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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 29-10-2017 08:23

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

Originally Posted by robbievardon (Post 2508590)
Dh I don't understand the waffle that you did not write the post I quoted 576. You then go on to justify your remark and fail to advise/respond to my question as to why you repeated your incorrect statement in the first place.
Following my question regarding visual distance to the horizon+ extension to Bridge, one would assume that the Merchant ship regardless of electronics would see and follow the track of the sailboat,judge it to be stand on and make an obvious change of course as required by Cregs. well in advance of any risk of collision. Assuming sailboat is approaching port side of vessel, I would anticipate a turn to port. There then would be no requirement for the sailboat to change course. In the posts 518,520 videos of a,collision and b, near miss, I would like to hear your views and the exact actions you believe all the captains should have taken and this question is open to all to respond to.
I am in the Gulf at the moment, but do keep a sailboat (37 foot) on Lake Ontario to use when I come up to visit Relatives, so I am familiar with "Lake Sailing" and it is by no means a walk in the Park. Conditions can change very quickly and have sent a lot of Lakers to the bottom along with entire crews and I am talking about steel ships under power.

You need to help me out here -- I don't know what "wrong statement" you are referring to. Could you be specific, and I'll try to answer.

Concerning "lake sailing" -- no one said it is a "walk in the park". I grew up sailing in lakes and know all about the vicious and sudden land-based weather events which happen in lakes. It is a special set of challenges. But collision avoidance is totally different, and if you try to project experiences there to open water, blue water conditions you will come up with some really silly ideas.

As to the video in Post 518 -- what is there to discuss? This has nothing to do with open water collision avoidance at all. Fishermen had anchored a small powerboat in a shipping channel. You can see the channel marker in the video. To avoid this situation, just anchor OUTSIDE the channel -- how smart do you have to be to know that? Likewise, in such waters, you don't need AIS or radar or anything -- just stay out of the channels until there is no ship coming. Unlike the case in blue water, when there are channels or fairways, you don't need any other information to know where to stop, to avoid getting run down.

That ship is moving with barely steerage way on, by the way -- 5 or maximum 6 knots.

Paul Elliott 29-10-2017 08:44

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
2 Attachment(s)
Here are two AIS plots captured aboard VALIS as we were heading out on the race to Hawaii. We had just crossed under the Golden Gate bridge and the 800-ft tanker "Yang Ning Hu" was passing us (and three other sailboats) in the outbound shipping channel. Our AIS CPA was 659 ft. The tanker had full control of this close encounter, although we did hold our course as it approached. The tanker was certainly "restricted in ability to maneuver".

BTW, when racing on SF Bay you are generally disqualified if you cause a ship to sound five horn blasts, If you survive.

One screenshot shows normal, and the other shows relative vectors. I usually display normal vectors but you can see how well the relative vectors display the situation. If you extend the relative vectors from multiple targets far enough you can simultaneously see the CPAs for all of them as the vectors pass near your boat. Naturally, if someone changes course then all bets are off.

robbievardon 29-10-2017 08:46

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
DH very simple, pp39 post 576 you state "It is specifically forbidden" (which it is not), would you like me to quote a line no counting from the top down? Interesting their is no comment on the second video about the sailboats course in relation to the cargo boat or how close it came to a collision and no comment on the sailboat that did collide to say you won't comment on it because of where it occurred!!!

Exile 29-10-2017 08:56

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

Originally Posted by Dockhead (Post 2508602)
That ship is moving with barely steerage way on, by the way -- 5 or maximum 6 knots.

This is an important "by the way" that some of us may not realize. At least I don't think I quite did. To the only moderately experienced (like me), it may appear as though the ship is moving too fast under the circumstances and doing nothing to slow down. Maybe goes to show how different experience levels, sailing areas, and perspectives may influence one's judgement in the various scenarios being discussed.

Exile 29-10-2017 08:59

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

Originally Posted by Paul Elliott (Post 2508638)
BTW, when racing on SF Bay you are generally disqualified if you cause a ship to sound five horn blasts, If you survive.

