Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

[El Pinguino]

Originally Posted by Exile

No question about that, and a bit startling to think some of those guys may be the ones on the bridge in an encounter. But also found it ironic that the 'Wafinator' was the most sensible and had the kindest words for our ilk.

Couldn't help wondering if OP 'MarkJ' was the same of local CF fame.

Indeed...

1) ARPA is the only approved collision avoidance system we have on board. This is from both a practical and legal sense. AIS is an aid and a good visual indicator on the ECIDS or radar overlays, but is NOT for collision avoidance. It is fine for ballparking a CPA, but should never be relied on. The reason is that the AIS target I see, is generating it's CPAs based on the target's own AIS equipment. I'd rather not rely on someone else's equipment or calibration of that equipment. We have the ability to overlay AIS on the ECDIS and Furuno radars we have, but typically leave it off the radars because it overlays the target echos and doesn't allow you to easily acquire the return if AIS is on.

2) As a watch officer, I follow whatever the Master's Standing Orders are for that captain, but generally they include something along the lines of "...maintain at all times a CPA greater than 1nm". I am free to maneuver as necessary within the Rules and take prudent and effective action to avoid collision while following the standing orders.

3) This might depend on the area. For instance though, I know San Francisco VTS enforces a 1nm CPA in the offshore precautionary area.

4) We can filter based on a number of conditions (the same with ARPA), but the type of AIS class is not one of them. Class B targets tend to be obvious offshore though, they don't update as often from my experience and don't appear until closer in.

5) It all depends on the watch officer and what their standing orders are. The captains I sail with don't give specific instructions, just the guidelines to stay within. I maneuver according to Rule 8 and within my comfort zone for that particular situation. With a large vessel, that very well may be 10nm depending on how he is behaving in general, whether I could hail him on VHF, how he sounded on the radio (did he really understand the situation?), etc; or sometimes it's at a time before CPA instead so we're not deviating too early for a slowly developing situation. With small targets, I tend to wait until we are closer. I've found that small vessels might not appreciate a course change so early, and their perception of danger or a collision situation doesn't occur until closer ranges. At 10nm, they might not even be aware that there is a situation developing with this shadow they may or may not see near the horizon.

6) Honestly, I will always take action as necessary within the Rules, but if I discern that the echo on the radar or the weak lights I see on the horizon belong to a small vessel, I know I might be in for a stressful situation. From a strictly electronic standpoint, I can discern from the radar return the size of the vessel and even if it is fiberglass. Smallish fishing boats won't pop up until 8-10nm, but usually will deliever a half-way decent return (typically being metal), fiberglass recreational vessels show up even closer with a weaker return. If your vessel has AIS, then it should be indicating the correct vessel type, and I would look at that too just to get an idea. I will also look at destination info and ETA, sometimes this lets me know how much of a hurry the guy is in. But for example, if I see a weak return suddenly pop up at 6nm going 5knots... bingo, sailing vessel. And of course, I'm looking out the window too and at night I'll have a dedicated lookout on the bridgewing. I take advantage of other radar features too to help me identify targets.

7) I for one, follow the navigation rules. There may be some here that play by tonnage, but that is far from an acceptable excuse if something were to happen. But the Rules are mutual, and the commercial sailors on here have all had close calls that muddy our perspective, shoot, even my username is remnant of that!! But I've learned that not every sailboat is a W.A.F.I.; that is reserved for a special breed, and over time the ratio of good to bad that I've encountered has improved. I am a professional mariner, this is my job, my career, I take pride in playing by the rules and being good at what I do, and I think we all share that here. Your questions here are all about getting to a mutual understanding, and I applaud your interest. All bets are off though if you are obviously not following the Rules; maintaining an effective radio watch is one of them.

That said, if I am offshore and am the stand-on vessel, I will stand on. Preferably, we will discuss each other's intentions on the radio and clarify our responsibilities. If the other vessel is the give-way, I will always impress that upon them in the first contact so there is no question, and set the tone right away (some might call this "bullying", I prefer "effective communication"). Certain terms or phrases like "I intend to maintain course and speed", "I will alter course to starboard and meet you port to port", etc, etc, should be in your brain when communicating. Foreign vessels where english is the second language know the rules and how they are written -- speaking the rules when communicating will make sure everyone is on the same page. It sounds hokey to inland guys who have their own lingo (I've been there), but it is the clearest way to avoid miscommunication. All foreign watch officers are required to speak english; how well they do can be a crap shoot. Now, if you are sailing erratically and you are the stand on, I expect you to stand-on. The rules make no allowances for a vessels that feel free to do whatever they want; everyone has responsibilities. Part of my job as a watch officer is to monitor your actions as well to make sure you are doing what we discussed and what you are required to do within the Rules.

