Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

[ramblinrod]

Originally Posted by Dockhead

Did you miss the words "usual" and in "most circumstances"?

I never said "all circumstances." I specifically mentioned, maybe in the other thread, that a few cables can be ok when passing behind, or if you are being overtaken.

In open sea, 1 mile is a good rule to follow, because it is a safe CPA in almost every circumstance, even with a difference in speed, and besides that, this is the distance which the ships you encounter are likely to be using as a minimum CPA (it might be 2 miles in light traffic areas). As I wrote, if you do pass closer than 1 mile, you may cause problems on the ship, where standing orders are likely to require the bridge to call the captain.


But none of that means that a CPA of less than a mile is dangerous in itself, in all circumstances, and I never said that. In open sea, a CPA of less than a mile very often can be, though, so if you do plan to pass closer than that, you had better understand the crossing with good data, better than you can get from a stanchion, unless it's something obvious (obviously passing behind, overtaking, etc.).

Why do ships follow a "rigid rule" like 1 mile or 2 miles? They don't calculate in every case -- can I safely pass 7 cables off? Or 6 cables? Even though such crossing might be pretty safe depending on the geometry. That's because it's bad process, to do it ad hoc, every time. What if you miscalculate once? Why create the work load, when you can just do it the same way every time and know you'll be safe? Good routine, good habits, good process, is what makes safety in something like this -- so you do the safe thing, in muscle memory. So keeping a mile away from every ship in open water is a good policy. You can depart from such a "rigid rule" if you need to -- say because you're dealing with another ship coming from a different direction, and passing a little closer is necessary to make it all work out.

Ships make exceptions for overtaking, but they usually have another "rigid rule" for safe CPA in that case -- 5 cables is common. I've heard them complaining to each other for overtaking closer than that, and of course overtaking is not an inherently safe maneuver (actually the most common type of collision in the North Sea).

*Just as an aside, there is a CHIPS report where one ship complained that one mile was not enough, and that the other ship ignored requests for more room than that, and the first ship was deemed to be in the right.

This sounds to me, like someone talking out of both sides of their face.

After all this, I hear you saying one thing, defending it vehemently, then suggesting your position is something else, something softer and closer to my position, but then going back and defending your original position.

It does sound like someone who is trying to claim a less staunch position than they truly have.

What is YOUR position (not the generic professional mariner you often attempt to represent) on the "safe distance" to be kept from another vessel under Colregs?

Please be as succinct as possible, so that I and others can truly understand what your position really is on this matter.

It has oft been said, that if one can't summarize their position on a subject in 20 words or less, they probably don't understand the subject matter (their position).

What is your position?

[Exile]

Originally Posted by Dockhead

By "won't press stand-on obligation in a potential collision situation" -- do you mean "won't FULFILL stand-on obligation"? I suggest this might not be a good idea, while the obligation exists, but that might be only brief period in a crossing in such waters.

In this thread, we've been talking about collision avoidance in open sea, which works rather differently from pilotage waters where ships are following defined channels and fairways.

Where you are dealing with ships following defined channels and fairways, you don't really need to think that much about CPA's and so forth. You can see where they will be and it's easy to avoid those places. You can approach to much closer distances in perfect safety since you can stop before the edge of the channel.

You're certainly doing it right, if you stay out of the channels and fairways until the coast is clear, and generally avoid getting into risk of collision situations with commercial vessels in pilotage waters. That may be required by Rule 9 in some cases, but it's good practice even if you are not required (for example, a defined fairway might not always be a "narrow channel" in the Rule 9 sense). Just note that your action under Rule 9 should be completed prior to risk of collision arising. If you do get into a risk of collision situation, even in a narrow channel, the normal rules apply, and theoretically you may be even required to stand on if it's necessary to allow the ship to make a maneuver. I say "theoretically" because I can hardly imagine such a case in a narrow channel which is not beyond the stage where any standing on is going on -- the normal maneuver for us would be to get the heck out of the channel. Maybe the pros on here could comment.

No, definitely not one of the pros here commenting. Just that I read Mark P. to also be raising the scenario of commercial vessels in inland waters that are not following narrow channels or defined fairways. To the extent there's a longstanding practice of them not giving way to stand on vessels, it seems Rule 2 may nevertheless apply (same language for int'l & inland waters) (emphasis mine). But this is more of a question than a statement.

