US Navy destroyer collision

[Snowpetrel]

^^ Hpeer, I agree about the awareness. All CPA info Accuracy varies depending on the situation. So its hard to be precise on this. Steady state conditions give reasonable accuracy, but dynamic changing courses or speed make all CPA calculations unreliable until things settle down again.

[Snowpetrel]

Here is a quick radar plot showing what could happen if the warship (147°T) increased speed from 13 to 20 knots at a similar time to the container ship altering course from 070°T to 130°T. The net effect of both alterations (assuming both are instantaneous and simultaneous) is that both vessels would still be on a collison course. 6 minute plot, 6 mile range, 1 mile range rings.

The courses and speeds are just plucked out of thin air. And much of what the Acx Cystal's captain has said doesn't seem to compute well with this scenario.

[Snowpetrel]

Originally Posted by Astrid

Snowpetrel, might the range scale on the ARPA have been set wrong?

Unlikely, these guys are using the gear all the time. At least on a merchant ship the ARPA, Charts and ECS (or ECDIS) are the tools of the trade and the use becomes second nature pretty quickly.

I guess if the system was new or unfamilar to the OOW mistakes would be more likely.

[Dockhead]

Originally Posted by Snowpetrel

Here is a quick radar plot showing what could happen if the warship (147°T) increased speed from 13 to 20 knots at a similar time to the container ship altering course from 070°T to 130°T. The net effect of both alterations (assuming both are instantaneous and simultaneous) is that both vessels would still be on a collison course. 6 minute plot, 6 mile range, 1 mile range rings.

The courses and speeds are just plucked out of thin air. And much of what the Acx Cystal's captain has said doesn't seem to compute well with this scenario.
Attachment 150859

That's very useful!

Yes, but I think that a very plausible scenario starts to emerge -- Fitzgerald maneuvering very late, simultaneously with Crystal's Rule 17(a)(ii) maneuver. Crystal doesn't even perceive the new CPA because is not receiving AIS. Fitzgerald doesn't realize soon enough, that Crystal's maneuver cancels the effect of their own maneuver, and so crashes right into Crystal. Fitzgerald using its ability to increase speed quickly to try to "dart across", but this further compresses the unfolding situation and eliminates any time there might have been to correct.

Very similar to what happened with Porter and very plausible.

[Astrid]

Yes, that makes perfect sense.

[El Pinguino]

To get an idea what it can be like on the bridge in an area of heavy traffic this is worth a thorough read....

http://www.bahamasmaritime.com/wp-co...ver-Decent.pdf


Re reliance on AIS and Arpa ... 'He relied heavily on the use of radar for his anti-collision work, and did few visual checks.'

[Dockhead]

Originally Posted by El Pinguino

To get an idea what it can be like on the bridge in an area of heavy traffic this is worth a thorough read....

http://www.bahamasmaritime.com/wp-co...ver-Decent.pdf


Re reliance on AIS and Arpa ... 'He relied heavily on the use of radar for his anti-collision work, and did few visual checks.'

An interesting case, reminiscent of other collisions in this busy part of the North Sea, an area I have transited many times. One thing about collision avoidance that's important to keep in mind -- what is relatively straightforward, when only two vessels are involved, can become fantastically complex, when there are several, and the Rules don't really tell you what to do in such cases.


"Overreliance" on radar was not the cause of this collision, however -- on the contrary, according to the report, "The OOW was not using his radars/ARPA’s to the best advantage." He was overloaded with information from multiple targets and was distracted by a VHF call from the vessel he subsequently crashed into (a call which was worse than useless according to the report). He confused relative with true vectors, and mistook how he was passing, and thus made the wrong alteration, too late.

So on the issue of technology -- this is not too much, but more likely, too little technology. If he had been using OpenCPN, he would have had a graphic view of how he was crossing. Of course, the radar screen set on relative motion, and correctly interpreted, would also give that information. Bare eyes would not.

[Pelagic]

Thanks for the plot Snowpetrel... it does seem quite plausible.
(But again we are guessing

I took some screenshots of the AIS track of ACX Crystal to help give us a better overview and more accurate SOG and COG

Not sure what the Time stamps are on the recording, but the public report by Captain states

01:15 AM Target Red 40..... apparently no collision concern)
01:20 AM Target starts moving (Implies stationary before)
Final 10 minutes.... Starts Flashing Lights....
Then emergency turn to Starboard
WHY NO DANGER SIGNAL WITH HORN reported?? as it is much more effective than lights.

Seems that if the Fitz had done nothing, they would have been fine

After the Collision, ....looking at the Traffic Density I think the Captain wanted maneuverability at speed before turning around, which given the shock of the collision, seemed reasonable.

[estarzinger]

Originally Posted by Dockhead

Fitzgerald maneuvering very late . . . . .