8) It all depends on the propagation at the time. Remember, AIS is just a VHF signal, generally line of sight, but atmospherics play a role too. I've seen targets with display information 300nm out with good atmospherics, but typically, within 30nm for a commercial AIS. Class B doesn't seem to show up until perhaps 10nm, but that is really just a guess because I can't tell the type of AIS, just what I've gathered.

9) At night all depends on your lights. The combined lights atop the mast work better in this regard. During the day, good luck depending on the sea conditions. On the radar, it is pretty iffy, but in the 6-8nm range at best, but probably not an acquirable echo. Fiberglass gives a terrible return; combine that with pitching and rolling and going into the trough, ARPA has a tough time latching on. I use target trails as a backup to ballpark it, true or relative depending on the situation, sometimes one on each radar. I work in some pretty nasty conditions, so depending on the sea conditions and how I have to tune my radars to get anything appreciable out of them, there is the possibility that I might not see you at all. Then again, in those conditions, I doubt a sailing vessel would be afloat. Like Kennebec Captain mentioned, there is always the possibility the watch officer has the radar tuned down too far. Clutter controls always have drawbacks, as they typically reduce close-in and weak returns. I use true trails in this situation ("snail trails"), even through clutter and weak echos, it will still draw a straight line behind a target; you see that in the midst of a bunch of clutter, theres a decent chance a vessel is out there. But this is why we maintain an effective lookout.

As far as other advice... Read, understand, and abide by the Rules of the Road if you haven't done so already. Keep a copy on board like you're required to and refer to it when necessary. Get a good radar reflector for your mast. Also, I know someone who sails regularly and he uses a radar detector, like for a car. They pick up X-band radar signals; lets you know a ship's radar is within line-of-sight. Some detectors can indicate the direction it is coming from. A pretty good tool to aid in large-vessel awareness offshore.

And lastly, get a good VHF radio, two perhaps, set one to 13 and one to 16 offshore, and install antennas as high as possible. Nothing is more infuriating when you are hailing a vessel and get no response, then suddenly they want to play the Rules card on you. Nope, sorry. I tried, you failed in your responsibilities, I am now following what I feel to be the best course of action. Something I've picked up from pilots is to repeat the phrase "negative contact" over the radio if I fail to get a response. The USCG records 13 and 16 (within range), and if I have to say that phrase, at that point I have given up on resolving the situation mutually and have switched to preparing for potential litigation. Don't let it get to that point."

I don't think the Wafinator was one of the bunch of watchkeepers Dockhead interviewed for his 'book'.

[Dockhead]

Originally Posted by El Pinguino

. . .
I don't think the Wafinator was one of the bunch of watchkeepers Dockhead interviewed for his 'book'.

He wasn't, as far as I know, but why do you say so? This all sounds entirely consistent with what others have said. And quite sensible.

One thing new in this post is the bit about starting all radio calls by stating his position about who is supposed to be stand-on and who give-way, even if it sounds like "bullying". Seems like great advice to me -- surely the first thing you want to be clear about between the two vessels. If there are different understandings of this, surely you want to know that immediately, before discussing anything else.

Concerning ARPA vs. AIS -- this gets us back to what is an appropriate CPA. The standard of accuracy of ARPA for plotting CPA is +/- 0.5 miles. What that means is that on ARPA, anything from -0.5m to +0.5m CPA might actually be a 0 CPA.

Yet another element of uncertainty which drives the definition of what is a safe CPA.

AIS, if you are broadcasting it, will give a better calculation, but guess what -- the accuracy is different on board the ship, than it is on board your yacht.

Why?

Because Class "B" only transmits once every 30 seconds and is a far weaker signal (1 watt) via a no doubt much worse and worse installed antenna. The ship won't get your position updated often enough to have so much confidence in the CPA calculation -- one reason for the primacy of ARPA.

On your yacht, your AIS will give you much better information since he is transmitting every few seconds. Your own ship data comes straight from your GPS. But you don't know where his antenna is, and neither of you, especially you, is keeping course and speed exactly. So you shouldn't be fooled by the "false precision" of the CPA displayed -- it can't possibly be much more accurate than about a cable, and may be far less accurate than that.

