Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

[ramblinrod]

Originally Posted by Dockhead

Maybe we could get this back on topic.

Cockcroft writes about the "Four Stages of Collision Situation":


"When two vessels in sight of each other are approaching with no change of compass bearing, so that when there is risk of collision one of them is required to keep out of the way by a Rule from Section 11, there may be four stages relating to the permitted or required action for each vessel:

"1. At long range, before risk of collision exists, both vessels are free to take any action.

"2. When risk of collision first begins to apply the give-way vessel is required to take early and substantial action to achieve a safe passing distance and the other vessel must keep her course and speed.

"3. When it becomes apparent that the give-way vessel is not taking appropriate action in compliance with the Rules the stand-on vessel is required to give the whistle signal prescribed in Rule 34(d) and is permitted to take action to avoid collision by her maneuver alone, but a power-driven vessel must not alter course to port to avoid another power driven vessel crossing from her own port side. The give-way vessel is not relieved of her obligation to keep out of the way.

"4. When collision cannot be avoided by the give-way vessel alone the stand-on vessel is required to take such action as will best aid to avoid collision.

"The distances at which the various stages begin to apply will vary considerably. They will be much greater for high speed vessels involved in a fine crossing situation. For a crossing situation involving two power-driven vessels in the open sea it is suggested that the outer limit of the second stage might be of the order of 5 to 8 miles and that the outer limit for the third stage would be about 2 to 3 miles."

Attachment 157202

Cockcroft & Lameijer, 6th edition, page 114


You cannot do this effectively, if you don't understand the distance frames of these stages -- what is going on, on the bridge of the ship. Some important points (for open sea):

* By 8 miles out and no less than 5 miles, if not earlier, a ship crossing with you will consider that a fully developed risk of collision exists and he will maneuver at this point if not constrained by other traffic or some other circumstance, or will expect you to maneuver if you are give-way.

* If he is give-way and he hasn't maneuvered by 3 or 4 miles out, it is reasonable to conclude that he is not going to. Time to call him to find out his intentions, or maneuver yourself if you are stand-on. A potentially fatal misunderstanding many of us have, is to keep waiting until a mile (or less!) for him to maneuver. Ain't happening. That is beyond the range of that phase, for him. What is crucial to understand is what happens during this phase between 3 or 4 miles and 1 mile -- you are now free to maneuver, and you are obligated to get ready to do it. You must not just sail on waiting for him to maneuver.

* This varies with speed, and varies with the type of crossing, but if he is at sea speed, then by one mile off, options to prevent a collision are dwindling by the second. This is already in extremis -- Cockcroft's last stage. In open sea, you just should not be here. If you ever at all get within a mile of a fast moving ship in open sea, it should only be if you are clearly passing astern. Once you get within a mile and you have an unresolved collision course, there is no easy or safe way to unwind it.

Why? Let me count the ways:

1. Because you are in the fourth stage of maneuvering and both vessels are obligated to maneuver. So you by this time, you have lost the chance already to have coordinated maneuvering where one vessel stands on and the other takes control. Uncoordinated maneuvering -- probably "desperate maneuvering" would be the right word -- is much more dangerous because of the risk of two maneuvers of two ships conflicting with each other.

2. Once you are down to a few seconds, if you make a maneuver and it doesn't work, you won't have another chance. The Rules require

3. At some point (depending on the configuration of the ship), you can't be seen, either by sight or by radar, and the ship can no longer do anything to avoid you.

4. With a big difference in speed, your ability to get out of his way diminishes fast as you get closer.

So the interaction of 3 and 4 can be really deadly -- he can't see you and doesn't know where you are beneath his bows, and you can't get out of his way because you are too slow.

For all these reasons:

* Maintain an appropriate CPA

* Be aware of the stages of collision avoidance, and which one you are in.

In summary, after an initial defamatory post about my seamanship skills, and almost 20 pages of arguing nonsense about a fixed minimum distance that must always be maintained, and categorizing me with a group you refer to as "f'n idiots" you posted an excerpt from an authority on the subject, that apparently you have studied at great length, and evenly personally interviewed or consulted the author, that confirms my original position that the minimum distance, and the time/distance to initiate actions, is dependant on the circumstances.

So if you agree with Cockroft on this, then you agree with me. Why are you arguing?

[Dockhead]

Originally Posted by Juho

This staged approach is good since it can explain many of the complexities of colregs in one simple framework that can be used by sailors also as a clear procedure to follow.

