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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 27-10-2017 13:08

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
The basic point being that whether it requires superhuman powers or a high pucker factor, and whether or not you'd be toast, it violates multiple provisions of the Colregs, is unquestionably unsafe, and defies common sense & rudimentary logic. And these are single ship scenarios I gather in open water.

So it all begs the obvious question: Why do it? And maybe the slightly less obvious question: Why propose doing it, or even suggest doing it on a thread involving serious discussions about real-life collision avoidance? Except as rational posters have done here, namely as a hypothetical learning exercise to demonstrate why it should never be attempted.

Dockhead 27-10-2017 13:13

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
[QUOTE=ramblinrod;2507293]
Quote:

Originally Posted by Dockhead (Post 2507238)

What does the following ship have to do with the cross between two ships at high speed?

Seriously?

Obviously, there is a need to miss hitting the lead ship AND the following ship.



Wow, you are still trying to use strawman arguments. Amazing.

I never ever ever said it was "safe" to attempt this crossing at all. And of course, what is "safe" is subjective. There's a big difference between "safe" and "successful".

It is highly unlikely anyone would consider this maneuver "safe". However, I certainly consider the one that gets across the other side (me) is much safer, and more "successful" than the one that gets nailed by the following ship (you) if the ships maintain course and speed.



Nope.

And not the point at all. The point is that the 3 cable CPA you proposed behind the lead ship was not safe, AND you got nailed by the following ship. Did you not get that?



Seriously?

You are crossing between two ships. Anything you do to affect distance from one, also affects distance from the other.

If you navigate in congested waters, only looking at how your maneuvers affect your relationship with one vessel, well I'm surprised as heck you are still here.



First of all, the scenario was based on the ships not responding to communications. There is nothing magic that makes the 180 CPA a "collision course" and the 3 cable CPA not. In either case, the bow of the sailboat is pointing ahead of the bow of the ship (initially) and the distance between is closing rapidly. In the end, your 3 cable CPA leaves you running into the following ship.

Bang, Glug Glug Glug.



You can setup a CPA of 0 with the stern of the lead ship if you wish.

180 ft CPA is not a "collision course". If the CPA is maintained and the ships maintain course and speed, there is no collision.

The 3 cable CPA you proposed is a "collision course". You will most definitely hit the vessel following, even if the plan is executed flawlessly.

OK, I think we've been through all this before. It looks like the argument goes like this:

"180 foot CPA with a fast ship is dangerous -- too close to attempt to pass."

"No it's not. If you pass with a greater margin, you run into the ship behind."

"Maybe you run into the ship behind, but it's still not safe to attempt to pass so close to the ship ahead."

"If you pass further, you run into the ship behind."

"What does that have to do anything? If that's true, then you can't pass at all!"

Then throw in some taunts "Bang bang, glub glub."

Etc., etc., repeat ad nauseum. All the detailed technical explanations are apparently wasted, and I don't want to bore anyone by repeating myself. Anyone who found any of it interesting can find it further back in the thread.

TJ D 27-10-2017 13:17

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
I've said this a few times, but nobody seems to have picked up on it.

Rod was suggesting this 180' stuff LONG before the 'line of ships' scenario was introduced. He was talking about doing it right from the start, and then invented the scenario afterwards to support this 180' business.

It was being presented to us, forcefully, as safe and appropriate if only your 'pucker factor' was high enough.

The line of ships thing came later, presumably as cover for a reckless contention made prior.

Exile 27-10-2017 13:29

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

Originally Posted by TJ D (Post 2507353)
I've said this a few times, but nobody seems to have picked up on it.

Rod was suggesting this 180' stuff LONG before the 'line of ships' scenario was introduced. He was talking about doing it right from the start, and then invented the scenario afterwards to support this 180' business.

It was being presented to us, forcefully, as safe and appropriate if only your 'pucker factor' was high enough.

The line of ships thing came later, presumably as cover for a reckless contention made prior.

Yes!! And I would think most figured it out awhile back, but nicely summarized.

Stu Jackson 27-10-2017 16:19

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

Originally Posted by ramblinrod (Post 2507060)
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>

I'm sorry you had such difficulty rounding a moving target in close proximity. I would have had to see it, to understand what you did so terribly wrong.

Thanks for responding. I've been on the water all day, just pulled in. Haven't caught up completely yet.

However, I would appreciate your observations on what I did "so terribly wrong" given my post which I thought explained it, and why he was long gone by the time I "got there."

Thank you.

ramblinrod 28-10-2017 09:58

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

Originally Posted by Stu Jackson (Post 2507476)
Thanks for responding. I've been on the water all day, just pulled in. Haven't caught up completely yet.

However, I would appreciate your observations on what I did "so terribly wrong" given my post which I thought explained it, and why he was long gone by the time I "got there."

Thank you.

Already answered.

I would have had to see it, to understand what you did so terribly wrong.

ramblinrod 28-10-2017 10:03

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

Originally Posted by TJ D (Post 2507353)
I've said this a few times, but nobody seems to have picked up on it.

Rod was suggesting this 180' stuff LONG before the 'line of ships' scenario was introduced. He was talking about doing it right from the start, and then invented the scenario afterwards to support this 180' business.

It was being presented to us, forcefully, as safe and appropriate if only your 'pucker factor' was high enough.

The line of ships thing came later, presumably as cover for a reckless contention made prior.

Incorrect.

The earlier reference to 180 ft, was with regard to holding stand-on when approaching a give way ship at 90 degrees, until 1/4 nm away, to give them ample time to execute their plan, and not interefere with their plan, should they have been holding off execution for some good reason.

