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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)

ramblinrod 09-10-2017 09:17

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

Originally Posted by Dockhead (Post 2495167)
Maybe you could support Rod with more substance. Do you believe it's OK to approach a ship moving at 20 knots to a distance of 1/4 mile on a 0 CPA before maneuvering? What do you consider a safe distance for a collision avoidance maneuver? Safe CPA in open sea? Explain.

Global warming is very complex, with a lot of ideology and politics. Collision avoidance is much more straightforward, with practices which are clearly safe, and some practices which are clearly unsafe.

Very much like electricity - is it safe to wire up your boat without breakers? It's not a matter of ideology or politics.

Electricity and navigation are not the same thing. Not similar. Not even close. What is the proper and reasonable DX from the ships course (which in open, uncongested sea, will most likely be straight as an arrow) for the stand-on sailboat to assume the ship is not going to meet obligation to avoid collision? In my opinion this is around 1/4 mile away from the potential collision point of the ships course. The ship may maneuver when it is 5 miles from the collision intersect point. If the sailboat is doing 5 knots and the ship 20, the sailboat is 1.25 miles away from that point.

A sailboat skipper who is anal. may react at this distance and fail
To meet their obligation to stand on, potentially foiling the planned solution of the ship. It could now have placed itself on a collision course with the ships yet to be executed plan (perhaps they had another, more serious situation to stay clear of first). Between that 5 miles and 1 mile off the collision intersect point, the ship would have ample time to make a maneuver to miss the sailboat. At 1/4 mile from the collision interesct point, it would be reasonable for the non-anal sailboat skipper to assume the ship is not going to avoid them. If the sailboat tuns 90 Degrees to a reciprocal and parallel course to the ship, there is no risk of collision, unless the ship now immediately turns 15 degrees, toward the sailboat.
If his did happen, the sailboat could be mowed down in 3 minutes.
If the sailboat made its maneuver when 1.25 miles from the collision intersect point (5 miles from the ship) and the ship turned some small amount more than 15 degrees (with a plan of ducking behind he sailboat) if the sailboat who failed to stand on and reacted prematurely), does not change course again they will be mowed down in less than 15 minutes.

TeddyDiver 09-10-2017 10:11

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

Originally Posted by ramblinrod (Post 2495394)
..... At 1/4 mile from the collision interesct point, it would be reasonable for the non-anal sailboat skipper to assume the ship is not going to avoid them.....

At that stage non-anal sailboat skipper prays the ship doesn't even try, becouse if it tries it's bow has not started to turn a bit when the stern would be plowing sideways over you.. :nonono:

Dockhead 09-10-2017 10:13

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

Originally Posted by ramblinrod (Post 2495394)
Electricity and navigation are not the same thing. Not similar. Not even close. What is the proper and reasonable DX from the ships course (which in open, uncongested sea, will most likely be straight as an arrow) for the stand-on sailboat to assume the ship is not going to meet obligation to avoid collision? In my opinion this is around 1/4 mile away from the potential collision point of the ships course. The ship may maneuver when it is 5 miles from the collision intersect point. If the sailboat is doing 5 knots and the ship 20, the sailboat is 1.25 miles away from that point.

A sailboat skipper who is anal. may react at this distance and fail
To meet their obligation to stand on, potentially foiling the planned solution of the ship. It could now have placed itself on a collision course with the ships yet to be executed plan (perhaps they had another, more serious situation to stay clear of first). Between that 5 miles and 1 mile off the collision intersect point, the ship would have ample time to make a maneuver to miss the sailboat. At 1/4 mile from the collision interesct point, it would be reasonable for the non-anal sailboat skipper to assume the ship is not going to avoid them. If the sailboat tuns 90 Degrees to a reciprocal and parallel course to the ship, there is no risk of collision, unless the ship now immediately turns 15 degrees, toward the sailboat.
If his did happen, the sailboat could be mowed down in 3 minutes.
If the sailboat made its maneuver when 1.25 miles from the collision intersect point (5 miles from the ship) and the ship turned some small amount more than 15 degrees (with a plan of ducking behind he sailboat) if the sailboat who failed to stand on and reacted prematurely), does not change course again they will be mowed down in less than 15 minutes.

