Over-Reliance on AIS -- Collision off Dungeness

[Dockhead]

Originally Posted by Polux

. . .
On the very rare eventuality that on coastal waters at 6NM a ship had already assume a collision possibility, have considered me the stand on vessel and make a deviation, I will just adjust mine. If he returns to his course, good for him, it was what I wanted in the first place and I will adjust it again. Everything is done at more than 5nm of CPA. Completely safe and with plenty of time . . .

Saying that this way of avoiding any close approach, or possibility of collision course with ships is wrong or contrary of COLREGS or even worse that I did not have an accident because I am lucky does not make any sense.
. . . .

This scenario is exactly what the COLREGS strives to avoid. A series of uncoordinated course changes is one of the most common causes of collisions. It is absolutely essential to the proper functioning of collision avoidance, that maneuvering is done by one vessel, and one vessel alone, while the other vessel holds its course and speed.

If some "professional captain" taught you that this is an ok way to do collision avoidance, you should demand your money back, because it is wrong, dangerous, and forbidden.

It doesn't matter that it's 5 miles off, if one vessel is thinking of the other as stand-on or give-way, then you are already in the maneuvering phase of the crossing where someone must hold course and speed. Those 5 miles disappear in a flash, when maneuvering is uncoordinated like this, and not conducted according to the Rules. ESPECIALLY if the uncoordinated maneuvers are small and/or repeated course changes, as you advocated in one of the previous posts.

[Polux]

Originally Posted by TeddyDiver

This is when things start to go south and suddenly there's no more time..

BR Teddy

You mean no more time 6nm away? Compared when a ship has not seen you or does not acknowledge your stand on status, at less then 1nm when you take emergency deviation to avoid collision and still don't know if them will see you and will change course too

[boatman61]

[Polux]

Originally Posted by Dockhead

This scenario is exactly what the COLREGS strives to avoid. A series of uncoordinated course changes is one of the most common causes of collisions. It is absolutely essential to the proper functioning of collision avoidance, that maneuvering is done by one vessel, and one vessel alone, while the other vessel holds its course and speed.

If some "professional captain" taught you that this is an ok way to do collision avoidance, you should demand your money back, because it is wrong, dangerous, and forbidden.

It doesn't matter that it's 5 miles off, if one vessel is thinking of the other as stand-on or give-way, then you are already in the maneuvering phase of the crossing where someone must hold course and speed. Those 5 miles disappear in a flash, when maneuvering is uncoordinated like this, and not conducted according to the Rules. ESPECIALLY if the uncoordinated maneuvers are small and/or repeated course changes, as you advocated in one of the previous posts.

It was not one but several on several courses. You seem not to understand that regarding to a sailboat that moves at 6K it makes no sense to talk about a stand away vessel at over 6NM. And that a boat is not under COLREGS unless there is a possibility of collision.

There is a distance where COLREGS regarding a course should be applied you seem to think that distance is the same regarding two ships traveling at 18k and a Ship traveling at 18k and a sailboat traveling at 6k.

That is nonsense in my opinion. The two ships will meet their CPA much more quickly. A ship does not change frequently of course, like a sailboat that has to follow wind variations.


As it was said here repetitively on coastal heavy traffic waters, like many European ones the habitual distance for a ship to start to take evasive action regarding a sailboat that has stand of the way status is about 3nm.

I talked about 6nm and 6nm on most cargo ships will correpond to about 20m, not a flash.

[jackdale]

Here is a reason for not altering course.

Us - sailboat port tack close hauled.

Them - ocean going crossing from port to starboard.

The boat owner get me up to deal with the situation. Using MARPA ( ihave had sucess with it) and the EBL lines I determine that he will pass our bow with lots of room to spare.

The owner wants to bear away. That would actually accelerate the boat and put us on a collision course. I radioed the ocean going and he indicated that he was passing our bow with lots of room to spare.

[MarkJ]

Originally Posted by Dockhead

This scenario is exactly what the COLREGS strives to avoid. A series of uncoordinated course changes is one of the most common causes of collisions. It is absolutely essential to the proper functioning of collision avoidance, that maneuvering is done by one vessel, and one vessel alone, while the other vessel holds its course and speed.


it is wrong, dangerous, and forbidden.

Plus, as we have discussed its difficult to judge distance at 1 nm being 500 meters out, so how can you do it at 6nms? That's a 1.5nm error!

Finally, how could you do that when avoiding 3 simultaneous targets like my AIS screenshot showed in Florida straits or the English Channel where the incident that started the thread occured?

Play ducks and drakes with multiple ships and the bs factor goes up. You wouldn't really do it at sea... only on the internet

[Polux]

Originally Posted by boatman61

Yes, I guess you are right, I am losing my time. I will go away, you have to find something else to pass the time

[Polux]

Originally Posted by MarkJ

...
Finally, how could you do that when avoiding 3 simultaneous targets like my AIS screenshot showed in Florida straits or the English Channel where the incident that started the thread occured?

