Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

[Dockhead]

Originally Posted by ramblinrod

Oh really?

Please let me draw your attention to your post...

Re: Collision Avoidance -- Dealing with Multiple Targets #101, 21-08-2017, 16:37

Where you clearly stated, with respect to maintaining distance from a ship...



and...



Then in post # 151, 27-08-2017, 06:37


*
So I guess I need to ask the question...

...At what point in this discussion did you change your position that one should keep a minimum CPA of 1 nm for all circumstances at sea, to the one which seems to be considerably different (and more in line with my position) that you are claiming is your position now?

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.

[Dockhead]

Originally Posted by markpierce

Recognize large ships are restricted to navigable channels, but many commercial vessels are not. But I've observed it is best to avoid all commercial vessels regardless of the Colregs (won't press stand-on obligation in a potential collision situation). That tactic, as in taking early action, has worked well for me commanding both sail and motor vessels.

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.

[Juho]

My rule of determining the distances (mainly the start and end points of the stand on / give way phase of the crossing) is as follows.

The target is not to use subjective evaluation in the sense that I would do my operations at different time than some other people would. Quite the opposite. I have to use subjective evaluation in the sense that I must estimate what the joint understanding of the two involved vessels of the appropriate distances is and should be.

Quite easy, isn't it. Just some mind reading that you learn when you spend some time sailing .

I however try to avoid those distances and make my moves already before I even need to think which vessel is stand on and which one is give way.

[Dockhead]

Originally Posted by Juho

My rule of determining the distances (mainly the start and end points of the stand on / give way phase of the crossing) is as follows.

The target is not to use subjective evaluation in the sense that I would do my operations at different time than some other people would. Quite the opposite. I have to use subjective evaluation in the sense that I must estimate what the joint understanding of the two involved vessels of the appropriate distances is and should be.

Quite easy, isn't it. Just some mind reading that you learn when you spend some time sailing .

I however try to avoid those distances and make my moves already before I even need to think which vessel is stand on and which one is give way.

This is an excellent post, and underlines an important aspect of collision avoidance which we keep forgetting here -- that the different stages of maneuvering must be COORDINATED, in order to be effective. There is no point in ever standing on, if you're not doing it at the right time -- that is, the time when the give-way vessel should be maneuvering. And if you don't do your giving-way during the time when the other vessel is expecting it -- when you are give-way -- then you screw everything up. If you wait until too late, then he will already start to maneuver without you, and you fail to have coordinated maneuvering, which is one of the essential key aspects of proper collision avoidance procedure.

So you can't just make up this stuff according to your subjective pucker factor feelings -- you have to have some understanding of the time and distance frames being applied by the other vessel, and get into the dance.

The stand-on vessel, in standing on, is in effect saying "After you, sir!". And waits for you to take the initiative, take control of the crossing, and make your move. If you don't do anything during the time when he expects you to make your move, then he will take a step himself (or he should do so), and then you are already not in coordinated maneuvering.

If you are stand-on, and you fail to stand-on when you are required to, then you are like a dancer who just spins around without regard to what the partner is doing. The stand-on vessel is like the girl -- wait for your partner to take the initiative. Only step yourself, if he fails to take the initiative after having been given a decent chance to do so.

[Stu Jackson]

Originally Posted by markpierce

during my thirty years of boating experience in limited waters , i've never observed a commercial vessel avoiding a recreational vessel. as a result, I avoid all commercial vessels.

Mark, during my years sailing SF Bay (1978-2016) I found that the ferries were extremely respectful of all vessels/boats under sail, all us WAFIS!!!Including the fast catamaran Vallejo ferry.

It is the ONLY place on earth I know of where this occurs.

[carstenb]

Originally Posted by markpierce

during my thirty years of boating experience in limited waters , i've never observed a commercial vessel avoiding a recreational vessel. as a result, I avoid all commercial vessels.

well Mark, we've had it happen so many times that I can't remember all of them - but certainly the time that Emma Mærsk (world's largest ship) was exiting the VTS lanes at Cape Finisterre and made a 90 degree turn to starboard to avoid us stands out.

We've also had a number of VHF calls when we've felt the CPA was a bit tight and the ships have given way.

Only once have we not been able to contact a commercial vessel - that was at the mouth of the Chesapeake. We were going to misss each other, but there is a confluence of channels there and we wanted to be sure what his intentions were. he didn't answer so despite being the stand on vessel, we gave way.

[Kenomac]

Originally Posted by Stu Jackson

Mark, during my years sailing SF Bay (1978-2016) I found that the ferries were extremely respectful of all vessels/boats under sail, all us WAFIS!!!Including the fast catamaran Vallejo ferry.

It is the ONLY place on earth I know of where this occurs.

San Francisco is a parallel universe.

[skipmac]

Originally Posted by Stu Jackson

Mark, during my years sailing SF Bay (1978-2016) I found that the ferries were extremely respectful of all vessels/boats under sail, all us WAFIS!!!Including the fast catamaran Vallejo ferry.

It is the ONLY place on earth I know of where this occurs.

Actually, I have seen similar back in Kenomac's old neighborhood. With family on the island I frequently take the ferries from Woods Hole or New Bedford to Martha's Vineyard. Summer time there's always lots of boats of all descriptions in Buzzards Bay and Vineyard Sound. The ferries definitely go out of their way (literally) for WAFIs and stinkpots.

