Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

[StuM]

Originally Posted by Dockhead

So a lawyer trying to get the ship out of liability would have to prove not only that the nav lights were faulty, but that their faultiness actually contributed to the accident. If that was not the case, then it would be dishonest and unethical to attempt to prove it.

I realize that wouldn't stop a lot of lawyers (why our profession doesn't have the best reputation), but you are really not supposed to do this sort of thing.

Present company excepted: in my experience - that would stop few, if any, lawyers

[Hoofsmit]

Originally Posted by Dockhead

It looks like a 200+ m vessel heading TOWARDS you. But what's key here is the perception of DISTANCE. It would seem like a ship far away. You wouldn't need to be a plonker to make that mistake.

There have actually been some collisions which happened that way.

I am sure you are correct , collisions have happened, but if we are being pedantic with not showing a tri colour with other lights then the same applies, you would only see two white lights on a vessel over 50m at anchor

A vessel over 50 m (rule 23 - not 200m+) with two mast head lights will also show side lights - if you can miss understand the lights shown, your a plonker in my book

[Jim Cate]

Originally Posted by Hoofsmit

I am sure you are correct , collisions have happened, but if we are being pedantic with not showing a tri colour with other lights then the same applies, you would only see two white lights on a vessel over 50m at anchor

A vessel over 50 m (rule 23 - not 200m+) with two mast head lights will also show side lights - if you can miss understand the lights shown, your a plonker in my book

However, when seen at a distance, a +50 m vessel's two white masthead lights can be seen while the side lights are below the horizon. I've seen this many times myself...

This seems as if it exacerbates the distance confusion that DH was talking about.

I agree that it should not be too damn confusing, since a quick check on the radar will show the distance off.

Jim

[ramblinrod]

Originally Posted by Jim Cate

However, when seen at a distance, a +50 m vessel's two white masthead lights can be seen while the side lights are below the horizon. I've seen this many times myself...

This seems as if it exacerbates the distance confusion that DH was talking about.

I agree that it should not be too damn confusing, since a quick check on the radar will show the distance off.

Jim

Agreed!

It seems some keep switching back and forth from OOWs being total donkeys to brilliant professional seaman depending on which supports their argument of the moment.

I guess there are all kinds in every occupation.

[Uricanejack]

Originally Posted by ramblinrod

Agreed!

It seems some keep switching back and forth from OOWs being total donkeys to brilliant professional seaman depending on which supports their argument of the moment.

I guess there are all kinds in every occupation.

I've met both. I operate on the principle presume "Donkey" until pleasantly surprised.

[ramblinrod]

Originally Posted by Dockhead

It's a good question, from both legal and ethical side.

The law says if the accident was caused by the watchkeeper's having been asleep, so that proper navigation lights wouldn't have changed the outcome, then the sailor is not to blame.

So a lawyer trying to get the ship out of liability would have to prove not only that the nav lights were faulty, but that their faultiness actually contributed to the accident. If that was not the case, then it would be dishonest and unethical to attempt to prove it.

I realize that wouldn't stop a lot of lawyers (why our profession doesn't have the best reputation), but you are really not supposed to do this sort of thing.

Let me get this straight.

You are suggesting that a lot of lawyers, who are highly educated and trained in professional ethics would ignore their training and oath of ethical practice and pursuit of truth and justice, to get a deadbeat OOW off the hook for a tragic maritime accident causing death and possibly leaving someone's family destitute, as a result of their incompetence?

This does truly make an excellent argument for displaying lights correctly regardless if anyone with any brains couldn't confuse deck level running lights and a trilight on a small sailboat with something else.

[Uricanejack]

Originally Posted by Dockhead

OK, sorry if I was misunderstanding you.

You interchanged the terms "act at one mile" and "maintain one mile CPA" -- I was just warning against confusing these different concepts.

My second point was about the phrase "sailing along at your pleasure". It sounds like you are advocating just not worrying about it -- relying on your stand-on status and letting the ship deal with it, which is a very common mistake. If what you really mean is you are watching carefully, checking other traffic, and getting ready to make your own move -- then that's fine -- but it sure doesn't sound like "sailing along at your pleasure".

