Cruisers & Sailing Forums (https://www.cruisersforum.com/forums/)
-   Seamanship & Boat Handling (https://www.cruisersforum.com/forums/f90/)
-   -   Collision Avoidance, Cones of Uncertainty, and Appropriate CPA (https://www.cruisersforum.com/forums/f90/collision-avoidance-cones-of-uncertainty-and-appropriate-cpa-189919.html)

El Pinguino 31-10-2017 13:44

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by evm1024 (Post 2510108)
Reminds me of Hitchikers Guide....

Only Zaphod Beeblebrox is reported to have survived the Vortex unscathed (and then to have eaten the small piece of fairy cake). When it showed him the "You Are Here" marker, Zaphod correctly interpreted the Vortex as simply telling him that he was the most important being in the universe.

As a character, Zaphod is hedonistic and irresponsible, narcissistic almost to the point of solipsism, and often extremely insensitive to the feelings of those around him.

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?

I think the usefulness of this thread ceased about 826 posts ago.

I also note that I am no longer considered ... by the font of all knowledge ... to be a professional contributor to this thread.... must have been something I said.

I also think that , as Godwin's Law applies to the introduction of Hitler into a debate.... Ping's Law should apply to the introduction of Cockcroft into debates re 'the rules'... for the same reasons.

Golly would you look at this... I have an AIS contact on a fishing boat down near Cape Horn... 42.71 miles away to be exact... interesting considering Isla Navarino.. a not insubstantial bit of terra... is between us and her....

ramblinrod 31-10-2017 13:49

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Jim Cate (Post 2510309)
rod, you forgot the step where Scotty beams your boat into this position 180 feet away from the ship. I don't think folks are saying that the rest of your proposal is incorrect, it's just that it isn't feasible to arrive at your initial spot reliably without a very high risk of collision.

And mate, you might back off on the self-proclaimed victories. They are not becoming to you.

Jim

Oh c'mon already.

There is no Star Trek transporter, nor Guide to the Galaxy needed.

Are you guys really serious????

The significance of a constant bearing has already been discussed in this thread.

Everyone here should know how to do this.

It's simple.

From how ever far out you wish, line up a constant bearing with the port stern quarter of the vessel to be crossed.

As with any course, steer to hold this course, (constantly compensating course error and speed variables).

When you get close enough, fall off a hair as required to position yourself in the spot desired.

In my case 180 ft is just dang close to 6 of my boat lengths. This is exactly two times my mark room zone under RRS. As does any racer, one learns to eyeball this pretty dang close, while watching the nearby boats for overlap. (There may be many.)

Regarding your last sentence, I'm really really trying to be humble, but seriously, do I have to teach everybody everything?

This stuff all the self-proclaimed experts are declaring "impossible", many sailors do, every single time out on the water.

I can (and have) threaded needles much tighter than 1.25 nm all day long.

I haven't done it with ships, as they wouldn't think it all that much fun, but often with boats going up to double my speed. Regardless, the principles are exactly the same as I described regardless of vessel speed.

If one can hold a constant bearing, they can do it.

How much plotting is required to do this? ZERO!!!!!!!!!

Again guys, get yer heads out of yer electronics and arses; obviously yer not just going out and sailing enough.

:whistling::smitten::whistling::smitten::facepalm: :smitten::facepalm::smitten:

ramblinrod 31-10-2017 14:01

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by Dockhead (Post 2510311)
Rod, you are not going to rattle anyone's world with your home-made methods and made-up terminology. They don't work. I'm not going to waste my time on this, but if you can find someone else to argue with, you can have a go - in another thread. I'll start it, for convenience.

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?

:smitten::smitten::smitten::smitten::smitten::smit ten::smitten::smitten:

JPA Cate 31-10-2017 14:07

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Rod, please cool your jets. The grist mill of fate may grind exceeding slow, but it grinds extraordinarily fine.

JPA Cate

evm1024 31-10-2017 14:21

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by ramblinrod (Post 2510341)
Oh c'mon already.

