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Old 20-10-2017, 06:14   #511
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Lodesman View Post
That said, you can make an arrangement over VHF, to act contrary to the rules - it happens all the time, with "head-ons" agreeing to pass green to green, starboard offering a port turn and other such actions. If you call the tug on 13 and offer to stay out of the way, it would do a lot to alleviate the master's stress level.
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Originally Posted by David M View Post
I hear ship pilots agreeing frequently to pass starboard to starboard in narrow channels...by VHF.

They are not breaking the COLREG"s.
Giving this some more thought since David brought it up - I realized that what we see as normal in N America, is actually legitimized in the rules here:

Quote:
Canmods 34(l)
Notwithstanding this Rule and Rule 9, if positive mutual identification of the vessels has been made in the Canadian waters of a roadstead, harbour, river, lake or inland waterway, a vessel may use a bridge-to-bridge radiotelephone instead of the prescribed whistle signals to reach agreement in a meeting, crossing or overtaking situation. If agreement is not reached, then whistle signals shall be exchanged in a timely manner and shall prevail.
Quote:
US Inland 34(h)
A vessel that reaches agreement with another vessel in a head-on, crossing, or overtaking situation, as for example, by using the radiotelephone as prescribed by the Vessel Bridge-to-Bridge Radiotelephone Act (85 Stat. 164; 33 U.S.C. 1201 et seq.), is not obliged to sound the whistle signals prescribed by this Rule, but may do so. If agreement is not reached, then whistle signals shall be exchanged in a timely manner and shall prevail.
My feeling is that this probably happens in other jurisdictions as well, regardless of whether or not it's been codified. I can't honestly think of an occurrence in foreign(to me) waters, but it's not something that is likely to stick in the memory.
A lot of people fall back on rule 2(b) as a "get out of the Rules free" card - but it is not. It very clearly phrases the requirement to depart from the rules being contingent on it being 'necessary to avoid immediate danger', so it being 'convenient' is not a permissible reason within the Int'l Colregs. Perhaps some forumites outside Canada/US would care to chime in?
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Old 20-10-2017, 06:24   #512
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by StuM View Post
Have you ever actually sailed close to a large ship travelling at speed?

Even if you turn 90° to port when you clear the port transom corner, you will get no closer to the lead boat if you are doing 5 knots and it is doing 20 knots!

So with a ship bearing down on you at 20 knots and you doing 5 knots, you turn so that you are in his path for a longer period? Madness!
Of course that would be madness.

Of course if you turn 90 degrees to port, directly in the path, you will be run down by the following ship.

I didn't say to turn 90 degrees to port.

I said, "Turn to port as required to maintain the maximum distance from the following boat".

This will obviously be considerably less than 90 degrees.
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Old 20-10-2017, 07:03   #513
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by ramblinrod View Post
Of course that would be madness.

Of course if you turn 90 degrees to port, directly in the path, you will be run down by the following ship.

I didn't say to turn 90 degrees to port.

I said, "Turn to port as required to maintain the maximum distance from the following boat".

This will obviously be considerably less than 90 degrees.
I didn't say to turn 90 degrees to port either.
You said: " I will also turn to port as soon as I clear that corner, by the degree required to get no closer to the lead boat,..."

I pointed out the fallacy in that statement by saying that even if you turned 90 degrees to port you wouldn't "get closer to the lead boat". (Since it is moving away from you at 10 metres per second.)

As for "to maximum distance from the following boat" . It certainly will be less than 90 degrees. It will be 0 degrees.

You will "maintain the maximum distance from the following boat" by getting to a safe distance on the other side of his track as quickly as possible - i.e. by moving at 90 degrees to his path. .

It doesn't matter how many degrees you turn to port. Any turn will lengthen the time that you are in the immediate path of the oncoming ship which is closing on you at 10 metres per second...
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Old 20-10-2017, 07:23   #514
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by StuM View Post
Have you ever actually sailed close to a large ship travelling at speed?
I try not to as the wind goes all pear shaped

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Old 20-10-2017, 07:26   #515
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by ramblinrod View Post
But if I don't screw up, and come within 180 ft of the lead boat transom as planned, and stay as far as possible out of the way of the following boat,.
Let's look at what this 180ft (50 metres near enough) of the lead boat transom means in practice.

