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-   -   Collision Avoidance, Cones of Uncertainty, and Appropriate CPA (https://www.cruisersforum.com/forums/f90/collision-avoidance-cones-of-uncertainty-and-appropriate-cpa-189919.html)

Exile 15-10-2017 23:43

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by ramblinrod (Post 2500116)
...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?

Here are the examples DH just posted above:

For the record, I also agree that a 1nm CPA is not necessary in every case, and I never said that. You don't need it in pilotage waters where you have other ways of knowing where the ship will be, and you don't need it with certain crossings, like, for example, an overtaking situation. You don't need it if your speeds are similar.

So in DH's opinion, you don't necessarily "need" a 1nm CPA in (1) pilotage waters, (2) overtaking, (3) similar speeds, maybe others. If you want to avoid what you complain are "straw man" arguments (whatever those may be), then similarly provide examples where you believe it is safer to maneuver at 1nm CPA or less in the types of crossing scenarios you have been advocating (whatever they are). Or do you agree with DH that they are generally limited to the examples he just provided?

I understand your generalized comment that a closer in maneuver may be preferable so as not to interfere with a commercial ship's crossing plan, but by the time you're that close then isn't it safe to say that the ship has no plan and you're now in control? Obviously if you're stand on and the ship has not given way at that point, then the obligation falls on you. Colregs compliance or not, wouldn't it just make more sense to back the whole thing up and allow more time for both vessels to sort things out as needed? Or is this where "pucker factor" somehow plays a role in communicating intentions between vessels?? :confused: Obviously much depends on what type of crossing scenario is presented.

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? Maybe it's a reading comprehension problem on my part, but if so it shouldn't be hard for you to clarify for me & maybe others who have repeatedly asked you questions which it doesn't appear you have answered.

Or maybe it's just your personal preference and, if so, then that's fine too, but I think it's now clear why merely the end result of your maneuver avoiding a collision doesn't necessarily equate with compliance. Fwiw, I don't think you need worry about anyone trying to actually restrict your freedom to sail your boat as you wish. It's only a harmless internet forum after all, where people are simply exchanging thoughts & ideas.

Exile 15-10-2017 23:49

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by markpierce (Post 2500136)
Large ships are limited in the SF Bay/Delta waters but the tugs either alone or towing/pushing a barge act the same without a nautical reason. Safest to avoid them all. ... Aren't we all just boys-on-toys in their eyes?

Don't know, but as I recall you are correct that tugs & tows don't have priority (if you will) over sailing vessels under sail (could be wrong). But I just remembered you are a power vessel. But either way, if the expectation -- right or wrong -- is that they won't be giving way for you then both common sense and the Rules support keeping out of their way! :smile: (Sounds analogous to the Chesapeake Bay watermen from another thread).

markpierce 16-10-2017 00:00

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Exile (Post 2500128)
Depends on what you mean by "limited waters," but could very well be right in line with the Colregs. If the other vessels are in designated channels, restrained by draft, etc. If so then you have the obligation to give way.

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.

Quebramar 16-10-2017 00:15

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by markpierce (Post 2500122)
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.



Not sure what limited waters means for you. In my case, crossing the TSS at SE England, I once was going to cross at 90deg with the gennaker and I saw one oil carrier at approx 6-8NM (not exactly sure, it was a while ago) with too close a CPA (less than 1NM) for my "comfort" shall I say, actually my personal safety rule. Conditions were very good, calm sea and good visibility.
I was the give way vessel and took the sock down on the genny and slowed down, couple of minutes later the ship had changed course 2-3deg resulting in a much better CPA and there went the sock up again. It did not cost much to the merchant ship as further down the shipway was turning in that direction so it merely anticipated that part, going quite a bit into the centre of the lane.
Skipper grateful of this gentleman's kind gesture in return to my precautionary one which, as I sense from some comments, some would consider as not being required.

Exile 16-10-2017 00:32

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by markpierce (Post 2500142)
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.

I do the same, and would like to think it's also compliant with the Rules since there are provisions which explicitly mandate taking whatever appropriate actions are necessary under the circumstances to avoid collision. (Someone will chime in with the Rule no. & actual text I'm sure :smile:). In the Chesapeake, for ex., the tugs all seem to run down the west side of the Bay, perhaps to stay clear of fast moving freighters & tankers moving fast through the big ship channel. The tugs do so quite predictably and it seems accepted practice amongst recreational vessels (sail & motor) to stay well clear.

Dockhead 16-10-2017 01:08

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by ramblinrod (Post 2500116)
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 16-10-2017 01:26

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by markpierce (Post 2500142)
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 16-10-2017 03:00

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
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 :smile:.

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 16-10-2017 04:36

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Juho (Post 2500192)
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 :smile:.

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 16-10-2017 04:42

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by markpierce (Post 2500122)
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!!!:facepalm::smile::smile::smile:Including the fast catamaran Vallejo ferry.

