Another Collision.

maybe from a Pilot's perspective, the closing speeds are so fast that if a plane appears to not move relative to your position, you may be on a collision course. However, there is certainly relative motion.
In the case of the ships, this relative motion should have been apparent and plenty of time to react
 
Mariners develop little limericks so help the memory.

"Red over White Fishing at Night" etc.

"Constant Bearing Decreasing Range"

I've been hearing

"If it's Gray Stay Away"
 
If it's yellow you might be a lucky fellow, if it's brown run aground. But my observations in the Bahamas tell me that black is certainly going to be an issue with coral heads. Brown not so much.
 
quote:
Originally posted by getakey

maybe from a Pilot's perspective, the closing speeds are so fast that if a plane appears to not move relative to your position, you may be on a collision course. However, there is certainly relative motion.
In the case of the ships, this relative motion should have been apparent and plenty of time to react

Click to expand...


You need to think about that one long and hard, or go read Chapmans. It will tell you the same thing.

Oh crap, I will help you out

https://en.m.wikipedia.org/wiki/Constant_bearing,_decreasing_range

http://www.gulfcoastsailingschool.c...60537/constant_bearing_-_decreasing_range.pdf
 
Boatbum, Exactly--not enough money to build more ships and not enough ships. downsized by our last CIC.
 
quote:
Originally posted by GeeBee

quote:
Originally posted by getakey

maybe from a Pilot's perspective, the closing speeds are so fast that if a plane appears to not move relative to your position, you may be on a collision course. However, there is certainly relative motion.
In the case of the ships, this relative motion should have been apparent and plenty of time to react

Click to expand...


You need to think about that one long and hard, or go read Chapmans. It will tell you the same thing.

Oh crap, I will help you out

https://en.m.wikipedia.org/wiki/Constant_bearing,_decreasing_range

http://www.gulfcoastsailingschool.com/uploads/4/6/8/6/46860537/constant_bearing_-_decreasing_range.pdf

Click to expand...


There is relative motion and relative velocity between the 2 boats. It may be difficult to judge whether you can cross safely or not, but recreational boaters encounter this situation all the time. A billion dollar Navy vessel should be able to avoid this situation whether they are the give way boat or not.
 
It's basic seamanship.you look at the other guy, if he doesn't appear to be moving you re on a collision course. Period.
 
Bigger has nothing to do with the physiology of constant relative bearing. It is how our brains sort out fixed objects versus live threats. To the human brain, a non changing relative bearing is considered the same as a wall, or a tree. This was all sorted out after Aeromexico 498 collided with a light plane near LAX. A constant relative bearing regardless of change in size is often disregarded by the brain as a fixed object simply because the center of the object does not move. This is in part a survival instinct so we do not overload our brain processing. Predators have adapted tactics as well as if they must stalk on the flank, they will remain at constant relative bearing to hide themselves and when the leap forward they are on an immediate collision course with the prey. Unfortunately for humans, they moved into vehicles before they dropped this defense mechanism of disregarding things on a constant relative bearing. That is why after due consideration, collision avoidance technology was developed to aid the human.
 
Bearing is one thing. Relative velocity/motion is another.
 
So would you agree there is Relative motion, but the brain blocks it out?
 
But the Doppler radar as well as MARPA should still show that clearly.
 
Two vessels traveling next to each other at the same speed on the same course have with respect to each other a relative velocity of zero. Two approaching each other head on 180 degrees apart in course, heading, or whatever, with respect to each other have a relative velocity of V1 + V2.
As their course, heading, whatever changes from those two cases (excepting one axis since we are on the water) their relative velocity is the sum of the vectors or component velocities.
If the reference point shifts to another object of course the relative velocity changes appropriately and is the sum of the component velocities.
 
Steaming along at 10 kts, I look to my Stbd bow, and see a vessel (contact) in the distance, apparently attempting to cross in front of me. It's position is approximately 60 degrees relative (relative to my position). Few minutes later, the vessel is still at 60 degrees relative. A minute later, still at 60 degrees.

This is called a contact at a Constant Bearing, and it is an indication of a collision course.

Another visual indication of a collision course is when the background behind a contact (trees/skyline) doesn't appear to move, but you are moving . . .
 
Thanks, Sandy,
I cannot understand how with all the Radar and other electronics on these ships that such collisions can occur. Isn't someone watching the radar all the time. Isn't there warning given by electronics when another ship is within a certain danger zone? For two ships to overlook the potential for a collision is not explicable.
Agree that the Commander of the 7th Fleet has been relieved of his duty, The problem is somewhere in the upper brass to not have proper control of the operations.
Off topic, but
Just found out that my Marine Grandson stationed in North Carolina on active duty is headed to Texas tomorrow
for several months. Proud that he will be helping the Harvey victims.
 
quote:
Originally posted by getakey

So would you agree there is Relative motion, but the brain blocks it out?

Click to expand...


If there is no change in relative bearing how can there be relative motion?
 
A change in velocity by either vessel will accomplish that (change in relative motion).

At this point I consider this thread hijacked.

The bottom line remains. Two of our world class ships of defense have found themselves at the mercy of the merchant marine. No weaponry was involved and the ships were totally compromised.

Blame it on CRM, whatever, I don't care. Lives were needlessly lost and I would like to know just what the Navy is going to do about ensuring this sort of B.S. does not occur again.
 
If you don't learn from other's mistakes, you are bound to make them yourself.
 
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