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

Dockhead 01-09-2017 08:38

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

Originally Posted by robbievardon (Post 2469107)
DH/Lodesman my view is that you appear to have 2 scenarios rolled into one.If your sailing vessel is proceeding up the channel then in my view the tanker is an overtaking vessel and is thus required to keep clear as per rule 13. If however a vessel which according to rule 3a means every type of water craft crosses a narrow channel in such a way as to cause your tanker to alter course then is that craft not impeding the tanker rule 9d particularly if it crosses from starboard side and then suddenly becomes the stand on vessel. At what point does this change occur? My understanding of the word impede is based on US dictionary = bar or hinder the progress of, obstruct or delay. Could you please advise when you are referring to USCG regs for inland waters and rivers as they are not all the same as International c regs, Does Canada use the USCG regs or do they have their own rules?

"At what point does this change occur?" -- Stu answered that above -- the ship has to give way when a risk of collision arises. The obligation of the yacht to "not impede" arises earlier than that. But note that the ship's having to give way is not exactly a "change" -- the yacht's obligation to "not impede" continues even while the ship becomes obligated to give way.

I'm not talking about Inland Rules at all -- don't know about Lodesman, but I doubt whether he is, either.

robbievardon 01-09-2017 09:12

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Lodesman, (DH) ref my post 135 and yours 133 ,134 I find it interesting that your Guru of the collision regs apparently has not been able to deal with what appears a simple but much misconstrued situation which in your view creates "Preposterous" beliefs. Dh any signs of those examples I requested. Possibly slight aside but it is interesting to see the amount of usage the USCG make of the dreaded words "right of way"
Stu, if your sailing vessel is tacking and not within the arc prescribed in 13b, what rule are you going to apply? It seems to me that too many sailors look at the situation from their position only and never give a thought to the situation of the professional seamen

Lodesman 01-09-2017 11:02

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

Originally Posted by Dockhead (Post 2469075)
I have always thought it to be fairly logical that if while sailing across a TSS, if I put a ship in a lane in a position where it had to maneuver to avoid me, that I had violated my obligation to "not impede".

Your point is well argued, though. Is there any reading on this you can recommend? I have to write something on this and I have to be sure that I have read everything on the subject which is important. Or maybe you'd like to write this chapter?

If you look at the specific requirement from 8(f) itself, you are only required to "take early action to allow sufficient sea room for the safe passage of the other vessel." If the rule-makers had wanted you to "stay out of the way of" or "give way to" the ship, then they would have written it that way. They didn't and I believe they had a good reason to write it the way they did. They are considering that vessels that would normally be the stand-on vessel to large PDVs (from Rule 18, which most of us agree denotes a hierarchy of manoeuvrability) will not be as constrained by draught and narrowness of a channel, as the vessel that would normally give way. So the rule is worded to say to the smaller albeit less-manoeuvrable vessel is to give the large vessel the room to pass; and the large vessel (generally being more manoeuvrable) shall follow the rules to avoid a collision if risk of collision exists.
From that understanding, if the VNTBI has sufficient sea room for safe passage, and the VRTNI would be stand-on if risk of collision existed, then the VRTNI should stand on. If there is not sufficient sea room, then the VNTBI has been impeded, the VRTNI although 'stand-on' would be required to take action to allow sufficient sea-room, which Cockcroft points out, is consistent with rule 17(a)(ii).

While I believe Cockcroft's explanation of "not impede" seems enigmatic, my understanding of it comes from reading and rereading his explanation along with the applicable rules. Other guides I have read are similar to Cockcroft. I have read the interpretation you ascribed to "some commentators", but those have been less-reputable sources, and the notion itself fails any logical test.

Lodesman 01-09-2017 11:43

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

Originally Posted by robbievardon (Post 2469107)
DH/Lodesman my view is that you appear to have 2 scenarios rolled into one.If your sailing vessel is proceeding up the channel then in my view the tanker is an overtaking vessel and is thus required to keep clear as per rule 13. If however a vessel which according to rule 3a means every type of water craft crosses a narrow channel in such a way as to cause your tanker to alter course then is that craft not impeding the tanker rule 9d particularly if it crosses from starboard side and then suddenly becomes the stand on vessel. At what point does this change occur? My understanding of the word impede is based on US dictionary = bar or hinder the progress of, obstruct or delay. Could you please advise when you are referring to USCG regs for inland waters and rivers as they are not all the same as International c regs, Does Canada use the USCG regs or do they have their own rules?