Rod, this is not indeed the scenario we were talking about. Here is what you wrote:

Quote:

Originally Posted by ramblinrod (Post 2493540)
If I have determined there is a risk of collision and 1/4 nm away, I estimate they have waited too long to avoid me, and I take action to miss them by 180 ft, what rule in Colregs, have I violated?


Could you please stop talking about the "collision intersect". We've talked about this before. This is not an applicable term. You have no way of knowing with any precision where this is, and you have no way of knowing even approximately where that is without plotting it, which I am absolutely sure you do not do, and which no one could be doing in the "seconds" you say it takes you to evaluate a potential collision and execute a maneuver. When we do collision avoidance, we know range, from radar or AIS, and we know bearing, from either of those plus a HBC. These are the data we work with.

Here is a decent course on collision avoidance plotting, which is relevant, and which you might find rewarding: https://www.youtube.com/watch?v=plunSlYEbUc

Lodesman 09-10-2017 12:10

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

Originally Posted by ramblinrod (Post 2495394)
At 1/4 mile from the collision interesct point, it would be reasonable for the non-anal sailboat skipper to assume the ship is not going to avoid them. If the sailboat tuns 90 Degrees to a reciprocal and parallel course to the ship, there is no risk of collision, unless the ship now immediately turns 15 degrees, toward the sailboat.

Rod, I guess you haven't had a chance to get back to me on my post 304; it's only been a couple days, so please continue to cogitate on it.
If your plan is to alter course 3 mins TCPA, by 90, why would you assume you'd pass him by 180 ft? Surely, it would be a 1/4 mile CPA?

El Pinguino 09-10-2017 16:00

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
That last youtube thingo with some superannuated fat old bugger banging on about using radar ... fmtt ... you can tell by his gut he hasn't been to sea in the last few decades....

Yachts do not use radar to determine distance...they use the eyeball... works in the real world.... but then again in cyberspace maybe the one eyed man really is king....

And no... I am not going to support the OP in his savaging of Rod.

If this thread hasn't been given the kiss of death by morning I'll share my little story about near death experiences , karma, and life in the real world.......

Not going anywhere soon... forecasting on the high side of 50K north of Isla de la Estados this weekend....

TJ D 09-10-2017 16:16

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Well, you have to admit it's been entertaining! We have a show in the US called 'Jerry Springer'. Most episodes end up in some kind of a scuffle on stage. This sort of reminds me of that. Good fun...

Hopefully nobody's too offended here, and I'm sure that everybody has the best of intentions.

I'm at sea (commercially) right now, so it's been fun to go across the bridge and refresh the thread from time to time to enjoy the latest salvos.

james247 09-10-2017 20:35

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

Originally Posted by markpierce (Post 2493839)
Oh! the acrimony! ... Don't most of us boat in restricted waters where ships have little choice in maneuver? That's my environment, and I defer to all commercial traffic, which based on their behavior, is expected.



This is a cruisers forum and as such we should be considering the safety of the forum members. Forget the rules and observe the truth. Avoid collision at any cost.

Exile 09-10-2017 21:02

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

Originally Posted by james247 (Post 2495841)
This is a cruisers forum and as such we should be considering the safety of the forum members. Forget the rules and observe the truth. Avoid collision at any cost.

Why would you think that avoiding collision at any cost requires disregarding the Rules? :confused::confused: Disagreement on the distances vessels should make maneuvers (or not) in a potential collision scenario are one thing, but I sense that, despite all the protracted explanations & examples, there's still confusion over how, why, or maybe even whether the Rules apply to recreational vessels. Why on earth would anyone think that compliance puts you at greater risk??