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

carstenb 16-10-2017 04:57

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by markpierce (Post 2500122)
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 16-10-2017 05:17

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Stu Jackson (Post 2500226)
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!!!:facepalm::smile::smile::smile: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 16-10-2017 05:39

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Stu Jackson (Post 2500226)
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!!!:facepalm::smile::smile::smile: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. :biggrin:

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 16-10-2017 05:45

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
3 Attachment(s)
Quote:

Originally Posted by Kenomac (Post 2500247)
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 :D


Attachment 157806

Condor Ferry

Attachment 157807

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

Kenomac 16-10-2017 07:06

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by skipmac (Post 2500261)
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. :biggrin:

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." :smile:

skipmac 16-10-2017 07:14

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Kenomac (Post 2500302)
Locally, they are referred to as "Massholes." :smile:

So I heard. :wink:

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 16-10-2017 07:36

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by skipmac (Post 2500306)
So I heard. :wink:

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. :nonono: 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. :wink:

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

ramblinrod 16-10-2017 07:50

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Exile (Post 2500139)
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 16-10-2017 08:15

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by ramblinrod (Post 2500323)
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 16-10-2017 08:35

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Dockhead (Post 2500336)
If you're "puckering", you're doing it wrong.

Simple advice to (perhaps literally) live by! :thumb:

ramblinrod 16-10-2017 08:45

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Dockhead (Post 2500154)
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 16-10-2017 08:54

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Dockhead (Post 2500160)
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.:smile: 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 16-10-2017 09:03

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by ramblinrod (Post 2500352)
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 16-10-2017 09:04

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Dockhead (Post 2500336)

* 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 16-10-2017 09:19

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Exile (Post 2500355)
No, definitely not one of the pros here commenting.:smile: 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 16-10-2017 09:24

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by skipmac (Post 2500306)
So I heard. :wink:

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 16-10-2017 09:34

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Kenomac (Post 2500302)
Locally, they are referred to as "Massholes." :smile:

Quote:

Originally Posted by Kenomac (Post 2500302)
Locally, they are referred to as "Massholes." :smile:

So I heard. :wink:

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 16-10-2017 09:37

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by ramblinrod (Post 2500365)
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 16-10-2017 10:08

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Exile (Post 2500315)
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. :nonono:

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.


Quote:

Originally Posted by Exile (Post 2500315)
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. :wink:

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

skipmac 16-10-2017 10:10

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Kenomac (Post 2500386)
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. :thumb:

Exile 16-10-2017 11:41

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Dockhead (Post 2500383)
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. :smile: Now whether it translates into my becoming a better seaman remains to be seen. :whistling:

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 16-10-2017 11:47

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Exile (Post 2500498)
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. :smile: Now whether it translates into my becoming a better seaman remains to be seen. :whistling:

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 16-10-2017 11:50

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
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 16-10-2017 12:12

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by David M (Post 2500512)
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

Quote:

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 16-10-2017 12:20

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by conachair (Post 2500525)
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.

David M 16-10-2017 12:21

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
I AM a commercial mariner and I communicate by radio numerous times every time I get underway. Much of these communications are for making passing arrangement so there is no doubt whatsoever which side we plan to pass, cross or overtake.

Communicating and making a definite plan is the most predictable and therefore the safest way of passing. Creating angles so as to make it (hopefully) clear which side we wish to pass and figuring out CPA's is less predictable although that can be safe as well. We are not ignoring the Rules at all when making passing arrangement. For example we will typically pass port to port when it is close. Making passing arrangements by radio is also in the Rules!...it is indeed.

I don't know what an MCA is. So I went to an acronym finder and went through hundreds of acronyms with MCA. (Maritime & Coast Guard Agency in the UK?) Avoiding acronyms when everyone who reads this may not know what the acronym means is always helpful. It only takes a few extra seconds to fully spell out what you wish to communicate. I am sometimes guilty of it as well with all my oceanography acronyms. I can forget that those not in the business may not know what the hell I am talking about :)

Quebramar 16-10-2017 12:22

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by conachair (Post 2500525)
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.



Calling on the VHF in open seas may not be a big deal, but try in anything less than 50NM of Dover.... :nonono: So better go for prevention (Colregs) rather than cure (radio), no?

Dockhead 16-10-2017 12:27

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by David M (Post 2500533)
Communicating and making a definite plan is the most predictable and therefore the safest way of passing.

I don't know what an MCA is. Avoiding acronyms when everyone who reads this may not know what the acronym means is always helpful. It only takes a few extra seconds to fully spell out what you wish to communicate. :)

The MCA is the Maritime and Coastguard Agency of the United Kingdom, the world's preeminent maritime authority, whose guidance notes are studied all over the world. One of the vestiges of Britannia's ruling the waves. We Yanks have nothing to compare with it.

conachair 16-10-2017 12:51

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by David M (Post 2500533)
I don't know what an MCA is.

Link was a bit of a giveaway ;)


Quote:

I AM a commercial mariner and I communicate by radio numerous times every time I get underway. Much of these communications are for making passing arrangement so there is no doubt whatsoever which side we plan to pass, cross or overtake.
Is that more in pilotage waters? Sort of thing you'll her all the time in the Thames estuary (You happy with green to green ) but not nearly so much out in more open waters like the channel.

Jim Cate 16-10-2017 13:08

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
I wonder if the MCA's aversion to radio contact was formed in pre AIS days, when it was often completely unclear what vessel was calling what other vessel? When calling by specific vessel name, this uncertainty is eliminated and confusion reduced.

Sailing in pilotage waters in Australia, VHF communictions are often initiated by the merchant vessel. I suspect the pilots know how ignorant WAFIs are about COLREGS and wish to circumvent close calls well in advance.

Jim


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