Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

[ramblinrod]

Originally Posted by Exile

Funny, I've only read high compliments from DH about you.

Respectfully, I don't think you are correct that DH's first post can only be read as a way to humiliate Rod or other recreational sailors who make mistakes which give rise to WAFI comments from commercial mariners. Maybe there's some history here I'm not aware of, but I thought the initial post was more about mistakes that are often made by recreational sailors generally, and the use of Rod's rather extreme examples from the prior thread were a way for DH to highlight what he wanted the new thread to focus on. But to the extent it could be interpreted in the way you and apparently Rod did, then DH repeatedly stated that was not his intent and also repeatedly apologized. I don't recall him spending much time arguing over it, and he's been trying to keep to the merits ever since, even to the point of indulging Rod on his rather far-fetched scenarios but arguing his points based on math & logic rather than personalities. And I don't know how DH honestly admitting a mistake in his calculations is consistent with trying to be the smartest guy in the room or overly "clever" as you say.

So I guess I'm not sure why you (and Rod) are still beating these drums over 800 posts later? In Rod's case, whatever actual or perceived humiliation he may have suffered has long since been explained and apologized for. The frustration and at times contempt Rod has engendered since is solely of his own making. Surely you can see the distinction.

Others may not see in this what I see. That's OK.

They may have blinders on, don't care because they are not the brunt of the attack, pile on so hopefully they won't be, or are just completely oblivious to back-handed comments.

Saying one is sorry, or that no harm is intended, while repeatedly trying to kick someone in the gahones, is not very sincere IMHO.

My Dad taught me, "Never start a fight, but always be the last one standing."

So I tend to stand my ground when confronted by a bully, and do my best to land a punch for everyone received.

To the offender(s), every time you stand up and take another swipe, I will knock you down, again, and again, and again.

For God's sake, all you have to do to stop my retaliation, is just stop throwing punches.

[Lodesman]

Originally Posted by ramblinrod

As for the optimum angle to turn to port, my estimate based on speeds, (I didn't bother to perform the actual calcs) was around 15 degrees.

I knew this would not increase distance from the following ship much (but a small distance more ahead of a fast moving ship, with no down side, is better than none). However, because I knew the distance away gained was minimal, I didn't bother to perform the calcs, and include that in my analysis.

You are completely delusional. And now it comes that you knew all along that 15º was optimal and it wouldn't matter much - you aren't fooling anyone; your posts said all that needed saying. You don't have a clue.

[QUOTE=ramblinrod;2510292]Only two ways to figure it out....
....Reeeeeally?
I hate to rattle your world but...
The sailboat starts out, with bow perpendicular to, and 180 ft away from the port stern corner of the lead ship.
This places the sailboat 1.25 nm forward of the following ship.
At 90 degrees from the ships course, the sailboat has to travel 320 ft, to cross the original 180 ft to the port course line, the 100 ft beam of the ship, and clear the starboard course line with it's 40 ft length, in advance of the following ship.
At 5 knots this takes 0.1017 hours.
In that time the ships will have advanced .213 nm.
Take the original distance the sailboat is forward of the following ship, and subtract the distance the following ship travels in the time for the sailboat's transom to cross completely, and we have 1.25 nm - 0.213 nm = 1.037 nm
This calculation does not take into account:
1. The shape of vessels (for simplicity and due to variation in vessel design)
2. The beam of the sailboat, (negligible influence, and just makes crossing close to the lead ship even more important).
3. The sailboat turning to port slightly to maximize distance from the following ship. (Limited benefit for the 180 ft CPA but increasingly important for the longer CPAs proposed).
Are you kidding me, after all of this, none of you have this figured out yet?
A guy sailing a small sailboat on Lake Ontario with no formal navigation training, using simple D = S x T calcs, figures this out in seconds, and outwits the self-proclaimed armchair navigation pros all over the world, now having weeks to figure it out using plotting boards and then professing to need simulators (yet to be created) to be able to "visualize" it?
Only 2 ways to figure it out, you say?
Too funny!
Consider yourself educated!
:bigg rin:: biggrin:
PS, I think I'll stick with my way thanks. You know, the one where I didn't run into the following ship, vs using your methods where you did.
hee, hee, hee, hah, hah, hah, ho, ho, ho.[/QUOTE]

You actually believe you are no longer in front of the ship astern at this point?!?
This is absolutely laughable. I mean rolling on the floor laughing my arse off - laughable!