TJ D 09-10-2017 21:20

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

Originally Posted by Exile (Post 2495847)
Why would you think that avoiding collision at any cost requires disregarding the Rules? :confused::confused: Disagreement on the distances vessels should make maneuvers (or not) in a potential collision scenario are one thing, but I sense that, despite all the protracted explanations & examples, there's still confusion over how, why, or maybe even whether the Rules apply to recreational vessels. Why on earth would anyone think that compliance puts you at greater risk??

Spot on. It is the responsibility of all mariners to observe the rules-not 'forget' them.

The whole concept of the rules really boils down to predictability. If you're the stand-on vessel, then stand on. If you're to give way, do so early and definitively. Just 'getting out of the way' is not right, and it's this kind of thing that drives the pros nuts. It most often leads to erratic, unpredictable maneuvers on the part of the recreational boat, and that is FAR less desirable than dealing with a recreational boater who is sailing in compliance with the rules.

TeddyDiver 09-10-2017 21:59

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

Originally Posted by El Pinguino (Post 2495688)
....

Yachts do not use radar to determine distance...they use the eyeball... works in the real world.... but then again in cyberspace maybe the one eyed man really is king.....

Some do, but aside that the principle could be the same whatever method one uses. Bearing with bearing compass and distance by eyeballing relative to horizont..

Exile 09-10-2017 22:44

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
I've sort of lost the plot in all the back & forth of this thread, but the basis of some misunderstandings might be that requiring one to deviate from the normal stand on/give way regimen when circumstances warrant somehow "violates" the Rules. On the contrary, the Rules expressly contemplate, indeed require such maneuvers when an unpredictable or potentially dangerous situation on the water necessitates. So while I certainly understand why someone can misapply the Rules and thereby create confusion & danger, proper application of the Rules themselves is entirely (and obviously) consistent with avoiding collisions.

Having said that, this thread has again confirmed for me that recreational vessels who are stand on, mine included, generally maneuver way too early under the mistaken impression that the oncoming commercial ship has failed to give way in timely fashion, or that it's easier for the recreational sailor to just "get the hell out of the way regardless." In those situations there should still be plenty of time to maneuver if need be, but it sounds like more often than not the big ship has already done so to allow a safe crossing with plenty of room.

But then there are always those WAFI-haters on the bridge Ping kindly linked us to that we need to watch out for. :whistling: (not the "WAFInator" mind you, but the WAFI-haters! :wink:).

El Pinguino 10-10-2017 03:50

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

Originally Posted by TeddyDiver (Post 2495860)
Some do, but aside that the principle could be the same whatever method one uses. Bearing with bearing compass and distance by eyeballing relative to horizont..

Ed Zackery..... watching change ( or not) of bearing v. change in range works .... but that can't be learn't in a classroom... only comes with experience.

And also.... if you are using radar all you need to do is have (relative... pretty much a given on a yacht ) target trails turned on... extend the tail past the centre of your PPI and Bingo! Pingo! you can see the CPA at a glance.

All that stuff in that youtube thingo that took a full 21 minutes to waffle through simply gives you the OoI's course and speed ( or - if you are using an unstabilized radar on a yacht - an approximation of same.

And considering that we are talking about clear vis here you can establish all you need to know about her course speed and aspect just by looking at her.

ramblinrod 10-10-2017 07:28

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

Originally Posted by Lodesman (Post 2495508)
If your plan is to alter course 3 mins TCPA, by 90, why would you assume you'd pass him by 180 ft? Surely, it would be a 1/4 mile CPA?

The 180 ft is just a number from a prior discussion.

For this scenario I advised that if the sailboat turned 90 degrees 1/4 nm from the potential collision intersect point on a parallel reciprocal course for 3 minutes and then turned back, they would never be closer than 1/4 nm, and would cross the ships course 1.25 nm astern the ship.

This is a very reasonable scenario.

If the sailboat turns earlier, they could be foiling the plan of the ship that has yet to be executed.

If the sailboat turned too early (say at 1.25 nm from the potential collision intersect point) when the ship was 5 nm from the potential collision intersect point, and the ship executed a turn toward the sailboat with intent to pass astern, the sailboat could be run down in about 15 minutes.

The sailboat is then at fault for not standing-on.

