Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

[Dockhead]

Originally Posted by markpierce

A frequent tactic of mine is to turn parallel and then duck behind when safe.

I'm surprised no one mentioned this before now.

This is an obvious tactic for harbours and approaches because you can just sail along the edge of the channel or fairway.

But it also works in open water. Why? Because while it is impossible to line up an approach to pass very closely behind at a 4:1 speed difference (moving along a line which is only 14 degrees off his course line), it is NOT impossible to set up a safe head-on approach, even with naked eyes, because you have very good information from his aspect in this kind of crossing.

The only problem with this is that you will have to set this up from pretty far ahead -- so far ahead that you might as well just cross ahead of him, no? And secondly, you still have to maintain a safe CPA -- not measured in parts of a cable. And lastly, if you turn when you see his quarter, you won't get all that close to him, if he's moving fast. On reciprocal courses your relative speed is the sum of both your speeds -- so 25 knots in the example.

Still it's a sound, common-sense, KISS approach which is good to have in mind.

[El Pinguino]

Originally Posted by Lodesman

So most of the world use lakers, then?
Open water for them is a couple hundred miles at a time - the rest of it is speed limited, so it makes no sense to build them speedy.

As to Rod, you have got to be kidding. He has carried on with childish antics, complaining that he hasn't had his questions answered, when 3 or more different people have answered them; ironically refusing to answer questions that are pertinent to the discussion, but he has dismissed as silly (Rod-speak for "too difficult or embarrassing"); and persisting in his ******** suggestion that one can pass a ship going 20 kts by 180 feet, regardless of whether or not you believe ships can go 20 kts, when it is clear he hasn't come any closer than 1/2 mile or even greater to ships in a narrow channel limited to 10 kts. Only reason to keep reading is for the comic relief.

You have an uncanny knack of missing the point that is being made... I was speaking of ship speeds not ship types... but I think you knew that.

'persisting in his ******** suggestion' .... and you wonder why this thread has been closed twice already.... only to be reopened again by the OP while wearing his moderator's hat.

I would refer you back to post #1 where quotes from another thread were used to start this one ... basicaly using the form 'look at this foolish pair..... I'm smarter than them .... and over the next 750 posts I shall demonstrate how remarkably smart I am.........

[Lodesman]

Originally Posted by El Pinguino

You have an uncanny knack of missing the point that is being made... I was speaking of ship speeds not ship types... but I think you knew that.

'persisting in his ******** suggestion' .... and you wonder why this thread has been closed twice already.... only to be reopened again by the OP while wearing his moderator's hat.

I would refer you back to post #1 where quotes from another thread were used to start this one ... basicaly using the form 'look at this foolish pair..... I'm smarter than them .... and over the next 750 posts I shall demonstrate how remarkably smart I am.........

You have an uncanny knack for cherrypicking certain ships and saying that represents all ships.

I stand by my remark - his suggestion is complete and utter BS. He has never passed 60 yards on the quarter of a ship going 20 kts, and never would have.

I could refer you back to the mother thread where this started - Rod dismissed the OP's point with the very same BS statement. He had a large hand in those 750 posts trying to demonstrate what a superior, ballsy mariner he is...

[Lodesman]

Originally Posted by ramblinrod

All Dockhead had to do was pass between 2 ships, 1-1/4 nm apart. Whether the following ship he ran into was in the English Channel or Lake Ontario makes little difference how smashed up his vessel would be.

Get over yourself. You had no idea how close you would come to the following vessel, until I pointed it out. Twice. And that after others had provided similar clues. Up until then you figured you'd be passing a mile ahead. You still seemingly can't seem to grasp that you would need to thread a fast moving needle - a 2 cable slot that's moving at 20 knots, and set up for it from well over 5 miles away. It could only work on paper. Clueless, utterly clueless.

[El Pinguino]

Originally Posted by Lodesman

You have an uncanny knack for cherrypicking certain ships and saying that represents all ships.

I stand by my remark - his suggestion is complete and utter BS. He has never passed 60 yards on the quarter of a ship going 20 kts, and never would have.

I could refer you back to the mother thread where this started - Rod dismissed the OP's point with the very same BS statement. He had a large hand in those 750 posts trying to demonstrate what a superior, ballsy mariner he is...

