience (at least relative to yours), but these add'l factors of commercial vessel speed & size which have arisen in the past 40-50 years don't seem -- in my mind anyway -- to change the basic application of the Rules. If anything, it may necessitate earlier & more prudent action on our parts, but still well within the ranges that Cockcroft suggests and big ship caps seem to agree are safe to operate under. If unsure what's coming at you, I suppose you would want to assume higher speed & less maneuverability in planning your own maneuver (if necessary). In other words, if your late maneuver creates a close call with a fast, highly maneuverable ship, then it's theoretically also too close with a slow speed, slow maneuvering ship. And in some scenarios, of course, maybe the other way around! As for size, I'm not sure what that has to do with it since we're talking about sufficient margins that should keep us well clear of any sized ship.


What am I missing?

All this seems entirely reasonable to me.

A small comment to the question about size --

Probably doesn't make a difference if you're maintaining reasonable CPA's, not measured in fractions of cables. But at some point, the size of the ship affects how hard it is to get out of its way. A bigger ship covers a bigger piece of ocean. If you find yourself on an actual 0 CPA from its bow (something you can't measure precisely, but imagine you blunder into such a position), you have further to go, to get out of his way. To travel this further distance from danger to safety, you need to maneuver earlier.
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Old 14-10-2017, 15:17   #379
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by ramblinrod View Post
Asked and answered.

Your post is very eloquent, but extremely flawed by idealism (either intentionally or unintentionally) in my opinion.

I tend to be a realist.

In any circumstance where one is required to do something at an unspecified "safe" distance, those who have personal need for greater "safety" will respond sooner and more conservatively than those who have personal need for lesser "safety".

But it IS specified, but only as a range of distances to account for the myriad of variables that present themselves out on the water. Not only "Cockcroft," but we've read all sorts of opinions on this from experienced & knowledgeable mariners. For commercial vessels in a give way position we've been reading anywhere from 10 to 2 miles it seems, and even 1 mile but that seems frowned upon. As for our vessels where we often find ourselves stand on, it's similarly inexact but there are objective limitations on both ends. Most seem to agree on this; the discussion falls more into the category of what are "best practices." So maybe rather than asking what meets the Colreg's objective defn. of "reasonableness," the question should be posed as what's objectively UNreasonable. This is what renders some of your examples & analysis confusing & potentially misleading. IMHO that is . . . .

This may be referred to as "Pucker Factor".

If the term "Pucker Factor" offends anyone, please use the synonym, "Personal opinion of what is safe."

I doubt it offends anyone, but is objectionable because it implies a subjective standard in determining best & safest practices. Any doubt about this is resolved by your own defn. above, namely:

In any circumstance where one is required to do something at an unspecified "safe" distance, those who have personal need for greater "safety" will respond sooner and more conservatively than those who have personal need for lesser "safety". (emphasis mine)

This is correct ONLY if you are executing a maneuver that is clearly not contemplated by the Colregs! And even then it's irrelevant which vessel cap may have a more tolerant "pucker factor!!" If for no other reason then how are you supposed to know?? The distances for maneuvering contemplated by the Rules & followed by conscientious mariners are expressly designed to avoid such stresses however defined, as well as (hopefully) facilitate some degree of predictability even when the Rules are not being followed. The problem with introducing subjectivity into the equation is not necessarily that it's a bad plan on its own merit, but that most everyone else is following a different plan that is based on a set of commonly-accepted, established Rules. Reasonable minds can differ on whether standing on until 5 miles or 2 miles is "best practice," but absent compelling circumstances, the 180 feet you suggested seems outside the bounds of objective reasonableness, regardless of whether it might happen to avoid collision or otherwise be satisfactory to you or not.

On the race course, if I have to give way in a crossing, I will wait to the very last moment to ensure that conditions don't change, and that I really have to duck, and then will miss by the closest margin possible as to not give up any more ground than absolutely necessary.

One with less tolerance, or confidence in their skills, may respond sooner, and by a wider margin.

In other words, some have a greater "Pucker Factor" than others.

That is the race course.

I used to roadrace 1000cc motorcycles, so I can relate! But I tried to avoid pucker factor at all costs when I was riding on the street. If I had it on the street then it didn't matter what the conditions were or how many bad drivers were out there with me. Never any question in my mind that I was doing something wrong.