There is no Star Trek transporter, nor Guide to the Galaxy needed.

Are you guys really serious????

The significance of a constant bearing has already been discussed in this thread.

Everyone here should know how to do this.

It's simple.

From how ever far out you wish, line up a constant bearing with the port stern quarter of the vessel to be crossed.

As with any course, steer to hold this course, (constantly compensating course error and speed variables).

When you get close enough, fall off a hair as required to position yourself in the spot desired.

In my case 180 ft is just dang close to 6 of my boat lengths. This is exactly two times my mark room zone under RRS. As does any racer, one learns to eyeball this pretty dang close, while watching the nearby boats for overlap. (There may be many.)

Regarding your last sentence, I'm really really trying to be humble, but seriously, do I have to teach everybody everything?

This stuff all the self-proclaimed experts are declaring "impossible", many sailors do, every single time out on the water.

I can (and have) threaded needles much tighter than 1.25 nm all day long.

I haven't done it with ships, as they wouldn't think it all that much fun, but often with boats going up to double my speed. Regardless, the principles are exactly the same as I described regardless of vessel speed.

If one can hold a constant bearing, they can do it.

How much plotting is required to do this? ZERO!!!!!!!!!

Again guys, get yer heads out of yer electronics and arses; obviously yer not just going out and sailing enough.

:whistling::smitten::whistling::smitten::facepalm: :smitten::facepalm::smitten:

OK, I'll try one more time.

Rod, so you do admit that you have not attempted to pass 180' CPA behind a ship doing 20 kts to your 5 kts.

So you admit that you have extrapolated your racing experience to close encounters with ships going 4 times your speed.

So you admit that you think (nay, you know) that you can eyeball a 14 degree relative course line to a ship that is 5 miles away from you when you are 1 mile from the intersect point.

So you admit that you think that this crossing needs to be done with eyes only so that you can make course corrections along the way.

So you know that everyone else is wrong and you are right.


OK, I'll bite.....

evm1024 31-10-2017 14:47

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
.... I've decided to embrace Rod's panache and do the crossing as he would.

So I'm motoring along at 5 kts and I see a line of ships moving along what looks like an equal distances apart. I'm guessing that they are 1.25 nm apart and doing 20 kts. My eyes are out of the electronics and my Balls are made of Iron (eat your heart out you brass monkeys). Besides I don't need no stinking electronics, I'm a racer, I've got experience.

I decide that a crossing with a 90 degree angle is best so I alter my course and eyeball a heading that looks to be 90 degrees to the line of ships. I see one to port about 1.25 miles away and another further to port. There is the one right ahead of me and then there are those oncoming ships to starboard. The first is about 1.245 miles away.

I decide that I can do this so I go for it. Go, no-go I'm going.

Every 3 and 3/4 minutes another ship passes across my bow. I was planning on passing under the stern of the 2nd ship but he is long gone. I'll go under the stern of the 3rd ship.

Now I'm guessing that I am about 1 nm from the path of the ships. I realize that I need to find the ship that has a constant bearing and pass astern of that one. Is it the 2nd ship, no he is pulling forward of the relative bearing. Darn how about the 3rd. Shoot, his angle is pulling forward too. I get out my binoculars and take a look at the 4th. Um, I'm not sure, may be. No, moving forward. Damn, I need to keep a more steady course if I am going to figure out who to pass behind. OK it it either the 4th or the 5th ship I'll pass behind. The 5th ship is about 5.3 nm away but that is just a guess. It looks tiny from here.

Just keep going I'll figure it out when I get there.

Closer, Closer. OK got it I'm going under the stern of the 5th ship. Adjust my course to keep that 5th ship just a tad ahead of my beam. Closer, Closer. Bigger, bigger. No sweat, no pucker factor.

OK there it is - the 5th ship is off my bow. Focus on her stern head for it. I got skill, I can pass 180' from her. I gotta stay close so that the 6th ship does not run me over. Closer, closer.