The length of each stage is an interesting question. I think the most important parameter that defines then is maybe the time to collision or TCPA. I.e. timing could be the same for all vessels, but distances would be longer for fast vessels.

Another parameter could be the smallest safe distance/time (margin) for manoeuvres. For large tankers with poor visibility forward the distance/time would be larger than for smaller vessels with same speed. The value of this parameter could depend also on the current speed of the vessel, but maybe better to keep it simple.

When two vessels with different speed meet, TCPA is the same for both vessels, but the smallest safe distance/time to manoeuvre may be different. I'll skip the detailed formulae to count times and distances for the different stages for now. Maybe something like the longer of the safe distances/times + some amount of TCPA for each stage.

It is possible that timing would be about the same for both in open waters and when in situations with some constraints. If there are multiple vessels, I guess timing can be often calculated separately for each pair of vessels.

Just some thoughts to feed up your thoughts.

Good thoughts. Absolutely agree that TCPA is a key issue, and this means that the stages go by faster, when closing speed is higher.

Note however the complicating factor of a big difference in speed -- the slower vessel needs more time to create a safe CPA, than the faster one does. So the slower vessel (that's us) can't wait as late, as the faster one can, before doing whatever it's going to do.

Unfortunately we have the opposite in the minds of many of us -- we think in much shorter distances, where we really need to thinking further ahead, than they do.

[Dockhead]

Originally Posted by ramblinrod

In summary, after an initial defamatory post about my seamanship skills, and almost 20 pages of arguing nonsense about a fixed minimum distance that must always be maintained, and categorizing me with a group you refer to as "f'n idiots" you posted an excerpt from an authority on the subject, that apparently you have studied at great length, and evenly personally interviewed or consulted the author, that confirms my original position that the minimum distance, and the time/distance to initiate actions, is dependant on the circumstances.

So if you agree with Cockroft on this, then you agree with me. Why are you arguing?

Rod, I never defamed you, and if you ever felt insulted by anything I wrote, I apologize.

I'm really not interested in carrying out this kind of argument where someone is trying to "get" someone else. I'm not interested in doing that to you, or anyone else. I'm only interesting in digging into the truth of all of this, trying to learn something, trying to help others -- if they want it.

OF COURSE the distances depend on circumstances. No one would disagree with that. OF COURSE the time and distance varies. I never said otherwise.

What an acceptable time for maneuvering doesn't vary down into, however, is down to a few cables in open water, crossing with a ship moving at sea speed. Arguing that is not the same as saying -- it never varies.

And the other thing I said was you can't just make up your own fantasy about when the risk of collision arises, and set up your stages of collisions avoidance according to that, without knowing or caring about what stage the ship is in. COLREGS is all about COORDINATED maneuvering -- in particular, the giving-way and standing-on stage MUST occur at the same time, to have any meaning. So if in a given situation the ship is doing:

1. >8 miles -- no risk of collision yet
2. 8 miles to 4 miles -- risk of collision, but it's still not too late for my give-way move
3. 3 miles to 1 mile -- it's late enough that you can reasonably decide to maneuver yourself
4. <1 mile -- we are in a desperate, in extremis crossing now, and it's every man for himself

That's pretty typical but not of course cast in stone -- sometimes longer, sometimes shorter.

This timetable would be in total conflict with what you're doing, if you think there's no risk of collision in your opinion before 4 miles, and crossing 1/4 mile off is fine (for example). What this means is that you will not make your moves in coordination with the ship -- you will be standing on way past the point when you needed to maneuver; you would have gotten too close for the ship to do anything effective; etc.

That's what I was trying to say -- not that you don't vary the times and distances according to circumstance.

What Cockcroft said at the end of the quoted passage is that in particular, the times and distances will be totally different in harbors and approaches, because of the frequent changes of course, etc. And he doesn't say it, but also because of the well-defined fairways etc. Which is why I'm always careful to say "in open water" -- where the principles are different.

[ramblinrod]

Originally Posted by Dockhead

Rod, I never defamed you, and if you ever felt insulted by anything I wrote, I apologize.

I'm really not interested in carrying out this kind of argument where someone is trying to "get" someone else. I'm not interested in doing that to you, or anyone else. I'm only interesting in digging into the truth of all of this, trying to learn something, trying to help others -- if they want it.

OF COURSE the distances depend on circumstances. No one would disagree with that. OF COURSE the time and distance varies. I never said otherwise.

What an acceptable time for maneuvering doesn't vary down into, however, is down to a few cables in open water, crossing with a ship moving at sea speed. Arguing that is not the same as saying -- it never varies.