You are doing 2.5 m/s, the ship is doing 10 m/s.

5 seconds before reaching your planned position off his port transom, you need to be pointing directly at his stern and be 12.5 metres from it.

10 seconds before reaching your planned position, you need to be pointing directly at a point on his hull 50 metres from his stern and be 25 metres away from it.

Do you really think that is prudent seamanship?

I repeat my question, have you ever actually sailed close to a large ship traveling at speed?

Do you have any idea of what the conditions are like 12.5 metres from the stern of a ship traveling at 20 knots?
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Old 20-10-2017, 07:49   #516
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by StuM View Post

5 seconds before reaching your planned position off his port transom, you need to be pointing directly at his stern and be 12.5 metres from it.
I don't know where you are getting this from but it is incorrect. If I am crossing at 90 degrees, to be 180 ft off (nearest distance) his port transom corner, at any time before reaching this point, I am further away from him.

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Do you really think that is prudent seamanship?
Yes, as required to provide "safe distance" from this vessel and the bow of the following ship, which requires greater distance to be "safe distance".

Quote:
I repeat my question, have you ever actually sailed close to a large ship traveling at speed?
As I have declared in this thread several times, I repeat my answer, "Yes".

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Do you have any idea of what the conditions are like 12.5 metres from the stern of a ship traveling at 20 knots?
Yes. There is a wake, as there is with any boat, especially a 40 ft motor yacht not yet on plane. As I said, during the approach, I would evaluate those conditions. And as I said, the nearest I "may" be to the boat, depending on those conditions, is 180 ft (over 50 m).
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Old 20-10-2017, 08:01   #517
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Pete7 View Post
I try not to as the wind goes all pear shaped

Exactly. This is why one should keep maximum distance from the bow of the following boat in the scenario I posted.

In the scenario I painted, if the ship is 100 ft wide, and I was 180 ft from his port corner, if I kept my original course (90 degrees), by the time I passed the course of his starboard stern corner, I would be 400 ft from it.

If I turned to port to some degree, I could reduce that gap with the lead boat, while maintaining maximum distance from the following vessel by the time they pass my crossing course.
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Old 20-10-2017, 08:15   #518
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

Quote:
Originally Posted by StuM View Post
Let's look at what this 180ft (50 metres near enough) of the lead boat transom means in practice.

You are doing 2.5 m/s, the ship is doing 10 m/s.

5 seconds before reaching your planned position off his port transom, you need to be pointing directly at his stern and be 12.5 metres from it.

10 seconds before reaching your planned position, you need to be pointing directly at a point on his hull 50 metres from his stern and be 25 metres away from it.

Do you really think that is prudent seamanship?

I repeat my question, have you ever actually sailed close to a large ship traveling at speed?

Do you have any idea of what the conditions are like 12.5 metres from the stern of a ship traveling at 20 knots?
Clear at this point that the actual answer to all 3 questions is NO, despite claims to the contrary. Also clear what is motivating the resistance to acknowledging the obvious.

Back to your questions, here's some sense of what things might be like.

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Old 20-10-2017, 08:15   #519
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by ramblinrod View Post
Exactly my point, that many has been rejecting.

Thank you for acknowledging.

This is the Pucker Factor.

To me, cutting close (maybe to 180' from the transom, if I believe I can safely do so) behind the lead ship, to maintain max distance from the crossing the bows of the following ship, WILL BE acceptable RISK to me.

If I screw up, and cause a collision, OF COURSE I AM AT FAULT, the same as if I screw up and cause collision under any circumstance.

But if I don't screw up, and come within 180 ft of the lead boat transom as planned, and stay as far as possible out of the way of the following boat, I have maintained a "safe distance" UNDER THOSE CIRCUMSTANCES, according to Colregs.
No, you didn't get the point at all.

