Collision Avoidance -- Dealing with Multiple Targets

[Dockhead]

Originally Posted by Snore

Back to the original question.

When dealing with multiple targets -#1 is ColRegs. However since multiple target can be a s@@t show I will get on the radio. The example I use in classes is crossing the GS in a sailboat and dealing with the conga line of cruise ships out of Miami and Ft Laud. Given the speed differentials and that the ships sometimes all go slower than normal to make their destinations around sunrise, getting by safely is a challenge.

One radio call and obliging ships will gladly open a gap in the conga line for the give way vessel to get through.

Someone else mentioned the radio call, and I entirely agree that a multiple target situation is one of those cases where a radio call can be just about indispensable.

The thing is, though, you have to have worked out carefully what you need, before you make the call.

What I do is what everyone else on here seems to be doing (except the robot ships mentioned in the interesting dissertation someone posted) -- I work it out in a analogue way in my mind, probably with recursive scenario analysis. I always thought there must be some better way, which is one reason why I started this thread. So you see you can get past A and B with course alteration X, but then you have a problem with C -- but if he would only alter a bit to starboard, it would all work out (or if he would only hold his course and speed). For example. Then you know who to call and what to ask for.

[Stu Jackson]

Originally Posted by bmz

1. Arrogant and ignorant sailors like you who will ignore all evidence and continue to believe that a large freighter must give way to you. You arrogantly look down on Joe sixpack and his formula racing boat; but his ignorance won't get him killed because he is fast enough that at the very last minute he can get out of the way of the stand on freighter.

2. "Following is the order of increasing maneuverability. Any boat lower on the list must give way to boats higher on the list:
1) A disabled boat,  2)A boat that is difficult to maneuver, like a dredge or barge in tow  3)A boat whose maneuverability is restricted by size or draft, like a freighter 4) A boat engaged in commercial fishing, like a trawler  5)A boat being rowed  5)A sailboat  6)A recreational powerboat
http://wow.uscgaux.info/Uploads_wowI..._Sailboats.pdf

1. Thank you for that helpful and collegial response. It sure helps the discourse. I ask a simple question and you get snarky. Seems to be your MO, on this and other threads to which you "contribute." Sorry, but it's not an approach that makes much sense.

For example, you wrote this in another thread on electronics: "Large commercial vessels are constrained by their lack of maneuverability and are therefore always the stand on vessel, even in blue water." It seems just incorrect. Please note that I did NOT call you ignorant or arrogant.

Joe Sixpack in his fast boat, based on my 45 years of what you'd probably call limited and ignorant and arrogant "experience," 99% of the time has NO CLUE about what's going on, lacks situational awareness, doesn't care a whit about his wake because he never looks back, and hasn't ever read a safe boating presentation; his behavior so indicates. I do not believe "that a large freighter must give way to" me. I never said so. Where do you make this stuff up from? "...because he is fast enough that at the very last minute he can get out of the way of the stand on freighter..." - Oh, like the USS Fitzgerald? When will you learn that personal insults are poor examples of communication?

2. I know this already. Thanks for copying it.

Look, Dockhead asked a pertinent and useful question. I appreciate his experience and efforts. If you'd like to contribute, without casting unnecessary aspersions, please join us.

[Juho]

Originally Posted by Dockhead

Thanks-- that's an actual procedure, and interesting.

A couple of people have mentioned slowing down.

Just want to mention that although taking way off is specifically mentioned in the COLREGS, you need to be really sure that taking way off will have the effect you desire -- of defusing the situation. To be sure about that, you have to do a certain amount of work. So in my opinion, taking way off should not be a quick automatic reaction to a potential conflict.

All the more because less speed means less ability to maneuver -- less ability to increase the CPA. Outside of harbors and approaches to harbors, power to control a crossing is all about speed, and not at all about a high ROT.

Ships almost never take way off in a risk of collision situation, and neither do I, unless it's a situation in a harbor or approach to a harbor when I'm approaching a fairway. But even then, a change of course is usually just as effective, and without the effect of losing your ability to make distance between you and some dangerous spot in the water.