No doubt Ping will now remind us that we should also be using our eyeballs -- which of course is correct.

[El Pinguino]

Originally Posted by Dockhead

He wasn't, as far as I know, but why do you say so? This all sounds entirely consistent with what others have said. And quite sensible.

One thing new in this post is the bit about starting all radio calls by stating his position about who is supposed to be stand-on and who give-way, even if it sounds like "bullying". Seems like great advice to me -- surely the first thing you want to be clear about between the two vessels. If there are different understandings of this, surely you want to know that immediately, before discussing anything else.

No doubt Ping will now remind us that we should also be using our eyeballs -- which of course is correct.

No need , my new best friend has done it for me.. ' At night all depends on your lights.'.... that is of course a two way street...... in good vis much depends on what you can see of her lights.....

[ramblinrod]

Originally Posted by Dockhead

Yes, I've read Cockcroft, of course, and you are right to point this out.

But here he was writing about situations between vessels of similar size and speed.

A big difference of speed changes things. If you are travelling at a fraction of the speed of the other vessel, then your action must be earlier, to be effective, than would be the case if your speeds were roughly the same.

I'm not saying it's necessarily wrong to do it at 2 or 3 miles, and in fact I do sometimes, but if he's moving fast (>15 knots) and I'm moving slow (<8 knots) I think it is best not to leave it much past 3 miles, and I don't think 4 miles is too early.

All of Cockroft's "suggestions" are based on 2 large vessels, which may be heavily laiden and traveling at high speed.

For these vessels, there may be a significant amount of time required for each step of the maneuver:

1. Situation first identified.
2. Confirmed.
3. Plan developed.
4. Approval (if required).
5. Plan communication.
6. Plan execution.

...meanwhile, minutes and miles may have gone by.

For a cruising sailboat, between situation identification and corrective action execution may be only a few seconds and a few feet.

[Dockhead]

Originally Posted by ramblinrod

All of Cockroft's "suggestions" are based on 2 large vessels, which may be heavily laiden and traveling at high speed.

For these vessels, there may be a significant amount of time required for each step of the maneuver:

1. Situation first identified.
2. Confirmed.
3. Plan developed.
4. Approval (if required).
5. Plan communication.
6. Plan execution.

...meanwhile, minutes and miles may have gone by.

For a cruising sailboat, between situation identification and corrective action execution may be only a few seconds and a few feet.

"Situation identification" and "corrective action" taken within a few seconds, and especially when left until far too late, is otherwise known as "erratic, spontaneous, unplanned, unanalyzed, unpredictable maneuvering" -- exactly the thing they hate us for. And rightly so. Collision avoidance is correctly done in a planned, systematic way, and in plenty of time.

"It’s not just the difference in perception of risk of collision. There is a difference in approach to collision avoidance. A professional mariner is more likely to take a more methodical approach, for example plan to take action at specific distance. On the other hand the amateur is more likely to make collision avoidance decisions based on his feelings of comfort or fear."

A seasoned ship's captain, posting on GCaptain, the pro mariners' forum, complaining about the problems of dealing with recreational sailors using the "pucker factor technique" of collision avoidance.

The reason why pros do it at the distances they do, is not because they have to "get approval" -- it's because the level of risk is completely different, for correcting a collision situation at different distances. The longer you wait to do it, the riskier it is, for reasons of simple physics and geometry.

8(a). Any action to avoid collision shall be taken in accordance with the Rules of this Part and shall, if the circumstances of the case admit, be positive, made in ample time and with due regard to the observance of good seamanship.

"Ample time" means, at the very least, soon enough to avoid an in extremis situation.

And last but not least -- the CPA you are maneuvering to get, must be safe. It must leave enough space between you and the ship to take account of the different uncertainties in calculating CPA. As we've seen, +/- 0.5 miles is the limit of accuracy of ARPA, and ARPA is the primary collision avoidance tool on ships (for different reasons). You should not pass so close that a minor variation of course in the last seconds will cause a collision. You should not pass closer than you have reasonable certainty, that you know he WON'T be there. It is generally accepted that the minimum in open sea is one mile, with few exceptions. One mile is not arbitrary -- that is about how much space you need to account for uncertainty and errors, and to leave enough space for a last minute correction if something goes wrong. If you pass much closer than that, the risks go up exponentially. Actually two miles is preferable, and there are cases where one ship complained to authorities about another passing one mile away when it would have been possible to have a better CPA.