What is an acceptable risk to you -- in your subjective judgement, be it sound or unsound -- does not determine either whether a given maneuver is actually safe, or whether it is allowed under the COLREGS.

If what you were saying were true -- that it's perfectly OK as long as you don't actually have a collision -- would mean that I could run across a busy interstate as long as I didn't get run down, and that would be perfectly fine.

It would mean that all those Darwin Award winners would have been perfectly right, had they merely gotten away with it.

It would mean that you could run a jet ski at 50 knots right through a crowded anchorage, and that would be perfectly fine so long as you don't actually kill a swimmer or collide with anything.

Although the Rules don't set speed limits, running through a crowded anchorage at 50 knots is definitely not OK, and it's a serious violation of the Rules. Likewise, a 180 foot CPA with a big ship moving at 20 knots, is not OK. By the way, you could not even get within 180 feet of him, by the method you mentioned, for the reasons Stu pointed out. You don't understand the maneuver. The only way to get that close to his stern, sailing at 5 knots, would be to sail hard at his bow such that you barely fall short of getting run down, then run down his side and barely miss his quarter, and you simply could not set that up except by pure luck, with a big chance of just getting run down.


The Rules require you to take action "in ample time, and with due regard to the observance of good seamanship." They require you to pass at safe distances, and maintain safe speeds. You don't get to decide, according to your own wisdom or foolishness, or your own "pucker factor", what that is. Safe distances vary according to circumstances, and the Rules don't attempt to specify specific distances, but that doesn't mean that every cowboy gets to decide himself what that is. You are not only taking risks with your own life and property, you are taking risks with another vessel and the people on it. You might not be able to do a lot of damage to a 400 meter box ship with your little boat, but you can sure ruin a deck officer's career, including possible criminal charges, by impaling yourself on his bow and getting yourself killed.
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Old 20-10-2017, 09:41   #520
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Exile View Post
Clear at this point that the actual answer to all 3 questions is NO, despite claims to the contrary. Also clear what is motivating the resistance to acknowledging the obvious.

Back to your questions, here's some sense of what things might be like.

Nice video of a near miss. Just doing some guesstimates of distance traveled in time I would say that ship is doing 8 to 10 knots. 10 knots is about 17 feet per second.

The bow wave is rather small for a ship that size if it were going at a normal cruising speed.

I think that the voices say it all....
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Old 20-10-2017, 09:56   #521
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by ramblinrod View Post
Exactly. This is why one should keep maximum distance from the bow of the following boat in the scenario I posted.

In the scenario I painted, if the ship is 100 ft wide, and I was 180 ft from his port corner, if I kept my original course (90 degrees), by the time I passed the course of his starboard stern corner, I would be 400 ft from it.

If I turned to port to some degree, I could reduce that gap with the lead boat, while maintaining maximum distance from the following vessel by the time they pass my crossing course.
OK, but how would you get there? Can you draw it for us?
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Old 20-10-2017, 10:07   #522
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by evm1024 View Post
Nice video of a near miss. Just doing some guesstimates of distance traveled in time I would say that ship is doing 8 to 10 knots. 10 knots is about 17 feet per second.

The bow wave is rather small for a ship that size if it were going at a normal cruising speed.

I think that the voices say it all....
Did you notice the red sea buoy off to the big ship's starboard? (red-right-return in US waters). It probably had minimal room or time to maneuver and, as you pointed out, had probably been trying to slow for awhile. Maybe one of the big ship mariners on here will comment. But even if fully exonerated in the end, I wouldn't be surprised if there were negative implications for the guys on the bridge.
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Old 20-10-2017, 10:25   #523
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Lodesman View Post
Giving this some more thought since David brought it up - I realized that what we see as normal in N America, is actually legitimized in the rules here:

Quote:
Canmods 34(l)
Notwithstanding this Rule and Rule 9, if positive mutual identification of the vessels has been made in the Canadian waters of a roadstead, harbour, river, lake or inland waterway, a vessel may use a bridge-to-bridge radiotelephone instead of the prescribed whistle signals to reach agreement in a meeting, crossing or overtaking situation. If agreement is not reached, then whistle signals shall be exchanged in a timely manner and shall prevail.

Quote:
US Inland 34(h)
A vessel that reaches agreement with another vessel in a head-on, crossing, or overtaking situation, as for example, by using the radiotelephone as prescribed by the Vessel Bridge-to-Bridge Radiotelephone Act (85 Stat. 164; 33 U.S.C. 1201 et seq.), is not obliged to sound the whistle signals prescribed by this Rule, but may do so. If agreement is not reached, then whistle signals shall be exchanged in a timely manner and shall prevail.


My feeling is that this probably happens in other jurisdictions as well, regardless of whether or not it's been codified. I can't honestly think of an occurrence in foreign(to me) waters, but it's not something that is likely to stick in the memory.

A lot of people fall back on rule 2(b) as a "get out of the Rules free" card - but it is not. It very clearly phrases the requirement to depart from the rules being contingent on it being 'necessary to avoid immediate danger', so it being 'convenient' is not a permissible reason within the Int'l Colregs. Perhaps some forumites outside Canada/US would care to chime in?
Are you referring to the more specific waiver from the whistle (horn) requirement in the Inland rules when agreement is reached, or the general waiver from the Rules when agreeing via radio, at least in head-on crossings? Might have missed it, but the US Inland rules don't seem to be different.

Rule 14 - Head-on Situation

(a) ‹‹ Unless otherwise agreed ›› when two power-driven vessels are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision each shall alter her course to starboard so that each shall pass on the port side of the other.
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Old 20-10-2017, 10:49   #524
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Exile View Post
Are you referring to the more specific waiver from the whistle (horn) requirement in the Inland rules when agreement is reached, or the general waiver from the Rules when agreeing via radio, at least in head-on crossings? Might have missed it, but the US Inland rules don't seem to be different.

Rule 14 - Head-on Situation

(a) ‹‹ Unless otherwise agreed ›› when two power-driven vessels are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision each shall alter her course to starboard so that each shall pass on the port side of the other.
The "unless otherwise agreed" is added only in the US Inland rules; it doesn't exist in the Int'l colregs, nor for that matter, the Canadian rules. I'm not certain of the meaning of your question, but from what I gather you're asking - I think the Cdn and US rules intentionally imply that if you come to a solution via VHF, you do not have to follow the letter of the rules when head-on, crossing or overtaking. Otherwise regarding these situations, the rules tend to be rather prescriptive and don't offer a method to swap the responsibilities of 'stand on' and 'give way' or to alter port in rule 14.

I wonder if 'green to green' on a head-on (or other situations where the stand on vessel might choose to give way) are common outside of N America?
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Old 20-10-2017, 11:05   #525
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Lodesman View Post
The "unless otherwise agreed" is added only in the US Inland rules; it doesn't exist in the Int'l colregs, nor for that matter, the Canadian rules. I'm not certain of the meaning of your question, but from what I gather you're asking - I think the Cdn and US rules intentionally imply that if you come to a solution via VHF, you do not have to follow the letter of the rules when head-on, crossing or overtaking. Otherwise regarding these situations, the rules tend to be rather prescriptive and don't offer a method to swap the responsibilities of 'stand on' and 'give way' or to alter port in rule 14.

I wonder if 'green to green' on a head-on (or other situations where the stand on vessel might choose to give way) are common outside of N America?
OK, I missed this in the Amalgamated version of the Rules (Intl & Inland US) I was looking at:

Text unique to either Rules is shown within a dual columned, dual bordered table or within angle brackets: with the International Rules text within ‹ single angle brackets › and Inland Rules text within ‹‹ double angle brackets and italicized ››

Not your question I realize, but it seems odd that an exception for agreement via radio would be explicitly included in US Inland Rule 14 (head-on), but not the inland rules for overtaking (13) or crossing (15). As you say, maybe it is implied.
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