So much for the use of "pucker factor" as a way of gaining an advantage when racing. But sailing on SF Bay, let alone racing, presents its own set of heightened challenges.

ramblinrod 29-10-2017 09:04

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

Originally Posted by Dockhead (Post 2508602)
You need to help me out here -- I don't know what "wrong statement" you are referring to. Could you be specific, and I'll try to answer.

Concerning "lake sailing" -- no one said it is a "walk in the park". I grew up sailing in lakes and know all about the vicious and sudden land-based weather events which happen in lakes. It is a special set of challenges. But collision avoidance is totally different, and if you try to project experiences there to open water, blue water conditions you will come up with some really silly ideas.

As to the video in Post 518 -- what is there to discuss? This has nothing to do with open water collision avoidance at all. Fishermen had anchored a small powerboat in a shipping channel. You can see the channel marker in the video. To avoid this situation, just anchor OUTSIDE the channel -- how smart do you have to be to know that? Likewise, in such waters, you don't need AIS or radar or anything -- just stay out of the channels until there is no ship coming. Unlike the case in blue water, when there are channels or fairways, you don't need any other information to know where to stop, to avoid getting run down.

That ship is moving with barely steerage way on, by the way -- 5 or maximum 6 knots.

Lake Ontario is 193 miles long by 53 miles wide. So what pray tell is so different crossing a ship here (out of site of land in any direction) and crossing a ship in Bluewater (except for minor Colregs vs inland water rule variations), other than the obvious, that there is more water beyond what the eye, AIS, and radar can see (so it may just as well be infinite in dimension from a navigation stand point.)

robbievardon 29-10-2017 09:11

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
DH ref my post, 571 why is collision avoidance on a VAST lake different from on the Ocean? I have never bothered to measure the Great Lakes, bar Niagra on the lake to Toronto which is about 37 miles. The lake is maybe 150 miles long. Ontario is probably the smallest of the lakes

Dockhead 29-10-2017 09:46

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

Originally Posted by robbievardon (Post 2508641)
DH very simple, pp39 post 576 you state "It is specifically forbidden" (which it is not), would you like me to quote a line no counting from the top down? Interesting their is no comment on the second video about the sailboats course in relation to the cargo boat or how close it came to a collision and no comment on the sailboat that did collide to say you won't comment on it because of where it occurred!!!

Ah, about a series of small changes of course.

Yes, I already said that I probably went too far saying it is "specifically forbidden". It would have been more precise to say "specifically mentioned, and discouraged." The exact words are "a succession of small alterations of
course and/or speed should be avoided."

But so what? One of the worst things you can do in a collision avoidance situation is to go into a risk of collision and make frequent small alterations of course. This is extremely bad practice -- a real WAFI approach.

The MCA's Marine Guidance Note #369 is more blunt than the Rules:

"Do not make a series of small alterations"

This particular MGN concerns action in restricted visibility, but the principle is equally applicable in all conditions.

The law books are full of cases where collisions were caused by failure of one vessel to take early and decisive action which is readily apparent to the other vessel.

There is hardly a more fundamental principle of collision avoidance -- that action taken should be done in a way which makes it clear from a safe distance that you are passing safely -- the object is for everyone to be holding course and speed near CPA to pass at a safe distance and in a manner which is understood by both vessels. Doing it early and then holding your course and speed is not only to clarify your intentions, but also to give the other vessel a chance to evaluate whether it is comfortable with your maneuver and the resulting manner and CPA of the crossing.


