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Old 25-08-2017, 09:29   #76
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by ramblinrod View Post
If crossing perpendicular astern, and suddenly becalmed, so what? It just makes the distance greater.
Indeed! Passing astern of a vessel which is much faster than you is quite safe for this reason. The old salts like to say that if you can see the transom (or stern light) of a faster vessel, then you are absolutely safe, and that is true.

If you are in open water and you set up to cross astern from an appropriate distance -- 5 miles or more -- you can still get in trouble, though, if you end up going faster than you planned or other errors kick in, so you still need some kind of margin of error. But I agree with you that it is much less than if you pass ahead. A few cables is generally safe enough as long as you stay alert and ready to correct if something goes off (and I'm sure you'd be doing that anyway right?).

But as a matter of courtesy, at least, it is still better to stay a mile away from ships in open water even if passing behind. As some of the commercial mariners in here have said -- standing orders will likely require the OOW to get the master out of his bed for any pass closer than 1 mile.
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Old 26-08-2017, 06:07   #77
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

I have been looking into another (possibly) important factor. Apart from propelling the vessel, a propellor also sucks water in front of it and pushes it out at it's back. That means that, in front of the propellor, the water level is lowered and behind it it is raised. I image it looks like a ball in a stretched sheet.

To see the effect for slow cruising large vessels, see youtube:



There are videos on youtube of ships and jet skis being "sucked" into large vessels. Actually, it is not so much "sucking" as is is "falling", somewhat like riding doen a wave. Imagine again the sheet with a ball in the middle (the way gravity is explained on TV) and you will see that any area in front of the propellor slopes into the propellor. Th closer you get, the steeper the slope.

That means that, als you get closer to the vessel, you fall towards it more and more. Now I guesstimate that, as you get further away, the effect drops squared. But it also means that, if you get close, you'r in a **** load of trouble. And many videos on Youtube seem to confirm that. It's nearly impossible to escape if you pass the "event horizon".

That means that missing a 400ft beam ship is just not enough. Passing it at 50ft is going to set you off down the slope! Happy skiing!
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Old 26-08-2017, 07:13   #78
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

another nice video demonstrating this effect of a ship passing at really low speed:
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Old 26-08-2017, 09:26   #79
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by JPA Cate View Post
Dockhead,

Trig may be basic math to you, but I never had anything beyond high school algebra. Now, my guess is that many, maybe even most of the men here have that knowledge, but unless you propose a Trig for Dummies class here on CF, can you show us maths ignoramuses another way to do this, please?
Google "radian rule". You can estimate what course you need to take to achieve a desired passing distance, based on the information you get from radar, AIS or reasonable estimations. For example, you spot a small coastal freighter about 5 miles ahead and take a compass bearing. As it closes to about 3 miles, with the bearing steady, you've determined (either from the electronics or estimating the range and timing the closing rate) that the TCPA (time to CPA) will be 10 mins. If your speed is 6 kts, then you know that CPA position is 1 mile ahead of you (10 mins at 6 kts= 1nm). You can plot an imaginary X in the ocean at that point. If he maintains course and speed, the freighter will be at that X in 10 mins. Radian rule tells us that if you were to alter course be 6º you would open the distance on that X by one-tenth of your current distance from it. So 1/10 of 1nm is 1 cable or 200 yards. If you wanted to avoid the ship by 500 yards, you would need to change your course by 15º. If you wanted 1/2 nm separation, you would need to turn 30º, and so forth.
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Old 27-08-2017, 07:29   #80
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Lodesman View Post
Google "radian rule". You can estimate what course you need to take to achieve a desired passing distance, based on the information you get from radar, AIS or reasonable estimations. For example, you spot a small coastal freighter about 5 miles ahead and take a compass bearing. As it closes to about 3 miles, with the bearing steady, you've determined (either from the electronics or estimating the range and timing the closing rate) that the TCPA (time to CPA) will be 10 mins. If your speed is 6 kts, then you know that CPA position is 1 mile ahead of you (10 mins at 6 kts= 1nm). You can plot an imaginary X in the ocean at that point. If he maintains course and speed, the freighter will be at that X in 10 mins. Radian rule tells us that if you were to alter course be 6º you would open the distance on that X by one-tenth of your current distance from it. So 1/10 of 1nm is 1 cable or 200 yards. If you wanted to avoid the ship by 500 yards, you would need to change your course by 15º. If you wanted 1/2 nm separation, you would need to turn 30º, and so forth.
Thanks very much. All these traditional skills are really useful. All but lost in this age of video game navigation.
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Old 28-08-2017, 19:10   #81
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