Rollocks.....

The OP seems fixated with 1000 ft boxboats doing 20+ knots... I simply suggested that most ships are not that fast or that big..... not that there were no big fast ships....

[Pete7]

Originally Posted by Dockhead

I'm surprised no one mentioned this before now.

This is an obvious tactic for harbours and approaches because you can just sail along the edge of the channel or fairway.

But it also works in open water. Why? Because while it is impossible to line up an approach to pass very closely behind at a 4:1 speed difference (moving along a line which is only 14 degrees off his course line), it is NOT impossible to set up a safe head-on approach, even with naked eyes, because you have very good information from his aspect in this kind of crossing.

By the same token I have on several occasions as the give way boat; carried out a large circle when driving a powerboat across the channel rather than get too close to a large ship. The advantage is it keeps the powerboat up on the plane and travelling at speed rather than face slowing, wallowing about for a while at displacement speeds and then getting up on the plane again. I also hope such an action will be quiet evident to the crew of a large ship that not only do I not want to approach too closely but I don't want to be near their wash either.

Pete

[Dockhead]

Originally Posted by El Pinguino

Rollocks.....

The OP seems fixated with 1000 ft boxboats doing 20+ knots... I simply suggested that most ships are not that fast or that big..... not that there were no big fast ships....

Peace, my brothers. Of course this is true. It's all much simpler with smaller, slower vessels. The puzzle with a faster, bigger one just highlights a specific problem.

Not completely academic, since some of us DO cross with big, fast ships, from time to time, in blue water.

[ramblinrod]

Originally Posted by Lodesman

You had no idea how close you would come to the following vessel, until I pointed it out.

I think you are confused.

It was actually Dockhead who proposed a solution too close to the following ship (and had no idea until I pointed that out).

His proposed distance behind the lead ship was exactly the knee-jerk reaction I expected, before I even posted the scenario.

It's why I posted it.

This small boat sailor on quiet Lake Ontario (yes moi) did know where 180' ft behind the lead ship would place him with the following ship.

Dockhead???? "To be a safe distance, one must not pass closer than 2-3 cables from the lead ship." "After all, I frequently sail the Straights of Dover, the busiest marine traffic in the world".

This would be followed by, "Oh crap, there's the following ship; what have I done?"

Bang, glug, glug, glug.

Please stop distracting me; I have to get to work on the screen-play.

[Stu Jackson]

Originally Posted by Dockhead

I'm surprised no one mentioned this before now.

Isn't this one of those "jinkin'" things?

This is an obvious tactic for harbours and approaches because you can just sail along the edge of the channel or fairway.

Juho or someone else mentioned this.

But it also works in open water. Why? Because while it is impossible to line up an approach to pass very closely behind at a 4:1 speed difference (moving along a line which is only 14 degrees off his course line), it is NOT impossible to set up a safe head-on approach, even with naked eyes, because you have very good information from his aspect in this kind of crossing.

The only problem with this is that you will have to set this up from pretty far ahead -- so far ahead that you might as well just cross ahead of him, no? And secondly, you still have to maintain a safe CPA -- not measured in parts of a cable. And lastly, if you turn when you see his quarter, you won't get all that close to him, if he's moving fast. On reciprocal courses your relative speed is the sum of both your speeds -- so 25 knots in the example.

That was my experience in my example.

Still it's a sound, common-sense, KISS approach which is good to have in mind.

Yes, good summary of options.

[Dockhead]

Originally Posted by ramblinrod

I think you are confused.

It was actually Dockhead who proposed a solution too close to the following ship (and had no idea until I pointed that out).

His proposed distance behind the lead ship was exactly the knee-jerk reaction I expected, before I even posted the scenario.

It's why I posted it.

This small boat sailor on quiet Lake Ontario (yes moi) did know where 180' ft behind the lead ship would place him with the following ship.

Dockhead???? "To be a safe distance, one must not pass closer than 2-3 cables from the lead ship." "After all, I frequently sail the Straights of Dover, the busiest marine traffic in the world".

This would be followed by, "Oh crap, there's the following ship; what have I done?"