Of course, nobody in their right mind would cut so close in a crossing between a large ship and a sailboat, intentionally, and obviously I am not suggesting this for one second, so I am quite troubled by the "chicken" inference in this post.

Well, I predicated my "chicken" analogy with an acknowledgment that it may not have been what you intended to say. I was merely looking for an explanation as to why you believe "pucker factor" has any relevance or application outside the race course. And even then the racing rules try to balance the aggression needed to be competitive with a more specific set of rules which try & offset the greater risk of collision in such a scenario. You acknowledge the difference to some extent, yet cling to the idea in the cruising context that personal safety or comfort margins should play a role. Whether it's a maneuver at 2 miles or 8 (depending), there should be plenty of safety margin if working within the broad parameters set forth in the Rules. If not, then hopefully the Rules can be applied to reduce the enhanced risk.

Never-the-less what can be considered a "safe" distance, will vary depending on the conditions (as Cockcroft clearly states) and the skill, and the "Pucker Factor" of the person responsible for the call.

In every case, for every maneuver, "Pucker Factor" comes in to play.

1. Under what wind conditions will we leave the dock?

2. At what wind level do we reef? 3. How far before shallows do we tack?

3. And so on and so on and so on...every action where safety could possibly be involved.

To suggest that every move one makes aboard has to be in accordance with "case history" where the rules do not specify values, is ridiculous.

If that was the case, I would not wish to sail, and I doubt many others would either. The reason I hear most declare they get enjoyment from sailing is "freedom", not "adherence to rules and case history".

Speaking only for myself, I can't tolerate that level of "Pucker Factor". It wouldn't be fun anymore. Others may be wound so tight they cannot be happy until they can suck themselves inside out. That is OK for them, just don't try to convince me that I should be like that. I shouldn't. It wouldn't work. Not at all.

You lost me here. We're talking about proper application of the Rules within their own, nonspecific, and broad parameters, not the level of risk sailors may or may not opt to take in the physical operation of their boats. Nobody is suggesting -- certainly not the drafters or enforcers of the Colregs -- that maneuvering distances be more specifically defined, only that mariners try and operate within their broad parameters. And this is only to promote predictability btwn. vessels, an obviously worthy goal that only operates to promote freedom on the seas since it reduces its risks.

Correction: No, the inference was not intended and it is not the same thing, not at all. The only similarity is that there are two vehicles involved. That inference is offensive.

You were critiquing my "chicken" analogy here and have explained why you thought it was wrong. Fair enough. But I think I was clear that there was no intent to "offend." There's a big difference btwn. challenging argument designed to clarify & educate vs. that which is designed to personalize & offend. I'd only say that whether you feel offended in these particular circumstances is entirely up to you.

Or is your point simply that, since the Colregs are designed to avoid collisions, and since you've avoided collision by executing one of the close maneuvers you've cited, you have therefore not violated the Colregs?



But even leaving the 'legalities' aside, why as a practical matter would you deliberately wait so long -- assuming you have the option that is -- to exercise your obligation to maneuver when confronted with a give way vessel who is not properly giving way?

Asked and answered. The main reason, a desire not to act prematurely so as to interfere with a give way vessel's plans. Secondly, my level of "Pucker Factor" does not necessitate what I would consider a "premature" action over someone who has greater "Pucker Factor".

OK, the bolded part makes sense in the abstract, but maybe you can provide a specific example where maneuvering closer in is preferable safety-wise to maneuvering further out. As for your second factor, any particular person's "pucker factor" is completely inconsequential unless it can be communicated to the other ship! And if you achieve communication with the other ship, then you can presumably sort out the crossing w/o the need to explain your level of personal discomfort!!

Thus far your examples seem to try & justify based only on the fact that they avoided collisions, so therefore . . . . It seems to me that if you act prematurely too far out (like I often do ), your only risk is some unseen, unknown OOW calling you a WAFI under his breath (or maybe out loud!). But if your maneuver comes too late, then you risk being immortalized as a WAFI! The Rules provide a generous middle ground which any objective mariner would deem reasonable, absent compelling circumstances that is. My question all along has simply been, "what are those compelling circumstances, and why would the type of close-in maneuvers you have proposed be more advantageous safety-wise than acting earlier whenever possible?" It's certainly been asked but I respectfully disagree that you've answered in anything but the abstract.


Actually, the tone and thrust of the message was argumentative, in contrast to this last sentence.

