Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

[ramblinrod]

Originally Posted by evm1024

The motivation for displaying deck level navigation lights and a mast head tricolor is not to mitigate any confusion with shore lights.

So now you know what motivates everyone to do anything.

Thank you for your insight.

[Exile]

Originally Posted by ramblinrod

First of all, the photos provided (excellent) show that from the elevation of the bridge from a large ship, a trilight (shown properly) may be confused with shore lights and deck level nav lights may be more easily seen.

On the other hand, to vessels with a lower viewing angle like a motor yacht, the deck mounted lights may be confused with shore lights. Additionally in any significant wave, they may be seen very intermittently when the vessel observed is in a trough, so a mast head mounted trilight would be more effective.

What to do? (

Perhaps showing both would be better for all circumstances listed above.

Blasphemy.

Not exactly blasphemous, but potentially foolhardy. You are speculating whether different types of vessels under different scenarios "may" be more or less visible depending on which types of lights are used, but at the same time discounting the potential confusion of running both types of lights as recognized under the Colregs and carefully explained by others.

The Colregs may not always prescribe the "best" rule for every scenario, but are designed to establish rules that are logically consistent & predictable for as many potential scenarios & variables as possible. By time & again advocating your own rules, you are introducing unpredictability & inconsistency that increases the odds of creating confusion & potential danger. Even if your approach could be "right" in any one particular scenario, it would necessarily be "wrong" overall because it conflicts with these basic goals of the Colregs.

Originally Posted by ramblinrod

And ultimately, IMHO even though the yacht puled some boneheaded stunts, the ship should be more to blame, if for no other reason, than the expectation of a higher level of competence expected, to avoid mowing down a sailboat, even under these conditions.

I think you have this skewed. A higher level of competence is expected from the commercial ship because of its size, complexity, and the training & professional standards of its crew. But it doesn't necessarily follow that such higher levels of competence translate to a higher level of culpability or legal liability. Such a determination depends instead on how the different types of crew executed their respective responsibilities given the facts of each individual case. Maybe you can point out where in the Lysagt/Grunter report or in the Colregs different types of vessels & crews are held to the types of different standards you apparently have in mind.

You may recall the discussion in a previous case where a recreational vessel was run down from behind by a commercial ship, and how both vessels/crews were held 50% liable for both vessels not maintaining a proper watch. How does this square with your repeated assertions that commercial ships are held to higher standards in the event of a collision at sea?

[evm1024]

Originally Posted by ramblinrod

So now you know what motivates everyone to do anything.

Thank you for your insight.

You are very welcome Rod. I'm happy to see that you are coming around to my way of thinking.

[evm1024]

Originally Posted by Exile

Not exactly blasphemous, but potentially foolhardy. You are speculating whether different types of vessels under different scenarios "may" be more or less visible depending on which types of lights are used, but at the same time discounting the potential confusion of running both types of lights as recognized under the Colregs and carefully explained by others.

The Colregs may not always prescribe the "best" rule for every scenario, but are designed to establish rules that are logically consistent & predictable for as many potential scenarios & variables as possible. By time & again advocating your own rules, you are introducing unpredictability & inconsistency that increases the odds of creating confusion & potential danger. Even if your approach could be "right" in any one particular scenario, it would necessarily be "wrong" overall because it conflicts with these basic goals of the Colregs.



I think you have this skewed. A higher level of competence is expected from the commercial ship because of its size, complexity, and the training & professional standards of its crew. But it doesn't necessarily follow that such higher levels of competence translate to a higher level of culpability or legal liability. Such a determination depends instead on how the different types of crew executed their respective responsibilities given the facts of each individual case. Maybe you can point out where in the Lysagt/Grunter report or in the Colregs different types of vessels & crews are held to the types of different standards you apparently have in mind.

You may recall the discussion in a previous case where a recreational vessel was run down from behind by a commercial ship, and how both vessels/crews were held 50% liable for both vessels not maintaining a proper watch. How does this square with your repeated assertions that commercial ships are held to higher standards in the event of a collision at sea?

Wow - I wished that I had written this. It really hits the points. Well worth reading a second time especially if you disagree with it in the first reading.

[Uricanejack]

Originally Posted by El Pinguino

So, did he get you off?

I've posted this before but it is still worth a read

https://www.atsb.gov.au/media/25004/mair12_001.pdf

I have made my views on tri-lights clear enough - with photos - in another thread.

Thanks, Very interesting.

[Uricanejack]

Originally Posted by Exile

Not exactly blasphemous, but potentially foolhardy. You are speculating whether different types of vessels under different scenarios "may" be more or less visible depending on which types of lights are used, but at the same time discounting the potential confusion of running both types of lights as recognized under the Colregs and carefully explained by others.

The Colregs may not always prescribe the "best" rule for every scenario, but are designed to establish rules that are logically consistent & predictable for as many potential scenarios & variables as possible. By time & again advocating your own rules, you are introducing unpredictability & inconsistency that increases the odds of creating confusion & potential danger. Even if your approach could be "right" in any one particular scenario, it would necessarily be "wrong" overall because it conflicts with these basic goals of the Colregs.