And yes, I agree with you, that if the ship does take control of the crossing, then he will set up whatever CPA he thinks he needs, and if he does do that, and you are also comfortable with that CPA and with the crossing in general, then you don't need to do anything but monitor the situation and hold course and speed. I think I wrote that. But here are cases where it is not the ship which unilaterally determines the CPA -- we determine it (an in the hypothetical you were referring to, the ship is stand-on), or we influence it. In those cases we need to consider not only what we personally feel comfortable with, but also what is the "ordinary practice of seaman", including the normal CPAs for these waters and that type of vessel. That's not just a question of causing problems for the guys on the ship -- it's also a question of safety in and of itself. If you force a crossing at a CPA which is not going to be acceptable for the ship, then most likely he will maneuver himself. If that happens in close quarters, it can be quite dangerous, for different reasons.

The point is that it is important to be aware of and be sensitive to and take account of the way they do it on ships, including customary CPA's, and not just make up something ourselves, in a vacuum. Coordinated maneuvers, where everyone has similar expectations and standards, where everyone understands what the other is doing, and where everyone is in the same phase at the same time, is safe. Uncoordinated maneuvers, especially where the vessels don't understand each other, and don't know what to expect from each other, are not.

No worries. I agree with quite a bit of what you say. I will have to go back an re read the hypothetical scenario.
Changing the sailboat to a stick boat under power changes the whole situation.
Now talking about the mile makes sense.

Personally I prefer to be give way, One advantage of "not impede" it gives me the freedom to act in my own self interest.
Even so standing on is no big deal if you have a plan and are prepared to act if required.

I tend not to use "distance" to determine action when sailing, I use eyeball. Aspect and bearing change. Much less precise.

I often wonder if the apparent precision of GPS AIS results in margins being cut and closer passes.

[Uricanejack]

Originally Posted by Stu Jackson

2. That may well be true, and one could never know it. Not an issue at all. Only reason it was brought up was that input to Dockhead from seasoned big ship officers mentioned it repeatedly. Good to know.

1. The entire point of this thread, I believe, has been to point out that fast moving ships represent a completely different scenario than those of us blow-boaters are used to in crossing situations with other sailboats and slower moving ships. Once the difference in speed becomes 3 or 4:1, those old standby "use the stanchion" methods no longer work very well because of the geometry of the crossing (angles). My experience back on page 17 (I think) discuss that in detail. I've learned a lot by reading and participating in this thread. "The distance is up to the sail boat." If you follow the math explained by many respondents here, that statement begins to become very questionable once a ship traveling four times your speed is within 4 nm. The awareness of learning to NOT apply a "rounding the marks when sailboat racing" technique to a crossing with ships traveling very fast is critical.

Just my opinion. The old Mk1 eyeball is still the best quickest and most reliable way to determine risk of collision. It will not give precision re distance. Wow that looks big and its getting bigger fast.
There are quite a few relatively big fast vessels where we sail.

[Uricanejack]

Originally Posted by evm1024

Hey, Welcome to the thread. Nice to see it go back to Collision Avoidance. And cones of uncertainty.

For my part I base where I as the skipper of the sailboat (under power as I recall) start to get real interested in the crossing situation when the boat is 1 mile from the path of the ship (and the ship 4 miles out). Or more likely as much further out as possible when I see that the ship is heading for a close encounter with me.

I suggest that each of us look at this crossing not as an exercise on paper but to visualize it as if it were unfolding in real time.

The uncertainties are our own speed, the ships speed, the angle at which we will be crossing and where we will be in relation to each other at that crossing.

When we think of this as I'll pass 180' off his stern (CPA of 180') we are running the event backward in time from that point. But in reality we cannot backtrack to understand it, we need to look at this in forward projection from our starting point. For me the starting point is with the ship 4 miles out. And that is just for ease. It might actually be 5 miles out or whatever.

So ship 4 miles out - we know that it is coming our way. Now we are really paying attention to it. All we know is that it is about 14 degrees forward of our beam.

Ship 2 miles out - still 14 degrees forward of our beam. We have realized that we likely are on a collision course. the relative bearing has not changed. And the ship is much closer. And that it only took 6 minutes to get this close.

Ship 1 mile out - still 14 degrees forward of our beam. Crap it is close and moving fast. It only took 3 minutes to get there. We are 0.25 nm and 3 minutes from the intersect but we have no way of knowing that with any certainty. I imagine that there is mild to severe panic on the edges of my mind. What am I going to do to avoid getting run down?

For me if the ship is 4 miles out and is still holding a constant relative bearing then I feel that they have not given way as required and thus I am bound to take corrective action. (17a-ii)

My only experience on the bridge of a (big) ship is with their Transas systems. Great big displays with radar and AIS overlay the charts. If their radar sees our boat we would be on the displays and the bridge crew would be working a solution for the crossing. Plus they "should" have seen us and taken action to avoid a close crossing.