One ship's captain commented to me, confidentially, that once a sailboat gets within a half mile or so on a 0 CPA -- which can happen if the sailboat turns suddenly instead of standing on -- trying to avoid a collision, which at half mile, with a spontaneously maneuvering rec sailor is already impossible to do with certain outcome, becomes secondary to preparing for litigation -- that is, sounding signals and making maneuvers which will look better in court, and logging them.


Lastly: "Situation identification and corrective action within a few seconds", and at the last minute, is EXACTLY the collision avoidance technique which was being used on the USS Porter (

https://www.youtube.com/watch?v=hA2WMgtkuoY

). Just as some recreational sailors think "I'm highly maneuverable; I can turn and stop in seconds", the destroyer bridge crew thought "We are highly maneuverable and faster than those other ships -- we can identify and maneuver in seconds, so we can leave it to the last minute." This is the WRONG way to do collision avoidance in both cases. But it's much worse when we do it this way -- the destroyer at least has speed. With our low speeds, we must think FURTHER ahead than fast moving ships do, because the moment when we lose the ability to get out of the way, comes sooner.

[Kenomac]

I like to pop in from time to time on this argument/discussion just to let RamblinRod know he's not alone in his views. It's become like one of those global warming type CF threads where all the folks who wanna be part of the cool, smart gang... pile on anyone who disagrees with the prevailing train of thought.

[Dockhead]

Originally Posted by Kenomac

I like to pop in from time to time on this argument/discussion just to let RamblinRod know he's not alone in his views. It's become like one of those global warming type CF threads where all the folks who wanna be part of the cool, smart gang... pile on anyone who disagrees with the prevailing train of thought.

Maybe you could support Rod with more substance. Do you believe it's OK to approach a ship moving at 20 knots to a distance of 1/4 mile on a 0 CPA before maneuvering? What do you consider a safe distance for a collision avoidance maneuver? Safe CPA in open sea? Explain.

Global warming is very complex, with a lot of ideology and politics. Collision avoidance is much more straightforward, with practices which are clearly safe, and some practices which are clearly unsafe.

Very much like electricity - is it safe to wire up your boat without breakers? It's not a matter of ideology or politics.

[Kenomac]

Originally Posted by Dockhead

Maybe you could support Rod with more substance. Do you believe it's OK to approach a ship moving at 20 knots to a distance of 1/4 mile on a 0 CPA before maneuvering? What do you consider a safe distance for a collision avoidance maneuver? Safe CPA in open sea? Explain.

Global warming is very complex, with a lot of ideology and politics. Collision avoidance is much more straightforward, with practices which are clearly safe, and some practices which are clearly unsafe.

Very much like electricity - is it safe to wire up your boat without breakers? It's not a matter of ideology or politics.

I won't be drawn into this discussion by your relentless "straw man" arguments and demeaning statements towards anyone who opposes your view on this subject.

It's sufficient to say simply that I agree with RamblinRod; you owe him a truckload of beer IMO.

[El Pinguino]

Originally Posted by Dockhead

A seasoned ship's captain, posting on GCaptain, the pro mariners' forum, ........
......

One ship's captain commented to me, confidentially, that once a sailboat gets within a half mile or so on a 0 CPA -- which can happen if the sailboat turns suddenly instead of standing on -- trying to avoid a collision, which at half mile, with a spontaneously maneuvering rec sailor is already impossible to do with certain outcome, becomes secondary to preparing for litigation -- that is, sounding signals and making maneuvers which will look better in court, and logging them..

OK... the time has come for me to put on my 'seasoned ship's captain' seasoned ship master's hat.

When I retired AIS was just being introduced on big ships, it was still unknown on yachts and fishing boats, etc.

Having made an early alteration ( 'early' being entirely dependant on situation... one mile ... five miles... often didn't see them during the day until a few miles off.... every situation is quite unique ) I never once had one go into panic mode.

Passing distance... one mile , half a mile, half a cable.... whatever... once again situation dependent.... and quite different to the clearance given to other merchant ships which would be one mile plus.... If Napoleon had won it would probably be 2 kilometres plus..... its a number... a handy number easily remember is the number '1'.

All done with no chitterchatter on the radio.

Speaking of pucker factor there is one solo circumnavigator out the there who gets their panties in a knot if ships have a CPA of less than 5 miles and will get on the radio and tell 'em to bugger orf.....