And the other thing I said was you can't just make up your own fantasy about when the risk of collision arises, and set up your stages of collisions avoidance according to that, without knowing or caring about what stage the ship is in. COLREGS is all about COORDINATED maneuvering -- in particular, the giving-way and standing-on stage MUST occur at the same time, to have any meaning. So if in a given situation the ship is doing:

1. >8 miles -- no risk of collision yet
2. 8 miles to 4 miles -- risk of collision, but it's still not too late for my give-way move
3. 3 miles to 1 mile -- it's late enough that you can reasonably decide to maneuver yourself
4. <1 mile -- we are in a desperate, in extremis crossing now, and it's every man for himself

That's pretty typical but not of course cast in stone -- sometimes longer, sometimes shorter.

This timetable would be in total conflict with what you're doing, if you think there's no risk of collision in your opinion before 4 miles, and crossing 1/4 mile off is fine (for example). What this means is that you will not make your moves in coordination with the ship -- you will be standing on way past the point when you needed to maneuver; you would have gotten too close for the ship to do anything effective; etc.

That's what I was trying to say -- not that you don't vary the times and distances according to circumstance.

What Cockcroft said at the end of the quoted passage is that in particular, the times and distances will be totally different in harbors and approaches, because of the frequent changes of course, etc. And he doesn't say it, but also because of the well-defined fairways etc. Which is why I'm always careful to say "in open water" -- where the principles are different.

Please, you have referred to me multiple times as an f'n idiot, and someone who doesn't know, doesn't want to know, doesn't care about collision avoidance.

Now you suggest you had no intent to offend, and expect me to accept this?

This is the biggest insult of all.

If a large, heavily laiden ship is approaching my stand-on sailboat, and from some distance out they have not taken action to avoid me, one of 3 conditions exist:

1. They didn't see me:
2. They did see me, but determined no action is required.
3. They determined action is required, but haven't executed yet.

If I have determined there is a risk of collision and 1/4 nm away, I estimate they have waited too long to avoid me, and I take action to miss them by 180 ft, what rule in Colregs, have I violated?

Cite the rule number please. That's it. No other rhetoric, nothing else.
Just the rule number, not your personal opinion or some value pertaining to other vessels standing orders, or some guideline by someone else, that I am not obliged to comply with. Only the Colregs rule violated.

Are you man enough to answer this as requested?

[Dockhead]

Originally Posted by ramblinrod

Please, you have referred to me multiple times as an f'n idiot,

Sorry this is not true. Not even under my breath! If you can find an incident of this, I'll send you a case of beer for every time I called you this or any other name.

Originally Posted by ramblinrod

and someone who doesn't know, doesn't want to know, doesn't care about collision avoidance.

I never referred to you personally. I allowed as how some people are nerds about this or another subject, and others just don't care. I think I was agreeing with a similar (and gracious) statement you had made.

Originally Posted by ramblinrod

If a large, heavily laiden ship is approaching my stand-on sailboat, and from some distance out they have not taken action to avoid me, one of 3 conditions exist:

1. They didn't see me:
2. They did see me, but determined no action is required.
3. They determined action is required, but haven't executed yet.

If I have determined there is a risk of collision and 1/4 nm away, I estimate they have waited too long to avoid me, and I take action to miss them by 180 ft, what rule in Colregs, have I violated?

Cite the rule number please. That's it. No other rhetoric, nothing else.
Just the rule number, not your personal opinion or some value pertaining to other vessels standing orders, or some guideline by someone else, that I am not obliged to comply with. Only the Colregs rule violated.

Are you man enough to answer this as requested?

Good lord, ask me something hard, will you?

Rule 2

"(a). Nothing in these Rules shall exonerate any vessel, or the owner, master or crew thereof, from the consequences of any neglect to comply with . . . of any precaution which may be required by the ordinary practice of seamen. . . ."

To approach a large vessel in open sea moving at sea speed to within 1/4 mile on a 0 CPA is flagrantly poor seamanship. If a collision resulted, and if I were the lawyer for the shipping company, I would have you on gross negligence.


Rule 8 Action to avoid collision

(a). Any action to avoid collision shall be taken in accordance with the Rules of this Part and shall, if the circumstances of the case admit, be positive, made in ample time and with due regard to the observance of good seamanship.

1/4 mile, in open sea, when crossing with a ship moving at sea speed, is not "ample time"! This is already an in extremis situation, where a large ship moving at sea speed probably can't any longer even do anything to avoid you, and within seconds won't even be able to see you. You must maneuver far earlier than this -- two stages back would be the right time.