Slowing down (when facing a problem with multiple targets) may sometimes not be the best solution. It may however often be a good solution, especially if one is uncertain of what one should do.

Slowing down probably solves the problem with the first vessel. But it is possible that it would introduce another problem with some other vessel. It is also possible that the first vessel slows down as well or changes course (because of some other vessels) so that the problem continues. Also manoeuvrability could be a problem as you point out. But if in doubt, slowing down may be a better quick reaction than speeding up or changing course in a way that may not turn out to be a good solution.

I don't know what you exactly mean with taking way off, but I think that a good sailor should always have a backup plan, plan B (and maybe also plan C), in case plan A does not work. Having those plans means that one maybe need not slow down or end up in problematic situations if one just branches to plan B well before problems emerge. This approach should actually be part of the algorithm that the sailor follows. He should follow plan A only if it seems to work well, and otherwise move early enough to plan B. He has to monitor the viability of plan B (in addition to plan A) all the time in order to avoid painting himself in a corner.

[conachair]

Originally Posted by Dockhead

Anyone have anything to add to this?

Couple of general thoughts IMHO -

In congested areas like the channel it's well worth having at the front of your mind that the big boats have been keeping an eye on their CTS with regard to you (if you have a decent radar return/AIS transmission) and all the other big boats around you since way before they appeared over your horizon, and are also dealing with ships beyond you which you can't even see yet. The circle of sea they are sailing in is a lot bigger than yours. In general they are very good at what they do, if something odd happens it may well be because of another ship you aren't even aware of.

Jumping on the radio seems to be a bit of a kneejerk reaction on this thread, IMHO it's should be further down the list of things to do and is explicitly frowned upon the the english channel by the MCA -
http://solasv.mcga.gov.uk/m_notice/mgn/mgn324.pdf
Which isn't to say don't , but maybe hold back instead of jumping onto the vhf straight away. More "pilotage" waters this changes though, heading up the Thames Estuary you'll hear more of "Calypso, dredger Avalon, happy with green to green, Jimmy?"

Dockhead knows all this of course, but maybe worth reiterating.

[tenchiki]

In the San Francisco Bay area, the Coast Guard occasionally comes on ch16 to "remind all mariners that Rule 9 applies throughout the bays and approaches"

[David M]

Originally Posted by The Way

This reminds me of a question I've had often in crowded harbors -- some vessels are monitoring 16, others 13. What do I do, try to hail on each one? But while waiting for an answer on the wrong channel, time is getting shorter.

Thanks for any advice,
Jack

If you only have a single radio then scan on both frequencies. Also, contact the other vessel well before time is getting so short that this does not become a problem. In the COLREGS it is called early and apparent action to avoid a collision.

The term "constrained by her draft" is found in the International Rules but not the Inland Rules. It is found in Lights and Shapes, Rule 28

[Snore]

Originally Posted by The Way

This reminds me of a question I've had often in crowded harbors -- some vessels are monitoring 16, others 13. What do I do, try to hail on each one? But while waiting for an answer on the wrong channel, time is getting shorter.



Thanks for any advice,

Jack

Another reason for a handheld! Boat radio on 16 and handheld is on the working channel.

[Quebramar]

Or vhf put on dual watch... very handy I must say. It helps catching weather forecast etc whilst keeping the watch on 16

[Dockhead]

Originally Posted by conachair

Couple of general thoughts IMHO -

In congested areas like the channel it's well worth having at the front of your mind that the big boats have been keeping an eye on their CTS with regard to you (if you have a decent radar return/AIS transmission) and all the other big boats around you since way before they appeared over your horizon, and are also dealing with ships beyond you which you can't even see yet. The circle of sea they are sailing in is a lot bigger than yours. In general they are very good at what they do, if something odd happens it may well be because of another ship you aren't even aware of.

The conflict between time and distance horizons of WAFIs, and those of ships' bridges, seems to me to be one of the fundamental problems of collision avoidance, too little discussed. I have thought about this a great deal.