Bang, glug, glug, glug.

Please stop distracting me; I have to get to work on the screen-play.

This is a childish game of one-upmanship – complete with childish taunts -- which I have declined to get caught up in. It is distracting and unhelpful to the good folks reading this thread, who are interesting in actually learning something about the issues presented, and discourages them from presenting their own points of view.


But the nonsense gets thicker and thicker with every repetition, and I can’t let this one go.


First of all, let’s be clear that in the given problem, you can’t do it, you can’t get through, if you can’t pass BOTH ships safely. It has been thoroughly demonstrated that you can’t set up a pass in a 5 knot sailboat, to pass 60 yards from the quarter of a big ship making 20 knots. You can’t do it, and it would be extremely dangerous to attempt it, for the simple reason that you would have to approach on a collision course – 14 degrees off the ship’s course line. This has been analyzed and done to death.


So if you can’t execute a safe pass with the ship ahead, then you can’t do it at all. However close or far the ship behind is, does not make the pass with the ship ahead any safer – that is totally fallacious to say that it’s ok (or even possible) to pass this close to the ship ahead, just because “you would have to”, in order to pass safely with the ship behind.


At the beginning of this, we were discussing the pass with the ship ahead, and I was showing why it would need to happen at a safe distance. I did not carefully plot the pass with the ship behind and made no assertions about it. At some point I realized that I should check it, and after plotting it, realized that a 2 cable pass from the ship ahead would create a 1 cable CPA with the ship behind, which is totally unacceptable, and I immediately posted about that. That does not in any way change the analysis of the pass with the ship ahead, which is the threshold issue. All this other stuff is a distraction from this fundamental point – a distraction which serves only this childish one-upmanship and makes it harder for other people to get anything out of the discussion.


As Ping and others have said -- it’s an artificial situation. Sure. As Lodesman said – it’s threading a needle, a needle moving at 20 knots. Now could we please discuss other questions raised in this thread, in a more adult fashion? Since we’ve really done to death, the question of whether or not there is any such thing at all as a safe CPA (or whether it’s just down to “pucker factor”), why don’t we discuss what IS a safe CPA? Ping thinks that smaller CPAs are ok with small boats, compared to between ships. Do we agree with this? It’s an interesting question and it’s exactly on topic.

[Dockhead]

Ping said that in crossings between small boats and ships, you don't need as much room as between two ships.

Do we agree with this? I don't know the answer.

From the point of view of the ship -- you certainly have more control over the crossing, with a slower, smaller vessel. Maybe you could shave it closer.

On the other hand, I have talked to a number of deck officers and masters sailing in the Channel who say that because of the low level of skill on board yachts, which results in unpredictable maneuvering, they prefer to keep, on the contrary, a longer distance away -- so that the yacht can't do anything stupid at the last moment.

From the point of view of the yacht -- I don't think I would be comfortable with a smaller CPA, than ships maintain between each other. With less speed, I have less control, which means the area ahead of him where I can't get out of his way, is bigger. If he's much faster than you are -- and already not talking about 4:1, but even 2:1 -- I think your options start to dwindle very fast once you get closer than a mile in open water.

[robbievardon]

OK post 781 assuming sailboat is approaching from port side of cargo ship,in order to pass down alongside of it, sailboat is stand on vessel,firstly at what distance does the sailboat change course to run down side of cargo boat? Does this require a turn to Port first? On board CB at what point in time /distance off does Captain of CB take action to comply with Cregs and presumably alter course to Port to avoid sailboat standing on? Is this not simply setting up another potential collision course? It seems to me to that sailing 2 sides of the triangle as opposed to sailboat electing to go around stern and not forcing CB to change course would be a lot simpler and safer.As to applying this to a possibly crowded Harbour!!!!

[ramblinrod]

Originally Posted by Dockhead

First of all, let’s be clear that in the given problem, you can’t do it, you can’t get through, if you can’t pass BOTH ships safely. It has been thoroughly demonstrated that you can’t set up a pass in a 5 knot sailboat, to pass 60 yards from the quarter of a big ship making 20 knots.

Of course it CAN be done.

Whether one considers it "safe" or not, is a completely separate matter.