Concerning the video -- the posts you refer to are both the same video, with the anchored fishing boat. I can't comment without knowing which video you have in mind.

robbievardon 29-10-2017 10:01

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Exile 754,755, as DH has not replied to my post,I will give you my view. The Tanker started blowing her whistle 15 to 20 secs before collision (approx) which suggests a late decision by the sailboat to cross channel also supported in my view that sailboat crew were not prepared to deal with spinnaker flapping at bow.I don't believe the tanker Pilot/Captain could have done anything to prevent the collision as emergency astern would do little to slow the vessel and might have caused the stern to swing to one side causing problems for all the yachts passing down each side. There is some commentary that suggests that the race was close to finishing the course which perhaps influenced the poor decision by the skipper of the sail boat. With the second video I am amazed that the yacht that the video was taken from took such a course for so long before deciding to come to Starboard and must have caused great alarm on the ship not knowing if the sailboat intended to dash under its bow or not against Cregs or not (consider 1st video). I don't know if the fishing boat was inside the lane or not,as one would have to see the next buoy to starboard to draw a line, however having said that I certainly would not have stopped so close to the lane.

Dockhead 29-10-2017 10:11

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

Originally Posted by robbievardon (Post 2508660)
DH ref my post, 571 why is collision avoidance on a VAST lake different from on the Ocean? I have never bothered to measure the Great Lakes, bar Niagra on the lake to Toronto which is about 37 miles. The lake is maybe 150 miles long. Ontario is probably the smallest of the lakes

Because traffic on such a small body of water, consisting predominantly of slow, small lake ships, moves in defined lanes. Near ports, it moves in buoyed channels and fairways. It is a totally different exercise.

El Pinguino 29-10-2017 10:19

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Is this thread still going? golly.......

A bloke goes to sea for a fortnight and what does he come back to??????

Quote:

Originally Posted by Dockhead (Post 2508576)
Yes, it's important to remember that a 1 mile CPA is a small CPA for open water, considered tolerable only in busy areas. There are incident reports on CHIRP where one vessel filed a formal complaint against another for passing less than 2 miles from another (but more than 1), refusing to give more room.

Not just mid ocean, but anywhere without so much traffic that maintaining 2 miles everywhere becomes impractical.

What book did you read that in?

Sorry but there is a world of difference between ship/ship and ship/small craft.

We only saw 3 distant fishermen and two passenger ships in two 500 mile sea passages.

The passenger ships were both encountered in hours of darkness ... One passed with a CPA of 4 cables... the other with a CPA of six.... distances taken off the AIS.

Did they alter course to maintain a CPA of 1 mile... no they did not

Did I alter course to maintain a CPA of 1 mile ... no I did not

Did I construct elaborate vector diagrams etc?... nope

Did they? Doubt it.....

Such is life in the real world outwith the confines of CF.

Ping
Back in Williams after a shopping trip to the FI.

Dockhead 29-10-2017 10:26

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

Originally Posted by robbievardon (Post 2508710)
Exile 754,755, as DH has not replied to my post,I will give you my view. The Tanker started blowing her whistle 15 to 20 secs before collision (approx) which suggests a late decision by the sailboat to cross channel also supported in my view that sailboat crew were not prepared to deal with spinnaker flapping at bow.I don't believe the tanker Pilot/Captain could have done anything to prevent the collision as emergency astern would do little to slow the vessel and might have caused the stern to swing to one side causing problems for all the yachts passing down each side. There is some commentary that suggests that the race was close to finishing the course which perhaps influenced the poor decision by the skipper of the sail boat. With the second video I am amazed that the yacht that the video was taken from took such a course for so long before deciding to come to Starboard and must have caused great alarm on the ship not knowing if the sailboat intended to dash under its bow or not against Cregs or not (consider 1st video). I don't know if the fishing boat was inside the lane or not,as one would have to see the next buoy to starboard to draw a line, however having said that I certainly would not have stopped so close to the lane.

Are you talking about the Hanna Knutsen collision off Cowes?

These are my home waters -- I see the very spot from where I'm writing this. The video tells you absolutely nothing about what happened.

I actually have some sympathy for the yacht skipper -- he was not sailing as stupidly as it looks from the video. Of course like many racers, he was working with too much balls and pucker factor and too little brains, but he was actually counting on the ship to change course up the Thorne Channel rather than carrying on Westwards down the Solent, and then the ship did not, and so the yacht's maneuver miscarried. He was in an actual race, and in Cowes Week to boot, so you can actually understand why he would be willing to shave it closer than you might ordinarily be willing to do, but he went too far. In the event, he got a criminal conviction.