I think you have this skewed. A higher level of competence is expected from the commercial ship because of its size, complexity, and the training & professional standards of its crew. But it doesn't necessarily follow that such higher levels of competence translate to a higher level of culpability or legal liability. Such a determination depends instead on how the different types of crew executed their respective responsibilities given the facts of each individual case. Maybe you can point out where in the Lysagt/Grunter report or in the Colregs different types of vessels & crews are held to the types of different standards you apparently have in mind.

You may recall the discussion in a previous case where a recreational vessel was run down from behind by a commercial ship, and how both vessels/crews were held 50% liable for both vessels not maintaining a proper watch. How does this square with your repeated assertions that commercial ships are held to higher standards in the event of a collision at sea?

When I read the posted report I did not see any mention of fault or blame.
Blame is for lawyers ,courts and insurance companies. It rarely contributes to accident prevention.

[Exile]

Originally Posted by Uricanejack

When I read the posted report I did not see any mention of fault or blame.

My understanding is that such reports are precluded from assessing fault or liability by design. It is outside their mandate.

Blame is for lawyers ,courts and insurance companies. It rarely contributes to accident prevention.

Why do you say that? I would think some cases could lead directly to safer practices.

[Uricanejack]

Originally Posted by Kelkara

Just for fun, and going back to CPAs and cones of uncertainty... I wrote a quick Excel macro to plot the position of an approaching ship on a radar-like display ... including uncertainty in the observations of the ship's position/course. (The table shows values for the median course)

This shows the possible relative positions that the ship may move to over the next 30 minutes. Obviously as the ship gets closer it will start to become apparent which course the ship is on, and whether a risk of collision exists.

The red dots are possible positions of the ship with less than 10 degrees change in bearing from the initial sighting. i.e. appearing to be on a collision course.

In this example (a simple 90 degree crossing) the ship is first sighted 5 miles away on a bearing of 069. The uncertainty in my observations of the ship means that the CPA might be over 1nm or a very near miss ... from the sailboats point of view I can't tell yet ...

Even in the best case scenario with just over 1nm CPA the ship is less than 10 minutes away before I am likely to determine that there is no risk of collision, and in the worst case I won't know that it's going to miss until less than 1 minute.

If the ship doesn't alter its course, the question is: when should I decide to alter my course ... if I'm under sail and stand-on? or under power and give-way?

If the ship is on the median course ... After 8 minutes with the ship just 3 miles away I still can't tell if we're on a collision course or not, so I make a 45deg turn to starboard (second pic) and after another 3 minutes it's clear that the CPA will be a bit less than 1nm. Alternatively at this point the ship finally sees me and makes a 10deg turn to starboard (3rd pic), and now the CPA is likely a little over 1nm.

Just a fun way to try and visualise the original premise of the thread.

I presume you have used a head up unstabilised radar display as the template for the example. Included a Yaw effect on the target vessel of
10 deg? so the target appears to have spread aprox 10 deg.

This would represent a level of uncertainty trying to predict the CPA, TCPA, Aspect, true course, and speed.of the approaching vessel in restricted visibility.
The scenario was for vessels in sight of each other.
Much of the uncertainty could be eliminated by visual observation of the approaching vessel. Particularly a compass bearing. Or just eyeballing it against a station or background.
Typically commercial ships have fairly accurate course and speed. With little variation of either unless intended. While it is not possible to accurately predict the navigation plan or route of another vessel. It may alter course for some unknown reason.
Their course and speed is usually very predictable.
The uncertainty comes form the observers own vessel not being able to hold a very accurate course and or speed.
Most of this uncertainty can be eliminated by observation by other means as well as radar. I good visibility.
Using radar alone ie in restricted visibility.
You need to increase your margin of error.
In other words act sooner and more decisively.

Good illustration.

[ramblinrod]

Originally Posted by Exile

I think you have this skewed. A higher level of competence is expected from the commercial ship because of its size, complexity, and the training & professional standards of its crew. But it doesn't necessarily follow that such higher levels of competence translate to a higher level of culpability or legal liability. Such a determination depends instead on how the different types of crew executed their respective responsibilities given the facts of each individual case. Maybe you can point out where in the Lysagt/Grunter report or in the Colregs different types of vessels & crews are held to the types of different standards you apparently have in mind.

OK enough with the strawmen already.

1. I stated earlier in this thread that commercial vessels should be excepted to have a higher level of competence aboard due to the size, weight, speed and corresponding risk to other boaters, and due to the number of crew and training.

2. I stated earlier in this thread and have always held that Colregs apply to all boaters equally.

3. I never said this report held anyone to different standards (though commercial vessels are held to different standards than rec vessels.)

4. What I did say is I feel the ship should be held to higher percentage of blame, because those boys should be well enough trained and skilled not to run down a sailboat despite a faulty trilight and no radar reflector.

In other words, Colregs apply to both, additional regulations apply to commercial vessels, and a higher standard of competence should be expected on a big, fully crewed ship vs a little short-handed sailboat.

And any professional seaman that doesn't get that has a major problem IMHO.