RULE 2 Responsibility
(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 these Rules or of the neglect of any precaution which may be required by the ordinary practice of seamen, or by the special circumstances of the case.
(b) In construing and complying with these Rules due regard shall be had to all dangers of navigation and collision and to any special circumstances, including the limitations of the vessels involved, which may make a departure from these Rules necessary to avoid immediate danger.

[Dockhead]

Originally Posted by ramblinrod

This sounds to me, like someone talking out of both sides of their face.

After all this, I hear you saying one thing, defending it vehemently, then suggesting your position is something else, something softer and closer to my position, but then going back and defending your original position.

It does sound like someone who is trying to claim a less staunch position than they truly have.

What is YOUR position (not the generic professional mariner you often attempt to represent) on the "safe distance" to be kept from another vessel under Colregs?

Please be as succinct as possible, so that I and others can truly understand what your position really is on this matter.

It has oft been said, that if one can't summarize their position on a subject in 20 words or less, they probably don't understand the subject matter (their position).

What is your position?

Stated clearly in my previous post.

Let us know if you have any questions after reading.

[ramblinrod]

Originally Posted by Dockhead

* One mile minimum CPA in open sea when crossing with ships, particularly faster ones, is really good practice. Do it consistently and as a habit, as part of a methodical approach to collision avoidance -- that adds a lot to safety.

* One mile minimum CPA in open sea will be consistent with usual standing orders on ships and so will avoid causing problems for watchstanders -- we care about that, don't we?

* There are some cases where one mile is barely enough, and others where you can still be actually safe with less. For example, if speeds are not so different, or one vessel is overtaking or when you are CLEARLY passing behind. If you NEED to pass closer than one mile, THEN you need to dig into whether it will be actually safe in this individual case. And it's always a good practice to call the ship and agree, if you plan to pass closer than this, because a pass of less than one mile in open sea is likely to trigger different procedures -- often including calling the captain.

* A pass of less than one mile may also trigger a maneuver by the ship, which may maneuver in order to fulfill standing orders to always have at least one mile CPA. Two vessels maneuvering at the same time within less than a mile of each other is concretely dangerous. Even if the geometry of the pass is otherwise safe. That's another reason to avoid getting closer than one mile to a ship, if you don't have a good reason to do so.

* Exceptions to all of the above may occur if you have a good reason for it -- like trying to dodge through a line of ships, or trying to untangle a situation with multiple vessels. Perhaps even to avoid a tack at the wrong time. Just be aware that once you are less than a mile from a ship travelling at sea speed in open water, unexpected things can happen, and it can become dangerous in a very short period of time. It's a good practice to call and agree what is going to happen, if you need to pass so close.


I hope that this is very clear now, and I apologize for any misunderstanding.

Thank you.

Your position is now clearer to me, but still not "very clear" as you declare you had hoped.

It still seems to contain a lot of unnecessary verbage and innuendo, and representative of the supposed position of others rather than yourself, making it less clear than it could and should be.

Can you clarify your position of what is "safe distance" under Colregs?

BTW, I completely disagree with your position that...

"Two vessels maneuvering at the same time within less than a mile of each other is concretely dangerous."

I believe this completely wrong.

My contrary position is that there are a multitude of reasons why it may be necessary for both vessels to maneuver at the same time within less than a mile of each other, and if exercised in compliance with Colregs, is not dangerous at all.

[Dockhead]

Originally Posted by Exile

No, definitely not one of the pros here commenting. Just that I read Mark P. to also be raising the scenario of commercial vessels in inland waters that are not following narrow channels or defined fairways. To the extent there's a longstanding practice of them not giving way to stand on vessels, it seems Rule 2 may nevertheless apply (same language for int'l & inland waters) (emphasis mine). But this is more of a question than a statement.

RULE 2 Responsibility
(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 these Rules or of the neglect of any precaution which may be required by the ordinary practice of seamen, or by the special circumstances of the case.
(b) In construing and complying with these Rules due regard shall be had to all dangers of navigation and collision and to any special circumstances, including the limitations of the vessels involved, which may make a departure from these Rules necessary to avoid immediate danger.

