jlf1961
Posts: 14840
Joined: 6/10/2008
From: Somewhere Texas
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quote:
ORIGINAL: WickedsDesire
M6? Actually I have driven that English Jackal road often.
So whats the radar and tracking technology about? Before I whip out my abacus.
Why did this happen and how could it happen?
Uh, did you NOT read what I said?
Radar is great to keep track of something until it gets within about 2 miles, then the margin of error creeps in due to what is called 'immediate environmental clutter.'
So, this means that ship 'a' is using radar to track ship 'b.'
Ship 'b' gets within two miles of ship 'a' and its radar transmitter. At that point, the Radar is not only picking up ship 'b' but also dealing with every little possible echo including ocean waves, radio noise from other sources and a shit ton of 'garbage' inherent in the technology.
The only thing ship 'a' is getting clearly is ship 'b's' transponder transmission, but that is being displayed on the radar screen and thus, is partially obscured by the garbage return.
This problem is inherent in every radar transmitter mounted on the ground or on a ship, which is why an accurate collision avoidance system for ships is one of the wishful thinking dreams, since the damn things may read a ship 3 miles away as a possible collision hazard and start screaming at you.
So, on ships, even today, you have look outs to help with avoiding close in hazards.
And human eyes while great during the day are less than perfect at night, and night vision googles are not the wonderful super great things that Hollywood makes them out to be, which is why look outs still use binoculars, with night vision augmentation, but still depends on the human eye to brain communication for the person using them to decide "We are about to get smacked by a really big ship."
Now with that said, and please, use a dictionary if this is hard to understand.
The pictures of the damage to the destroyer shows the impact is limited to a section of the ship slightly forward of the bridge super structure center line on the starboard side, which means the closest analogy would be a near t-bone collision between two cars, when the car hit was struck on the front right door.
So, the container ship hit the US destroyer on the right side, slightly forward of the main bridge structure, but not quite at a 90 degree angle.
This means the destroyer was turning left.
So, the helmsmen of the destroyer was ordered to make a hard turn to port (left) which had to been initiated due to the risk of a head on bow to bow collision, and the decision to turn left was due to the fact that turning right would have put the destroyer in danger or running aground on the shoals along the inshore side of the channel.
Now, for those unfamiliar with the waters in and around the Japanese islands, the shoals are rarely wonderfully soft sand, but are primarily hard volcanic rock, with a thin layer of sand.
Now, rock of any kind is detrimental to the continued water tight ability of a hull, be it steel or other wise.
So, we have a large container ship in the wrong sea lane heading for an American destroyer.
Now, the rules of the road (internationally agreed maritime regulations governing the passage of ships on the oceans) dictate that the smaller vessel (in this case, the destroyer) move to the right until it is no longer safe to do so to avoid a collision.
Considering where the destroyer was hit, I am assuming until further information is available, that the Officer of the Watch had already crowded the inshore boundary of the channel as much as he thought it safe and prudent to do so, and thus as a last resort ordered the turn to the left.
That covers the conduct of the destroyer.
Now, as for the container ship.
He executed a turn to port and continued the turn until he was actually going the opposite direction than he had originally been going, and in the process of completing that maneuver, had moved his course track to the left of his original track, going in the opposite direction.
He then repeated the maneuver but turning right which then put him in the sea lane for traffic going the opposite direction.
Again these ships do not turn on a dime, so it would be akin to you walking in one direction, then turning 90 degrees, walking three feet and then turning 90 degrees again.
You are now going the opposite direction but on a parallel path three feet to the side of the original. Now you turn again, but this time you walk three feet further away from your original path before resuming your original direction of travel.
You are now going the same way you originally were going, but six feet away from and parallel to your original line of travel.
Now, the radar on the destroyer would have 'seen' all of this, and the officer of the deck would have ordered a course correction to crowd the inshore limit of the channel to avoid the collision.
At some point, it became clear that move was not going to avoid the collision and he ordered the hard turn to the left.
And that is when he got hit.
As I said before, judging the distance between to objects at night on the sea is difficult. The human eye needs reference points for the brain to make the proper connections.
It is this very reason that the lookouts on the Titanic waited too long before warning the bridge of the impending impact.
However, in the case of the Titanic, the iceberg was not under its own power.
So, you are looking at a large object, heading toward you at night on the ocean with no fucking way to determine how fast it is moving toward you and no way to accurately decide how far away it is.
Your question, valid as it is, makes the assumption that the technology on ships is as Hollywood (or the UK equivalent) portrays it, accurate to the inch and infallible.
In the case of a radar transmitter at the surface (on shore or on a ship) you are subject to surface clutter, so you do not get that nice crisp blip you see in the movies.
On an aircraft it is different.
There is nothing to clutter up the receiver so collision avoidance systems will work as designed (as long as the pilot knows what the fuck he is doing) which is why modern mid air collisions are almost always the result of pilot error.
To carry the misrepresentation of maritime technology in the movies further, sonar is just as tricky.
While sound travels great through a universal liquid medium, the ocean is far from a universally constant medium.
For example, in world war two, German uboat skippers discovered that if they could get deep enough fast enough and get below the thermocline (the line separating the surface water from deep water in temperature, the sonar waves would either be reflected off the colder, denser deep water or refracted in such a way as to give a false return.
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Paranoid Paramilitary Gun Loving Conspiracy Theorist AND EQUAL OPPORTUNI
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American Sailors cannot navigate or use radars - 
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