At the beginning of this, we were discussing the pass with the ship ahead, and I was showing why it would need to happen at a safe distance. I did not carefully plot the pass with the ship behind and made no assertions about it.

Incorrect!

The scenario was clearly stated to cross a convoy between two ships. This most definitely does and has always involved passing behind a lead ship, and ahead of a following ship.

Now I see why you are having so much difficulty with multiple targets, that you feel everyone needs a guide. You simply don't know how to deal with more than one vessel at a time.

At some point I realized that I should check it, and after plotting it, realized that a 2 cable pass from the ship ahead would create a 1 cable CPA with the ship behind, which is totally unacceptable, and I immediately posted about that.

Wouldn't a prudent navigator consider this before proposing a solution to pass a lead ship in a convoy? Was that "some point" AFTER I declared your solution was flawed BECAUSE you would hit the following ship?

And your proposal wasn't a 2 cable pass from the ship ahead. It was 2-3 cables. At the least of the range, 2 cables, you would be perilously close to the following ship, by a margin that would be much more dangerous than I to the lead ship. At the other end of the range, 3 cables, you would most definitely be into it.

Now could we please discuss other questions raised in this thread, in a more adult fashion?

Sure, lead the way, admit your error without the myriad of excuses and back-handed comments towards me, and I'll be glad to drop it with you.

(You see, you are still posting about it too.)

However, if others continue to discuss it, I may choose to respond, to defend my statements or position, if they are brought into question. (That's kinda what forum debates are about; one person doesn't get to dictate what others can post about, if they don't agree with their position.)

That would be kind of like someone sitting on a high horse stating their version with no dissention allowed. Not very effective for getting to the truth.

BTW, I'm not shocked you feel the need to ask this new question at this point.

Cockcroft clearly indicates that all of the "safe distances" you are relying on for all of your arguments, are between "two large ships".

Of course commercial vessels are expected to plot complex solutions from greater distance off. They pose a much greater risk to general marine traffic safety if they get it wrong. They also are required to have the resources (equipment, training, personnel) to do it.

My boat is not required to have AIS, radar, or even VHF. I am required to have a radar reflector if in an area where ships may be travelling. Why? Because the ships are required to have this equipment, training, and personnel to use it, and are expected to see me, and avoid running into me, even if I don't adhere to Colregs.

In my opinion, any professional mariner who considers a husband and wife team on a sailboat a WAFI, because they don't plot their every move from 10 miles away, is a blithering imbecile.

I also suggest anyone who considers themselves an authority on "collision avoidance" should know this without consulting a cruising forum, to deflect attention away from their own short-comings.

[robbievardon]

evm1024, bit biased to quote Restricted versus GREAT LAKES data? I would think it pretty obvious that the concentrated line of traffic in Ontario is quite simply the shortest route.
Lodesman, I thought you pretty fair minded but your post 784 goes against Fact as per post 773.

[Exile]

Originally Posted by Dockhead

Ping said that in crossings between small boats and ships, you don't need as much room as between two ships.

Do we agree with this? I don't know the answer.

From the point of view of the ship -- you certainly have more control over the crossing, with a slower, smaller vessel. Maybe you could shave it closer.

On the other hand, I have talked to a number of deck officers and masters sailing in the Channel who say that because of the low level of skill on board yachts, which results in unpredictable maneuvering, they prefer to keep, on the contrary, a longer distance away -- so that the yacht can't do anything stupid at the last moment.

From the point of view of the yacht -- I don't think I would be comfortable with a smaller CPA, than ships maintain between each other. With less speed, I have less control, which means the area ahead of him where I can't get out of his way, is bigger. If he's much faster than you are -- and already not talking about 4:1, but even 2:1 -- I think your options start to dwindle very fast once you get closer than a mile in open water.

I don't think the question should be whether between a large ship and small boat less room is needed, but whether there is sufficient room to produce the predictability & consistency the Colregs try and promote. Otherwise we're back to Rod's equating mere survival of the crossing with compliance. The big ship doesn't know if Ping is behind the helm of the small boat and they need not be concerned, or perhaps someone who is waiting until the last minute so as to not "interfere" with any maneuvers the big ship may still need to make.