Well, if you hadn't gotten a tad argumentative in the recent Smartgauge thread, many of us may have been left believing that their battery monitoring techniques were woefully inadequate and would have run out & maybe unnecessarily bought SG's! So again, argument & challenging dialogue often play a useful role, assuming no offense is intended . . . nor received!

The questions have already been asked and answered many times. The analogies used are (or should be) knowingly flawed. The presumptions of the reasons for my position are (or should be) knowingly flawed.

Due to the many variables inherent on the water, real life or hypothetical examples have to be used for clarification & understanding. I for one am certainly not intending to put words in your mouth or deliberately misconstruing your comments. Oftentimes misunderstandings are simply unintentional, and yes, sometimes unavoidable.

However, based on you many prior posts in this thread that I did believe were very valuable and sincere, I do sincerely hope that this response helps to clarify my position on this discussion.
Thanks Rod! And also thanks again for the invaluable help on many of the maintenance threads (esp. electrical! ). Perhaps at this point this particular (Colregs) horse has been beaten well enough, but who knows. Hey, if I didn't respect your views I wouldn't bother weighing in!
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Old 14-10-2017, 15:19   #380
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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RR,

Some just seem to be way more anal about stuff with a very tight "pucker factor."
Well put!
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Old 14-10-2017, 17:54   #381
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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That is the US military usage of the expression.... which is quite different to the mercantile usage.
Pray tell, what is the mercantile usage?
I'm fairly certain it derived from military usage in WWII, and specifically refers to the puckering of the anus, because you're clenching your butt cheeks so tightly, to prevent what has previously been called a "brown trousers" moment.
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Old 14-10-2017, 18:08   #382
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

https://sofrep.com/23983/know-your-m...pucker-factor/

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The “Pucker Factor” (PF) is a scale that seeks to measure fear by the force of contraction exerted on the sphincter muscles surrounding the anus during a given situation of danger. The scale is from 1 to 10.

1 is the normal level, while a 10 Pucker, or PF10, is an anal contraction so strong that it’s audible within a 2 meter radius. It is said to sound like a door being slammed. A 10 Pucker is also said to cause a popping in the ears because of the sudden change of internal pressure within the body. Depending upon the danger stimulus encountered, a Pucker condition can persist for hours, days or even weeks, causing constipation, irritation and other symptoms that vary by subject. A permanent state of 10 Pucker is known to exist in certain people. They are commonly referred to in the military as “Tight Asses,” and in spite of their chronic condition, are afforded little sympathy.
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Old 14-10-2017, 20:50   #383
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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By George, I think you've got it! ;-)
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Old 14-10-2017, 23:44   #384
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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I doubt it offends anyone, but is objectionable because it implies a subjective standard in determining best & safest practices. Any doubt about this is resolved by your own defn. above, . . .
Well, there a few things going on with this "pucker factor" business, I think.

First of all, it says that different people have different tolerance for risk, and some will be more "anal" than others. This is obviously true.

To the extent it describes an approach to avoiding collisions based on subjective feelings, rather than method and system, I think it's not the best way to do it. It's strikingly like what one of our commercial captains described on GCaptain:

"It’s not just the difference in perception of risk of collision. There is a difference in approach to collision avoidance. A professional mariner is more likely to take a more methodical approach, for example plan to take action at specific distance. On the other hand the amateur is more likely to make collision avoidance decisions based on his feelings of comfort or fear."

Cite is above in this thread.


I'm not saying Rod is saying this (I don't think he is), but I do know a certain number of sailors who think they don't need to study collision avoidance, because they think they have bigger balls than others do. They think they don't need to do any preparation, don't need to do any analysis of a crossing, can just dodge out of the way at any moment their personal "pucker factor" allows. In reality this means that what they do is not really effective, and they mostly are relying on luck, or on the skill of the guys on the bridge of the ship, to avoid a collision. If "balls" are considered a substitute for brains, they are not of value in this kind of work, in my opinion.


One more thing, which I think is important: It has been said in this thread that every crossing is different, and so there is no fixed scale of distances you can apply equally to every crossing. That is definitely true. But it doesn't mean that any distance is ok -- there is a point in every crossing where the situation becomes desperate (the point where the Rules require both vessels to maneuver despite the risk of maneuvering into each other). It's not OK to stand on into that stage. In every crossing, there is a certain distance, beyond which a safe and smooth maneuver, visible to the other vessel in good time, and with time to spare for corrections if necessary, becomes impossible. And this depends not only on your subjective "feelings of comfort or fear", but on the objective geometry of the situation, and importantly, on the distance frames being followed by the other vessel, so that you don't maneuver in conflict with each other.