We've all had a laugh at the Joe Sixpack bow rider types and their Rule of Gross Tonnage etc., but in fact what is going on here, I am convinced, is a conflict of time/distance horizon. When these guys talk about always giving way to ships, regardless of what the Rules say -- they are actually right, within their own horizon of time/distance awareness. A mile off to them seems like a long ways, but a larger vessel is already fully committed, and we call it in extremis. Four or five cables even seems like a long ways to the bay sailor in his San Juan 24, but he often cannot even be seen already from the bridge of a large commercial vessel, nor by the radar. It would really be deadly for him to think that the ship about to run him down, four cables off, is going to change course.

I think it is extremely important to raise awareness of this issue, and teach boaters that the phase of giving way and standing on is over, long before they realize it. It's also another reason why we have to hammer into their heads to stop using the term "right of way", which is a completely different concept, also in this context.

Originally Posted by conachair

Jumping on the radio seems to be a bit of a kneejerk reaction on this thread, IMHO it's should be further down the list of things to do and is explicitly frowned upon the the english channel by the MCA -
http://solasv.mcga.gov.uk/m_notice/mgn/mgn324.pdf
Which isn't to say don't , but maybe hold back instead of jumping onto the vhf straight away. More "pilotage" waters this changes though, heading up the Thames Estuary you'll hear more of "Calypso, dredger Avalon, happy with green to green, Jimmy?" . . .

I agree of course, and I don't think anyone has suggested going to the radio light-mindedly. It should never be necessary in a straightforward crossing involving two vessels. I've written a whole chapter on this, including extensive discussion of the MCA MGN. I completely agree with the MCA that radio comms should not be used to support sloppy non-Rules compliant maneuvering. If everyone follows the Rules in a standard crossing, then communications are not needed at all, are a waste of time, and can be crucially distracting. But a complex multi-vessel crossing is the classical case for agreeing passing arrangements, if you are unable to work out a solution on your own. Green to green passing, however, is the most common situation.

Needless to say, AIS has dramatically reduced the risks of using the VHF for passing arrangements.

[Dockhead]

Originally Posted by Juho

. . . Slowing down probably solves the problem with the first vessel. .

Only if you really have a 0.00 CPA or are passing slightly behind. If you're passing slightly ahead, it might make the situation worse. To know the difference, even with AIS, you have to do some work. In a small boat under sail with variations in course and speed, it takes a bit of time to discern the average course and speed and really get much of an idea about the CPA.

And even if you have a 0.00 CPA, slowing down is weak, having less effect on CPA than a large course change. Meanwhile, having lost your speed, you've lost your ability to make further maneuvers. You've made yourself into a sitting duck.

Larger vessels powered by low speed two stroke diesels can't just "cut the throttle" at sea speed -- they have to have engineers in the engine room to change the engine regime. That's probably the main reason why you almost never see a larger vessel slow down, but I bet they wouldn't anyway except in the rarest of cases. Maybe Ping or Nigel or one of our other commercial mariners would speak up on this.

In the great majority of cases, I think a 180 degree turn, or a tack or other large course change, while maintaining speed, is a better maneuver.

Of course there are exceptions to all of this.

[TJ D]

Hi all,

Regarding ships slowing down, they do so when it makes sense. Sometimes, dropping the speed by a bit is a lot less drastic of an action than a course change.

Back to the topic at hand-

I'll start by saying that, from a commercial perspective, It's REALLY helpful if the WAFI's just follow the colregs as they should. There are few things more frustrating from the bridge than having a pleasure boat start making random course changes to 'stay out of the way' of a commercial boat. As Dockhead often points out on these threads, we typically have things sorted out before you've even started to think about taking action. Wiggling around hither and yon doesn't help anyone.

If you're the 'stand-on' vessel, just maintain your course and speed as you should (until it becomes apparent that the other vessel isn't taking necessary action, of course), and all works out better. If you're to give way, do so early.


Dock, I think that you're facing a pretty daunting task here. Each case is so different, it would be hard to expand on the colregs in a way that fits all, or even most, multi-target situations.

But, if I had to try to describe a complex procedure, it would be along these lines- this assumes a single watchkeeper, as most of us are running this way a lot of the time.