I mean, just the thought of Mister Get-your-head-out-of-the-electronics punching away on a calculator nearly made me spit my Cab all over my keyboard. Hilarious!

I know you don't answer any of my questions, but how about you do me a solid and just this once, prove what a high-PF super-brain you are and tell me - how many degrees are you from the heading of the ship astern, when you profess to no longer be ahead of that ship (at the end of your 320' journey)?

I challenge you, nay double-dog dare you to answer just one question before I give you the answer.

[Exile]

Originally Posted by ramblinrod

Others may not see in this what I see. That's OK.

They may have blinders on, don't care because they are not the brunt of the attack, pile on so hopefully they won't be, or are just completely oblivious to back-handed comments.

Saying one is sorry, or that no harm is intended, while repeatedly trying to kick someone in the gahones, is not very sincere IMHO.

My Dad taught me, "Never start a fight, but always be the last one standing."

So I tend to stand my ground when confronted by a bully, and do my best to land a punch for everyone received.

To the offender(s), every time you stand up and take another swipe, I will knock you down, again, and again, and again.

For God's sake, all you have to do to stop my retaliation, is just stop throwing punches.

The retaliation you speak of and your Dad advised may be effective at maintaining your credibility in response to a personal attack, and certainly if that attack was physical. But that credibility is lost if the same sort of response is used to counter an attack on your ideas. Merely hitting back for the sake of hitting back doesn't work in a more intellectual debate where the hits need to be honest, logical and sincere. But as you point out, we see things differently and I see more challenges to your ideas vs. attacks on your person. So be it.

[evm1024]

Originally Posted by ramblinrod

Others may not see in this what I see. That's OK.

They may have blinders on, don't care because they are not the brunt of the attack, pile on so hopefully they won't be, or are just completely oblivious to back-handed comments.

Saying one is sorry, or that no harm is intended, while repeatedly trying to kick someone in the gahones, is not very sincere IMHO.

My Dad taught me, "Never start a fight, but always be the last one standing."

So I tend to stand my ground when confronted by a bully, and do my best to land a punch for everyone received.

To the offender(s), every time you stand up and take another swipe, I will knock you down, again, and again, and again.

For God's sake, all you have to do to stop my retaliation, is just stop throwing punches.

My dad taught me the same thing. But he went further. He taught me that I should never let defense become offense. Looks like you missed out on a few lessons.

He also taught me that arguments even spirited arguments are just ideas. They are won on concepts, facts and truth. And oh so often lost when your emotions rule your thoughts.

Your emotions cloud your thinking on this. You have been offensive and a bully. You took it very personally.

But, this is not about you.

This is about how really difficult and extremely stupid it is to attempt to pass 180' behind a ship doing 20 kts.

It is really too bad that when you read that an idea is stupid you think I am stupid. And therefore you hit and hit and hit until all who oppose you stay down.

Pathetic.

And yet again you are asked a question and will not answer it. It is not my question but no matter:

I know you don't answer any of my questions, but how about you do me a solid and just this once, prove what a high-PF super-brain you are and tell me - how many degrees are you from the heading of the ship astern, when you profess to no longer be ahead of that ship (at the end of your 320' journey)?

It just goes to show that you are unable to debate the merits of an idea and totally blind to any reality but your own.

The question is very cogent. Let me put it more clearly for you -

When you are (in your own head) no longer ahead of the following ship. What do the mariners on the bridge of that ship see?

[Dockhead]

Originally Posted by ramblinrod

Oh please, please, please.

Don't go away now.

I was hoping you would take even more time (what's it been now 2 weeks?), and plot our solutions out and post it here, to demonstrate to everyone your superior navigation skills.

Please, post it as a quote attachment, to my post showing me being just over 1 nm ahead of the following ship, and you being plastered into the starboard bow (with your 3 cable CPA proposal).

Got the guts?
:

Rod, this is a thread was intended for fairly advanced collision avoidance subjects.

What is CPA and how to calculate it is a 101 level question. Unlike some people, I'm not in this thread to score points. You will find other people who can explain it to you. I don't need to prove anyone that I attended the first class in navigation.

I'm just struggling to understand WHY you would start this argument. Do you really suppose that everyone is so ignorant? Do you never doubt that someone might actually know something about this? Lodesman for example is a professional navigator and ship's master with decades of experience.