That they did not at 4 miles out tells me it is up to me for whatever reason....

At 4 miles out or wherever I invoke Rule 17a-ii I usually drop my speed to get the other vessel to draw forward of me. I am usually on a track and like to stay on it (check all routes in the GPS/plotter for hazards and going off track triggers another look at the entire new track).

If by a speed change alone the ship does not start drawing forward I will invoke a (typically) 90 degree turn and speed up to attempt to run parallel to them till they draw forward. And if that does not work then I do a further 90 degree turn (reverse my course as it works out to be) to run for cover.

Of course I'm on the radio and making sure that I can be seen and sounding my horn.


Regards

I can see it can be nerve racking when a ship is coming and getting bigger quickly. One thing this thread may be raising awareness of is just how quickly they can appear and then be real close.


I prefer not to get into specific distances regarding when to act. 4 mile to apply rule 17. Might be a bit early.
planning yes. communicating ok if you want to. Make sure you both know who you are talking to. I would tend to avoid radio com with ESL vessel.

At 4 miles I would expect there is still a very strong possibility the ship is still planning to alter.


What you are fee to do if you wish is act in accordance with rule 2. The ordinary practice of seamen. Using this provision if you think a close quarters situation may develop you may act early to eliminate the close quarters situation or risk of collision developing in the first place.


I tend to do this with more often in congested coastal waters with a tug and tow.

[Uricanejack]

Originally Posted by evm1024

Hey, Welcome to the thread. Nice to see it go back to Collision Avoidance. And cones of uncertainty.

For my part I base where I as the skipper of the sailboat (under power as I recall) start to get real interested in the crossing situation when the boat is 1 mile from the path of the ship (and the ship 4 miles out). Or more likely as much further out as possible when I see that the ship is heading for a close encounter with me.

I suggest that each of us look at this crossing not as an exercise on paper but to visualize it as if it were unfolding in real time.

The uncertainties are our own speed, the ships speed, the angle at which we will be crossing and where we will be in relation to each other at that crossing.

When we think of this as I'll pass 180' off his stern (CPA of 180') we are running the event backward in time from that point. But in reality we cannot backtrack to understand it, we need to look at this in forward projection from our starting point. For me the starting point is with the ship 4 miles out. And that is just for ease. It might actually be 5 miles out or whatever.

So ship 4 miles out - we know that it is coming our way. Now we are really paying attention to it. All we know is that it is about 14 degrees forward of our beam.

Ship 2 miles out - still 14 degrees forward of our beam. We have realized that we likely are on a collision course. the relative bearing has not changed. And the ship is much closer. And that it only took 6 minutes to get this close.

Ship 1 mile out - still 14 degrees forward of our beam. Crap it is close and moving fast. It only took 3 minutes to get there. We are 0.25 nm and 3 minutes from the intersect but we have no way of knowing that with any certainty. I imagine that there is mild to severe panic on the edges of my mind. What am I going to do to avoid getting run down?

For me if the ship is 4 miles out and is still holding a constant relative bearing then I feel that they have not given way as required and thus I am bound to take corrective action. (17a-ii)

My only experience on the bridge of a (big) ship is with their Transas systems. Great big displays with radar and AIS overlay the charts. If their radar sees our boat we would be on the displays and the bridge crew would be working a solution for the crossing. Plus they "should" have seen us and taken action to avoid a close crossing.

That they did not at 4 miles out tells me it is up to me for whatever reason....

At 4 miles out or wherever I invoke Rule 17a-ii I usually drop my speed to get the other vessel to draw forward of me. I am usually on a track and like to stay on it (check all routes in the GPS/plotter for hazards and going off track triggers another look at the entire new track).

If by a speed change alone the ship does not start drawing forward I will invoke a (typically) 90 degree turn and speed up to attempt to run parallel to them till they draw forward. And if that does not work then I do a further 90 degree turn (reverse my course as it works out to be) to run for cover.

Of course I'm on the radio and making sure that I can be seen and sounding my horn.


Regards

Sorry apparently editing time is limited

I can see it can be nerve racking when a ship is coming and getting bigger quickly. One thing this thread may be raising awareness of is just how quickly they can appear and then be real close.


I prefer not to get into specific distances regarding when to act. 4 mile to apply rule 17 a 11. Might be a bit early.
Planning yes. communicating ok if you want to. Make sure you both know who you are talking to. I would tend to avoid radio com with ESL vessel.

At 4 miles I would expect there is still a very strong possibility the ship is still planning to alter.