Better watch out people,according to Dockhead there is no such thing as "right of way" and it seems his views are the only acceptable ones. Most of the time the posts seem to suggest 2 vessels meeting which should really be easy to deal with. In reality the problems arise when there are many boats involved, and it seems to me that little thought is given to the fact that masters of merchantmen have to be like good chess players working out 5 or more moves ahead.Follow the Regs but make your moves early and all is well I say.
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Old 28-08-2017, 19:53   #82
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by robbievardon View Post
Better watch out people,according to Dockhead there is no such thing as "right of way" and it seems his views are the only acceptable ones. Most of the time the posts seem to suggest 2 vessels meeting which should really be easy to deal with. In reality the problems arise when there are many boats involved, and it seems to me that little thought is given to the fact that masters of merchantmen have to be like good chess players working out 5 or more moves ahead.Follow the Regs but make your moves early and all is well I say.
Robbie, I don't think DH said that but tried to change the mindset of those who look at right of way as a black and white issue

Many people do not fully understand the intent of
Rule 17
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.
and
Rule 2
Responsibility
(a) Nothing in these Rules shall exonerate any vessel, or the owner, master, or crew thereof, from the consequences of any neglect to comply with these Rules or of the neglect of any precaution which may be required by the ordinary practice of seamen, or by the special circumstances of the case.
(b) In construing and complying with these Rules due regard shall be had to all dangers of navigation and collision and to any special circumstances, including the limitations of the vessels involved, which may make a departure from these Rules necessary to avoid immediate danger.
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Old 28-08-2017, 20:28   #83
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

Pelagic,unfortunately my last post was based on postings from another thread on the C regs in which he made this comment. Unfortunately I tend to dump old thread posts so can't give you the link, perhaps you could pose the question to him on this thread?
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Old 28-08-2017, 20:44   #84
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

Pelagic, you could try http//cruiserforums/f57/thread-for-basic-colregs-questions-189778-new-post.html/ that is the best I can do as it seems I have been banned from that thread,so cannot quote from it. obviously asked the wrong questions or posed the wrong answers!!!
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Old 30-08-2017, 21:49   #85
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Pelagic View Post
Robbie, I don't think DH said that but tried to change the mindset of those who look at right of way as a black and white issue

Many people do not fully understand the intent of
Rule 17
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.
and
Rule 2
Responsibility
(a) Nothing in these Rules shall exonerate any vessel, or the owner, master, or crew thereof, from the consequences of any neglect to comply with these Rules or of the neglect of any precaution which may be required by the ordinary practice of seamen, or by the special circumstances of the case.
(b) In construing and complying with these Rules due regard shall be had to all dangers of navigation and collision and to any special circumstances, including the limitations of the vessels involved, which may make a departure from these Rules necessary to avoid immediate danger.
I think the whole issue at hand, is the assumption that everyone who knows colregs, believes "right-of-way" to mean something different than "stand-on".

I don't believe this is true.

When referring to collision avoidance, I use "right-of-way" and "stand-on" as synonyms.

I have yet to meet a single person who knows colregs, who on a starboard tack, would do anything but "stand-on", when told they have "right-of-way" over a port tack boat on a collision course.