Notwithstanding rule 13, as Dockhead said, the "not impede" rule comes into effect before risk of collision. I specifically used a smaller PDV instead of a sailing vessel, to accentuate the absurdity of a certain interpretation of the "not impede" clause; an under-20 m PDV is not required to use a TSS, but may do so. If that vessel detected (radar or AIS) the tanker 10 miles astern, you would not consider risk of collision to exist; it's too far away - this is borne out by Cockcroft et al in discussions of rule 17. Yet if it's in the lane and approaching, it would be deemed that risk of collision is likely to occur. By the obsolete guidance:
Quote:


When a vessel is required not to impede the passage of another vessel, such a vessel shall
so far as practicable navigate in such a way as to avoid the development of risk of collision


the small PDV would be expected to - move to the other side of the lane?, - exit the lane?, - something else?
Obviously, there is no logical recourse. There should be no reason for a vessel following a lane to be required to leave it, short of an emergency.
Going to the requirement of rule 8(f) to "take early action to allow sufficient sea room for the safe passage of the other vessel" what would the small PDV be required to do? Moving to one side or other of the lane, to allow sufficient room for the tanker to pass safely, within the lane, is the only logical solution. So if in doing so, the tanker then has to alter a couple degrees to effect that safe passing, can you consider it was impeded? Logically the answer is "no."
You ask where the change occurs if the situation is a crossing in a narrow channel. There is no change - both criteria are separate. Is there sufficient sea room for the tanker to proceed up the channel, whether it has to alter course to avoid the crossing vessel, or not? If 'yes' then not impeded, vessel to starboard stands on, and tanker takes avoiding action. If 'no' then is impeded, crossing vessel must take action to provide sea-room and the tanker must take what action it can to avoid the crossing vessel.
Canada has its own rules; they are similar in many respects to the US Inland rules: Collision Regulations

Dockhead 01-09-2017 12:19

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

Originally Posted by Lodesman (Post 2469222)
If you look at the specific requirement from 8(f) itself, you are only required to "take early action to allow sufficient sea room for the safe passage of the other vessel." If the rule-makers had wanted you to "stay out of the way of" or "give way to" the ship, then they would have written it that way. They didn't and I believe they had a good reason to write it the way they did. They are considering that vessels that would normally be the stand-on vessel to large PDVs (from Rule 18, which most of us agree denotes a hierarchy of manoeuvrability) will not be as constrained by draught and narrowness of a channel, as the vessel that would normally give way. So the rule is worded to say to the smaller albeit less-manoeuvrable vessel is to give the large vessel the room to pass; and the large vessel (generally being more manoeuvrable) shall follow the rules to avoid a collision if risk of collision exists.
From that understanding, if the VNTBI has sufficient sea room for safe passage, and the VRTNI would be stand-on if risk of collision existed, then the VRTNI should stand on. If there is not sufficient sea room, then the VNTBI has been impeded, the VRTNI although 'stand-on' would be required to take action to allow sufficient sea-room, which Cockcroft points out, is consistent with rule 17(a)(ii).

While I believe Cockcroft's explanation of "not impede" seems enigmatic, my understanding of it comes from reading and rereading his explanation along with the applicable rules. Other guides I have read are similar to Cockcroft. I have read the interpretation you ascribed to "some commentators", but those have been less-reputable sources, and the notion itself fails any logical test.

Enlightening and persuasive as usual.

I agree that Cockcroft is enigmatic on this point, and in fact, I told him so!

StuM 01-09-2017 14:49

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

Originally Posted by Lodesman (Post 2469232)
Is there sufficient sea room for the tanker to proceed up the channel, whether it has to alter course to avoid the crossing vessel, or not? If 'yes' then not impeded, vessel to starboard stands on, and tanker takes avoiding action. If 'no' then is impeded, crossing vessel must take action to provide sea-room and the tanker must take what action it can to avoid the crossing vessel.

Excellent clarification of "impeding". Thank you. :thumb:

matt w 03-09-2017 10:06

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

Originally Posted by StuM (Post 2468768)
As I tell the missus when driving around a strange city. I'm not lost, I'm just temporarily geographically uncertain.

I say, I'm not lost, we're exploring!

matt w 03-09-2017 10:51

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Very interesting discussion, I am learning from this, especially the last few pages. Thank you all for sharing your knowledge to help me better understand the rules.

Dockhead 03-09-2017 15:31

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

Originally Posted by robbievardon (Post 2469141)
Lodesman, (DH) ref my post 135 and yours 133 ,134 I find it interesting that your Guru of the collision regs apparently has not been able to deal with what appears a simple but much misconstrued situation which in your view creates "Preposterous" beliefs. Dh any signs of those examples I requested. Possibly slight aside but it is interesting to see the amount of usage the USCG make of the dreaded words "right of way". .

Robbie, the Coast Guard is very careful to use the phrase "right of way" to refer to only one case -- downstream with a following current, under Inland Rules. They are very careful to say that "right of way" does not exist in other cases. I think the Coast Guard is very much on the same page as Stu and Lodesman and me.

Concerning Cockcroft and Rule 9 -- I presume that's what you're talking about -- the controversy is much narrower than it seems you think. Contrary to what some people have posted, Rule 9 does NOT indeed make the Vessel Not To Be Impeded the stand-on vessel -- about that there is no controversy in serious sources; in fact the Rule themselves say so explicitly. The question is much more subtle than that -- are you obligated to maneuver so that the VNTBI doesn't have to maneuver at all? Or just provide "sufficient sea room"? The Rules talk about "sufficient sea room."