Of course the ship could not have done anything, although it was moving very slowly -- the one thing you CAN see from the video, is that even in crowded waters like the Solent, he was too close to the ship, and he assumed too much about what the ship would do. He was not even visible, either by eye or radar, to the bridge, from that distance.

In the Solent, like sailing in a lake, even though the Solent is 10x more crowded than any place you can find in North America, collision avoidance is simple -- you don't need AIS or radar, just stay the hell out of the channels when ships are coming, and don't cross closely ahead.

We have special regulations here which prohibit small vessels from approaching large ones within 100 meters (330 feet or half a cable), and 1000 meters ahead (5 cables). Good policy anywhere, actually.

Exile 29-10-2017 10:36

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

Originally Posted by robbievardon (Post 2508710)
Exile 754,755, as DH has not replied to my post,I will give you my view. The Tanker started blowing her whistle 15 to 20 secs before collision (approx) which suggests a late decision by the sailboat to cross channel also supported in my view that sailboat crew were not prepared to deal with spinnaker flapping at bow.I don't believe the tanker Pilot/Captain could have done anything to prevent the collision as emergency astern would do little to slow the vessel and might have caused the stern to swing to one side causing problems for all the yachts passing down each side. There is some commentary that suggests that the race was close to finishing the course which perhaps influenced the poor decision by the skipper of the sail boat. With the second video I am amazed that the yacht that the video was taken from took such a course for so long before deciding to come to Starboard and must have caused great alarm on the ship not knowing if the sailboat intended to dash under its bow or not against Cregs or not (consider 1st video). I don't know if the fishing boat was inside the lane or not,as one would have to see the next buoy to starboard to draw a line, however having said that I certainly would not have stopped so close to the lane.

Your comments sound reasonable. I was referring to the last video you mentioned involving the small fishing boat unable to move for some reason out of the way of the freighter. Not sure if that was the one DH also commented was likely moving along at 5-6 kts., i.e. just enough to maintain steerage for a ship that size.

Dockhead 29-10-2017 11:10

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

Originally Posted by El Pinguino (Post 2508730)
Is this thread still going? golly.......

A bloke goes to sea for a fortnight and what does he come back to??????



What book did you read that in?

Sorry but there is a world of difference between ship/ship and ship/small craft.

We only saw 3 distant fishermen and two passenger ships in two 500 mile sea passages.

The passenger ships were both encountered in hours of darkness ... One passed with a CPA of 4 cables... the other with a CPA of six.... distances taken off the AIS.

Did they alter course to maintain a CPA of 1 mile... no they did not

Did I alter course to maintain a CPA of 1 mile ... no I did not

Did I construct elaborate vector diagrams etc?... nope

Did they? Doubt it.....

Such is life in the real world outwith the confines of CF.

Ping
Back in Williams after a shopping trip to the FI.

Two miles is widely considered and widely taught to professionals as a good minimum CPA when traffic allows it. You should know that. By now this is part of the Ordinary Practice of Seamen, Rule 2.

From the story you posted earlier, we can guess that standards of professionalism are quite a bit more relaxed in Argentinian waters, than they are up here. Up here you can't get within a mile of a ship in open water without avoiding action or an angry VHF call.

ramblinrod 29-10-2017 12:24

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

Originally Posted by Dockhead (Post 2508720)
Because traffic on such a small body of water, consisting predominantly of slow, small lake ships, moves in defined lanes. Near ports, it moves in buoyed channels and fairways. It is a totally different exercise.

Incorrect.

Most Lake Ontario cargo ships are 600 ft long and travel 15 knots +. There are defined lanes north and south of Main Duck Island, but that's it. There are no buoyed channels or fairways.

I don't see any difference. Do you see any difference?


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