An activity like collision avoidance involves a lot of routine -- most crossings are not dangerous. Many rec sailors don't understand anything about it at all, and can go for decades or whole lifetimes without an accident. But good collision avoidance procedure is designed to deal with the rare but real cases where you would get run down, if you didn't do it right. Where in reality you are approaching a ship with a 0 CPA to his bow but your AIS tells you that you have a cable CPA, for example. Where you think you see a changing bearing, but in reality your course is not steady or he is in a slow turn. Where he doesn't see you. Etc.

Doing it smoothly and systematically, without drama, using brains rather than balls, at safe distances leaving time and sea room for later corrections if necessary because of a wrong assumption or because of an unexpected gust or lull in the wind or unexpected turn by the other vessel, or whatever. Doing it in muscle memory according to a system which is followed every time. I would offer that this is the right way to do it.

Pilots don't land planes according to "pucker factor". It's a similar kind of undertaking.
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Old 15-10-2017, 00:26   #385
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Kenomac View Post
RR,

You're doing a great job! I'm still with you bro.

Some just seem to be way more anal about stuff with a very tight "pucker factor." Others like us... are just out enjoying a worry-free day in the sun. Honestly, I can't be troubled by ships still cresting the horizon, we just wait a bit longer to figure stuff out.
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Well, there a few things going on with this "pucker factor" business, I think.

First of all, it says that different people have different tolerance for risk, and some will be more "anal" than others. This is obviously true.

To the extent it describes an approach to avoiding collisions based on subjective feelings, rather than method and system, I think it's not the best way to do it. It's strikingly like what one of our commercial captains described on GCaptain:

"It’s not just the difference in perception of risk of collision. There is a difference in approach to collision avoidance. A professional mariner is more likely to take a more methodical approach, for example plan to take action at specific distance. On the other hand the amateur is more likely to make collision avoidance decisions based on his feelings of comfort or fear."

Cite is above in this thread.


I'm not saying Rod is saying this (I don't think he is), but I do know a certain number of sailors who think they don't need to study collision avoidance, because they think they have bigger balls than others do. They think they don't need to do any preparation, don't need to do any analysis of a crossing, can just dodge out of the way at any moment their personal "pucker factor" allows. In reality this means that what they do is not really effective, and they mostly are relying on luck, or on the skill of the guys on the bridge of the ship, to avoid a collision. If "balls" are considered a substitute for brains, they are not of value in this kind of work, in my opinion.


One more thing, which I think is important: It has been said in this thread that every crossing is different, and so there is no fixed scale of distances you can apply equally to every crossing. That is definitely true. But it doesn't mean that any distance is ok -- there is a point in every crossing where the situation becomes desperate (the point where the Rules require both vessels to maneuver despite the risk of maneuvering into each other). It's not OK to stand on into that stage. In every crossing, there is a certain distance, beyond which a safe and smooth maneuver, visible to the other vessel in good time, and with time to spare for corrections if necessary, becomes impossible. And this depends not only on your subjective "feelings of comfort or fear", but on the objective geometry of the situation, and importantly, on the distance frames being followed by the other vessel, so that you don't maneuver in conflict with each other.


An activity like collision avoidance involves a lot of routine -- most crossings are not dangerous. Many rec sailors don't understand anything about it at all, and can go for decades or whole lifetimes without an accident. But good collision avoidance procedure is designed to deal with the rare but real cases where you would get run down, if you didn't do it right. Where in reality you are approaching a ship with a 0 CPA to his bow but your AIS tells you that you have a cable CPA, for example. Where you think you see a changing bearing, but in reality your course is not steady or he is in a slow turn. Where he doesn't see you. Etc.

Doing it smoothly and systematically, without drama, using brains rather than balls, at safe distances leaving time and sea room for later corrections if necessary because of a wrong assumption or because of an unexpected gust or lull in the wind or unexpected turn by the other vessel, or whatever. Doing it in muscle memory according to a system which is followed every time. I would offer that this is the right way to do it.

Pilots don't land planes according to "pucker factor". It's a similar kind of undertaking.
Sincere question:

How can you possibly be so anal about this stuff and still enjoy a day of sailing? You even worry about people like Ron and I not being as anal and worried as you are.