1. Monitor vessels in the area at as great of a range as possible. A couple of degrees one way or the other at 10 miles is preferable to a major alteration when closer.
2. Determine the most critical CPA/TCPA targets as a first step.
3. Determine which ones you are to give way to, and which ones give way to you.
4. Take your first action on the most critical target, remaining aware that any changes will change all of your situations.

As an aside, I nearly always run both my own ship vectors and target vectors on 30 minutes. I find that this is a really good visual presentation on the plotter, giving plenty of time to do what's needed. I might switch down to 15 or less if there's a lot of congestion, and we need to stay pretty 'zoomed in' to avoid information overload.

AIS integrated into the plotter is invaluable here. Yes, you still need to keep the HBC/RADAR in play, but when it gets really busy, I'm spending a lot more time watching the AIS than anything these days-bearing in mind that not everyone's transmitting, of course.

5. I typically try to visualize the effect on everyone of a course/speed change before doing so, but I have on a few occasions made a change (at longer ranges) that I wasn't necessarily intending to keep. Call it a 'trial maneuver'. When you're trying to sail the boat alone, sometimes there's too much to process, and I've found that it's helpful to do this.

6. I try to stay off the radio too, but there are times when it's really the only way to go.

7. Finally, remember that the big guys sometimes blow it, too. On a recent crossing from Guernsey, I watched a complete bonehead on a Westbound freighter fail to give way to a container ship traveling SE. The freighter kept telling the container ship that he should just turn to port, and all would be GREAT! The problem was that the freighter had another guy off his starboard side, and this would have been the worst thing possible. Finally the captain of the container ship, with a few words that wouldn't be allowed on CF, got the other guy straightened out.

Finally- TRANSMIT AIS! It's completely changed the yacht/ship interaction.

I don't know if that's really helpful or not, but it's the best I can come up with...

TJ

[Suijin]

I think looking at the issue exclusively from the perspective of CPA is a dangerous and often self-defeating approach. As David stressed, always turning to starboard, and always obeying COLREGS should take priority. Obviously the greater the CPA with multiple targets the greater the safety, but engaging in confusing maneuvers to try and secure it can undermine your solution and make matters dramatically worse.

In my experience the single best feature of AIS is being able to hail a ship by name, which increases the likelihood of getting a response by about 1000%, particularly in major shipping channels with lots of international traffic. I pick up the mic if there is even a hint of doubt about what the other party is doing or what their intentions are.

Dockhead thank you for that example of the differing horizons of sailboats and ships. It is not something that many boaters appreciate for the simple fact that they have not been at that wheel.

[Juho]

Originally Posted by Dockhead

Only if you really have a 0.00 CPA or are passing slightly behind. If you're passing slightly ahead, it might make the situation worse. To know the difference, even with AIS, you have to do some work. In a small boat under sail with variations in course and speed, it takes a bit of time to discern the average course and speed and really get much of an idea about the CPA.

And even if you have a 0.00 CPA, slowing down is weak, having less effect on CPA than a large course change. Meanwhile, having lost your speed, you've lost your ability to make further maneuvers. You've made yourself into a sitting duck.

I was thinking of a scenario where the 0.00 CPA point is one mile ahead. If I drop my speed to half, the other boat will be half a mile in front of me at the calculated collision time (new CPA is probably somewhat smaller (hopefully not, but potentially 0.00 if the difference of our courses is 0° or 180°)). Changing course would be nicer, but we assumed that at least the primary course changing plan did not work because of other vessels.

One problem with slowing down is that the other vessel probably can not see our change of speed as easily and clearly as it would see our change of course.

Larger vessels powered by low speed two stroke diesels can't just "cut the throttle" at sea speed -- they have to have engineers in the engine room to change the engine regime. That's probably the main reason why you almost never see a larger vessel slow down, but I bet they wouldn't anyway except in the rarest of cases. Maybe Ping or Nigel or one of our other commercial mariners would speak up on this.

The idea of maintaining also plan B would make sense to them (to avoid having to slow down when plan A doesn't seem to work).

In the great majority of cases, I think a 180 degree turn, or a tack or other large course change, while maintaining speed, is a better maneuver.

Yes. But we need also something for situations where the most natural change of course does not work because of the other vessels.