Rule 17 Action by stand-on vessel

"(b). When, from any cause, the vessel required to keep her course and speed finds herself so close that collision cannot be avoided by the action of the give-way vessel alone, she shall take such action as will best aid to avoid collision."


Once it is evident that the give-way vessel is not going to maneuver, you are allowed to maneuver yourself, and good seamanship demands that you start getting ready, at least, to do so. Once you get within a few cables at the very least on a 0 CPA, and probably more like a mile, depending on the angle of the crossing, you MUST maneuver yourself. In open water in a crossing with a ship moving at sea speed, 1/4 mile is far too late.


If you don't believe me, I can show you case law on it. But only next week when I'm near my law books.

[conachair]

Originally Posted by ramblinrod

If I have determined there is a risk of collision and 1/4 nm away, I estimate they have waited too long to avoid me, and I take action to miss them by 180 ft, what rule in Colregs, have I violated?

Right near the start - 2A.

180 feet?? That's awful seamanship.

[Quebramar]

Some of the ships I come across around the Sandettié in the North Sea (crossing of multiple TSS causing headaches as to where to look for threats) have a beam of over 180ft. Just google Maersk e-class . You'll understand that with their speed around 25kts I monitor them from over 5NM and keep much distance. I know this is not open seas per se, that they will follow the TSS and that I'm to give way... but such encounters have convinced me that in open seas, I'll keep them more than 1 NM away whatever this takes me, including changing course if they haven't, at as far as 3 or 4 NM from them. There is no room for luck in a scenario involving super container ships

[ramblinrod]

Originally Posted by Dockhead

Sorry this is not true. Not even under my breath! If you can find an incident of this, I'll send you a case of beer for every time I called you this or any other name.



I never referred to you personally. I allowed as how some people are nerds about this or another subject, and others just don't care. I think I was agreeing with a similar (and gracious) statement you had made.





Good lord, ask me something hard, will you?

Rule 2

"(a). Nothing in these Rules shall exonerate any vessel, or the owner, master or crew thereof, from the consequences of any neglect to comply with . . . of any precaution which may be required by the ordinary practice of seamen. . . ."

To approach a large vessel in open sea moving at sea speed to within 1/4 mile on a 0 CPA is flagrantly poor seamanship. If a collision resulted, and if I were the lawyer for the shipping company, I would have you on gross negligence.


Rule 8 Action to avoid collision

(a). Any action to avoid collision shall be taken in accordance with the Rules of this Part and shall, if the circumstances of the case admit, be positive, made in ample time and with due regard to the observance of good seamanship.

1/4 mile, in open sea, when crossing with a ship moving at sea speed, is not "ample time"! This is already an in extremis situation, where a large ship moving at sea speed probably can't any longer even do anything to avoid you, and within seconds won't even be able to see you. You must maneuver far earlier than this -- two stages back would be the right time.


Rule 17 Action by stand-on vessel

"(b). When, from any cause, the vessel required to keep her course and speed finds herself so close that collision cannot be avoided by the action of the give-way vessel alone, she shall take such action as will best aid to avoid collision."


Once it is evident that the give-way vessel is not going to maneuver, you are allowed to maneuver yourself, and good seamanship demands that you start getting ready, at least, to do so. Once you get within a few cables at the very least on a 0 CPA, and probably more like a mile, depending on the angle of the crossing, you MUST maneuver yourself. In open water in a crossing with a ship moving at sea speed, 1/4 mile is far too late.


If you don't believe me, I can show you case law on it. But only next week when I'm near my law books.

First of all, you owe me a case of beer for every time you referred to me or one who thinks as I do, as a WAFI. I'll count them up later.

Second, I clearly stated that the collision was avoided by 180 ft.

Now I'll give you a second chance to finally man up. Again I ask the same question, stop the rhetoric and BS, what Colreg rule did I violate?

[NSboatman]

...uh, I think dh has already done this. Several times. And it's more than one rule... [emoji849]

[Lodesman]

Originally Posted by Dockhead

* If he is give-way and he hasn't maneuvered by 3 or 4 miles out, it is reasonable to conclude that he is not going to. Time to call him to find out his intentions, or maneuver yourself if you are stand-on. A potentially fatal misunderstanding many of us have, is to keep waiting until a mile (or less!) for him to maneuver. Ain't happening. That is beyond the range of that phase, for him. What is crucial to understand is what happens during this phase between 3 or 4 miles and 1 mile -- you are now free to maneuver, and you are obligated to get ready to do it. You must not just sail on waiting for him to maneuver.

