Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
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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. |
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: https://www.youtube.com/watch?v=1BisTlNcwDk https://www.youtube.com/watch?v=8sEdgHH9F10 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! |
Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
another nice video demonstrating this effect of a ship passing at really low speed:
https://www.youtube.com/watch?v=93mCiEDKMLw |
Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
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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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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
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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. |
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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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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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
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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. |
Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
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Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
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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? |
Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
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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. |
Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
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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. |
Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
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