Quite so.

It's important to understand that standing-on has no purpose, if the other vessel does not intend to give way.

You are obligated to stand on -- IF the give-way vessel intends to give way. Once you have good reason to believe that the give-way vessel is not going to do it, then you may maneuver, and according to good seamanship, you NEED to maneuver. Rule 8(a), requiring all maneuvers to be made in ample time, kicks in prior to 17(b), which obligates the stand-on vessel to take action at the latest, when action by the give-way vessel alone can't solve the crossing.

What it boils down to is this -- SOMEONE needs to take control of the crossing at an early enough stage that "puckering" stuff doesn't happen. If you are the stand-on vessel, but you have objective, reasonable reason to believe that the give-way vessel is not going to take up the active role, then you should start acting early enough so that the whole crossing happens without drama.


One other thing which applies to this case, a very important thing -- in pilotage waters, even outside of defined fairways and channels, it's still different from open sea. You still know pretty well where the ship is going and where it will be. It is far easier to prevent a risk of collision from ever arising in the first place. That should always be Plan "A" for recreational vessels, in pilotage waters. That's nothing other than the "Rule of Gross Tonnage", properly understood and applied.

[Kenomac]

Originally Posted by skipmac

So I heard.

I do have to say, having driven in cities around the world and been stuck in rush hour traffic jams from Rio to Jerusalem to Los Angeles (haven't done the far east yet) I found Boston drivers in general to be the least tolerant and most unpleasant.

It also drives me insane that Boston (and a lot of MA in general) street signs only show the cross streets. Missed a turn once navigating through Boston (pre GPS) and drove miles looking for a sign to tell me what street I was on. They didn't exist.

You're just supposed to know... and I have to go back to that in four days.

[skipmac]

Originally Posted by Kenomac

Locally, they are referred to as "Massholes."

Originally Posted by Kenomac

Locally, they are referred to as "Massholes."

So I heard.

I do have to say, having driven in cities around the world and been stuck in rush hour traffic jams from Rio to Jerusalem to Los Angeles (haven't done the far east yet) I found Boston drivers in general to be the least tolerant and most unpleasant.

It also drives me insane that Boston (and a lot of MA in general) street signs only show the cross streets. Missed a turn once navigating through Boston (pre GPS) and drove miles looking for a sign to tell me what street I was on. They didn't exist.

[Dockhead]

Originally Posted by ramblinrod

Thank you.

Your position is now clearer to me, but still not "very clear" as you declare you had hoped.

It still seems to contain a lot of unnecessary verbage and innuendo, and representative of the supposed position of others rather than yourself, making it less clear than it could and should be.

Can you clarify your position of what is "safe distance" under Colregs?

BTW, I completely disagree with your position that...

"Two vessels maneuvering at the same time within less than a mile of each other is concretely dangerous."

I believe this completely wrong.

My contrary position is that there are a multitude of reasons why it may be necessary for both vessels to maneuver at the same time within less than a mile of each other, and if exercised in compliance with Colregs, is not dangerous at all.

There is no magic circle one mile around a ship, outside of which you are in perfect safety, and inside of which you are in mortal danger. Every crossing is different -- it depends on the geometry, relative speeds, and size of the vessels concerned.

But one mile is a widely accepted rule of thumb for a minimum safe CPA -- outside of that, you are still generally pretty safe in almost every situation, but inside of that the risks start to pile up rapidly. We use rules of thumb here like in many cases in order to avoid having to do a deep analysis of every case -- where there is likely not to even be time to analyze carefully.

In many cases, inside one mile may be so dangerous as to be an "in extremis" situation where both vessels are obligated to maneuver. If you get into an "in extremis" situation which could have been avoided, that is a violation of the COLREGS and a violation of good seamanship, because it's concretely dangerous, it's dangerous by definition -- because at the "in extremis" stage, vessels are now maneuvering uncoordinated, and there is no longer any time to recover from a mistake or miscalculation. One of the main goals of the COLREGS is to prevent uncoordinated maneuvering, to reduce the risk of vessels turning into each other.

