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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)

Dockhead 08-09-2017 07:25

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

Originally Posted by barnakiel (Post 2473854)
. . . 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 think you will find that most professionals will disagree with this.

The Rules don't so much REQUIRE a container ship making 20 knots, as they ALLOW the container ship to take control of the crossing and maneuver as it likes. I think most professionals would HATE the idea that they have to stand on, and rely on a bunch of WAFIs like us to come up with an effective maneuver. They would HATE to have to hold their course and speed while we flail around trying to figure out which way to turn, probably having initiated the maneuver too late anyway, and then trying to guess when they are allowed to finally start maneuvering themselves. The give-way vessel controls the crossing, and that is the position most professionals would prefer to have, once a risk of collision has arisen (of course they would all prefer that we avoided risk of collision altogether in the first place, but that's a different subject).

Besides that, "simply tack or gybe away" for a vessel making only 6 or 7 knots, is 3x less effective, than the maneuver of the container ship making 20 knots, in the open sea. Our so-called "maneuverability" is only meaningful at very short distances. In the open sea, we are more like sitting ducks, and more and more so, the bigger difference in speed. We have much less ability to change and resolve a dangerous crossing, than a fast moving ship does. Even our theoretically higher ROT doesn't exist once we have to tack or gybe.

robbievardon 08-09-2017 07:47

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
I don't believe any body sets up a course to miss another vessel by 180 feet. As the poster did not detail the relationship between the 2 vessels your response could be regarded as specious. In a head to head situation is there a need to make a course alteration of any discernable degree? Irma recently doing 300 kPH where is the relevance? Small alterations of course are not FORBIDEN as you state Rule 8b but it is written "should be avoided" considerably different statement.

TeddyDiver 08-09-2017 08:02

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

Originally Posted by robbievardon (Post 2473879)
I don't believe any body sets up a course to miss another vessel by 180 feet. As the poster did not detail the relationship between the 2 vessels your response could be regarded as specious. In a head to head situation is there a need to make a course alteration of any discernable degree? Irma recently doing 300 kPH where is the relevance? Small alterations of course are not FORBIDEN as you state Rule 8b but it is written "should be avoided" considerably different statement.

It's the cone of uncertainty, as the thread title says. Take into account for a huracan we look ahead for days while encountering other traffic the time frame is measured merely in minutes.

robbievardon 08-09-2017 08:05

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Dockhead I seem to recall recently the statement that one of the top hates of the Professional seamen was yachtsmen sailing in designated sealanes, I wonder why? In my previous post I should perhaps have said say 6 Kts rather than allow a faster speed to cloud the issue of maneuvreability. If you have ever watched a video of aircraft landing in strong cross winds you will know what I mean. This crosswind effect was also cited in the gulf collision as a point to consider when maneuvring.

Dockhead 08-09-2017 08:20

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

Originally Posted by robbievardon (Post 2473879)
I don't believe any body sets up a course to miss another vessel by 180 feet. As the poster did not detail the relationship between the 2 vessels your response could be regarded as specious.

In the other thread, a very knowledgeable person suggested exactly making a one degree course correction from 5 miles our for a 180 foot miss, and asserted that this was an adequate maneuver. I demonstrated mathematically that it is not.


Quote:

Originally Posted by robbievardon (Post 2473879)
Small alterations of course are not FORBIDEN as you state Rule 8b but it is written "should be avoided" considerably different statement.

On this, you are absolutely right, and I thank you for the correction.

I think it's really important, however, to keep in mind why small course changes in collision avoidance situations are really bad. I'm sure you know yourself why.

robbievardon 08-09-2017 08:25

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Dockhead always the lawyer!! I wonder if you asked the Professionals if the rules could be changed to sailboats giving way to power would they like it? as opposed to, they are stuck with the rules and they have to (happily!!!???) make the best of it.

Dockhead 08-09-2017 08:31

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

Originally Posted by robbievardon (Post 2473888)
Dockhead I seem to recall recently the statement that one of the top hates of the Professional seamen was yachtsmen sailing in designated sealanes, I wonder why? In my previous post I should perhaps have said say 6 Kts rather than allow a faster speed to cloud the issue of maneuvreability. If you have ever watched a video of aircraft landing in strong cross winds you will know what I mean. This crosswind effect was also cited in the gulf collision as a point to consider when maneuvring.

I'm not quite sure how many different points are in this post.

Concerning "designated sea lanes" -- do you mean channels? I don't think I was involved in that discussions. Small vessels should stay out of channels and fairways in harbors and approaches unless the coast is clear, even in situations where Rule 9 doesn't apply. But offshore, I don't see any problem using "designated sea lanes", including TSSs, as long as Rule 10 is obeyed, and I've never heard a commercial mariner say otherwise. I just did a full transit of the North Sea using the TSSs, and it was fine. Just stay at the edge of the lanes out of traffic, and you don't bother anyone.

In waters like the North Sea, it really makes sense, because outside of the TSSs is jam-packed with fishing vessels coming at you from all directions, oil platforms, uncharted wind farms, shoals, etc.

barnakiel 08-09-2017 11:22

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
"... making a one degree course correction from 5 miles our for a 180 foot miss ..."