Geez here's all we do.... AIS transponder turned on, VHF monitors Ch 16.... quick 360 glance.... we see ship on horizon.... is ship moving forward or aft in relation to our stanchion.... continue to monitor with quick glances every minute or so... slow down slightly or rarely speed up if necessary. No "tight-azz pucker factor" involved. At night we augment the above with radar.

Continue to enjoy nice day.... anxiety level remains at zero.
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Old 15-10-2017, 00:47   #386
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Sincere question:

How can you possibly be so anal about this stuff and still enjoy a day of sailing? You even worry about people like Ron and I not being as anal and worried as you are.

Geez here's all we do.... AIS transponder turned on, VHF monitors Ch 16.... quick 360 glance.... we see ship on horizon.... is ship moving forward or aft in relation to our stanchion.... continue to monitor with quick glances every minute or so... slow down slightly or rarely speed up if necessary. No "tight-azz pucker factor" involved. At night we augment the above with radar.

Continue to enjoy nice day.... anxiety level remains at zero.
I don't worry about people not being "anal". I said earlier in the thread, and say consistently, that many sailors don't really need to know this stuff. Most sailors never leave pilotage waters where you don't even use these techniques. Rod sails in a lake. I'm sure he's an excellent seaman.

I care about this stuff because I enjoy it. Collision avoidance, like navigation, pilotage, knots, sail trim, and diesel engine repair -- is a craft. It's a very complicated puzzle, which has given me a great deal of pleasure in trying to figure out. I was stimulated to do that by sailing in one of the few places in the world, probably, where you simply can't get by on pucker factor techniques, doing it with your stanchions, doing it by feel and inspiration. So, I learned how to do it and dug deeply into it. And I'm still learning.

For me like for many cruisers, learning these crafts is one of the very great joys of our sport.
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Old 15-10-2017, 02:52   #387
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Again, I'm coming at this with more book knowledge than experience (at least relative to yours), but these add'l factors of commercial vessel speed & size which have arisen in the past 40-50 years don't seem -- in my mind anyway -- to change the basic application of the Rules. If anything, it may necessitate earlier & more prudent action on our parts, but still well within the ranges that Cockcroft suggests and big ship caps seem to agree are safe to operate under. If unsure what's coming at you, I suppose you would want to assume higher speed & less maneuverability in planning your own maneuver (if necessary). In other words, if your late maneuver creates a close call with a fast, highly maneuverable ship, then it's theoretically also too close with a slow speed, slow maneuvering ship. And in some scenarios, of course, maybe the other way around! As for size, I'm not sure what that has to do with it since we're talking about sufficient margins that should keep us well clear of any sized ship.

What am I missing?
I'm not sure about others around here but I approach 15 metre power boat situations in quite a different fashion to how I approach a situations involving VLCCs.

This is the point I am trying to make about the infinite variety of 'situations'.

While Cockcroft is very very good it is written essentially for people studying for their 'tickets'... ie 2nd Mates and Mates. He gives examples ... he doesn't lay down definite rules. Mates are - or at least should be - flexible in their thought processes. Without that flexibility they won't be much good at their jobs.

Enough said..... there is a fair breeze in prospect... and I have a ship to get ready for sea....
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Old 15-10-2017, 03:02   #388
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Kenomac View Post
Geez here's all we do.... AIS transponder turned on, VHF monitors Ch 16.... quick 360 glance.... we see ship on horizon.... is ship moving forward or aft in relation to our stanchion.... continue to monitor with quick glances every minute or so... slow down slightly or rarely speed up if necessary. No "tight-azz pucker factor" involved. At night we augment the above with radar.
That's not actually what we *all* do as it only works if the we're going to miss the ship by a long way, if it's obvious that the transit is changing then all good-relax, I have some clothes pegs in the cockpit just for this. But it's a very imprecise method, if it isn't blatantly obvious then time for the hand bearing compass. If it isn't transmitting ais that is
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Old 15-10-2017, 05:08   #389
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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That's not actually what we *all* do as it only works if the we're going to miss the ship by a long way, if it's obvious that the transit is changing then all good-relax, I have some clothes pegs in the cockpit just for this. But it's a very imprecise method, if it isn't blatantly obvious then time for the hand bearing compass. If it isn't transmitting ais that is
Exactly.

