Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

[StuM]

Originally Posted by ramblinrod

Sorry, you don't get to change Colregs rules to suit your argument. When there is risk of collision established if I am stand on, I am obligated to hold course and speed until such point as the other vessel cannot maneuver in time to avoid collision by there maneuver alone. That is the rule. If I fail to stand on, while the other vessel had time to maneuver to avoid collision, and my action causes collision, I am in a heap o crap, because I violated Colregs; I turned or changed speed when I was supposed to hold course and speed.

No it's not the rule! If you are going to keep on arguing this, it would be a good idea to actually know what you are arguing about.

Rule 17:
(a) (i) Where one of two vessels is to keep out of the way the other shall keep her course and speed.
(ii) The latter vessel may however take action to avoid collision by her manoeuvre alone, as soon as it becomes apparent to her that the vessel required to keep out of the way is not taking appropriate action in compliance with these Rules.

You fail to grasp the difference between Rule 17 (a) (ii) and Rule 17(b)

(b) When, from any cause, the vessel required to keep her course and speed finds herself so close that collision cannot be avoided by the action of the give-way vessel alone, she shall take such action as will best aid to avoid collision

[Exile]

Originally Posted by ramblinrod

Sorry, you don't get to change Colregs rules to suit your argument. When there is risk of collision established if I am stand on, I am obligated to hold course and speed until such point as the other vessel cannot maneuver in time to avoid collision by there maneuver alone. That is the rule. If I fail to stand on, while the other vessel had time to maneuver to avoid collision, and my action causes collision, I am in a heap o crap, because I violated Colregs; I turned or changed speed when I was supposed to hold course and speed.

Who's "changing Colregs?" And who's arguing?? The Rules stay the same, but the specific distances involved in the various stages may differ based on variables that are obvious and have already been discussed. Cockcroft's distances for open water cited by Dockhead above are [I]suggestive[I], but obviously provide a good sense of what other vessels are relying on. In my case I have been operating on the erroneous assumption that the collision risk arises well after it actually does in the minds of professionals on fast moving commercial ships. So why on earth would I not want to adjust my thinking to be in sync with exactly the types of vessels which pose the greatest potential risk to me & my vessel? Even if you or someone else disagrees with the suggested distances, surely there is a reasonable middle ground that doesn't put you in the dangerously close proximity your examples pose.

[TJ D]

Originally Posted by StuM

No it's not the rule! If you are going to keep on arguing this, it would be a good idea to actually know what you are arguing about.

Rule 17:
(a) (i) Where one of two vessels is to keep out of the way the other shall keep her course and speed.
(ii) The latter vessel may however take action to avoid collision by her manoeuvre alone, as soon as it becomes apparent to her that the vessel required to keep out of the way is not taking appropriate action in compliance with these Rules.

You fail to grasp the difference between Rule 17 (a) (ii) and Rule 17(b)

(b) When, from any cause, the vessel required to keep her course and speed finds herself so close that collision cannot be avoided by the action of the give-way vessel alone, she shall take such action as will best aid to avoid collision

You beat me to it... I was just about to pounce on that one too.

I was also thumbing through the regs, and 8a comes to mind. "Any action taken.....shall be positive, made in ample time, and with due regard to good seamanship" I don't think that very many professionals would consider very close quarters maneuvering as has been suggested to be very seamanlike.

[Dockhead]

Originally Posted by Lodesman

I feel compelled to point out an inconsistency here - Cockcroft says 2-3 miles, not 3 or 4 miles. I might suggest if he hasn't moved by 4 miles that might be a good time to take soft measures, such as calling on VHF or lighting up the sails; and 3 miles as the beginning of the third stage where you can make your 17(a)(ii) action.

Yes, I've read Cockcroft, of course, and you are right to point this out.

But here he was writing about situations between vessels of similar size and speed.

A big difference of speed changes things. If you are travelling at a fraction of the speed of the other vessel, then your action must be earlier, to be effective, than would be the case if your speeds were roughly the same.

I'm not saying it's necessarily wrong to do it at 2 or 3 miles, and in fact I do sometimes, but if he's moving fast (>15 knots) and I'm moving slow (<8 knots) I think it is best not to leave it much past 3 miles, and I don't think 4 miles is too early.