I do not get this part.

Is it not a 530.43 ft?

How do we get this 180 ft?

b.

Paul Elliott 08-09-2017 11:26

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

Originally Posted by barnakiel (Post 2474011)
"... making a one degree course correction from 5 miles our for a 180 foot miss ..."

I do not get this part.

Is it not a 530.43 ft?

How do we get this 180 ft?

b.

The other vessel is moving too. Directly towards you, at 15+ kts.

Your number would be correct if you were trying to avoid a rock.

barnakiel 08-09-2017 11:29

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

Originally Posted by Dockhead (Post 2473863)
I think you will find that most professionals will disagree with this.

The Rules don't so much REQUIRE a container ship making 20 knots, as they ALLOW the container ship to take control of the crossing and maneuver as it likes. I think most professionals would HATE the idea that they have to stand on, and rely on a bunch of WAFIs like us to come up with an effective maneuver. They would HATE to have to hold their course and speed while we flail around trying to figure out which way to turn, probably having initiated the maneuver too late anyway, and then trying to guess when they are allowed to finally start maneuvering themselves. The give-way vessel controls the crossing, and that is the position most professionals would prefer to have, once a risk of collision has arisen (of course they would all prefer that we avoided risk of collision altogether in the first place, but that's a different subject).

Besides that, "simply tack or gybe away" for a vessel making only 6 or 7 knots, is 3x less effective, than the maneuver of the container ship making 20 knots, in the open sea. Our so-called "maneuverability" is only meaningful at very short distances. In the open sea, we are more like sitting ducks, and more and more so, the bigger difference in speed. We have much less ability to change and resolve a dangerous crossing, than a fast moving ship does. Even our theoretically higher ROT doesn't exist once we have to tack or gybe.

Having read this and having thought about the consequences I think you are 100% right.

Thanks for writing this up. At times we must hear the obvious to get our thinking straight.

Cheers,
b.

Dockhead 10-09-2017 03:05

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

Originally Posted by robbievardon (Post 2473901)
Dockhead always the lawyer!! I wonder if you asked the Professionals if the rules could be changed to sailboats giving way to power would they like it? as opposed to, they are stuck with the rules and they have to (happily!!!???) make the best of it.

This is a good question, and I did, in fact, ask this question. Some years ago, when I first started studying this question, I thought it might be better if we would always be give-way and simpler for everyone.

I was surprised at the time at the answer. Now that I know more, I am no longer surprised.

The answer given by virtually everyone was -- "We don't care so much and there's no need to change the rules [or no way -- it would just be worse]. The real problem is that you guys don't know and don't follow the Rules, and we can never predict what kind of dumb-azz move you're going to make. If you guys would just learn and follow the Rules there would be no problem."

nigel1 10-09-2017 03:20

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

Originally Posted by robbievardon (Post 2473901)
Dockhead always the lawyer!! I wonder if you asked the Professionals if the rules could be changed to sailboats giving way to power would they like it? as opposed to, they are stuck with the rules and they have to (happily!!!???) make the best of it.


Here's my take on this.

We are likely to detect you before you see us, having the advantage of height of eye and better radar, and we can have aids which can quickly work out relative track and CPA, we have probably worked out a passing solution before a small yacht even see's us.
Now, if we left it up to the yacht to make the avoiding action, it might be that the yacht is getting pretty close before it has worked out what to do and at this point I would be getting a bit twitchy.

My opinion, leave the rules as they are.

As a commercial skipper, and a yacht skipper, I really appreciate being the stand on vessel when under sail, especially as I usually sail single handed.

Lodesman 10-09-2017 06:22

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
+1 what Nigel said.

I can't see the rules working better if rule 18 got swapped around. If in the future, we all are sailing Hydropteres at 40 kts+, then maybe the Rules will need a re-jig. The faster ship has the manoeuvring advantage - Dockhead has described the reason for that mathematically. While certain risk of collision situations might have the sailboat being faster than the PDV, the PDV can maintain its speed on any heading - something the typical sailboat cannot. Note rule 13 allows for a sailboat to be the faster vessel and consequently puts the onus on it to give way.

IdoraKeeper 10-09-2017 09:19

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
I particularly agree with DH's point about maneuverability. Untill retirement I will not be sailing off shore so will not be worried too much about AIS targets that are hull down. In areas with shipping lanes I find that when a ship becomes visible, their 20 knot closing speed easily exceeds my ability to maneuver when it becomes clear that the rate of bearing change is slow or non existent. An early decision is critical. It needs to be really clear that it will be safe the pass ahead or I will choose to pass behind.

Exile 10-09-2017 09:36

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Well, there ya go. Three posts from professional big ship captains who are also recreational sailors, and that validate DH's previous post & many others with reasons why. I can understand why our small sailing vessels "standing on" in the face of big shipping seems counterintuitive, but I wish those who remain confused or doubtful would study these four posts and the plethora of well-reasoned prior explanations which support them.


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