Play ducks and drakes with multiple ships and the bs factor goes up. You wouldn't really do it at sea... only on the internet

Last post: I said repetitively when it is possible. There are cases where it is not.

[Stu Jackson]

Originally Posted by jackdale

Here is a reason for not altering course.

Us - sailboat port tack close hauled.

Them - ocean going crossing from port to starboard.

The boat owner get me up to deal with the situation. Using MARPA ( ihave had sucess with it) and the EBL lines I determine that he will pass our bow with lots of room to spare.

The owner wants to bear away. That would actually accelerate the boat and put us on a collision course. I radioed the ocean going and he indicated that he was passing our bow with lots of room to spare.

Very good example, thanks. Indicates a complete lack of understanding of situational awareness and STD cals by the owner. Creepy.

[nigel1]

Originally Posted by nigel1
....

The perception of when risk of collision would be seen to exist all depends on location, traffic density, status of the vessels, speed etc.

Deep sea, on a large tug, not hampered by a tow, if I was the give way vessel, I would make a course alteration as soon as the risk had been determined (within reason, not at 60 nm separation, but more like somewhere between 5 to 10 miles out)

In waters like the Dover Straits, things get a lot different. ..At 5 miles out, would be looking at avoidance manoeuvres if needed, and the impact on other vessels if we alter course. Course alteration might be made as close as 2 miles away, with the intention of maintaining CPA's of at least 0.5 nm.

Originally Posted by Polux

Thanks regarding your clarification

You missed out the first part of my post.
I said in congested waters, on my tug, we would be looking for potential problems from about 12 miles out, and at about 5 miles, making a decision on manoeuvres needed, (even if that action will take place a few minutes later).

So lets say I observe a small slow target at about 8 miles away, its going to take a few minutes to get a plot on it, in the mean time would we be visually looking for it, and checking AIS.
For the sake of argument, lets say the target is a sailing boat, crossing from stbd to port, in that situation I'm the giveway vessel. There may be another ship a couple of miles ahead which is being overtaken and a ferry crossing as well.

Decision made, we'll alter 30 degrees to stbd, that clears everyone.
Now, if the yacht then decides to be helpful, and makes an alteration, that can makes a problem. If the yacht is smart, he may have worked out that I would likely alter to stbd, so he makes his turn to stbd as well. On the other hand, he may think, the quickest way out of the situation is a turn to port. In that case, where does that leave us.

My experiences, and actions I would take, are based on the tugs I skipper on.

With 24,000 HP, twin screw CPP, high lift rudders, a 90 degree turn takes less than 15 seconds. From full speed to stopped can be accomplished in about 1.5 cables, so for me, I could fix the situation with not too much trouble.
For a VLCC or a large container ship, they dont have the luxury of being able to turn quickly or make a crash stop, and it could be a messy outcome, or at least a bollocking over the VHF.

[Polux]

Originally Posted by nigel1

...
So lets say I observe a small slow target at about 8 miles away, its going to take a few minutes to get a plot on it, in the mean time would we be visually looking for it, and checking AIS.
For the sake of argument, lets say the target is a sailing boat, crossing from stbd to port, in that situation I'm the giveway vessel. There may be another ship a couple of miles ahead which is being overtaken and a ferry crossing as well.

Decision made, we'll alter 30 degrees to stbd, that clears everyone.
Now, if the yacht then decides to be helpful, and makes an alteration, that can makes a problem. If the yacht is smart, he may have worked out that I would likely alter to stbd, so he makes his turn to stbd as well. On the other hand, he may think, the quickest way out of the situation is a turn to port. In that case, where does that leave us.
...

Again, I said if possible and obviously it is not possible on a situation that involves several ships and several courses. There the safest action for the sailboat is to approach the ship as stand on vessel and hope to be seen. I would also contact the nearest boat by VHF asking if he was seeing me.

I was talking of cases where it is possible to avoid to approach a ship on a situation of possible collision, namely situations regarding a single Ship and a sailboat with movements not restricted by islands or obstructions.

[TeddyDiver]

Originally Posted by Simonsays

actualy with a CPA > 5nm he is only chasing his own tail.

Until he isn't. He's says no other vessels around but there allways is, just not eyeballed it (them) yet.