Dockhead 08-09-2017 03:41

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Watching the news about Hurricane Irma reminds me of the original topic of this thread -- the Cone of Uncertainty concerning where the two vessels will be at their closest point of approach.

This thread was inspired by a post in another thread where someone asserted that all you have to do to avoid a collision is "not be in the exact same place" as the ship -- so 180 feet is plenty.

And the point is that we don't know the "exact same place" -- just like with a hurricane. So if you want to safely cross paths with a hurricane, you have to set your course to pass outside of the whole area where the hurricane COULD be, when you cross. Just like with a ship. Good article here: https://en.wikipedia.org/wiki/Cone_of_Uncertainty

Dockhead 08-09-2017 03:41

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Watching the news about Hurricane Irma reminds me of the original topic of this thread -- the Cone of Uncertainty concerning where the two vessels will be at their closest point of approach.

This thread was inspired by a post in another thread where someone asserted that all you have to do to avoid a collision is "not be in the exact same place" as the ship -- so 180 feet is plenty.

And the point is that we don't know the "exact same place" -- just like with a hurricane. So if you want to safely cross paths with a hurricane, you have to set your course to pass outside of the whole area where the hurricane COULD be, when you cross. Just like with a ship. Good article here: https://en.wikipedia.org/wiki/Cone_of_Uncertainty

robbievardon 08-09-2017 06:38

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Ref post 140, I wonder what the Professional seaman think of "large vessel more maneuverable than small,Large container ship versus tramp with strong cross wind. It seems to me that the theoretical scenarios answers are thought up first then the question follows to match. There are numerous examples of 2 vessels crossing which one would hope would pose little problem for a competent seaman. Multiple vessels crossing ie 3,4,5 + seem to be ignored and yet these must be the most difficult of situations for amateur sailors.
In the case of the collision in the Gulf I have talked about recently the Captain of one vessel was cited for failing to keep a "Proper Audible Watch" This arose as a result of several vessels being on the VHF at the same time and the one Captain Misunderstood who was agreeing to what maneuvre and he based his action on this information.

robbievardon 08-09-2017 06:58

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Dockhead, why is it that you feel the need to belittle/talk down to other posters? I refer to your post 145?146. It seems to me to be perfectly good statement perhaps based on a lighthearted approach. 180 ft , depends on circumstances but as I recall a Naval Officer from a recent post referred to similar distances. As to the Hurricane (Irma currently 300 K across I don't think even you would wish to make a 300 k diversion around another vessel.

barnakiel 08-09-2017 07:05

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
I often read and re-read colregs and at times I get this feeling the rules are so old that should be re-written to fit the boats and nav methods of today.

Requiring a container ship making 20kts to sail around an odd dot in the ocean (that's you) while the dot can simply tack or gybe away in seconds is not all that understandable.

I am not calling for a revolution, but perhaps some evolution could adjust the regs to what it is actually like out there nowadays.

b.

Dockhead 08-09-2017 07:15

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

Originally Posted by robbievardon (Post 2473848)
Dockhead, why is it that you feel the need to belittle/talk down to other posters? I refer to your post 145?146. It seems to me to be perfectly good statement perhaps based on a lighthearted approach. 180 ft , depends on circumstances but as I recall a Naval Officer from a recent post referred to similar distances. As to the Hurricane (Irma currently 300 K across I don't think even you would wish to make a 300 k diversion around another vessel.

I am not belittling anyone. This is a concrete, substantive discussion.

The question is this: How do you work out a maneuver to cross safely with another vessel?

The geometry of this is not understand by very many sailors, because they don't understand what they have to maneuver around. The answer: It's not the ship itself we have to maneuver around, but the place where the ship might be at the time of closest approach, considering the sum of all of the uncertainties concerning its course, speed, and position.

What it means is if you think that your maneuver is adequate, because you think you have created 180 feet of CPA from 5 miles out, you are definitely and objectively wrong -- because you cannot know within 180 feet where that ship will be five miles from now. That's why we do not make one degree maneuvers at five miles out -- the concrete example from the other thread, suggested by someone as being enough. (The other reason, of course, is that the Rules forbid small maneuvers, and especially a series of small maneuvers in a risk of collision situation, and for good reason.)

I am hoping that the hurricane example might be helpful in understand this. AIS is a fantastic tool, but like many of our tools, it is subject to "false precision" (https://en.wikipedia.org/wiki/False_precision), which can lead to some dangerous errors.

This information might be helpful to someone. If you already know it, then good for you. If you don't, then I hope it helps you.


All times are GMT -7. The time now is 05:46.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.


ShowCase vBulletin Plugins by Drive Thru Online, Inc.