I believe that Fitzgerald never knew they were in a "close cpa" situation, much less a collision situation. Because they never called the captain, and then they never sounded collision alarm (which they train very frequently with and should be 2nd nature). The fact they never did these two things is just about the only actual information we have about what was going on board FitzGerald.

But that is just a speculation, alternatively (but I believe way less likely), the OOD might have been "too busy" with the intercept to do either thing. . . . Or the captain might have slept thru his call to the bridge.

[hpeer]

Here is a 1:22 (one minute 22 second) video that may explains a lot.

If you have never seen it it's pretty neat.

DONT SPOIL IT FOR OTHERS!!!!!!

https://m.youtube.com/watch?v=vJG698U2Mvo

[Pelagic]

Originally Posted by estarzinger

....alternatively (but I believe way less likely), the OOD might have been "too busy" with the intercept to do either thing. . . . Or the captain might have slept thru his call to the bridge.

Actually, I think it is more likely that the OOD/Bridge was too busy to call the Captain

From AIS. Crystal is doing 18.5 knots when Fitz Target is Red 40° Range 3nm

If Fitz was stationary then CPA would have been around 1.8nm in about 10 minutes

But 5 minutes later Captain says Fitz started moving..... In those 5 minutes at 18.5 knots Crystal would have been about 1.57 mm closer to Fitz.

I think OOD may have been initially distracted with other tasks.... Then when aware at about 1.5nm range... ordered a turn to starboard while slowly bringing up speed....... thinking Crystal would continue on course and pass astern.

Now, 30 seconds later at about 1nm range OOD recieves reports of a constant bearing and gets startled with searchlight flashing his bridge.

Crystal is covering about 0.31nm per minute, if Fitz was also doing same speed, then it is only approx 90 seconds before collision, where OOD unsuccessfully tried last second counter of Crystal's turn to starboard.

If the Captain was called, it was probably only 90 seconds before collision.

[GordMay]

Originally Posted by hpeer

Here is a 1:22 (one minute 22 second) video that may explains a lot ...

Indeed!
I didn't see "it".

[Pelagic]

Originally Posted by hpeer

Here is a 1:22 (one minute 22 second) video that may explains a lot.

If you have never seen it it's pretty neat.

DONT SPOIL IT FOR OTHERS!!!!!!

It does explain how one can get distracted from a task as I did

[TwoBlocked]

Originally Posted by hpeer

Here is a 1:22 (one minute 22 second) video that may explains a lot.

If you have never seen it it's pretty neat.

DONT SPOIL IT FOR OTHERS!!!!!!

VERY GOOD!

A submariner line officer once told me how when becoming qualified he was amazed how a particular officer ALWAYS was able to determine the most imminent threat during various situations. When asked about it he said he just referred to the "waterfall display". That is what it was there for and so he used it. This was a while ago, and I don't know what sort of technology they have now, but gosh it is easy to miss the important things.

Like once on a USCG Cutter, we were considering tying up to a municipal dock after an arduous day. A bit of a current was running, and while approaching the dock, the Captain decided it was a bit risky due to the current and decided to go anchor. THEN someone noticed that our workboat-lifeboat was lowered to the rail. We would have smashed it. And NOBODY noticed it was there until we were veering away from the dock.

Another time, on a different cutter, we suddenly took a 5-10 degree list. At first, nobody thought it odd at first because we often did that when working buoys on deck with our boom, or making a tight maneuver on this 180 footer. But the captain wondered why they were working buoys during the noon meal and looked down on the buoy deck to see the Chief Boatswain Mate looking back up at the bridge, each wondering what the other was doing to cause the list. The Captain, that later became a rear Admiral, exclaimed "We're aground! Stop engines!"

Yeah, you can get distracted pretty easily...

[TwoBlocked]

Originally Posted by Dockhead

That's very useful!

Yes, but I think that a very plausible scenario starts to emerge -- Fitzgerald maneuvering very late, simultaneously with Crystal's Rule 17(a)(ii) maneuver. Crystal doesn't even perceive the new CPA because is not receiving AIS. Fitzgerald doesn't realize soon enough, that Crystal's maneuver cancels the effect of their own maneuver, and so crashes right into Crystal. Fitzgerald using its ability to increase speed quickly to try to "dart across", but this further compresses the unfolding situation and eliminates any time there might have been to correct.

Very similar to what happened with Porter and very plausible.

Yeah I am thinking, too, that last minute maneuvers by both vessels somehow countered each other to ensure a collision would happen even though each were trying to avoid a collision. With the ACX Crystal swinging and the USS Fitzgerald doing who knows what, it would be difficult for either vessel, either visually or electronically, to figure out how the situation was really developing, let alone the best action to take. Reminiscent of the Andrea Doria and Stockholm, but on a much shorter time scale.

Even being by the book (RoR), a stand on vessel may maneuver to avoid a collision when it is apparent the give-way vessel is not taking appropriate action. But if at that moment, the give-way vessel DOES take appropriate action, only to counter the stand-on vessel's actions, is anyone at fault? Perhaps not...