BR Teddy

[monte]

Keeping in mind the steering rules come into play when vessels are in sight if each other, not really when they are first detected by electronics. If you are using visual aids, hbc, lining up a winch or binoc's, you are already bound by the rules. Stand on or give way. That said, I have adjusted my course on a regular basis to accommodate working vessels, rather than require them to alter speed or course, but rarely under 45m to CPA without first discussing with the other vessel and never when there is more than one crossing situation occurring in the same time frame. An example might be where I am sailing south and a ship is sailing north on the same line. I see a CPA of 100' in 50 minutes when the ship is 15 miles away. I usually know why the other vessel is on the particular course, because he is clearing some headlands so it's obvious he hasn't already made evasive manoeuvres. A small course change by me will open up the CPA to half a mile. I guess I'm with Polux on this. I've never had a ship complain. I'd be interested to hear if they prefer me to stand on or make a small course correction in that case, possibly causing the OOW to wake the captain etc. Of course the wind can also force us to make course corrections in that case, as can starting the engine and turning on the steaming light..
Obviously Marks screenshot is a perfect example of why we need to hold course and speed when more than two vessels are involved.

[Robin3]

Originally Posted by Dockhead

A little Small World Story -- some six or seven years ago, when I was getting ready to make my very first Channel crossing, Robin helped with a ton of advice, and even calculated a CTS for me using his Neptune program. We knew each other from a different forum

From which I guess you arrived safely there OK then!

Concerning radar -- I have never had MARPA that worked very well, and indeed small boat radar is pretty poor for accuracy of bearings (very good for accuracy of range). However, one lovely low-tech radar technique is to set the EBL on the ship in question and just watch how the blip moves in relation to the EBL. The blip will be jigging around due to inaccuracy of the radar, but you can discern the TREND pretty easily. If it is drifting away from EBL, you are ok. If it is just walking down the EBL -- you've got a problem. You don't need to do a plot or anything -- very simple and useful trick.

We didn't have MARPA back in those days, in fact our first radar had a CRT and a hood to view the screen through. Our second one had a 'trail' function that showed the history of the targets from first acquisition, which when projected forwards was helpful in giving an idea of hit or miss. Our third set was similar, but with a shorter trail more like a tail much less helpful. it did allow 2 EBLs ( but had only one range mark) so we could watch if vessels deviated from the EBLs enough to assume a probable miss or needing some action from us. Our current Garmin HD Radar has MARPA and a modern fast heading gyro sensor feed to it,making it as good as affordable small boat stuff can and, unlike back in the 'old days.' We now also have AIS, transmitting as well as receiving. THE COLREGS (still) RULE OK of course.



The basics are still the same however and MK1 eyeball and HBC techniques are all still very relevant in the overall scheme of things and their understanding is indeed essential IMO to making the best understanding and use of the modern electronic stuff. We are as always just two up when sailing and carry two hand bearing compasses and two pairs of (illuminated) compass binoculars, two notepads and hopefully can even locate 2 pencils with sharp nibs.

[Polux]

Out of any polemic I would like to post bout some facts that are important and have not been mentioned.

The first regards what Nigel told about the assumption a sailboat with the sails up is for him a stand on vessel, assuming always it is not under mechanical propulsion. That seems to be standard practice regarding merchant captains.

On other way when the wind is weak most sailboats motorsail going under mechanical propulsion and using the wind to get an extra 0,5 or 1k. A sailboat under mechanical propulsion, even if it has the sails up, it is not by the COLREGS a sailing boat and the sailboat's skipper, playing by the rules would assume that regarding other sailboats or motorboats.

That would have as consequence that on some situations a ship and a sailboat under mechanical propulsion but motorsailing are attributing one to the other the role of stand on vessel, both executing maneuvers to avoid one another, not at 5or 6nm away but at close quarters, when they find that something is wrong, creating a dangerous situation.

Off course on that situation the sailboat should be carrying an inverted cone but it was already made explicit that a ship would not be able to see that at distance and that almost all sailboats don't use it for that reason.

Another problematic situation is that by the COLREGS the stand on vessel should maintain course and speed and in some situations under sails is not practical if hardly possible maintain speed or course.

I am talking about variable winds that are very frequent on coastal waters particularly of weak winds between 4 and 9k that on a modern fast sailboat, like mine can, without any change of sails, induce variations of 4K speed, doubling almost the speed of the boat. Some will not sail with weak winds but I sail when my boat is doing over 3K speed and for that on some points of sail less than 3k wind is needed.

The other situation where speed can vary greatly (on a modern fast cruiser) is downwind were on winds between 16K and 25K the boat will exceed hull speed and start to semi plan or in some boats will really plan. That means that with those winds (and the same sail) the speed can vary over 4k, on my boat between 8,5 and 13,5K (not pushing the boat).

Depending on the speed of the ship those differences in speed can create a variation of 1 nautical mile regarding the CPA. Nigel said that in some occasions he considers safe a CPA of 0.5K CPA, and I assume that will be the case with other merchant captains.

It is obvious the danger that represents regarding collision possibility those changes in speed regarding a deviation made by the ship assuming constant speed and course on the stand on vessel, as by the COLREGS.

I have also referred previously that in some conditions it is impossible to maintain sailboat course when the wind take a small deviation, particularly close upwind or downwind under spinnaker.