As to "plastered on the bow" -- according to your -- incorrect -- way of calculating "CPA", passing two or even three cables from the ship ahead would give you a safe result -- 3 cables in the worst case as you posted yourself earlier in the thread.

So you aren't even applying your own method. This is surrealistic. Let's take the argument about how CPA is calculated to another thread on the off chance that this one is not irredeemably ruined already.

If anyone wants to discuss what CPA is and how to calculate it, there's a thread here: http://www.cruisersforum.com/forums/...pa-193139.html. I won't be participating.

[Dockhead]

Originally Posted by ramblinrod

. . .To the offender(s), every time you stand up and take another swipe, I will knock you down, again, and again, and again.

For God's sake, all you have to do to stop my retaliation, is just stop throwing punches.

OK, now it's all in the open. There were never any actual ideas involved -- all these posts are just "punches".

And every time someone tried to explain something to you, that was a "punch" too.

You never understood what any of this was about, but OK! I won't answer any more of your posts, and we're good, right?

[Dockhead]

Originally Posted by Exile

The retaliation you speak of and your Dad advised may be effective at maintaining your credibility in response to a personal attack, and certainly if that attack was physical. But that credibility is lost if the same sort of response is used to counter an attack on your ideas. Merely hitting back for the sake of hitting back doesn't work in a more intellectual debate where the hits need to be honest, logical and sincere. But as you point out, we see things differently and I see more challenges to your ideas vs. attacks on your person. So be it.

Exactly. Many of these discussions work like this -- we express something we know or think we know, for the purpose of either sharing some knowledge, or finding out that there's more to it than we thought, or that we made a mistake. All three of those possible outcomes are good, especially the last one.

So if I say something which is wrong, then I hope to get called out about it. If I don't immediately see it, there might be some argument, but I'm careful to keep my mind open, and if I'm wrong, I soon see it. That's learning -- one of the main reasons I come on here. Happens to me almost every day -- whatever you know about any given subject, in Cruisers' Forum someone will come along who knows 10x more. It's fantastic.

Some people consider having their ideas challenged to be a personal insult, and will dig in and fight to avoid appearing to be wrong. That's really too bad, and their loss. How to explain that there is no shame in being wrong? And most people who disagree with you, are not actually "punching" you?

[Dockhead]

Originally Posted by El Pinguino

I think you are confused.. Dockhead is Zaphod...

I refer you back to post #1 in which Dockhead effectively called someone else a dickhead..... 'look at this foolish person ... I'm going to put him in a book I am going to write and show the world how foolish he is and how clever I am'

How exactly would you respond if he had said 'look at this foolish chap EVM1024'..... would you have just rolled over and let it pass or would you have stood your ground?. . .

It is true that I am a pedant -- runs in the family -- and you don't have to like my manner. But what you have written here is not true. I get no pleasure from making others look foolish, and I actually try hard not to do it. I have probably the thickest skin of anyone on here, but this hurts, Ping. You can say I'm wrong (as I am, all the time), you can say I'm stupid even (and I am, sometimes) -- that doesn't bother me at all. But that I would try to make someone look stupid, in order to aggrandize myself? Wow.

This thread was started purely because the problem was interesting. It's something I wanted to understand better, and something I thought others would find rewarding to discuss. Rod said some things which you and I and everyone on here know were wrong. There's no shame in that; we've all been there at one time or another. He stubbornly defended those ideas. Well, there's no shame in that, either -- it's his loss that he didn't listen to any of the helpful things people were telling him, but still it forced us to think through things which normally we take for granted that everyone understands -- that's useful, too. He took it personally, and started to "throw punches" -- that's where it went wrong, and that's just too bad for everyone.

Now you may be thinking -- why do I care about all these ideas? You guys overcomplicate everything; I just want to sail. Sailing and ideas are two different things. Sailing and talking about sailing are two different things. Most of us will never face such a crossing. Well, please don't begrudge it to those of us, who want to dig deeper into it. For some of us it's just interesting.

[transmitterdan]

So let me see if I have this right. When someone says something that we believe to be wrong we can't say so because that offends the originator of the wrong idea. Are we supposed to just let them go on believing they are right? When they or some unsuspecting reader tries to implement the wrong idea and gets killed who feels bad then? This whole notion of "don't offend anybody" is a recent disease in our culture that has to be one of the craziest things ever.