Ship's Captain, "We had a plan, but as we were making our course change to pass behind them, the sailboat turned onto a collision course with our new course, and with each successive course change we attempted to make to avoid them, they kept turning into a collision course with us. If at any time they had of just stood-on according to the rules, we would have avoided them; we kept trying to avoid them until the collision occurred, it was like they had a death wish."

Obviously it is possible to break from stand-on too late, leaving no room for either to avoid collision, resulting in "BANG, glug, glug, glug" (for the sailboat).

But it is also possible to break from the stand-on obligation too early.

For the sailboat to break from the stand-on obligation in a 90 degree crossing 1.25 nm from the collision intersect point, (ship 5 nm from the collision intersect point) is a violation of the rules and a dangerous action.

There is still lots of time and room for the ship to execute their plan to avoid the sailboat, that the sailboat may have just foiled.

If the sailboat keeps turning too soon, they could foil each subsequent solution the ship plans, until "Bang, glug, glug, glug".

While a cruising sailboat may have radar and AIS, few will use ARPA and most will be using eyeball navigation and the estimated positions and bearings of other vessels for collision avoidance.

As we saw in the radar collision avoidance plotting seminar video posted; the ship took about 12 minutes, to measure, analyse, and initiate the course change. Had the stand-on vessel initiated a turn to duck the give-way vessel 10 minutes after sighting, they would have foiled the give-way vessels starboard turn solution (by the time it was calculated and executed), and put themselves on a new collision course.

By the time the give-way vessel realizes the stand-on ship has not stood on, now it's a panic, with (unpredictable) emergency maneuvers going on by both, (each cursing each other for not following Colregs). This will likely end up in a "lucky" near miss or ..."Bang, glug, glug, glug".

The morrow of the story, "When obligated to stand-on, stand-on, until you have to take action to avoid collision." Premature deviation from the stand-on obligation, causes problems. If you want to call the ship while standing on to determine if they know you are there, that is your business, but even a "no response" does not give you any right to break from "stand-on" prematurely. "VHF communication is never the primary element used for collision avoidance."

Lodesman 10-10-2017 14:36

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

Originally Posted by ramblinrod (Post 2496044)
The 180 ft is just a number from a prior discussion.

Fair enough. Do you still think that's a safe distance to pass a ship going 20 kts?

For this scenario I advised that if the sailboat turned 90 degrees 1/4 nm from the potential collision intersect point on a parallel reciprocal course for 3 minutes and then turned back, they would never be closer than 1/4 nm, and would cross the ships course 1.25 nm astern the ship.

This is a very reasonable scenario.

Certainly a lot safer than what it appeared you had suggested previously. A little closer than necessary perhaps.

If the sailboat turns earlier, they could be foiling the plan of the ship that has yet to be executed.

You and I are in complete agreement about this. If you look at any of the other threads I've posted in, you'll see I advocate standing on when required to do so.

If the sailboat turned too early (say at 1.25 nm from the potential collision intersect point) when the ship was 5 nm from the potential collision intersect point, and the ship executed a turn toward the sailboat with intent to pass astern, the sailboat could be run down in about 15 minutes.
The sailboat is then at fault for not standing-on.
By the time the give-way vessel realizes the stand-on ship has not stood on, now it's a panic, with (unpredictable) emergency maneuvers going on by both, (each cursing each other for not following Colregs). This will likely end up in a "lucky" near miss or ..."Bang, glug, glug, glug".

Realistically, 15 min and 5 miles is a lot of room for the big guy to change his course again. In fact it happens all the time; I speak from experience ( and it's part of the reason the term "WAFI" exists). That said, I agree with you, that it is too early to move to the 3rd stage of the collision matrix. I've already stated that I'm with Cockcroft in believing this is one of those situations where 2-3 miles (from the ship, not the invisible X in the ocean) is the point where the sailboat could take 17(a)(ii) action (stage 3).
Are you on board with the concept that the stand on vessel isn't required to maintain course and speed to the point of near collision?

But it is also possible to break from the stand-on obligation too early.

