Collision Avoidance, Cones of Uncertainty, and Appropriate CPA

[Dockhead]

I met the game development guys about a simulator.

They said it's child's play if no uncertainty is modeled into the courses of the vessels. You create the vessels you want to use, with their dimensions, appearances, and maneuvering characteristics, then there are a number of open source building blocks, vector math engines and so forth, which you can put together to create the simulator.

There are apparently existing ship and submarine simulators, which are sold as games, which might already have the necessary functions.

However, if we want to model uncertainties -- which is what makes it interesting -- there is a lot of extremely complex math involved which would require outsourcing to Russian or Israeli programmers, and the cost goes up exponentially.

I have a relationship with a university which has a program in game development -- I might try to call in some chips and get this made into a class project.

But in any case, I think, given the extreme difficulties we've seen in visualizing some of these crosses, such a thing would be extremely useful.

I wonder if any of the pros on here have done any simulator training for collision avoidance. I know that bridge simulators are now widely used to practice maneuvering characteristics, but what about collision avoidance?

[El Pinguino]

Originally Posted by Dockhead

........

I wonder if any of the pros on here have done any simulator training for collision avoidance. I know that bridge simulators are now widely used to practice maneuvering characteristics, but what about collision avoidance?

They have been around for radar collision avoidance since at least the mid 1960's which is when the Radar Observer's Course became a compulsory extra when sitting second mates. Courses for serving ship masters were introduced at about the same time.

Primitive by today's standards but quite advanced for their time... by the early 70's it was a case of 3 x 2 man teams in separate cubicles with the 'man in charge' running another 3 or 4 ships from his 'command centre' ie his desk. They would give you Dover Straits and other hot spots... also show you 'classic collisions'...

That was all based around use of radar in fog. In clear vis you were expected to stay out of trouble with compass, eyeball and aspect.

The last course I was sent on in Port Klang about 12 years ago was more like a video game and treated as such....

Pic = Ping's bridge team on yet another Company funded beano.... C/0, 2/0 and 3/0

[Dockhead]

Originally Posted by El Pinguino

They have been around for radar collision avoidance since at least the mid 1960's which is when the Radar Observer's Course became a compulsory extra when sitting second mates. Courses for serving ship masters were introduced at about the same time.

Primitive by today's standards but quite advanced for their time... by the early 70's it was a case of 3 x 2 man teams in separate cubicles with the 'man in charge' running another 3 or 4 ships from his 'command centre' ie his desk. They would give you Dover Straits and other hot spots... also show you 'classic collisions'...

That was all based around use of radar in fog. In clear vis you were expected to stay out of trouble with compass, eyeball and aspect.

The last course I was sent on in Port Klang about 12 years ago was more like a video game and treated as such....

OK -- so the old ones showed just the radar screen?

And the recent one you get to look out the windows too?

When you say "treated as such" -- you considered it not to be worth much?

[El Pinguino]

Well...... when you are used to the real thing..... it isn't really real... a bit like learning ship handling with models in a pool...

Yes the modern ones have the big wall display... multi screens... set up like a proper bridge with buoyage and land and shallow bits and ships coming at you from all directions and proas and dugouts zipping to and fro ( which the wise totally ignore ) but it is still just what it is...

If you have just been taken off a lumbering old bulker and promoted to a Stena HSS yes of value...

Pics... taken by moi when on another company funded beano...
Harwich to the Hook on a Stena HSS ... asked the master how they dealt with other ships when doing 45.7 knots... he said they just treat everything else as if it was standing still. Radar pic is while crossing Nord Hinder TSS...

[El Pinguino]

Here is an interesting thing.... I just noticed they have the CPA alarm set to 1 cable and the TCPA alarm set to 1 minute....... they obviously didn't get the '2 mile' memo...

[Dockhead]

Originally Posted by El Pinguino

Well...... when you are used to the real thing..... it isn't really real... a bit like learning ship handling with models in a pool...

Yes the modern ones have the big wall display... multi screens... set up like a proper bridge with buoyage and land and shallow bits and ships coming at you from all directions and proas and dugouts zipping to and fro ( which the wise totally ignore ) but it is still just what it is...

If you have just been taken off a lumbering old bulker and promoted to a Stena HSS yes of value...

Pics... taken by moi when on another company funded beano...
Harwich to the Hook on a Stena HSS ... asked the master how they dealt with other ships when doing 45.7 knots... he said they just treat everything else as if it was standing still. Radar pic is while crossing Nord Hinder TSS...

Ha, ha. Yes, that kind of underlines the significance of difference in speed.

I talked to one of the Red Jet drivers in Cowes once -- 40 knots across the Solent twice an hour -- yowza!

He said the same thing -- he said it's like playing a video game. At 40 knots, you are in sole control of every crossing so you just dodge around. They generally stay out of the shipping channels and sail right across the Bramble Bank (obviously not at LWS!).