[Dockhead]

Originally Posted by transmitterdan

So let me see if I have this right. When someone says something that we believe to be wrong we can't say so because that offends the originator of the wrong idea. Are we supposed to just let them go on believing they are right? When they or some unsuspecting reader tries to implement the wrong idea and gets killed who feels bad then? This whole notion of "don't offend anybody" is a recent disease in our culture that has to be one of the craziest things ever.

Trying not to offend other people is elementary good manners, and not a "recent disease".

We should be able to have a vigorous debate without offending each other, which really spoils the fun, and kills the benefit of the whole exercise.

But a basic condition for this is that people need to be looking to get something healthy out of these discussions. Once somebody starts to want to "score points" or "knock down" someone, the whole process is perverted. Ideas start to get defended not because they are right, but because they are mine. Truth is the first victim.

Of course wrong ideas should be identified as such. What's the purpose of discussing anything, if not to try to better understand the issues, to figure out what actually is right? It just has to be done with respect towards the person who has said them, and also a person expressing some idea needs to be prepared to have people attempt to shoot it down, if it's wrong.

[El Pinguino]

Originally Posted by Dockhead

It is true that I am a pedant -- runs in the family -- and you don't have to like my manner. But what you have written here is not true. I get no pleasure from making others look foolish, and I actually try hard not to do it. I have probably the thickest skin of anyone on here, but this hurts, Ping. You can say I'm wrong (as I am, all the time), you can say I'm stupid even (and I am, sometimes) -- that doesn't bother me at all. But that I would try to make someone look stupid, in order to aggrandize myself? Wow.
........

If you aim was not to make others look ( possibly ) stupid it would have been best to not have named names but to have started the thread thus 'Some people think that the following is a good manuoever... however I do not... for the following reasons...'

So, instead we have over 800 posts and at a very conservative estimate over 80,000 words and we have achieved what exactly? Not much that I can see....
Is anybody in the future going to use this thread as a source of information? I doubt it... I would be more inclined to read 'War and Peace' in the Albanian edition....

The secret is to be able to express yourself in a concise manner and in such a manner that the class does not rise in revolt....

Meanwhile back on the offensive front..

'Two miles is widely considered and widely taught to professionals as a good minimum CPA when traffic allows it. You should know that. By now this is part of the Ordinary Practice of Seamen, Rule 2.
'

... I found that extremely offensive....

[Dockhead]

Originally Posted by El Pinguino

I. . .
Meanwhile back on the offensive front..

'Two miles is widely considered and widely taught to professionals as a good minimum CPA when traffic allows it. You should know that. By now this is part of the Ordinary Practice of Seamen, Rule 2.
'

... I found that extremely offensive....

Well, I apologize for that. Certainly no offense or disrespect whatsoever was intended -- I think you know from our years of interaction on here that I hold you in the highest respect.

I guess it was badly expressed, but I was simply responding to your post saying "who keeps 2 miles CPA's?". By "you should know that", I meant "I'm quite certain that you are aware." In fact, I could have -- and should have -- said "as you know far better than I do."

[transmitterdan]

I think my point is that we are all allowing ourselves to become offended much too easily. Offending someone requires a two-way deal. The person who is offended has much more control over this than the person who has supposedly offended. All I am saying is let's all try not to jump into the "I have been offended" camp so easily. Hopefully that sentiment is neither controversial nor offensive.

[Exile]

Originally Posted by transmitterdan

So let me see if I have this right. When someone says something that we believe to be wrong we can't say so because that offends the originator of the wrong idea. Are we supposed to just let them go on believing they are right? When they or some unsuspecting reader tries to implement the wrong idea and gets killed who feels bad then? This whole notion of "don't offend anybody" is a recent disease in our culture that has to be one of the craziest things ever.

Originally Posted by Dockhead

Trying not to offend other people is elementary good manners, and not a "recent disease".

Agreed, although as you go on to say in so many words, if intentions are sincere then it's also good manners for the other party not to take personal offense. I'm not sure this is exactly what's going on here, but generally speaking there does seem to be a more recent emphasis on people being "offended" by all manner of things, and to the extent it is interfering with truth it is unhealthy and thus appropriately called a "recent disease." Imho that is. Everyone has different sensibilities, but speaking personally I can't think of anything more "offensive" than the type of distortion, obfuscation, and ignoring of other peoples' posts we've endured here. It only seems to serve one person's very personal needs at the expense of the ideas most would prefer discussing rationally.

We should be able to have a vigorous debate without offending each other, which really spoils the fun, and kills the benefit of the whole exercise.