I'm not quite sure from your question whether you doubt that uncoordinated collision avoidance maneuvers are dangerous or not altogether, or only within one mile. If you do doubt this, then I suggest you read some of the basic literature. It's a key cause of collision -- vessels turning into each other.

Either maneuver by itself might have been safe, but the two maneuvers turn out to be in conflict with each other, and a collision results. At a certain distance, and in many cases that's already one mile -- maybe just a few minutes TCPA -- both vessels are obligated to maneuver, and if the maneuvers turn out to be in conflict with each other, then there is no time for correction and the collision becomes unavoidable.

Remember in all of this also that a large ship turning doesn't turn like a car. Large ships can be surprisingly maneuverable -- able to achieve very high rates of turn in short period of time -- but they don't turn like on rails -- the stern swings out, and there is displacement -- that is, the ship moves with sideways component.So if you are approaching a large ship traveling at sea speed, and you get within a mile and it puts the rudder over to avoid you, you may be facing the whole side of the ship coming at you at 20 knots. Some ships are two cables (!) long. This is why talking about 180 foot CPAs in relation to a fast moving, large ship, is -- well, hard to think of another term for it, but -- pure madness. You do not want to be there, not anywhere near that close, to a large ship, which is moving fast. There is a large piece of ocean where it might be a few seconds from now, much bigger than even the very large size of some of these ships, and to be safe you must be outside that whole piece of ocean.

[skipmac]

Originally Posted by Exile

I recall quickly learning that the best way to get anywhere was completely contrary to the "defensive driving" mantra we're supposed to follow and which works in other places. Instead, the trick seemed to be to drive a small, fast car, and not look the other driver in the eye when you were about to cut him/her off.

Same experience here. One of my first trips to Boston I was on 6 lane (each way) freeway in rush hour trying to get to a meeting. Had mapped it out (again pre GPS) and knew the exit I needed. Saw the sign for the exit a mile or two in advance so like a fool I hit the turn signal to indicate a move to the exit lane. From the reactions of the drivers in the next lanes you would have thought I threatened to shoot their dog, kidnap their first born and root for the Yankees.

I would look over my right shoulder to see when I had room to move over. All I could see were drivers that had turned red in the face, were screaming and cursing, showing the one finger salute and pulling up right to the bumper of the car in front of them so I could not move over. Was all quite amazing.

Finally to avoid missing my exit I just started moving to the right until someone had to let me in or collide. I was driving a well insured rental car so didn't care so I won.

Originally Posted by Exile

Now I live somewhere where people are so polite it often screws up the flow of traffic at 4-way stops. "No, no, please . . . after you!" All those good manners can really screw up a former Bostonian. Maybe if I left my Mass. plates on the car it would have helped.

Sounds like driving on Martha's Vineyard. Must be something about riding the ferry over that removes the MA attitude.

[skipmac]

Originally Posted by Kenomac

You're just supposed to know... and I have to go back to that in four days.

Know by intuition? Locals only?

My sympathies on your imminent return. Guess you'll need a few months boat therapy by spring.

[Exile]

Originally Posted by Dockhead

One other thing which applies to this case, a very important thing -- in pilotage waters, even outside of defined fairways and channels, it's still different from open sea. You still know pretty well where the ship is going and where it will be. It is far easier to prevent a risk of collision from ever arising in the first place. That should always be Plan "A" for recreational vessels, in pilotage waters. That's nothing other than the "Rule of Gross Tonnage", properly understood and applied.

Great stuff in your last two posts Dock. But then I'm one of the more pedantic ones I guess that actually like analyzing this stuff. Now whether it translates into my becoming a better seaman remains to be seen.

As for the para. quoted above, I often run into what I think may be a misperception that taking the common sense actions that Mark P., myself and I'm sure most recreational sailors describe under these circumstances requires not properly following the Colregs. In this case, and assuming the commercial tugs are not properly following the give way rules, it sounds like our recreational vessels responding by not engaging in the normally prescribed stand on procedure are in fact in compliance! More than a little counterintuitive I suppose, but not when you consider that the goal of the Rules is to promote predictability, with the end result of preventing collisions.

And yes, effectively the same as the "Rule of Gross Tonnage," but only as applied to some of these limited scenarios.