I was quite afraid of the Red Jets when I first started sailing in the Solent, but then relaxed once I understood that I had zero influence on any crossing with them. So you just ignore them and let them do their thing

They have an amazing record -- no collisions as far as I know, in how many tens or hundreds of thousands of high speed crossings in heavy traffic.

[Exile]

Originally Posted by El Pinguino

Pic = Ping's bridge team on yet another Company funded beano.... C/0, 2/0 and 3/0

Remarkable what we can all learn about the professional practices of big ship crews here on CF!

[Juho]

Originally Posted by Dockhead

I'm also interested to know if anyone thinks that safe passing distances should be less or more between ships and small vessels as opposed to ships and other ships.

One interesting point is that the relationship between small and large vessels is asymmetrical. Being 1 NM in front of the bow of a large fast vessel may be dangerous to all vessels (both large and small). But being 1 NM in front of the bow of a small slow vessel not very dangerous to any vessel.

The max CPA may be the same in both cases (large-large and large-small crossings), but CPA may be smaller in large-small crossings when the vessels meet in some other angle (other than the big one pointing the small one).

It may however be so that in practice large ships have only one collision avoidance procedure that applies to all vessels, small and large (keep it simple). Because it is their bow that is dangerous, they will start the procedure at the same distance in any case, and in open waters their actions (not the small boat's actions) determine the final CPA. The small slow boat is just a buoy for them.

[evm1024]

Originally Posted by Juho

One interesting point is that the relationship between small and large vessels is asymmetrical. Being 1 NM in front of the bow of a large fast vessel may be dangerous to all vessels (both large and small). But being 1 NM in front of the bow of a small slow vessel not very dangerous to any vessel.

The max CPA may be the same in both cases (large-large and large-small crossings), but CPA may be smaller in large-small crossings when the vessels meet in some other angle (other than the big one pointing the small one).

It may however be so that in practice large ships have only one collision avoidance procedure that applies to all vessels, small and large (keep it simple). Because it is their bow that is dangerous, they will start the procedure at the same distance in any case, and in open waters their actions (not the small boat's actions) determine the final CPA. The small slow boat is just a buoy for them.

I collision with a small boat is deadly to their career as well as to anyone on the boat.

[Lodesman]

Originally Posted by Dockhead

I wonder if any of the pros on here have done any simulator training for collision avoidance. I know that bridge simulators are now widely used to practice maneuvering characteristics, but what about collision avoidance?

When I came up, all our training was at sea on ships. Now the RCN uses bridge simulators for a large portion of that training. They tried to use them for all, but the end product was lacking, so now use a combination of simulator and time in training ships. The final polishing is done on operational ships as an apprenticeship. The simulators can do manoeuvring, berthing, collision situations, navigation training and are quite good for developing the mechanical skills of watchkeeping. They need the time at sea to see how it all comes together, and develop the nuances of watchkeeping.

[Lodesman]

Originally Posted by El Pinguino

Here is an interesting thing.... I just noticed they have the CPA alarm set to 1 cable and the TCPA alarm set to 1 minute....... they obviously didn't get the '2 mile' memo...

Perhaps being 1 of 2 radars on the bridge, they have that one set to squawk for serious dangers and the other set up for more typical parameters. Assume that one's the X-band?

[Lodesman]

Originally Posted by Lodesman

how many degrees are you from the heading of the ship astern, when you profess to no longer be ahead of that ship (at the end of your 320' journey)?

Well apparently I've scared off Rod, or he's giving me the silent treatment.

So radian rule tells us that a 6º angular distance is equal to 1/10th of our distance to the object(s). So being at 1 mile or 6000 ft (might as well round to a nice figure - the purpose is not accuracy to three decimal places, but an ability to do it in your head while maintaining that all-important eyes up and out of the electronics), 1/10 is 600 ft, which easily divides into 100'/1º. Rod's transom is 50' from the heading (path) of the ship, so that would be 0.5º. That's right - one-half of one degree. The centre of his boat would be 0.7º off the heading; his entire boat would fit within 0.9º of the ship's heading.

Another way to calculate the same thing and some peeps prefer to do it this way is to assume 1º = 33 yards for every mile of distance. Typically you read the bearing from the gyro, multiply that by the distance and again by 33 yds to determine CPA or distance off. Working backwards, and converting 33 yds to 100 ft, knowing the distance is 1 mile, work out that 1º would be 100', so 1/2º is 50'.

I'm sure there are differing opinions on this, but I'd say he's still ahead of the large ship, and will be for some time during the period his range to that ship is decreasing. Of course there will be a point where most experienced mariners will say he's no longer ahead of the ship, and on its bow instead, but even after that occurs, he will still be well within the cheerily-named "kill zone" until he's fairly close to CPA. I would say he's not past and clear until he's past the ship's beam. My 2cents FWIW.