[markpierce]

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.

[Dockhead]

Originally Posted by ramblinrod

Gentlemen, you are inflicting personal opinion as to what is adequate to suit your personal sensibilities.

I don't profess to be a collision avoidance expert, and yet without taking a week to review case law I can declare with 100% certainty, that if I as the stand-on vessel have decided 1/4 mile away, that the give way vessel has not met their obligation to give way, and no longer has the ability to avoid collision, that if I take necessary evasive maneuvers to miss them by 180 ft (actually a hair width as previously stated), I have met every single obligation under Colregs. PERIOD.

What's more, if I make evasive maneuvers while the give way vessel still has capability to avoid collision on their own, and we collide, I have violated Colregs, and will be found at some degree of fault if my measures actually cause collision, if the planned but yet to be executed measures of the give way vessel would have prevented collision, had I just stood on.

You are entitled to your own opinion, but not to your own physics or geometry. Good seamanship does involve many things which are objective, and not a matter of subjective opinion. As does safety.

1/4 mile off is too late to initiate a collision avoidance maneuver with a ship moving at 4 times your speed.

No collision avoidance maneuver involving this kind of difference of speed, starting from a 0 CPA, can possibly assure a safe pass at 180 feet. There is no such thing as a safe pass at 180 feet in the open sea at speed, because you cannot know within 180 feet where the ship will be when you reach him.

What is even much worse is that 1/4 mile off is already far within the zone, where the ship is obligated to maneuver himself in any case, no matter what. You are too close to have any assurance that the two of you don't maneuver into each other.

What would you do, for example, if you are under sail and approaching him from starboard on a perpendicular course. He doesn't see you and fails to maneuver. You wait until 1/4 mile off (!!) to make your magic move to pass, as you think, 180 feet behind him. There are two guys on the bridge -- one is in the toilet and the other is reading a porn mag (most ship's bridges are better run, but this does happen sometimes). The guy comes back from the toilet, suddenly sees you, and instinctively turns to starboard.

Over a wide range of his possible turns, because of the length of the ship, you are dead, Rod. And the shipping company's lawyers will take away your house from your widow, for gross negligence on your part, for seeing the ship and waiting until 1/4 mile to maneuver.

Even if he doesn't change course, your and his course naturally vary, and can eat up your 180 foot CPA in seconds. You cannot safely calculate and execute a maneuver for a safe pass at that distance, with a vessel travelling 20 knots. You don't even know where the GPS antenna for his AIS transmitter is, so you have no way of even calculating a 180 foot CPA. And at 1/4 mile, you can't tell anything with a HBC -- the bearing is changing noticeably already to various parts of the ship -- different parts of the ship already have different bearings, at that distance, and they already change at different rates (1 degree is only 80 meters at 1/4 mile). At 0 CPA at 1/4 mile, your eyeball can't discern whether you're passing ahead or behind and you don't know which way to turn. Nor can you travel far enough in the amount of time needed to close 1/4 mile, travelling at 5 knots, to get a safe distance away. We've been through this already -- these are the facts.

The COLREGS require TIMELY action -- action in ADEQUATE TIME. 1/4 mile off, in open sea, is never that, for all these reasons. And a 180 foot CPA is never enough in open sea. We can debate between one mile or two, but not 180 feet.


So all of these recommendations are just totally unseamanlike, and actually dangerous. And I cannot but call it what it is. Imagine if someone were to come on here, and say something like, "circuit breakers are for sissies -- I've gone without them for 40 years and I never had a fire. Therefore, they are unnecessary, and I advise you to go ahead and build your boat without them." Others would say -- "But there is always a risk of a short! Without breakers, you'll have a fire!" And the first guy says "Oh, if you have a short, just pull out the shore power cable, or disconnect the battery; it's not big deal." "But you can't pull out the shore power cable in time, if you even detected the short before the fire started!" And so on. I can just imagine what you would say to the first guy! You would tell it like it is, and you would owe the community here on CF your professional knowledge and clear explanation of why that is dangerous wrong.