[Dockhead]

Originally Posted by Exile

Great stuff in your last two posts Dock. But then I'm one of the more pedantic ones I guess that actually like analyzing this stuff. Now whether it translates into my becoming a better seaman remains to be seen.

As for the para. quoted above, I often run into what I think may be a misperception that taking the common sense actions that Mark P., myself and I'm sure most recreational sailors describe under these circumstances requires not properly following the Colregs. In this case, and assuming the commercial tugs are not properly following the give way rules, it sounds like our recreational vessels responding by not engaging in the normally prescribed stand on procedure are in fact in compliance! More than a little counterintuitive I suppose, but not when you consider that the goal of the Rules is to promote predictability, with the end result of preventing collisions.

And yes, effectively the same as the "Rule of Gross Tonnage," but only as applied to some of these limited scenarios.

Quite so. And I think it's really important to understand.

We see a lot of recreational sailors who think that if they follow the "Rule of Gross Tonnage", they don't need to understand anything else about the COLREGS. "I'm going to give up my 'right of way', so why do I need to follow any rules?" This is a dangerous pitfall -- the obligation to stand on, when it arises and as long as it goes on, is an important one.

But that doesn't mean that the "Rule of Gross Tonnage" doesn't exist -- it's part of ordinary common sense and good seamanship, required by Rule 2 -- just it has to be followed without ignoring the other Rules. Which means in general -- taking action prior to a risk of collision arising in the first place, which is usually practical in pilotage waters, but probably often not in open sea.

[David M]

So much of these technicalities such as angles, speeds, CPA's, knowing the Rules inside and out and other things that everyone is discussing and debating although important, can be much less of a worry by getting on the VHF and making passing arrangements with the ship. Try channels 16 and 13.

If there is any doubt whatsoever, you really should try to communicate by radio well before you get anywhere near a possible collision. Waiting is irresponsible and potentially dangerous.

Trust me, they don't want to hit you either. That can be very hard on their licenses.

[conachair]

Originally Posted by David M

So much of these technicalities such as angles, speeds, CPA's, knowing the Rules inside and out and other things that everyone is discussing and debating can be much less of a worry by getting on the VHF and making passing arrangements with the ship. Try channels 16 and 13.

If there is any doubt whatsoever, you really should try to communicate by radio well before you get anywhere near a possible collision. Waiting is irresponsible and potentially dangerous.

Trust me, they don't want to hit you either. That can be very hard on their licenses.

Not always though - the MCA would rather you didn't and stuck to the colregs as much as possible -
https://www.gov.uk/government/upload...io_and_AIS.pdf

3.8 Although the practice of using VHF radio as a collision avoidance aid may be resorted to on
occasion, for example in pilotage waters, the risks described in this Note should be clearly
understood and the COLREG complied with to their best possible extent.

Stick to colregs and calling VHF shouldn't be needed much anyway. In the channel they'll sometimes ignore you anyway - I'm sure there was a link ages ago regarding one shipping line telling crew to keep off the VHF unless really necessary. Can't find it now.

[Dockhead]

Originally Posted by conachair

Not always though - the MCA would rather you didn't and stuck to the colregs as much as possible -
https://www.gov.uk/government/upload...io_and_AIS.pdf



Stick to colregs and calling VHF shouldn't be needed much anyway. In the channel they'll sometimes ignore you anyway - I'm sure there was a link ages ago regarding one shipping line telling crew to keep off the VHF unless really necessary. Can't find it now.

In my opinion, you are both right.

VHF is not needed if you follow the Rules and maneuver in good time. And the VHF is a very poor substitute for simply maneuvering correctly, if there is no obstacle to doing so.

But David said "if in doubt" -- and I actually agree with him -- I think that in the age of AIS where we can know with a high degree of certainty, who we are hailing, radio communication can be really, really helpful to clarify intentions and avoid dangerous misunderstandings.

I became more convinced of this when I was doing my interviews of commercial mariners -- they said, almost to a man, that they want to hear from us, in case of any kind of doubt, including if we simply don't know what to do. Misunderstanding is really dangerous, in collision avoidance. I think the MCA guidance is too conservative.