[StuM]

Originally Posted by Uricanejack

When I read the posted report I did not see any mention of fault or blame.
Blame is for lawyers ,courts and insurance companies. It rarely contributes to accident prevention.

It does if we understand and learn from what the faults were. I always prefer to learn from other people's mistakes.

[Lodesman]

Originally Posted by StuM

It does if we understand and learn from what the faults were. I always prefer to learn from other people's mistakes.

+1

There's the added adage that you won't survive the process of making all the mistakes yourself.

[Uricanejack]

Originally Posted by Exile

Why do you say that? I would think some cases could lead directly to safer practices.

You pointed out yourself its normal practice for these types of investigations not to find fault or blame. MAIB NTSB TSB follow this so people will speak freely.

A criminal case only answers one question Guilty or Not Guilty.

A civil case is about money. fear of liability may influence cooperate action. Even so a civil case is about proving liability not determining how to prevent a future occurance

[Uricanejack]

Originally Posted by StuM

It does if we understand and learn from what the faults were. I always prefer to learn from other people's mistakes.

In my opinion you will learn much more from an accident investigation than a prosecution or law suit.
People make mistakes,

Occasional people may act intentionally and may need to be held accountable. Even so the accident investigation will provide better info and lessons

[Dockhead]

Originally Posted by Uricanejack

When I read the posted report I did not see any mention of fault or blame.
Blame is for lawyers ,courts and insurance companies. It rarely contributes to accident prevention.

I agree with this.

The idea that we "win" if there is an accident, but we are somehow less to blame -- that is, we can find some fault in the other actor -- is perverted. The U.S. legal culture is much to blame for these attitudes.

We should of course follow the Rules, but not primarily to avoid blame, but to prevent accidents. So everything we do should be aimed at helping the other vessel avoid the accident, too. No one "wins" is there is a collision. And maritime legal culture is very good on this -- almost always apportioning some responsibility to everyone involved and creating good incentives to avoid accidents by all means.

Originally Posted by Exile

An investigatory report can reveal the nature of the deficiencies in equipment and/or crew practices, along with their training & conduct, which may have contributed to an accident.

A criminal prosecution can reveal where the line is between ordinary negligence and reckless or willful misconduct which justifies criminal sanctions.

A civil case is about compensation for a loss, usually in the form of money, and often about add'l money damages to both punish prior negligence & deter similar types of negligence in the future. In the maritime world, civil cases can also help establish, clarify & define standards for both commercial & recreational vessels, and reinforce for some that both types of vessels are held to the same standards when it comes to violations of the Colregs.

I'd say that when it comes to accidents & incidents in the maritime world, studying all of these processes can help with accident prevention.

And I agree with this There is no contradiction between these two points of view.

[Dockhead]

Originally Posted by Uricanejack

I presume you have used a head up unstabilised radar display as the template for the example. Included a Yaw effect on the target vessel of
10 deg? so the target appears to have spread aprox 10 deg.

This would represent a level of uncertainty trying to predict the CPA, TCPA, Aspect, true course, and speed.of the approaching vessel in restricted visibility.
The scenario was for vessels in sight of each other.
Much of the uncertainty could be eliminated by visual observation of the approaching vessel. Particularly a compass bearing. Or just eyeballing it against a station or background.
Typically commercial ships have fairly accurate course and speed. With little variation of either unless intended. While it is not possible to accurately predict the navigation plan or route of another vessel. It may alter course for some unknown reason.
Their course and speed is usually very predictable.
The uncertainty comes form the observers own vessel not being able to hold a very accurate course and or speed.
Most of this uncertainty can be eliminated by observation by other means as well as radar. I good visibility.
Using radar alone ie in restricted visibility.
You need to increase your margin of error.
In other words act sooner and more decisively.

Good illustration.

The only thing I do not agree with here, is this:

Much of the uncertainty could be eliminated by visual observation of the approaching vessel. Particularly a compass bearing. Or just eyeballing it against a station or background.

It is certainly true, that it is easy to get confused with radar or AIS data, if it is not checked against visual observation. So visual observation is always the first thing we need to do, to understand and work out a risk of collision situation.

But you can't say this as a blanket statement -- visual observation does NOT indeed add accuracy to radar observation (and certainly not AIS) -- your bare eyes have FAR less discrimination of bearing and range, than your radar does. It's better with a quality hand bearing compass, used with skill, or compass binocs, but still far less than radar. And that's why God invented radar, and not only for seeing in fog.

So if your electronic data can't tell you that you are clearly passing safely, your bare eyes sure won't. But then what you go on to say, I agree with -- you need to act EARLY, and with a SUFFICIENT MARGIN OF ERROR -- that is, a safe CPA. You need to set up the crossing early enough that without drama, you pass with a sufficient distance from the approaching vessel that this CPA can absorb whatever uncertainties went into the original reckoning of the crossing, and also uncertainties resulting from variations of both vessels in course and speed.

If you don't have electronics, or don't know how to use them, then a safe CPA will be greater, than what you could get by with, if you have a skilled radar operator on board, or AIS, properly used, and "sense checked" with visual observation.