Author Topic: 'Force = Mass x Velocity"  (Read 387 times)

Offline HenryC

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'Force = Mass x Velocity"
« on: June 17, 2017, 10:11:01 AM »
This is what a network news reporter told us this morning, explaining the extensive damage suffered by a US destroyer in a collision with a fully loaded Philippine container ship in the approaches to Yokosuka, Japan. The equation is nonsense, of course. Mass times velocity is momentum, NOT force. Perhaps what he really meant was “Force = mass times acceleration”, which although physically meaningful, is irrelevant in this context.

It makes no difference. We don’t expect broadcast journalists to be knowledgeable about Newton’s Laws of Motion. Still, if you’re going to show off your erudition, you should at least make sure you get it right. Surely, there’s someone in a network news room who took high school physics. A blunder like that makes you wonder how much of the rest of the story is accurate.

I’ve been to Yokosuka (pronounced yo-KUS-ka, he got that wrong too) and its a busy commercial port and a big US Navy base. Its not unexpected that there might be a nightime maritime accident in those busy, crowded waters, where ships are often restricted in their ability to maneuver. I know very little of the details of this collision, but daylight TV footage of the two vessels show the destroyer was T-boned on the starboard side by the freighter, right about where her bridge is located. There was extensive damage to the warship’s hull, main deck and superstructure, and the freighter’s bow was stove in. The destroyer was low in the water and taking on water, down by the head. Several pumps were operating and it looked like they were barely keeping up with the flooding. There were injuries on the American ship (including the Captain who had to be medevaced), and seven sailors were missing, presumably knocked over the side or trapped in the wreckage.

There is no telling who was at fault in the accident, although the location of the damages suggests the freighter had the right-of-way at the moment of contact. Still, it is conceivable that either ship, or even both, could have been at fault. The fact the US skipper was among the casualties suggests he was on the bridge at the time of the accident, or in his sea cabin, which is always located nearby. Another likely location for him to be at was in the ship’s Combat Information Center, which on my destroyer in 1968, was located just aft of the bridge. CIC is where all information coming into the ship is directed, and decisions as to how to respond are made and communicated to the relevant departments. Equipment and procedures are designed to deal with multiple and simultaneous threats. In those busy waters at that time of night, I have no doubt the Captain was awake and on duty. It would be standard operating procedure.

US Navy warships are extremely careful about collisions. They have large crews and are always fully manned when underway. They are bristling with sensors and all traffic nearby is constantly monitored and tracked. On my ship, it was SOP for the Officer of the Deck to wake up the Captain if any vessel’s Closest Point of Approach was even expected to come within five nautical miles, even in the middle of the ocean, far from land with no one else around.

Commercial vessels do have a reputation for being a bit sloppy with their safety procedures. Rather than pay seamen overtime, they have been known to steam under automatic pilot, and not maintain a proper lookout. Blue water yachtsmen are always complaining of near misses. Still, accidents do happen, often due to training, fatigue, procedure, equipment or communications issues. This may even be one of those “radar-assisted collisions” you often hear about.
« Last Edit: June 17, 2017, 10:14:51 AM by HenryC »

Offline tmw

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Re: 'Force = Mass x Velocity"
« Reply #1 on: June 17, 2017, 09:57:58 PM »
I had the same reaction to force = mass x velocity.  I would have guess that energy to stop the ship being half the mass times velocity squared would be the most appropriate.

In my ROTC days I learned that the Navy Captain will likely be held fault, even if it's completely the commercial ship's fault.  This isn't a just or fair situation--the price one pays for being Captain is to be responsible no matter what happens, which is why as Henry states the Captain was likely awake and on duty in those busy waters.  In this case, I'd wager the Captain's career is over, no matter what is found in the investigation.

Offline HenryC

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Re: 'Force = Mass x Velocity"
« Reply #2 on: June 19, 2017, 12:47:36 AM »
Regrettably, you're probably right.  It's been a long time since I got out of the Navy, but that sure was the case when I was in.

Having been been a member of the bridge watch myself, and been involved in similar encounters, I know the standard underway procedures and standing orders should have protected the ship.  All traffic in the vicinity would have been monitored, and any contact on an unchanging bearing, or even any Closest Point of Approach under some healthy distance should have immediately set off evasive action.  Even if the container ship had deliberately tried to ram the destroyer, there should have been some time to maneuver, or at least set off the collision alarm and wake the crew up.

When I was a Navy Quartermaster, it was one of my duties on watch to constantly monitor the range and bearing to all contacts using the radar repeaters on the bridge and immediately report to the Officer of the Deck any course and speed change that presented a potential threat to us.  Since everybody was moving, the calculations were done on paper maneuvering boards, little vector diagrams that gave you the relative courses and speeds of the contacts.   I also listened to the telephone chatter from the lookouts, and I could check up on the contacts if they were near enough for their lights to be visible in binoculars. The radar specialists in the Combat Information Center also monitored the radars and kept up a relative motion plot, providing a backup and confirmation of my observations. You've seen these guys in the movies, they are always writing backwards on glass maneuvering boards keeping track of everybody within range of the ship's sensors.  Nowadays, this is probably all done automatically by computers hooked up to the radars, so what could possibly go wrong, eh?

Still, accidents happen, that's why they call them accidents.  Perhaps the conditions were very crowded, or other events distracted the crew, or there was a steering casualty on the freighter, or maybe somebody just screwed up.  I have no doubt the facts will all come out at the inquiry.

The destroyer was burdened under the rules of the road, she was hit on her starboard side.  That's like when you hit the rear end of the car in front of you! Its hard to conceive of a circumstance where Fitzgerald wasn't at least partly at fault.

I'm only speculating because I have no facts other than the location of the damage, and the so-far-unconfirmed report that the container vessel supposedly made a "sudden and unexpected U-turn".

But you guys know I frequently bring this up, its one of my pet peeves. Over-reliance on electronics and failure to back them up or check them with a low-tech alternative can have deadly results, even if the electronics are functioning perfectly. I suspect that technology, either its failure or the failure of a human operator to properly interpret or respond to it, probably will turn out to be the culprit.  Regardless of how much electronics you have, sometimes you really need to just look out of one of those little round windows.  Even with a radar failure, a trained Quartermaster should have been able to look at the nav light display of the approaching vessel and quickly determined its course was threatening.  Those lights are designed so that just a glance will tell you the orientation of another vessel relative to you, and even if some are turned off, it will be obvious and you will be warned something's amiss in plenty of time to take action.

As for the Captain, I have no idea what responsibility he might have for this accident, but its in his favor that his crew was properly drilled in how to save the ship with effective damage control, even when he was injured and unable to take command.  That kind of training for an emergency does not happen by accident.  His people responded magnificently and saved the ship, and he can take full credit for that.

« Last Edit: June 19, 2017, 01:12:45 AM by HenryC »

Offline BruceW

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Re: 'Force = Mass x Velocity"
« Reply #3 on: June 19, 2017, 07:40:05 AM »
In my training at OCS, the Nav instructor was frequently heard to reply to a wrong calculation: Portsmouth Naval Prison for you, you just ran aground, or you just had a collision.
Bruce Woods
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