Rule 17 requires a stand on vessel to stand on. As stated earlier by others this is an obligation. or burden.
Until it becomes apparent the give way vessel is not taking appropriate action as required by the rules.
First you are obligated to allow the give way vessel time to react.
Next when you are beginning to doubt the give way vessel is going to take appropriate action.
The stand on vessel is obligated to sound a signal to convey doubt about intentions Prior to taking action. As a stand on vessel.


The signal is of course 5 short on the whistle.


Although distance are not mention regarding when to act.


If you read the annex of the colregs defining whistles and the requirements of distance at which they must be audible in calm conditions you will find even for large vessels
it is 2 miles.


Generally speaking acting under rule 17 a 11. At a distance greater than which your sound signal can be reliably expected to be heard would be considered a bit early. Due to the obligation to sound a warning not having been met.

What you are fee to do if you wish is act in accordance with rule 2. The ordinary practice of seamen. Using this provision if you think a close quarters situation may develop you may act early to eliminate the close quarters situation or risk of collision developing in the first place.


I tend to do this with more often in congested coastal waters with a tug and tow.

[Uricanejack]

Well I went back and re read the very first post by the OP which included a quote from his pal Rod.


I read sailboat. No mention of power. I might have missed it. It changes everything on how I perceive the entire conversation.

[Uricanejack]

Well I guess everyone has gone down a rabbit hole about tri color lights now.

Yes its illegal to show the tri color along with the standard side lights or combined bow lantern.
I've seen it done quite a few times. Once seen its easy to figure out. I shrug my shoulders and carry on. At least she has lights. No point getting worked up about it.

Sodium Vapour they are anoying

[Dockhead]

Originally Posted by ramblinrod

Let me get this straight.

You are suggesting that a lot of lawyers, who are highly educated and trained in professional ethics would ignore their training and oath of ethical practice and pursuit of truth and justice, to get a deadbeat OOW off the hook for a tragic maritime accident causing death and possibly leaving someone's family destitute, as a result of their incompetence?

This does truly make an excellent argument for displaying lights correctly regardless if anyone with any brains couldn't confuse deck level running lights and a trilight on a small sailboat with something else.

A lot of lawyers are sharks. But I think everyone knows that.

But I don't think anyone argued that this is a major reason to display the correct lights. The major reason to display correct lights is to avoid confusion, and also simply because it is part of following the Rules. I think I remember that you argued a number of times in other threads that the main thing in collision avoidance is simply following the rules -- and here I heartily agree with you.

[Dockhead]

Originally Posted by Jim Cate

However, when seen at a distance, a +50 m vessel's two white masthead lights can be seen while the side lights are below the horizon. I've seen this many times myself...

This seems as if it exacerbates the distance confusion that DH was talking about.

I agree that it should not be too damn confusing, since a quick check on the radar will show the distance off.

Jim

Exactly right. I think anyone who has done much sailing at night in crowded waters will know how easy it would be to make this mistake. It's exactly because you don't see side lights, that it would be very natural to assume that the vessel you see is hull down on the horizon.

And radar will correct you most times, but not always -- the really dangerous situation is when there is confusion about the distance, and then you assume that the lights you see belong to a DIFFERENT vessel you see on radar (or AIS), much further away. There were some actual accidents like this. Small boats very often don't show up on ships' radar, especially S band.

Anyone who thinks this is easy, and that only idiots can confuse nav lights, just hasn't had enough experience, in my opinion. It can be really hard.

[evm1024]

Originally Posted by Dockhead

Exactly right. I think anyone who has done much sailing at night in crowded waters will know how easy it would be to make this mistake. It's exactly because you don't see side lights, that it would be very natural to assume that the vessel you see is hull down on the horizon.

And radar will correct you most times, but not always -- the really dangerous situation is when there is confusion about the distance, and then you assume that the lights you see belong to a DIFFERENT vessel you see on radar (or AIS), much further away. There were some actual accidents like this. Small boats very often don't show up on ships' radar, especially S band.

Anyone who thinks this is easy, and that only idiots can confuse nav lights, just hasn't had enough experience, in my opinion. It can be really hard.

I should point out that these anchor lights are all round white lights not masthead lights. Masthead lights are required to have 6 miles visibility and all round lights 3 mile. Also, they are not required to be both visible at the same time as are the 2 masthead lights that form a range.

Also, the stern light needs to be lower than the forward light. So one is typically hidden by the superstructure. In my experience when you are in line with the ship you typically only see one of the lights. I think I recall that that was the intent (to only see one when inline and to show the ends of the ship from the side).