The line of ships scenario is a different discussion other than it also has to deal with a ship crossing situation.

TeddyDiver 28-10-2017 10:04

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

Originally Posted by ramblinrod (Post 2507913)
Already answered.

I would have had to see it, to understand what you did so terribly wrong.

So doing what you've been promoting is terribly wrong? :flowers:

ramblinrod 28-10-2017 10:10

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

Originally Posted by Exile (Post 2507343)
The basic point being that whether it requires superhuman powers or a high pucker factor, and whether or not you'd be toast, it violates multiple provisions of the Colregs, is unquestionably unsafe, and defies common sense & rudimentary logic. And these are single ship scenarios I gather in open water.

So it all begs the obvious question: Why do it? And maybe the slightly less obvious question: Why propose doing it, or even suggest doing it on a thread involving serious discussions about real-life collision avoidance? Except as rational posters have done here, namely as a hypothetical learning exercise to demonstrate why it should never be attempted.

Why have the conversation?

Because:

a) We were discussing crossing situations.
b) We were discussing risk aversion.
c) We were discussion whether "safe distance" is subjective or objective.

I do have to say at this point, after all of this discussion by many posters, to ask why we have discussed it all, is pretty irrational.

It was discussed, because so many wished to discuss it I s'pose.

ramblinrod 28-10-2017 10:14

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

Originally Posted by TeddyDiver (Post 2507919)
So doing what you've been promoting is terribly wrong? :flowers:

No.

Apparently, doing what you did, did not work out as you had planned.

I have no idea why.

I wasn't there.

Exile 28-10-2017 10:30

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

Originally Posted by ramblinrod (Post 2507918)
The earlier reference to 180 ft, was with regard to holding stand-on when approaching a give way ship at 90 degrees, until 1/4 nm away, to give them ample time to execute their plan, and not interefere with their plan, should they have been holding off execution for some good reason.

The line of ships scenario is a different discussion other than it also has to deal with a ship crossing situation.

Correct. Two completely different scenarios. But as to the earlier reference, you advocate waiting until 1/4 nm away to allow the give way vessel "to give them ample time to execute their plan, and not interfere with their plan??" Oh but wait, you've suddenly changed the facts . . . now "they have been holding off execution for some good reason."

LOL!! The classic straw man you've been accusing others of using! Your comments are long past the point of being taken seriously. :nonono:

Quote:

Originally Posted by ramblinrod (Post 2507923)
Why have the conversation?

Because:

a) We were discussing crossing situations.
b) We were discussing risk aversion.
c) We were discussion whether "safe distance" is subjective or objective.

I do have to say at this point, after all of this discussion by many posters, to ask why we have discussed it all, is pretty irrational.

It was discussed, because so many wished to discuss it I s'pose.

Exactly right . . . for most everyone else to be sure. But I suggest you are here for different reasons. :whistling:

ramblinrod 28-10-2017 13:36

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

Originally Posted by Exile (Post 2507933)
But as to the earlier reference, you advocate waiting until 1/4 nm away to allow the give way vessel "to give them ample time to execute their plan, and not interfere with their plan??"

Oh but wait, you've suddenly changed the facts . . . now "they have been holding off execution for some good reason." :

Incorrect!

That was the exact same reason I gave back during that debate.

And by the way, the 1/4 nm away I referred to was my distance 90 degrees from their course line, not CPA.

I would prefer not to re-debate every old debate, again and again.

Especially not when someone presents the "alternate facts" to what was actually posted or debated. That is truly a "strawman argument".

ramblinrod 28-10-2017 13:48

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
[QUOTE=Dockhead;2507349]
Quote:

Originally Posted by ramblinrod (Post 2507293)

OK, I think we've been through all this before. It looks like the argument goes like this:

"180 foot CPA with a fast ship is dangerous -- too close to attempt to pass."

"No it's not. If you pass with a greater margin, you run into the ship behind."

"Maybe you run into the ship behind, but it's still not safe to attempt to pass so close to the ship ahead."

"If you pass further, you run into the ship behind."

"What does that have to do anything? If that's true, then you can't pass at all!"

You seem to be having better luck arguing with yourself. ;-)

Given the scenario, my plan could work if the ships held course and speed.

Your plan couldn't; you would hit the following ship.

Your plan was inherently "less safe".

Period.

End of story.

Now you seem to be arguing that your plan to pass 2-3 cables behind the lead ship, and running into the following ship, is better than passing just clear of the lead ship and clearing the following ship without hitting it.

Sorry, I don't get your logic.

I suggest that the one who lived (ramblinrod), is a whole lot better off than the one who died (Dockhead).

ramblinrod 28-10-2017 13:51

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

Originally Posted by Exile (Post 2507343)
Why do it? And maybe the slightly less obvious question: Why propose doing it, or even suggest doing it on a thread involving serious discussions about real-life collision avoidance? Except as rational posters have done here, namely as a hypothetical learning exercise to demonstrate why it should never be attempted.

Already answered.

It was to demonstrate how the skippers response to a scenario is subjective.

An extreme scenario was chosen to make the point.

To argue the scenario was too extreme, after proposing a navigation solution that is obviously severely flawed and causes a collision, is just sour grapes and deflection in my opinion.

Jim Cate 28-10-2017 14:14

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

Originally Posted by ramblinrod (Post 2508066)
Already answered.

Perhaps to your satisfaction, Rod, but others don't share that complacency.

Jim


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