The stanchion (or distant mountain) is the perfect way to do a first cut -- recognize those targets which are clearly not a problem and exclude them. But it's not of much help in distinguishing close cases. A perfectly safe pass may look like a collision course, against a stanchion. And this can lead to really bad consequences if unnecessary action is taken, based on what it looks like over a stanchion, which nullifies a maneuver the ship has already made.

The stanchion is very imprecise -- rather than a bearing relative to a compass, it's a bearing relative to where the stanchion is at the moment -- and that is always changing. It's supremely quick but very imprecise. The distant mountain is far better because the mountain doesn't move. But the mountain needs to be quite far away to work. A nearby shore is not useful because it moves relative to us anyway.

A decent hand bearing compass, or still better, compass binocs, is already much better than any of this, because you can get a bearing relative to the compass, which will be fairly steady. So this way you can already recognize some safe crossings which look dodgy against a stanchion.

But changing bearings themselves, even measured precisely, have significant limitations, and you need a pretty big CPA and pretty early decision point, to use this reliably as your only means of distinguishing a safe pass from a collision course. The Rules talk about these limitation explicitly:

Rule 7
Risk of collision

(a). Every vessel shall use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists. If there is any doubt such risk shall be deemed to exist.

(b). Proper use shall be made of radar equipment if fitted and operational, including long-range scanning to obtain early
warning of risk of collision and radar plotting or equivalent systematic observation of detected objects.

(c). Assumptions shall not be made on the basis of scanty information, especially scanty radar information.

(d). In determining if risk of collision exists the following considerations shall be among those taken into account:

(i). such risk shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change;
(ii). such risk may sometimes exist even when an appreciable bearing change is evident, particularly when approaching a very large vessel or a tow or when approaching a vessel at close range.


At a certain distance, speed, and size of vessel -- you can't tell anything, even with a hand bearing compass. The bearings to different parts of the ship will already be different, and all of them will be changing, even when you're on a collision course. When you're just about to T-bone a ship, a bearing against the bow will look like you're passing behind, a bearing against the accommodation block will look like you're passing ahead -- you have to shoot the specific part of the ship which is about to smash you to see the steady bearing, and where is that? And every shot for changing bearings takes time.

It is true that when you get close, then aspect becomes more meaningful, so in many cases a safe pass will be obvious because you're simply too far from his course line to get under his bow, and he's moving too fast for your to T-bone. If he's moving faster than you and you can see his transom you're definitely safe, no matter anything else whatsoever. But in a certain range of situations, when you're say half a mile off or closer, especially if there's a big difference in speed, and you're somewhere near his course line such that you have a small CPA with his bow, you just can't tell, not with your eyes nor with a HBC, which way to turn, or whether you need to turn. And as Ping pointed out, even your AIS can't tell you within a ship's length where the bow of the ship is -- AIS represents the ship as a mathematical point, but the ship is not a point -- it may be two cables long. These are all really, really good reasons not to leave it until the last minute. More precise methods (radar, AIS) let you cut it closer, but you always need a margin of error.
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Old 15-10-2017, 05:10   #390
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Dockhead View Post
I don't worry about people not being "anal". I said earlier in the thread, and say consistently, that many sailors don't really need to know this stuff. Most sailors never leave pilotage waters where you don't even use these techniques. Rod sails in a lake. I'm sure he's an excellent seaman.

I care about this stuff because I enjoy it. Collision avoidance, like navigation, pilotage, knots, sail trim, and diesel engine repair -- is a craft. It's a very complicated puzzle, which has given me a great deal of pleasure in trying to figure out. I was stimulated to do that by sailing in one of the few places in the world, probably, where you simply can't get by on pucker factor techniques, doing it with your stanchions, doing it by feel and inspiration. So, I learned how to do it and dug deeply into it. And I'm still learning.

For me like for many cruisers, learning these crafts is one of the very great joys of our sport.


I do share this interest. I came to sailing quite late at my mid-life crisis and the constant need to plan, anticipate, understand and eventually master boat and elements is what I do enjoy. It is a clear break from my rather intense work life and it brings me a lot of pleasure as I start to get better at it.

I wonder why some comments that were quite denigrating I would say, also came from people who justify their less attentive attitude (no judgment) by pressing to relax and take it easy.

Just a comment. If not sharing the same interest one can just move on and skip the specific thread, letting others continue enjoying the thinking.
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