Recently for the first time I saw a sailboat get five blasts. Ferry was just leaving the harbor and had a fairly wide channel to clear but still somewhat restricted. Sailboat was dead center in the channel and no clue anyone else was within miles. After coming to dead slow and waiting for a minute the ferry finally woke him up.

The odd thing are the local commercial fishing boats. A few of them act like they own the ocean and don't seem to care at all what other boats are doing. More than once I have seen fishing boats (not engaged in fishing) cross right in front of the ferry and force the ferry to slow or alter course. The ferry captains seem to ignore or even expect this and locals tell me it's not uncommon.

[Dockhead]

Originally Posted by Kenomac

San Francisco is a parallel universe.

Indeed!

But note that fast cat ferries everywhere, tend to follow a completely different collision avoidance procedure than normal vessels.

From a certain difference in speed, the slower vessel stops having any meaningful role in collision avoidance. A sailboat making 5 knots can't really do anything effective in a crossing with a 40 knot fast ferry.

So the drivers of those fast cats just steer around everything like playing a video game.

I don't even worry about the Red Jet ferries in the Solent. Before you can even figure out what's happening, they have already zoomed past you. They operate outside of the channels and they avoid everything -- there's just no way for them to stand on, at their speed, and wait for anybody, to do anything. So this is kind of a Rule 2 situation.

One of the fast Brittany Ferry cats -- monstrous huge things making 40 knots -- ran down a fishing boat and killed a bunch of fishermen, a couple of years ago, somewhere in the Channel Islands. I haven't seen the incident report, but I'm willing to bet dollars to doughnuts that this would be one of those rare cases where the ferry was 100% responsible, due to the total lack of any practical thing the fishermen could have done. Who was stand on and who give way would have been completely irrelevant.

Sure puts a lump in your throat when you see one of those on the horizon -- evil looking thing throwing up monstrous rooster tails. From horizon to you is just a couple of minutes, so you just have to believe in God while it zooms past




Condor Ferry



This could be you! If you don't get collision avoidance right.

[Kenomac]

Originally Posted by skipmac

Actually, I have seen similar back in Kenomac's old neighborhood. With family on the island I frequently take the ferries from Woods Hole or New Bedford to Martha's Vineyard. Summer time there's always lots of boats of all descriptions in Buzzards Bay and Vineyard Sound. The ferries definitely go out of their way (literally) for WAFIs and stinkpots.

Recently for the first time I saw a sailboat get five blasts. Ferry was just leaving the harbor and had a fairly wide channel to clear but still somewhat restricted. Sailboat was dead center in the channel and no clue anyone else was within miles. After coming to dead slow and waiting for a minute the ferry finally woke him up.

The odd thing are the local commercial fishing boats. A few of them act like they own the ocean and don't seem to care at all what other boats are doing. More than once I have seen fishing boats (not engaged in fishing) cross right in front of the ferry and force the ferry to slow or alter course. The ferry captains seem to ignore or even expect this and locals tell me it's not uncommon.

Locally, they are referred to as "Massholes."

[skipmac]

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.

[Exile]

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.

Spent a lot of time in earlier days driving in & around Boston. All the one-way, paved over colonial roads don't help. 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. 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.

Not really all that different from trying to adhere to the Colregs on the water I suppose. Be predictable & go with the flow.

[ramblinrod]

Originally Posted by Exile

Rather than more straw man accusations, why not just present a specific factual scenario as others have done & explain why your approach is safer & more advantageous towards everyone's goal of avoiding collisions? .

Based on previous posts (for which I went to the trouble to find exact quotes), it was quite clear to me that the position was that the distance off from a vessel in open sea should always be maintained at 1nm or greater under all circumstances

I didn't make this up; this is what was posted by the individual and what I sincerely understood the positon to be.

[Dockhead]

Originally Posted by ramblinrod

Based on previous posts (for which I went to the trouble to find exact quotes), it was quite clear to me that the position was that the distance off from a vessel in open sea should always be maintained at 1nm or greater under all circumstances

I didn't make this up; this is what was posted by the individual and what I sincerely understood the positon to be.

Let's not get distracted by "he said; she said", which is nonsense. Sorry you misunderstood me -- if it makes you feel better, let's agree that I expressed myself badly and it's my fault.

Is my position more clear now?

* 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.


In my experience over thousands of crossings in open sea, watchkeepers aren't bothered too much by our passing close behind. At a certain angle, a collision becomes impossible with a faster moving ship, and they know that (roughly, when we can see their transom). But they are VERY much bothered if we get close to their course line ahead. I got a few unpleasant VHF calls years ago while I was still figuring out how to do this right. They definitely want a mile, in almost all cases, if you're anywhere where it's possible for a collision to occur, and they do not want you closer. They may make desperate maneuvers if you appear to be passing ahead much closer than that. Good collision avoidance procedure should make every crossing drama-free -- just like a good airplane landing. It should be done methodically and systematically, with all moves made in plenty of time with comfortable margins of error, and in a way which makes it obvious to the other vessel what you are doing. You should always be in control of the situation -- control means safety. If you're "puckering", you're doing it wrong. In fact, if you are "puckering", you've violated Rule 8 (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."

[Exile]

Originally Posted by Dockhead

If you're "puckering", you're doing it wrong.

Simple advice to (perhaps literally) live by!