[Dockhead]

Originally Posted by Lodesman

Well apparently I've scared off Rod, or he's giving me the silent treatment.

So radian rule tells us that a 6º angular distance is equal to 1/10th of our distance to the object(s). So being at 1 mile or 6000 ft (might as well round to a nice figure - the purpose is not accuracy to three decimal places, but an ability to do it in your head while maintaining that all-important eyes up and out of the electronics), 1/10 is 600 ft, which easily divides into 100'/1º. Rod's transom is 50' from the heading (path) of the ship, so that would be 0.5º. That's right - one-half of one degree. The centre of his boat would be 0.7º off the heading; his entire boat would fit within 0.9º of the ship's heading.

Another way to calculate the same thing and some peeps prefer to do it this way is to assume 1º = 33 yards for every mile of distance. Typically you read the bearing from the gyro, multiply that by the distance and again by 33 yds to determine CPA or distance off. Working backwards, and converting 33 yds to 100 ft, knowing the distance is 1 mile, work out that 1º would be 100', so 1/2º is 50'.

I'm sure there are differing opinions on this, but I'd say he's still ahead of the large ship, and will be for some time during the period his range to that ship is decreasing. Of course there will be a point where most experienced mariners will say he's no longer ahead of the ship, and on its bow instead, but even after that occurs, he will still be well within the cheerily-named "kill zone" until he's fairly close to CPA. I would say he's not past and clear until he's past the ship's beam. My 2cents FWIW.

That seems entirely sound to me, and a great illustration of what you can and can't see.

The easiest way to visualize it, other than being there, at sea, is on a maneuvering board. Passing ahead of a ship with that difference in speed, he will be off your beam -- whatever point you are aiming at will be 14 degrees ahead of your beam, IF the courses are exactly perpendicular. In reality they won't be exactly perpendicular, so at some difference in speed, it becomes absolutely impossible to see with the naked eyes how you're crossing. 3 degrees here or there might be you passing ahead or behind, or it might be 3 degrees off of perpendicular.

[Dockhead]

Originally Posted by Juho

. . .

It may however be so that in practice large ships have only one collision avoidance procedure that applies to all vessels, small and large (keep it simple). Because it is their bow that is dangerous, they will start the procedure at the same distance in any case, and in open waters their actions (not the small boat's actions) determine the final CPA. The small slow boat is just a buoy for them.

It would be very, very interesting to graph different crossing situations -- different crossing angles, and different speed differences -- to see how much course change is required at what range to increase CPA by one cable. I guess it will very visible how the curve goes up to indicate an in extremis situation, then "collision unavoidable".

An experienced mariner will no doubt be able to just feel different crossings, and will just know that he can leave it until later in some cases, but do you really want to risk getting it wrong? Is it even worth the trouble? Wouldn't it be a great distraction from the rest of the collision avoidance workload, to be grappling with this in the heat of a crossing?

I think that's why we have rules of thumb -- keep everyone one mile off and you have an adequate margin of error across a wide range of crossings to have time to observe and confirm that you are crossing as you planned, and still have time to make another correction if necessary. Simplifying the process makes it more orderly and safer.

Another reason to follow something like a set sequence of distances is to facilitate COORDINATED maneuvering by both vessels. The whole system doesn't work if one vessel is giving way, at a different time than when the other one is standing on. Someone in another thread wrote something like "If at a quarter of a mile I determine that a risk of collision exists . . . " -- my hair stood on end. That can't work, being so out of synch with the distances at which the other vessel will be making his decisions and making his moves. The stand-on vessel really must have a good idea of when he can say "that guy over there should have maneuvered by now", in order to know what he can and should be doing himself. If it's anything from 10 miles to 1/4 mile, it just won't work -- you just can't guess the other vessel's intentions. Both vessels need to be working according to similar time frames, and I have long held that the much shorter horizon of awareness on board recreational vessels is one of the main problems we have with collision avoidance.


I thought Ping's comment was very interesting, about how he's happy with a much smaller CPA provided he's the one maneuvering, whereas if it's the ship maneuvering, it should be more. I'm still trying to get my head around that. Ping, is that because you can turn faster, if need be? I can see that if I'm passing behind a vessel without a big difference in speed, but in other cases, I think I would want MORE -- because ANY difference in speed reduces my control of the crossing, and reduces my ability to correct anything if it starts to look hairy when we are already close to CPA. I would think on the contrary that the greater the difference in speed, the closer the SHIP can shave it, with safety. Because the greater difference in speed, the less we can do to screw it up -- the more control he has. Or do you see it differently?

[Lodesman]

This is what a 225m long ship looks like from about 180 feet: