Collision Avoidance -- Dealing with Multiple Targets

[bmz]

Originally Posted by Suijin

Uh..

From my perspective, this is a grossly irresponsible recommendation. It's one thing to give priority to class A targets, in certain situations, but ignoring class B targets is foolish. It can lead to far more than a "scratch in the fiberglass".

As far as Dockhead's point, he was talking about situations where there are three or more vessels, at which point there are no burdened or give way vessels; all are required to what they can to avoid a collision. Yes following COLREGS to the greatest degree possible is best practice for the sheer point of predictability, but the situation has changed.

As far as "ability to maneuver" is concerned, Dockhead is right that the "event horizon" of a large ship is much greater than that of a small boat. They are traveling at 20+ knots and thinking miles ahead. The 30' sloop traveling at 6 knots has a much shorter horizon, and much more limited ability to maneuver if they find themselves at risk of collision. Of course meeting at sea is much different than meeting in a narrow channel.

I sure wish you guys would heed Dockhead's requests.

You allege that this is "irresponsible:" I did not advise "ignoring" class B vessels; I said "The class B targets are all small and maneuverable, and if you are a sailing vessel most of them will have to yield to you. In any event, when you get close enough you will both see each other easily and the burden vessel should yield" More importantly you can't get into "as much trouble" crashing into a class B vessel as a class A vessel;[Crash into a class B vessel and you will scratch your fiberglass] crash into a class A vessel, and you will die."

For the life of me I cannot see what is irresponsible about it, could you please elucidate?

Your allegation regarding three or more vessels is not quite correct. The steering and sailing rules continue to apply -- with respect to each crossing vessel individually. But Rule 2 allows you to deviate somewhat according to the necessities of the situation. And you apply Rule 2 to govern your actions when the other rules don't tell you what to do.

I agree with Dockhead's statement on "event horizon" and "ability to maneuver" when a collision is imminent. That's why it is so important for sailors to focus only on class A targets on their AISs to avoid a situation where they get so close to that large vessel that they have to maneuver to steer clear.

[Paul Elliott]

Originally Posted by ramblinrod

(Of course I do not force a larger commercial freighter to change course, when from 5 miles away I can simply change course of my "stand on" little boat, by one degree, especially when course corrections to hold intended course are prolly more than that.)

About that one degree course correction:

If you are looking at a head-on collision from five NM range, with the freighter going 15 kts and you sailing at five kts, your one-degree alteration will give you less than 180 ft of clearance at CPA.

Perhaps you should rethink your plan here...

[captmikem]

The more I read this, the more complicated it gets.. when in actuality it is very simple.

How you want or conceive it to be is one thing.

The reality is more like this:
In a congested area like a harbor entrance and inside Larger ships have the right of way.. simple, they need not be constrained by their draft, Rule 9 applies.. basically stay out of their way.

( I came into MIA on an 800’ container ship as second officer a long time ago on a Sunday afternoon. The entrance was covered with small boats, we could not see anything under about a mile ahead. I asked the pilot about all this traffic and how we handled it. “Ignore em” was his answer, we had no control over them, we certainly could not avoid them, so ignore them.)

At sea, in congested areas there are normally Traffic separation zones, follow the rules stated for them. Simple. (basically stay in your lane, cross perpendicular and quickly, and use the inshore lane to stay out of the way. Again, rule 9 applies.) Often there are VTS systems, give traffic a call and let them know who you are, where you are going and what your speed is, they will let ships in the area know about you, AND let you know about ships you may be in conflict with or near.

On the occasional time you meet a ship at sea, remember, YOU are hard to see at 12 miles. If he is a constant bearing and closing, try him on 13, (most ships actually turn the radio monitoring 16 down when near a harbor because there is so much senseless chatter on it, it becomes a distraction. Sometimes they forget to turn the volume up once at sea. If it gets down to six miles or less, alter for where they are now, they will be gone when you get there. (as long as they are forward of the beam).

At night, your little running lights are dim. A ships two masthead lights are what other ships are looking for. White shows up on the horizon a LOT farther than red or green. You may show up on radar, if the wx is not rough, if you do, and you are the stand on vessel the ship will alter for you, but ONLY after the watch officer and the lookout have spent time looking outside to see what the return is.

Remember at sea ships often will not see you! . Seeing those two whites get closer or farther apart means he is altering. If they stay the same and that bearing is not changing, You have the power make it change. Don’t wait too long.

Simple.

Then there are places like the straights of Florida where there is a lot of N S traffic, traffic entering and leaving MIA and FLL, tons of fish boats, sailboats, sightseeing boats and small craft. Fishboats often change course every minute, Headboats are drifting, sailboats are often becalmed or racing, and half the little boats out there haven’t a clue. You just deal with it. Like driving in Spain or Turkey.

M

[Dockhead]

Originally Posted by ramblinrod

Just out of curiosity, what do you believe the real and significant difference between having "right of way" and being a "stand on" vessel, or being the "burdened" or "give way" vessel, other than just terminology semantics?

I know there was a definite change in the "official" terminology many years ago, but my impression was that is was just semantics, perhaps to reduce the possible misinterpretation that a "right of way" boat had no obligation to avoid collision with a "burdened" boat, even though, to my knowledge, they always have, if the "burdened" boat, in fact, did not "give way".

You have asked a very important question.

Why don't we discuss it in a separate thread?

I've written an answer here: Thread for Basic COLREGS Questions - Cruisers & Sailing Forums

[Dockhead]

Originally Posted by captmikem

. . . The reality is more like this:
In a congested area like a harbor entrance and inside Larger ships have the right of way.. simple, they need not be constrained by their draft, Rule 9 applies.. basically stay out of their way.. . .

I think using the term "right of way" is unfortunate, but of course the substance of what you say here is absolutely correct.

In harbor entrances and approaches to harbors, where ships are coming in and out and following defined paths, stay out of their way. Not only when Rule 9 applies. This is Rule 2 -- don't cause a risk of collision situation, especially in a congested area where it can be difficult to unwind, when you can easily avoid it by staying out of the fairways and traffic lanes, and cross them only when the coast is clear.

The reason why you never, ever, ever sail across the bow of a box boat in your San Juan 24, three cables away, is not because the box boat has the "right of way" -- it's because 3 cables is not within the horizon of collision avoidance procedure for such a vessel. If you were crossing the English Channel under sail and outside of the TSS's, and the box boat saw you (you'd need a radar reflector) from its normal horizon, then in fact you would need to follow the Rules and stand on during that phase when you are obligated to. But it's completely different in harbor entrances.

[Dockhead]

Originally Posted by ramblinrod

This is nonsense!

Of course Col Regs covers multiple target situations.

Obligations are simply determined by considering 2 boats at a time, earliest collision first.

But one has to then consider all other possible subsequent collisions, by considering, 2 boats at a time.

If you must change course or speed to give way, only 4 things can happen.

A. All clear and no further risk of collision.

B. New collision risk, you are give way, and continue to alter course and speed in such a way that you can stand on.

C. New collision risk, your are stand on, and others alter course and speed to in such a way that they can stand on.

D. Some idiot doesn't follow the rules, and everyone has to avoid the idiot while staying clear of all other stand on vessels, still following the rules.

What am I missing?

(Of course I do not force a larger commercial freighter to change course, when from 5 miles away I can simply change course of my "stand on" little boat, by one degree, especially when course corrections to hold intended course are prolly more than that.)

To me the notion that Col Regs do not apply to multiple targets is absolutely ludicrous.

Peace -- you are both right.

Yes, of course, the COLREGS certainly apply to multiple vessel crossings, and the first thing to do with multiple targets, is to think it through one vessel at a time and see if you can deal with it with a series of maneuvers. The trouble starts when avoiding one vessel puts you under the bows of another (what seems to keep happening to U.S. Navy destroyers). That's what this is about.

As to your one-degree correction -- someone else has already commented.

It is a common misconception to overestimate the "maneuverability" of your small boat.

To find out the reality, just do this exercise:

Take your boat's maximum ROT and speed. Take a big bulker's maximum ROT and speed. From five miles out, figure who can change the CPA more. You will need basic trig. You will see that your ROT plays no role -- the bulker has complete command of the crossing. At 5 miles out, in fact, you are practically a sitting duck. It's good to know the basic mathematical facts of this and get rid of the illusion that you are so "maneuverable". Your high maximum ROT only matters in very close quarters.

[ramblinrod]

Originally Posted by Dockhead

Peace -- you are both right.

Yes, of course, the COLREGS certainly apply to multiple vessel crossings, and the first thing to do with multiple targets, is to think it through one vessel at a time and see if you can deal with it with a series of maneuvers. The trouble starts when avoiding one vessel puts you under the bows of another (what seems to keep happening to U.S. Navy destroyers). That's what this is about.

As to your one-degree correction -- someone else has already commented.

It is a common misconception to overestimate the "maneuverability" of your small boat.

To find out the reality, just do this exercise:

Take your boat's maximum ROT and speed. Take a big bulker's maximum ROT and speed. From five miles out, figure who can change the CPA more. You will need basic trig. You will see that your ROT plays no role -- the bulker has complete command of the crossing. At 5 miles out, in fact, you are practically a sitting duck. It's good to know the basic mathematical facts of this and get rid of the illusion that you are so "maneuverable". Your high maximum ROT only matters in very close quarters.

I don't understand. It is not an issue of who can get further away from whom faster. 180 ft is plenty of distance from any size vessel side or stern. On the race course, when avoiding, 1mm is best; in any circumstance all that is required.

I think you guys need to get your heads out of your instruments and mathematics and stop fretting about maintaining maximum distance, or some arbitrary minimum fixed distance from all vessels around you.

There's no need. All you have to do is avoid being in the exact same spot at the exact same time and that is very, very, easy. Just like when racing and trying to be at the exact same spot at the exact same time.

When I am in the St. Lawrence Seaway, or Niagara River, there are spots where it simply is not possible to be more than 50 ft away, and there may be 50 rec boats zipping around a convoy of freigthers all converging at a narrows.

[Kenomac]

Originally Posted by ramblinrod

I don't understand. It is not an issue of who can get further away from whom faster. 180 ft is plenty of distance from any size vessel side or stern. On the race course, when avoiding, 1mm is best; in any circumstance all that is required.

I think you guys need to get your heads out of your instruments and mathematics and stop fretting about maintaining maximum distance, or some arbitrary minimum fixed distance from all vessels around you.

There's no need. All you have to do is avoid being in the exact same spot at the exact same time and that is very, very, easy. Just like when racing and trying to be at the exact same spot at the exact same time.

When I am in the St. Lawrence Seaway, or Niagara River, there are spots where it simply is not possible to be more than 50 ft away, and there may be 50 rec boats zipping around a convoy of freigthers all converging at a narrows.

I absolutely agree 100%. Just keep a good watch and stop clogging up the radio with unessessary chatter. People can't be keeping a good watch, looking at their AIS screen and chart-plotter, screwing around with the radio all at the same time time.

Just stay out of the way and slow down if it's the best way to avoid a collision. Maintaining course and speed is ridiculous.

[Suijin]

Originally Posted by ramblinrod

I don't understand. It is not an issue of who can get further away from whom faster. 180 ft is plenty of distance from any size vessel side or stern. On the race course, when avoiding, 1mm is best; in any circumstance all that is required.

On a passage back from Bermuda I was in a Force 8/9 gale at night, moonless night, thunderstorms completely encircling me with a freighter bearing down on me who did not answer on any channel. He passed about 300 feet astern. It sure did not feel like plenty of distance at the time.

And he had way more maneuverability than I did, that's for damn sure.

Everything is relative, particularly when you're on a smaller boat. 50' in an orderly river with channel markers is very different than 50' in the open ocean with poor conditions and visibility.

And racing is a poor comparison. You have boats following a course with clear rules of order and everyone paying attention. And even then, at least in Annapolis, you have a couple of good solid (and extremely expensive) T-bone collisions every season and probably more clipped stern rails than you can count.

[roland stockham]

Originally Posted by ramblinrod

I don't understand. It is not an issue of who can get further away from whom faster. 180 ft is plenty of distance from any size vessel side or stern. On the race course, when avoiding, 1mm is best; in any circumstance all that is required.

When I am in the St. Lawrence Seaway, or Niagara River, there are spots where it simply is not possible to be more than 50 ft away, and there may be 50 rec boats zipping around a convoy of freigthers all converging at a narrows.

You are missing an important point - In a constrained channel large vessels are traveling a maneuvering speed or under tow by tugs. I the open sea the same vessel may be doing 24kn. This speed creates a suction effect along the flank and any small vessel within about 100m may get pulled in. If you are under sail the wind is also going to be effected so you may suddenly loose power. Even at fairly slow speeds you can feel the suction from the prop. I generally think 1/2 mile is minimum and 1m is better. But I do agree that a bit of racing does wonder for sharpening close quarters skills and would have many cruiser terrified!!!

[Dockhead]

Originally Posted by ramblinrod

I don't understand. It is not an issue of who can get further away from whom faster. 180 ft is plenty of distance from any size vessel side or stern. On the race course, when avoiding, 1mm is best; in any circumstance all that is required.

I think you guys need to get your heads out of your instruments and mathematics and stop fretting about maintaining maximum distance, or some arbitrary minimum fixed distance from all vessels around you.

There's no need. All you have to do is avoid being in the exact same spot at the exact same time and that is very, very, easy. Just like when racing and trying to be at the exact same spot at the exact same time.

When I am in the St. Lawrence Seaway, or Niagara River, there are spots where it simply is not possible to be more than 50 ft away, and there may be 50 rec boats zipping around a convoy of freigthers all converging at a narrows.

You didn't serve on the Fitzgerald, by any chance? Yeah, it's "very, very easy"


180 feet is not far enough from a ship travelling at sea speed! You need to stop projecting lake and bay-sailing frames of reference onto what happens at sea -- it's totally different out there. The distances are different, the timings are different, it is all different.

Less than one mile is dangerous, and a mile may be too close if passing ahead. Why? Because you can't be exactly sure within a about where that ship travelling at 24 knots will be. A small course error, or variation in set or drift will change the position of a vessel traveling at that speed by hundreds of feet. Besides that, a small boat under sail will vary a lot in course and speed as it goes along. The result is called the "cone of uncertainty", and if you want to be reasonably certain about not getting run down, you have to stay outside of it.

That's exactly why ships you meet at sea will have standing orders to keep usually one mile away from you and any other traffic, and they will set it up from usually 10 miles out, with last maneuvering typically at 3 or 4 miles out. From that point, they are committed to the crossing, and if you make some unpredictable move at a lesser difference, you will mess everything up. This kind of behavior is exactly why they call us WAFIs (wind assisted f**** idiots), and try to steer a wide berth around us.

If you screw up and end up less than a mile from a ship at sea, you may even get the watchstander in trouble, not to mention the risk getting yourself killed. 180 feet or 500 feet is not an acceptable passing distance in open water.

Once again -- this thread is not for these basic, general questions. If you want to discuss this kind of thing, let's please go to: Thread for Basic COLREGS Questions - Cruisers & Sailing Forums

[Dockhead]

Originally Posted by roland stockham

You are missing an important point - In a constrained channel large vessels are traveling a maneuvering speed or under tow by tugs. I the open sea the same vessel may be doing 24kn. This speed creates a suction effect along the flank and any small vessel within about 100m may get pulled in. If you are under sail the wind is also going to be effected so you may suddenly loose power. Even at fairly slow speeds you can feel the suction from the prop. I generally think 1/2 mile is minimum and 1m is better. But I do agree that a bit of racing does wonder for sharpening close quarters skills and would have many cruiser terrified!!!

Indeed!

Just don't try racing moves on ships!

[estarzinger]

I dont have any super clever tricks.

But I will suggest that it is different when you have say 4 targets vs when you have very crowded water - say circa +40 targets.

With +40 targets I believe the thought process needs to be changed. Rather than trying to avoid targets, you are trying to slot into and slide between clear zones/lanes. And rather than making 'clear bold' maneuvers you want to be entirely predictable and make small smooth incremental changes.

[StuM]

Originally Posted by Paul Elliott

About that one degree course correction:

If you are looking at a head-on collision from five NM range, with the freighter going 15 kts and you sailing at five kts, your one-degree alteration will give you less than 180 ft of clearance at CPA.

Perhaps you should rethink your plan here...

Also:"Any alteration of course and/or speed to avoid collision shall, if the circumstances of the case admit, be large enough to be readily apparent to another vessel observing visually or by radar; a succession of small alterations of course and/or speed should be avoided. "

[Pelagic]

Originally Posted by estarzinger

I dont have any super clever tricks.

But I will suggest that it is different when you have say 4 targets vs when you have very crowded water - say circa +40 targets.

With +40 targets I believe the thought process needs to be changed. Rather than trying to avoid targets, you are trying to slot into and slide between clear zones/lanes. And rather than making 'clear bold' maneuvers you want to be entirely predictable and make small smooth incremental changes.

Ironically, that was exactly the IMO design brief for ARPA radars.
It was called "PAD" (Predicted Area of Danger)

Raytheon came out with the tracked targets showing a Trapezoid shaped area extending from them that showed on your radar..the area NOT to go into

It was a great system for ML and dense traffic situations but copyright issues prevented it from being generally adopted and is probably only used now by the military
https://trid.trb.org/view.aspx?id=147010