Why use another term than the defined term in Colregs? Why ever use different words to represent the exact same thing? Every language on the planet is full of them. Why? Variety is the spice of life.
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Old 30-08-2017, 22:19   #86
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Why use another term than the defined term in Colregs? Why ever use different words to represent the exact same thing? Every language on the planet is full of them. Why? Variety is the spice of life.
And a god-send to lawyers.
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Old 31-08-2017, 01:55   #87
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by ramblinrod View Post
. . . I have yet to meet a single person who knows colregs, who on a starboard tack, would do anything but "stand-on", when told they have "right-of-way" over a port tack boat on a collision course.

Why use another term than the defined term in Colregs? Why ever use different words to represent the exact same thing? Every language on the planet is full of them. Why? Variety is the spice of life.
OK, I respect that, and your idea is well-stated.

But do you really think that this hypothetical person, being told he has "right of way", really knows that he is NOT free to maneuver?

"Right" means -- right -- perogative, you can do what you want -- continue on, or stop, or turn, or whatever. Standing on is just the opposite of that.

Does that really not bother you at all? I'm not going to tell you what should or should not bother you. But do you understand, at least, why it bothers us?
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Old 31-08-2017, 03:39   #88
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Dockhead View Post
OK, I respect that, and your idea is well-stated.

But do you really think that this hypothetical person, being told he has "right of way", really knows that he is NOT free to maneuver?

"Right" means -- right -- perogative, you can do what you want -- continue on, or stop, or turn, or whatever. Standing on is just the opposite of that.

Does that really not bother you at all? I'm not going to tell you what should or should not bother you. But do you understand, at least, why it bothers us?
OK, one final attempt to state my opinion as plainly as I can, then I'll shut up about this specific issue.

The key point which I stress when teaching new sailors is that they have no rights under COLREGs - only obligations. Using the term "right of way" immediately conflicts with that fundamental concept and can impart the wrong message.

There is one simple, officially recognised phrase which reinforces the correct message - "stand on"

It doesn't matter if the person using the expression understands that when they say "right of way" they actually mean "obligation to stand on", The problem arises when a less knowledgeable sailor hears it used and believes that he has does indeed have "right" to manoeuver as he wishes.

Ergo, it would be safer for everyone on the water if we all stopped using the misleading expression.
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Old 31-08-2017, 07:01   #89
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by Dockhead View Post
OK, I respect that, and your idea is well-stated.

But do you really think that this hypothetical person, being told he has "right of way", really knows that he is NOT free to maneuver?

"Right" means -- right -- perogative, you can do what you want -- continue on, or stop, or turn, or whatever. Standing on is just the opposite of that.

Does that really not bother you at all? I'm not going to tell you what should or should not bother you. But do you understand, at least, why it bothers us?
First, I object to the person ("standing on" when advised they have right of way) being referred to as "hypothetical", any more so than the one, when told "right-of-way" would do anything different but "stand on", and suddenly start evoking "rights" they clearly don't have.

Again, in my experience, if someone knows colregs, and is told they have "right-of-way" on starboard tack, they would know that to mean the same thing as "stand-on", and that is exactly what they would do.

Being told they have "right-of-way" to someone who knows colregs, does not invoke some crazy knee jerk reaction to start exercising "rights" they don't have.

Similarly, if someone is at the wheel who does not know colregs, it doesn't matter whether they are told to "stand-on" or they have "right-of-way", THEY DON'T KNOW WHAT THAT MEANS. The immediate reaction is, "What does that mean?" They will not start making guesses with someone's expensive vessel and crews safety in their hands.

If they are that ignorant to colregs, it would be wise for the person advising to ensure they know what either term means in that situation.

Using the regulation defined term "Stand-On", with someone who does not understand the underlying regulation, means absolutely nothing to them.

I completely disagree that anyone in their right mind, would suddenly start trying to invoke any kind of real or fictitious land right or suddenly turn toward someone trying to avoid them, because the other does not have "right-of-way". This is the most flagrant "strawman" argument of this whole discussion.