Small craft offshore where they were give way?.... quite happy if they altered at 2 or 3 miles and quite happy if they passed at less than a mile.

Tell us again how you would hoist a motoring cone while sailing so that you could act at will in contravention of the rules.... bearing in mind that your cone, - even if not obscured by a headsail - would not be visible at more than a mile or so.

'One ship's captain commented to me, confidentially, that once a sailboat gets within a half mile or so on a 0 CPA -- which can happen if the sailboat turns suddenly instead of standing on'

That really makes no sense....

So - lets see - by your own admission you have gone from zero to hero in 6 years.... have spoken to a few ( well you have said 'a bunch' but in a world populated by somewhere on the high side of 64,000 commercial ships I would suggest 'few' is a more suitable word ) and crossed the Dover Strait about ( if my memory serves ) 8 times and are about to write a book. Well done... we are all no end impressed. I hope your book is going to be more than just quotations from 'Cockcroft'....

Meanwhile, the problems with big ship v little yacht interaction occur primarily in pilotage waters.... not offshore

[Dockhead]

Originally Posted by Kenomac

I won't be drawn into this discussion by your relentless "straw man" arguments and demeaning statements towards anyone who opposes your view on this subject.

It's sufficient to say simply that I agree with RamblinRod; you owe him a truckload of beer IMO.

The 1/4 mile decision point and 180 foot CPA is not a straw man. It is the specific scenario proposed by Rod.

If you think it's safe, and think you can defend it, then have at it.

[Dockhead]

Originally Posted by El Pinguino

OK... the time has come for me to put on my 'seasoned ship's captain' seasoned ship master's hat.

When I retired AIS was just being introduced on big ships, it was still unknown on yachts and fishing boats, etc.

Having made an early alteration ( 'early' being entirely dependant on situation... one mile ... five miles... often didn't see them during the day until a few miles off.... every situation is quite unique ) I never once had one go into panic mode.

Passing distance... one mile , half a mile, half a cable.... whatever... once again situation dependent.... and quite different to the clearance given to other merchant ships which would be one mile plus.... If Napoleon had won it would probably be 2 kilometres plus..... its a number... a handy number easily remember is the number '1'.

All done with no chitterchatter on the radio.

Speaking of pucker factor there is one solo circumnavigator out the there who gets their panties in a knot if ships have a CPA of less than 5 miles and will get on the radio and tell 'em to bugger orf.....



Small craft offshore where they were give way?.... quite happy if they altered at 2 or 3 miles and quite happy if they passed at less than a mile.

Tell us again how you would hoist a motoring cone while sailing so that you could act at will in contravention of the rules.... bearing in mind that your cone, - even if not obscured by a headsail - would not be visible at more than a mile or so.

'One ship's captain commented to me, confidentially, that once a sailboat gets within a half mile or so on a 0 CPA -- which can happen if the sailboat turns suddenly instead of standing on'

That really makes no sense....

So - lets see - by your own admission you have gone from zero to hero in 6 years.... have spoken to a few ( well you have said 'a bunch' but in a world populated by somewhere on the high side of 64,000 commercial ships I would suggest 'few' is a more suitable word ) and crossed the Dover Strait about ( if my memory serves ) 8 times and are about to write a book. Well done... we are all no end impressed. I hope your book is going to be more than just quotations from 'Cockcroft'....

Meanwhile, the problems with big ship v little yacht interaction occur primarily in pilotage waters.... not offshore

Your suggested maneuvers sound fine to me. And how could they not? You certainly have the experience and knowledge to know how to do it, more than I have.

As to "most problems with yachts occur in pilotage waters" -- of course. And you don't really need a complete understanding of how to do collision avoidance to stay safe in pilotage waters - it works differently there. And that's exactly why so many of us have such a poor understanding of how it works in open water.

As to my experience - for the record, it's 8 transits of the North Sea including the Elbe approaches, 8 full transits of the Baltic, and more than 100 English Channel crossings. I’ve done thousands of risk of collision crossings with ships outside of pilotage waters, something I had hardly done at all prior to coming up here.

That was an eye-opener, and experience of course is important. But I’ve spent quite a bit of time studying this subject, and not only talking to mariners, and the study is at least as important as the experience.