This is exactly the same conversation. "Oh, just make a 180, 1/4 mile off, to miss a ship travelling at 20 knots, by 180 feet, you don't need a one mile CPA" -- that is EXACTLY the same as saying -- "Oh, just pull out the shore power cable, if you have a short, you don't need a breaker."

[markpierce]

Originally Posted by El Pinguino

Sorry, but you can't cherry pick the rules like that...

So, may I presume you sound your horn when leaving the berth as well as the marina?

[markpierce]

In my observations, sailboats sound proper horn signals less than five percent of the time, and motorboats maybe more than ten percent. Sailboaters seem to rely on canned air (I did) rather than electric or air-compresser-powered horns (as I do now) of powerboats. Thus, most sailboaters have limited horn capability, reducing their ability to comply with all Colregs.

Best to boat conservative and assume everyone else is ignorant of the regulations. Fortunately, most boaters believe in self-preservation and collisions are rare.

[StuM]

Originally Posted by markpierce

So, may I presume you sound your horn when leaving the berth as well as the marina?

Only when required by Rule 34 (a):

When vessels are in sight of one another, a power-driven vessel underway, when manoeuvring as authorized or required by these Rules, shall indicate that manoeuvre by the following signals on her whistle:

Which is rarely the case when leaving a berth. If a risk of collision exists, I don't leave the berth until the fairway is clear so no signal is required.

[Lodesman]

Originally Posted by markpierce

So, may I presume you sound your horn when leaving the berth as well as the marina?

From his profile, elpinguino is in Chile. The long blast departure signal is not in the international rules - just US Inland and Canadian rules.

[ramblinrod]

Originally Posted by Dockhead

You are entitled to your own opinion, but not to your own physics or geometry. Good seamanship does involve many things which are objective, and not a matter of subjective opinion. As does safety.

1/4 mile off is too late to initiate a collision avoidance maneuver with a ship moving at 4 times your speed.

No collision avoidance maneuver involving this kind of difference of speed, starting from a 0 CPA, can possibly assure a safe pass at 180 feet. There is no such thing as a safe pass at 180 feet in the open sea at speed, because you cannot know within 180 feet where the ship will be when you reach him.

What is even much worse is that 1/4 mile off is already far within the zone, where the ship is obligated to maneuver himself in any case, no matter what. You are too close to have any assurance that the two of you don't maneuver into each other.

What would you do, for example, if you are under sail and approaching him from starboard on a perpendicular course. He doesn't see you and fails to maneuver. You wait until 1/4 mile off (!!) to make your magic move to pass, as you think, 180 feet behind him. There are two guys on the bridge -- one is in the toilet and the other is reading a porn mag (most ship's bridges are better run, but this does happen sometimes). The guy comes back from the toilet, suddenly sees you, and instinctively turns to starboard.

Over a wide range of his possible turns, because of the length of the ship, you are dead, Rod. And the shipping company's lawyers will take away your house from your widow, for gross negligence on your part, for seeing the ship and waiting until 1/4 mile to maneuver.

Even if he doesn't change course, your and his course naturally vary, and can eat up your 180 foot CPA in seconds. You cannot safely calculate and execute a maneuver for a safe pass at that distance, with a vessel travelling 20 knots. You don't even know where the GPS antenna for his AIS transmitter is, so you have no way of even calculating a 180 foot CPA. And at 1/4 mile, you can't tell anything with a HBC -- the bearing is changing noticeably already to various parts of the ship -- different parts of the ship already have different bearings, at that distance, and they already change at different rates (1 degree is only 80 meters at 1/4 mile). At 0 CPA at 1/4 mile, your eyeball can't discern whether you're passing ahead or behind and you don't know which way to turn. Nor can you travel far enough in the amount of time needed to close 1/4 mile, travelling at 5 knots, to get a safe distance away. We've been through this already -- these are the facts.

The COLREGS require TIMELY action -- action in ADEQUATE TIME. 1/4 mile off, in open sea, is never that, for all these reasons. And a 180 foot CPA is never enough in open sea. We can debate between one mile or two, but not 180 feet.


So all of these recommendations are just totally unseamanlike, and actually dangerous. And I cannot but call it what it is. Imagine if someone were to come on here, and say something like, "circuit breakers are for sissies -- I've gone without them for 40 years and I never had a fire. Therefore, they are unnecessary, and I advise you to go ahead and build your boat without them." Others would say -- "But there is always a risk of a short! Without breakers, you'll have a fire!" And the first guy says "Oh, if you have a short, just pull out the shore power cable, or disconnect the battery; it's not big deal." "But you can't pull out the shore power cable in time, if you even detected the short before the fire started!" And so on. I can just imagine what you would say to the first guy! You would tell it like it is, and you would owe the community here on CF your professional knowledge and clear explanation of why that is dangerous wrong.

This is exactly the same conversation. "Oh, just make a 180, 1/4 mile off, to miss a ship travelling at 20 knots, by 180 feet, you don't need a one mile CPA" -- that is EXACTLY the same as saying -- "Oh, just pull out the shore power cable, if you have a short, you don't need a breaker."

Can you please just answer the question. 3rd request. 1/4 mile away, I determine the give way vessel is not giving way and doesn't have ability to avoid collision on their own. I change course and we miss by 180 ft; what Colregs rule did I break?

[Lodesman]

Originally Posted by Dockhead

I'm not saying it's necessarily wrong to do it at 2 or 3 miles, and in fact I do sometimes, but if he's moving fast (>15 knots) and I'm moving slow (<8 knots) I think it is best not to leave it much past 3 miles, and I don't think 4 miles is too early.

I get the impetus, when the speed differential is large - but I just caution that some watchkeepers (less experienced especially) tend to maintain course/speed to the inner limit of stage 2 before they take action, which they would generally see as the 2-3 mile range; if you take action at 4nm, you should be doubly cautious to avoid doing anything that would foul his likely course of action (which of course you would anyway).

[ramblinrod]

Originally Posted by StuM

No it's not the rule! If you are going to keep on arguing this, it would be a good idea to actually know what you are arguing about.

Rule 17:
(a) (i) Where one of two vessels is to keep out of the way the other shall keep her course and speed.
(ii) The latter vessel may however take action to avoid collision by her manoeuvre alone, as soon as it becomes apparent to her that the vessel required to keep out of the way is not taking appropriate action in compliance with these Rules.

You fail to grasp the difference between Rule 17 (a) (ii) and Rule 17(b)

(b) When, from any cause, the vessel required to keep her course and speed finds herself so close that collision cannot be avoided by the action of the give-way vessel alone, she shall take such action as will best aid to avoid collision

So tell me, what is the distance that Colregs specifies, the give way vessel must change course before 17a applies? Let's assume, they have identified the risk of collision, have developed a solution, but cannot execute yet due to an obligation to stay clear of another vessel or vessels you are not aware of. You just messed up their solution, that would have resulted in no collision, by your premature application of 17a. You were obligated to stand on, and didn't, due solely to your desire to maintain a minimum distance of arbitrary value that is not necessary at all to avoid collision. You got some 'splainin' to do. The truth of the matter is that if a collision occurs the stand on vessel can be faulted for applying either 17b too late, or under different circumstances 17a too soon.

[Lodesman]

Originally Posted by ramblinrod

Sorry, you don't get to change Colregs rules to suit your argument. When there is risk of collision established if I am stand on, I am obligated to hold course and speed until such point as the other vessel cannot maneuver in time to avoid collision by there maneuver alone. That is the rule. If I fail to stand on, while the other vessel had time to maneuver to avoid collision, and my action causes collision, I am in a heap o crap, because I violated Colregs; I turned or changed speed when I was supposed to hold course and speed.

Dockhead has explained the 4 stages, and Stu has pointed out to you rule 17 (a) and (b). Do you now acknowledge that your statement (I've bolded) is wrong?

Can you also explain how you think I've changed the Colregs to suit my argument?

Your 3rd request; my second answer - you've violated rule 8 and 17(b); see my explanation in my previous address to you.

[El Pinguino]

Originally Posted by markpierce

So, may I presume you sound your horn when leaving the berth as well as the marina?

Don't have a horn..... when I give my old MD17D a kick in the guts its warning enough to anyone in earshot.

Marina? ¿Qué 'marina'?