I agree that when teaching the regulations or writing an exam, it is best to use the most proper terms.

However, when talking with buds, who know the regs, one can use "stand-on" and "right-of-way" synonymously, and it makes no freaking difference whatsoever.

The next discussion will use one of about 1000 different terms to represent the attractive single lady at the end of the bar, and everyone will know that to mean "unwed female homo sapien". To insist they use that term, instead of any of the others that mean the exact same thing to everyone, is ludicrous.

We could get grammar police in here to jump all over everyone who doesn't apply it perfectly (according to them). Wouldn't that be fun?

Again, nitpicking on the words commonly used, because they are not the specific words used in the regulations, when applied in a context that we all know what it means, is just a waste of bandwidth.

When on a starboard tack, anyone who does not know what to do, with respect to a port tack boat on a collision course, should not be in control of the vessel. If they should be in control of the vessel, either term may be used synonymously, without detrimental effect.

To insist others use the exact term defined in the regulations every reference to the situation, in a cruisers forum, is just someone with too much time on their hands, attempting to make themselves feel superior by "correcting" (belittling) others, IMHO.
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Old 31-08-2017, 07:18   #90
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

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Originally Posted by ramblinrod View Post
First, I object to the person ("standing on" when advised they have right of way) being referred to as "hypothetical", any more so than the one, when told "right-of-way" would do anything different but "stand on", and suddenly start evoking "rights" they clearly don't have.

Again, in my experience, if someone knows colregs, and is told they have "right-of-way" on starboard tack, they would know that to mean the same thing as "stand-on", and that is exactly what they would do.

Being told they have "right-of-way" to someone who knows colregs, does not invoke some crazy knee jerk reaction to start exercising "rights" they don't have.

Similarly, if someone is at the wheel who does not know colregs, it doesn't matter whether they are told to "stand-on" or they have "right-of-way", THEY DON'T KNOW WHAT THAT MEANS. The immediate reaction is, "What does that mean?" They will not start making guesses with someone's expensive vessel and crews safety in their hands.

If they are that ignorant to colregs, it would be wise for the person advising to ensure they know what either term means in that situation.

Using the regulation defined term "Stand-On", with someone who does not understand the underlying regulation, means absolutely nothing to them.

I completely disagree that anyone in their right mind, would suddenly start trying to invoke any kind of real or fictitious land right or suddenly turn toward someone trying to avoid them, because the other does not have "right-of-way". This is the most flagrant "strawman" argument of this whole discussion.

I agree that when teaching the regulations or writing an exam, it is best to use the most proper terms.

However, when talking with buds, who know the regs, one can use "stand-on" and "right-of-way" synonymously, and it makes no freaking difference whatsoever.

The next discussion will use one of about 1000 different terms to represent the attractive single lady at the end of the bar, and everyone will know that to mean "unwed female homo sapien". To insist they use that term, instead of any of the others that mean the exact same thing to everyone, is ludicrous.

We could get grammar police in here to jump all over everyone who doesn't apply it perfectly (according to them). Wouldn't that be fun?

Again, nitpicking on the words commonly used, because they are not the specific words used in the regulations, when applied in a context that we all know what it means, is just a waste of bandwidth.

When on a starboard tack, anyone who does not know what to do, with respect to a port tack boat on a collision course, should not be in control of the vessel. If they should be in control of the vessel, either term may be used synonymously, without detrimental effect.

To insist others use the exact term defined in the regulations every reference to the situation, in a cruisers forum, is just someone with too much time on their hands, attempting to make themselves feel superior by "correcting" (belittling) others, IMHO.
OK, well, so that you know, I don't think that too many people on here argue for correct terminology in order to "feel superior by 'correcting'" other people. So that you know -- the term we've been discussing here bothers some of us simply because it expresses a persistent and widespread misunderstanding -- not one you suffer from! But many do. Believe it or not, some people just genuinely want to share knowledge and help others understand something better, with no other motive than that.
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