I feel compelled to point out an inconsistency here - Cockcroft says 2-3 miles, not 3 or 4 miles. I might suggest if he hasn't moved by 4 miles that might be a good time to take soft measures, such as calling on VHF or lighting up the sails; and 3 miles as the beginning of the third stage where you can make your 17(a)(ii) action.

[Lodesman]

Originally Posted by Juho

The length of each stage is an interesting question. I think the most important parameter that defines then is maybe the time to collision or TCPA. I.e. timing could be the same for all vessels, but distances would be longer for fast vessels.

TCPA is a factor, but not necessarily the most important. Determination of the stages is very dependent on experience. If I was going 20 kts head on with freighter doing 20 kts, a 15 min TCPA is 10 miles away, which I think we can agree is safely out at stage 1 where the rules don't yet apply. But if he's overtaking me at 21 kts, 15 min TCPA puts him 500 yards on my quarter, which would be considered dangerously close in open ocean, and well past the point that stage 3 came into effect.

[ramblinrod]

Originally Posted by Lodesman

I feel compelled to point out an inconsistency here - Cockcroft says 2-3 miles, not 3 or 4 miles. I might suggest if he hasn't moved by 4 miles that might be a good time to take soft measures, such as calling on VHF or lighting up the sails; and 3 miles as the beginning of the third stage where you can make your 17(a)(ii) action.

Gentlemen, you are inflicting personal opinion as to what is adequate to suit your personal sensibilities.

I don't profess to be a collision avoidance expert, and yet without taking a week to review case law I can declare with 100% certainty, that if I as the stand-on vessel have decided 1/4 mile away, that the give way vessel has not met their obligation to give way, and no longer has the ability to avoid collision, that if I take necessary evasive maneuvers to miss them by 180 ft (actually a hair width as previously stated), I have met every single obligation under Colregs. PERIOD.

What's more, if I make evasive maneuvers while the give way vessel still has capability to avoid collision on their own, and we collide, I have violated Colregs, and will be found at some degree of fault if my measures actually cause collision, if the planned but yet to be executed measures of the give way vessel would have prevented collision, had I just stood on.

[Lodesman]

Originally Posted by ramblinrod

Gentlemen, you are inflicting personal opinion as to what is adequate to suit your personal sensibilities.

I don't know what you're gibbering about.

I don't profess to be a collision avoidance expert, and yet without taking a week to review case law I can declare with 100% certainty, that if I as the stand-on vessel have decided 1/4 mile away, that the give way vessel has not met their obligation to give way, and no longer has the ability to avoid collision, that if I take necessary evasive maneuvers to miss them by 180 ft (actually a hair width as previously stated), I have met every single obligation under Colregs. PERIOD.

A freighter going 20kts, that has not yet manoeuvred, will likely be past the point of being able to avoid collision by her manoeuvre alone, from about 1000-1200 yards out - that would be the point that you shall take such action to best avoid collision; waiting past that point would be in conflict with rule 8.

What's more, if I make evasive maneuvers while the give way vessel still has capability to avoid collision on their own, and we collide, I have violated Colregs, and will be found at some degree of fault if my measures actually cause collision, if the planned but yet to be executed measures of the give way vessel would have prevented collision, had I just stood on.

Why don't you point us to a case where that has actually happened? You've worked yourself into a corner here - if you took action out at 2 miles, at the same time he takes action that would bring you back into contact, there is still time to recover and avoid - pull your last second dodge at the same time he does, then there is no margin to take another tack (so to speak).

[ramblinrod]

Originally Posted by Lodesman

Why don't you point us to a case where that has actually happened? You've worked yourself into a corner here - if you took action out at 2 miles, at the same time he takes action that would bring you back into contact, there is still time to recover and avoid - pull your last second dodge at the same time he does, then there is no margin to take another tack (so to speak).

Sorry, you don't get to change Colregs rules to suit your argument. When there is risk of collision established if I am stand on, I am obligated to hold course and speed until such point as the other vessel cannot maneuver in time to avoid collision by there maneuver alone. That is the rule. If I fail to stand on, while the other vessel had time to maneuver to avoid collision, and my action causes collision, I am in a heap o crap, because I violated Colregs; I turned or changed speed when I was supposed to hold course and speed.

[evm1024]

Rod,

I don't see where you are adding anything useful to the conversation.

Please help me understand your motivation in your posting to this thread. Why are you posting here?

Regards