Now I know I irritate you when I‘ve got my pedant hat on. I’m sorry about that – quite a bit of teaching in my CV, and son of academics – so can’t help it – it’s in my blood, just like salt is in yours. But it would be nice if you would not let go without your professional comment the idea that it is safe to wait until ¼ mile to evaluate risk of collision, when dealing with a fast-moving ship in open sea (NOT pilotage waters). Barely two ship-lengths in front of a medium size tanker or only a little over a ship-length in front of a big box ship. Come on, Ping – these are harmful misconceptions, and you know it. You can preface your remark with “Dockhead is an irritating pedant, but . . . “ I won’t mind

[Kenomac]

Originally Posted by Kenomac

I won't be drawn into this discussion by your relentless "straw man" arguments and demeaning statements towards anyone who opposes your view on this subject.

It's sufficient to say simply that I agree with RamblinRod; you owe him a truckload of beer IMO.

Originally Posted by Dockhead

The 1/4 mile decision point and 180 foot CPA is not a straw man. It is the specific scenario proposed by Rod.

If you think it's safe, and think you can defend it, then have at it.

Like I wrote, "I won't be drawn into this discussion," or more accurately... argument.

And furthermore.... I believe post #1 on this thread actually violates the forum rules in several ways. RambinRod was drawn in to defend himself due to his posts being taken (without his permission) from one thread then posted on another in an argumentative way and out of context.... to criticize his personal character and judgement.

Not fair to Rod at all.... phrases taken from the opening paragraph of this thread such as... "fundamental misunderstanding," "They don't understand," "misjudging it by miles" and "don't understand what safe passing distances are," certainly implied that Rod is incompetent.

I think he's owed a long overdue apology and a truckload of beer.

[Dockhead]

Originally Posted by Kenomac

Like I wrote, "I won't be drawn into this discussion," or more accurately... argument.

And furthermore.... I believe post #1 on this thread actually violates the forum rules in several ways. RambinRod was drawn in to defend himself due to his posts being taken (without his permission) from one thread then posted on another in an argumentative way and out of context.... to criticize his personal character and judgement.

Not fair to Rod at all.... phrases taken from the opening paragraph of this thread such as... "fundamental misunderstanding," "They don't understand," "misjudging it by miles" and "don't understand what safe passing distances are," certainly implied that Rod is incompetent.

I think he's owed a long overdue apology and truckload of beer.

Sorry but this is absolutely false.

"They" is not Rod.

To say that something Rod said involves a "fundamental misunderstanding" is not an insult. I did say that, and I stand by it. I think I even proved it. It does not surprise me that you do not want to try to contest this -- you are a smart guy.

There's no shame in having a "fundamental misunderstanding". I have them myself all the time. Having them pointed out to you is actually a great blessing. Feeling ashamed of it is a very great mistake.

[HiAndDri]

Originally Posted by boatman61

Likewise Ann.. however during many miles back, forth and along the English Channel I've never come close to being run down and my method is simple.. line the approaching/crossing vessel with a stanchions and it'll let you know if the ship will pass the bow or stern.. if it holds steady alter course.
Only thing that's ever hit me was a French yacht.. they hate Brits.

Absolutely spot on. It's called recognition primed decision making and it's why humans are still so much better than computers (at least the ones you find inside boat instruments) at making these decisions, however much math you use.

[Lodesman]

Originally Posted by Kenomac

And furthermore.... I believe post #1 on this thread actually violates the forum rules in several ways. RambinRod was drawn in to defend himself due to his posts being taken (without his permission) from one thread then posted on another in an argumentative way and out of context.... to criticize his personal character and judgement.

Oh puh-leeze! Rod got into with Dockhead in the other thread and Dockhead invited Rod to discuss this particular tangent in this thread - see here:

Originally Posted by Dockhead

That an obviously intelligent person like you could so totally misunderstand the basics of crossing with fast ships, is evidence that this discussion is really worth having. It might even save your life. I invited you to do the math and see for yourself; you didn't bother. I guess because you are so sure in your own concepts that you don't think you need it. Now I've done the math for you and you will see. But let's discuss it elsewhere, say here:

Collision Avoidance, Cones of Uncertainty, and Appropriate CPA - Cruisers & Sailing Forums

I'm fairly certain that disagreeing with someone is not against the forum rules. And it's hardly like anyone is piling on - I had only interjected occasionally to correct what I saw as misconceptions, and even defended Rod over the prolonged blast - Rod engaged me in this last volley. What's your purpose in being in this thread, if it's not to discuss the topic? That is against the rules:

Stay on topic by keeping discussions relevant and on track.