Of course there are exceptions to all of this.

Yes, the multiple vessel situation could be complex, and in principle there are also scenarios that have no good solutions. One almost fool proof solution would be to stop all the vessels, but that is not practical, and we can not assume that all the other vessels would follow our plan. Our plan should work even if other vessels will maintain their speed and course or if they make some surprising moves.

I think colregs are quite well written, and all we can do is to give some rules of thumb on how one could easily and efficiently and safely follow the colregs, and not make a mess of the multiple target scenarios.

[Pelagic]

[QUOTE=Dockhead;2460529
......In the great majority of cases, I think a 180 degree turn, or a tack or other large course change, while maintaining speed, is a better maneuver.

Of course there are exceptions to all of this.[/QUOTE]

Something to consider is that one of the weaknesses of many juinior commercial officer's is their reluctance to make a large deviation from their prescribed course. For Fear of the Master questioning their efficiency.... Etc...

GPS accuracy has everyone in a tight zone of optimum but convergent tracks.

in a ML situation with large ships operating at higher speeds, if sea room is available I purposely and obviously take myself out of the equation with a 90° turn to Starboard, then a complete round turn as a delaying action before resuming course which is offset from the popular track.

[Juho]

Originally Posted by TJ D

Hi all,

Regarding ships slowing down, they do so when it makes sense. Sometimes, dropping the speed by a bit is a lot less drastic of an action than a course change.

Back to the topic at hand-

I'll start by saying that, from a commercial perspective, It's REALLY helpful if the WAFI's just follow the colregs as they should. There are few things more frustrating from the bridge than having a pleasure boat start making random course changes to 'stay out of the way' of a commercial boat. As Dockhead often points out on these threads, we typically have things sorted out before you've even started to think about taking action. Wiggling around hither and yon doesn't help anyone.

If you're the 'stand-on' vessel, just maintain your course and speed as you should (until it becomes apparent that the other vessel isn't taking necessary action, of course), and all works out better. If you're to give way, do so early.


Dock, I think that you're facing a pretty daunting task here. Each case is so different, it would be hard to expand on the colregs in a way that fits all, or even most, multi-target situations.

But, if I had to try to describe a complex procedure, it would be along these lines- this assumes a single watchkeeper, as most of us are running this way a lot of the time.

1. Monitor vessels in the area at as great of a range as possible. A couple of degrees one way or the other at 10 miles is preferable to a major alteration when closer.
2. Determine the most critical CPA/TCPA targets as a first step.
3. Determine which ones you are to give way to, and which ones give way to you.
4. Take your first action on the most critical target, remaining aware that any changes will change all of your situations.

As an aside, I nearly always run both my own ship vectors and target vectors on 30 minutes. I find that this is a really good visual presentation on the plotter, giving plenty of time to do what's needed. I might switch down to 15 or less if there's a lot of congestion, and we need to stay pretty 'zoomed in' to avoid information overload.

AIS integrated into the plotter is invaluable here. Yes, you still need to keep the HBC/RADAR in play, but when it gets really busy, I'm spending a lot more time watching the AIS than anything these days-bearing in mind that not everyone's transmitting, of course.

5. I typically try to visualize the effect on everyone of a course/speed change before doing so, but I have on a few occasions made a change (at longer ranges) that I wasn't necessarily intending to keep. Call it a 'trial maneuver'. When you're trying to sail the boat alone, sometimes there's too much to process, and I've found that it's helpful to do this.

6. I try to stay off the radio too, but there are times when it's really the only way to go.

7. Finally, remember that the big guys sometimes blow it, too. On a recent crossing from Guernsey, I watched a complete bonehead on a Westbound freighter fail to give way to a container ship traveling SE. The freighter kept telling the container ship that he should just turn to port, and all would be GREAT! The problem was that the freighter had another guy off his starboard side, and this would have been the worst thing possible. Finally the captain of the container ship, with a few words that wouldn't be allowed on CF, got the other guy straightened out.

Finally- TRANSMIT AIS! It's completely changed the yacht/ship interaction.

I don't know if that's really helpful or not, but it's the best I can come up with...

TJ

Perfect