But a basic condition for this is that people need to be looking to get something healthy out of these discussions. Once somebody starts to want to "score points" or "knock down" someone, the whole process is perverted. Ideas start to get defended not because they are right, but because they are mine. Truth is the first victim.

Of course wrong ideas should be identified as such. What's the purpose of discussing anything, if not to try to better understand the issues, to figure out what actually is right? It just has to be done with respect towards the person who has said them, and also a person expressing some idea needs to be prepared to have people attempt to shoot it down, if it's wrong.

Originally Posted by El Pinguino

If you aim was not to make others look ( possibly ) stupid it would have been best to not have named names but to have started the thread thus 'Some people think that the following is a good manuoever... however I do not... for the following reasons...'

Perhaps DH could have left Rod's name out of it, but it probably would have been clear which poster he was talking about because of the content of Rod's posts. Who's responsible for that? And why would this be "humiliating" for Rod if he went on to defend his positions for this entire thread, is now gloating about how "correct" they have proved to be, and is rudely berating everyone else's opinions as incompetent and even life threatening? If Rod was humiliated, then it was because what he wrote didn't make sense as opposed to who he is. There's no shortage of otherwise competent people who are obviously not fools, but who nevertheless manage to act foolishly at times.

So, instead we have over 800 posts and at a very conservative estimate over 80,000 words and we have achieved what exactly? Not much that I can see....
Is anybody in the future going to use this thread as a source of information? I doubt it... I would be more inclined to read 'War and Peace' in the Albanian edition....

The secret is to be able to express yourself in a concise manner and in such a manner that the class does not rise in revolt....

Meanwhile back on the offensive front..

'Two miles is widely considered and widely taught to professionals as a good minimum CPA when traffic allows it. You should know that. By now this is part of the Ordinary Practice of Seamen, Rule 2.
'

... I found that extremely offensive....

Why take offense when you can respond the way you did, which in turn led to some discussion about potential distinctions that might be drawn btwn sailing in remote areas of the S. Atlantic vs. extremely busy waterways such as the English Channel? Or possible distinctions based on crossings btwn big ships and small boats? I interpreted DH's comment about leaving two miles as related to what was taught and maybe considered good practice by pro mariners. Maybe he was wrong, or maybe this is limited to areas such as the English Channel? Or maybe this is just the opinion of the pros he talked to and others like yourself have a different opinion? The Rules don't specify after all, and Rule 2's "ordinary practice of seaman" clause implies an objective standard that might be interpreted as leaving sufficient distance for a safe and orderly crossing given the body of water & traffic density.

I can understand how you & Rod could take offense at times even if others would not, and don't question your sincerity. But whatever DH did or didn't do to mitigate you & Rod's personal offense doesn't justify the offense subsequently meted out to the ideas that were being discussed & analyzed.

[evm1024]

Originally Posted by Lodesman

SNIP %< %< %<

I know you don't answer any of my questions, but how about you do me a solid and just this once, prove what a high-PF super-brain you are and tell me - [B]how many degrees are you from the heading of the ship astern, when you profess to no longer be ahead of that ship (at the end of your 320' journey)?

SNIP %< %< %<

The 320' of motion of the boat takes 37.9 seconds. In that time the ship astern has traveled (37.9 * 33.76) 1279.5'. So at that point the ship astern is now (1.25 nm or 7595' - 1279.5) 6315.5' from the boat.

The stern of the boat is even with the path of the stb sides of the ships and thus 50' from the centerline of the path. The boat is 40' long so the boat traveled that distance to clear the sides of the ships and thus the center of the boat is (50+40+20) 110' from the centerline of the ships path.

The angle seen from the ship astern to the center of the boat is (arctan(110/6315.5)) 0.9978 degrees off the bow of the ship astern.

So at this point when our intrepid boater thinks he is free and clear of the ship astern. And the bridge crew sees a boat dead ahead just 1.04 nm away.

The bridge crew is in full on collision avoidance mode.

My own bridge time on large ships has been confined as an observer on a 185' research vessel. And my license was no where near that tonnage to boot.

This exercise begs the question: At what point do you consider the crossing complete?

Offhand I would venture that the crossing is complete when no action of the boat (like doing a 180 and running across the ships bow) could cause a CPA of less than (pick some number, oh say) 1 nm.

More experienced hands please chime in.



BTW being 180' perpendicular to the port quarter of the ship ahead is not a 180' CPA. The differences are minor for this calculation and for the most part we all know that.