OK given your scenario, what point do you see as the earliest that one could 'legally' break from the "stand-on obligation"?

While a cruising sailboat may have radar and AIS, few will use ARPA and most will be using eyeball navigation and the estimated positions and bearings of other vessels for collision avoidance.

From what I've seen most wouldn't know their arse from a hand bearing compass, and many with AIS believe it to be the all-seeing eye. I would hope most with radar occasionally take a range, if for nothing else, to tune their eyeball assessments.

In your scenario, you're 15 on the freighter's bow - if he was to make a small course change out at 5 or 6 miles, to pass 1 mile astern of you, you won't see much change in his aspect - you'll still be on the freighter's bow, same side just finer. Just eyeballing it, it would fairly easy to believe he hasn't taken action.

As we saw in the radar collision avoidance plotting seminar video posted; the ship took about 12 minutes, to measure, analyse, and initiate the course change. Had the stand-on vessel initiated a turn to duck the give-way vessel 10 minutes after sighting, they would have foiled the give-way vessels starboard turn solution (by the time it was calculated and executed), and put themselves on a new collision course.

Didn't watch the video, but in the real world ARPA gives you a rough assessment in about 30 seconds, and has a pretty good plot after another minute or so. Back when we did it grease pencil on plotting head, then 12 minutes was more realistic, but even then a switched on OOW would have his contact sorted and reported in 6 minutes.

The morrow of the story, "When obligated to stand-on, stand-on, until you have to take action to avoid collision." Premature deviation from the stand-on obligation, causes problems. If you want to call the ship while standing on to determine if they know you are there, that is your business, but even a "no response" does not give you any right to break from "stand-on" prematurely. "VHF communication is never the primary element used for collision avoidance."

The problem with waiting until you're 1 mile in front of the ship, is that you may not have the chance to see his "wait til the last minute" manoeuvre. It probably takes 30-45 seconds for his rudder to respond to the command, then it can take up to a 1/2 mile before he visibly starts turning. If he's just at the start of his turn, and he suddenly sees you jink away, he might try to reverse his rudder, but it's going to take the better part of the 3mins between you for the rudder to come over, stop the swing and start the turn in the opposite direction. Far more likely to have "bang glug glug" in waiting to the last mile(between vessels).


El Pinguino 11-10-2017 01:22

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
2 Attachment(s)
Where do people keep finding these 20 knot ships that take half a day to respond to the rudder?

In the real world most ships poke along at about 15 knots and where I sail 8 to 10 is more the norm.

And any ship you encounter shall be somewhere in between....... an infinite number of sizes, aspects, speeds, etc etc which makes fixating on a single scenario a bit... how do you say it?...anal?

So... my recent near death experience and a little bit of karma.

There we were sailing merrily along on a beam reach on passage from Isla Anihue to Hornopiren... glorious vis -you could see all the way to Argentina.
Small ship - same same Pic 1 - appears to the south maybe 10 miles away.... steady bearing about 4 points on stbd bow.

So she stands on and we stands on and she stands and we stands on. We were probably doing 6 knots... she would have been doing 8 or 9.

By 2 or 3 miles her bearing had started to open very slighty but I was still expecting her to alter to port . She didn't and we passed maybe 100 metres ahead of her ie a ship's length.

Now where does the collective CF wisdom stand on this. When should I have altered? Which way ?

She had no AIS, I wasn't running radar not that it would have served any purpose, and I was watching the change in her bearing - which increased its rate of change as she drew closer - against the distant Andean peaks - a method I haven't seen mentioned anywhere in the last 500 give or take posts.

I suspect her watchkeeper had never encountered a yacht before, was not aware that I had 'right of way' and was wondering why I hadn't altered... or he may have just been happy with 100 metres.

Where does karma come into all this?

A few weeks later the ship in Pic 2 ( same company ) was intentionaly beached to prevent her sinking after bouncing off the bottom down near Punta Harchy... I just hope that he was the watchkeeper on her at the time and is now swelling the ranks of the unemployed.


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