God I'm good. Pegged that right. Perfect 180' CPA to her stern.

evm1024 31-10-2017 14:53

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
The game here is to imagine yourself at the helm of the boat doing 5 kts and figure out how many things had to go right to make it work. How much risk is involved if any one of those assumptions was not in your favor. To imagine just what kind of luck would be needed.

Simple things like assuming that the 6th ship is doing 20 kts and not 22 kts un-noticed while you try to get 180' from the 5th ship. Or that the 5th ships path is actually 600' closer than the other ships path (or the 6th ship is not futher away than you thought) giving you no options.

Theory verses reality.

TeddyDiver 31-10-2017 14:54

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by El Pinguino (Post 2510337)
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"

Prove he's right? What's Rod effectively done.. Or responding "Sorry, my mistake"

I understand your, may I call it frustration?, to dogmatic Dockhead as I'm a bit "laissez-faire" myself but that doesn't change the fact he's right.

BR Teddy

evm1024 31-10-2017 14:55

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Lastly, 180' is just a number that one outspoken person thinks is good. As long as we are doing theory and not reality then we should get as close as we can.

150'

theory

125'

theory

100'

theory

50'

25'

OK OK make it we have a CPA of 5'

In theory there was no collision so we are golden.

ramblinrod 31-10-2017 15:01

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by evm1024 (Post 2510398)
.... I've decided to embrace Rod's panache and do the crossing as he would.

So I'm motoring along at 5 kts and I see a line of ships moving along what looks like an equal distances apart. I'm guessing that they are 1.25 nm apart and doing 20 kts. My eyes are out of the electronics and my Balls are made of Iron (eat your heart out you brass monkeys). Besides I don't need no stinking electronics, I'm a racer, I've got experience.

I decide that a crossing with a 90 degree angle is best so I alter my course and eyeball a heading that looks to be 90 degrees to the line of ships. I see one to port about 1.25 miles away and another further to port. There is the one right ahead of me and then there are those oncoming ships to starboard. The first is about 1.245 miles away.

I decide that I can do this so I go for it. Go, no-go I'm going.

Every 3 and 3/4 minutes another ship passes across my bow. I was planning on passing under the stern of the 2nd ship but he is long gone. I'll go under the stern of the 3rd ship.

Now I'm guessing that I am about 1 nm from the path of the ships. I realize that I need to find the ship that has a constant bearing and pass astern of that one. Is it the 2nd ship, no he is pulling forward of the relative bearing. Darn how about the 3rd. Shoot, his angle is pulling forward too. I get out my binoculars and take a look at the 4th. Um, I'm not sure, may be. No, moving forward. Damn, I need to keep a more steady course if I am going to figure out who to pass behind. OK it it either the 4th or the 5th ship I'll pass behind. The 5th ship is about 5.3 nm away but that is just a guess. It looks tiny from here.

Just keep going I'll figure it out when I get there.

Closer, Closer. OK got it I'm going under the stern of the 5th ship. Adjust my course to keep that 5th ship just a tad ahead of my beam. Closer, Closer. Bigger, bigger. No sweat, no pucker factor.

OK there it is - the 5th ship is off my bow. Focus on her stern head for it. I got skill, I can pass 180' from her. I gotta stay close so that the 6th ship does not run me over. Closer, closer.

God I'm good. Pegged that right. Perfect 180' CPA to her stern.

Well, you are still assuming that you start the scenario when the first ship is perpendicular to you, besides my advising previously that doesn't have to be the case but you are still ignoring.

The lead ship that you are planning to cross could very well be the first or 20th ship in the convoy; makes no difference whatsoever.

Based on you incomprehension of how one could easily do this, I predict you have never ducked another boat in close quarters during a race.

(Otherwise you would not question the validity of everything I have proposed here.)

Boys, I never said do it without electronics, I very clearly stated you may wish to use electronics to start, but once you get within the accuracy limitation of the electronics , you must get eyes on it.

Notwithstanding, one could do this with nothing more than a hand bearing compass.

Exile 31-10-2017 15:06

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by El Pinguino (Post 2510337)
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?

I think the usefulness of this thread ceased about 826 posts ago.

I also note that I am no longer considered ... by the font of all knowledge ... to be a professional contributor to this thread.... must have been something I said.

I also think that , as Godwin's Law applies to the introduction of Hitler into a debate.... Ping's Law should apply to the introduction of Cockcroft into debates re 'the rules'... for the same reasons.

Golly would you look at this... I have an AIS contact on a fishing boat down near Cape Horn... 42.71 miles away to be exact... interesting considering Isla Navarino.. a not insubstantial bit of terra... is between us and her....

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

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.

evm1024 31-10-2017 15:16

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by ramblinrod (Post 2510416)
Well, you are still assuming that you start the scenario when the first ship is perpendicular to you, besides my advising previously that doesn't have to be the case but you are still ignoring.

The lead ship that you are planning to cross could very well be the first or 20th ship in the convoy; makes no difference whatsoever.

Based on you incomprehension of how one could easily do this, I predict you have never ducked another boat in close quarters during a race.

(Otherwise you would not question the validity of everything I have proposed here.)

Boys, I never said do it without electronics, I very clearly stated you may wish to use electronics to start, but once you get within the accuracy limitation of the electronics , you must get eyes on it.

Notwithstanding, one could do this with nothing more than a hand bearing compass.


Clearly you know nothing about me.

Clearly you think that your racing experience is enough to make you an expert in crossing ships in open water.

Clearly you cannot visualize what such a crossing would look like (which is why I described it, try to place yourself there)

Clearly you do not realize that 1st ship does not mean the 1st ship in the line of ships. Another failure of you to understand other peoples points of view. You are blind.

Clearly you did not read my post and understand it as if you did you would have picked up on the decision I made to set my course for a 90 degree crossing. This is after all my crossing and I get to do it how I like.

Based on your assertion of how easy this would be you clearly lack the knowledge and experience you profess.

ramblinrod 31-10-2017 15:30

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by evm1024 (Post 2510431)
Clearly you know nothing about me.

Clearly you do not realize that 1st ship does not mean the 1st ship in the line of ships.

No, you professed that it must necessarily be the 4th or 5th ship crossed (when it could be the very first one or the 20th for that matter)?

Wrong.

Clearly, you think posting a plethora of strawman arguments somehow makes your incorrect statements sound more plausible.

Fact. It can be done, quite easily, without any electronics, EXACTLY, as I have proposed.

(I must confess to using a calculator so my math took a few seconds instead of maybe a minute or two to do it by hand.)

Possibility 1: Ships don't see me, don't move, I get across.

Possibility 2: Ships see me, and wishing to keep a min 1 nm CPA, open up the gap, and I get across.

Possibility 3: Ships violate Colregs and move at the last possible second in such a way that they run into me. (If ships at 20 knots violate Colregs, we are all sitting ducks, no matter what we do.)

evm1024 31-10-2017 15:43

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Quote:

Originally Posted by ramblinrod (Post 2510442)
So if not, what are you talking about the necessity of crossing with the 4th or 5th ship specifically (when it could be the very first one or the 20th for that matter)?

It is a matter of references.

We have that line of ships, they are all the same but we must make the unique.

From the moment we decided to make a crossing (at 1 mile out in my description) the ship in front of us (assuming that we have made it a 90 degree crossing) is the first ship.

All the other ships are indexed from there. 1st, 2nd, 3rd etc. Just makes it easier to know which ship we are talking about.

( Just like running across road when on foot. "Not this car, let's go after the 3rd car".)

evm1024 31-10-2017 15:49

Re: Collision Avoidance, Cones of Uncertainty, and Appropriate CPA
 
Wow what happened there? It looks like Rod posted a non-combative message and then edited it when he realized what?

I thought we were making progress.... He asked a real question and I answered in kind.

See my answer to his "normal" question in post 839 along with his original question quoted.

Why the edits?


All times are GMT -7. The time now is 13:56.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.


ShowCase vBulletin Plugins by Drive Thru Online, Inc.