Spectre600
09-14-05, 01:27 PM
Calculating the course of a ship is easy if you are within visual range.. All you need are 2 locations at seperate times.
It has been mentioned before in this thread...
The method I use is to take one range/bearing reading, and wait 3 minutes 15 seconds and take another.. then just draw a line through your two points and that is the course. The advantage of waiting 3 minutes 15 seconds is you can calculate the course AND the speed of the target, instead of doing it in 2 operations.
Sometimes you cannot wait 3 minutes 15 seconds.. like in bad weather. I still have not perfected a method for these circumstances, but if you just take 2 range/bearing readings, then use the 'notepad' to get your speed (be carefull not to re-enter the AoB into your tdc!), this works pretty well for those hurried shots.
Now, the REAL question, is how to determine a rough course with just hydrophone contacts (no sonar). This is the toughest thing, but a good method would make extreme weather situations easier to deal with.
The one method I have had limited sucsess with is like this:
When you get a hydrophone contact, plot a line on that compass bearing of arbitrary lenght (I do 20 km, you cant really hear farther) and start the stopwatch.
Wait 3 min 15 seconds.
Plot a second line.
Now you have a 'v' on your map.
This is the tricky part, you have to assume the ships speed.. there are several ways to do this, all with certain error...
There are ways to figure out the speed of a target by the screw sounds, but I dont know how. The other is to ask your kind hydrophone op.. He will tell you 'slow, medium, fast, very fast'.
Slow is on average about 7 knots. Fast can be 15-20. Very fast is almost always 25.
Say for example you estimate the ship to be going about 10 knots. Plot a line in your 'v' that is 1 km long, and that fits into the 'v'. This is a very approximate range!
The variables that can mess this up is if the ship is moving towards or away from you, then it will seem like the ship is going slower than it really is. But your hydrophone operator will probably tell you if that is the case.
Repeat the whole process at another point and you can make a very rough course approximation.
I hope this all makes sense!
If anyone else has any methods for approximating courses with just hydrophone contacts, please let me know!
EDIT:
By the way, how can you get an accurate AOB from one visual observation? You would need alot of skill to get good, accurate readings.
I wonder if there is a way to take bearing readings from the bow and stern, and from that (and range readings) calculate the AoB from a known ship length.. Interesting...
It has been mentioned before in this thread...
The method I use is to take one range/bearing reading, and wait 3 minutes 15 seconds and take another.. then just draw a line through your two points and that is the course. The advantage of waiting 3 minutes 15 seconds is you can calculate the course AND the speed of the target, instead of doing it in 2 operations.
Sometimes you cannot wait 3 minutes 15 seconds.. like in bad weather. I still have not perfected a method for these circumstances, but if you just take 2 range/bearing readings, then use the 'notepad' to get your speed (be carefull not to re-enter the AoB into your tdc!), this works pretty well for those hurried shots.
Now, the REAL question, is how to determine a rough course with just hydrophone contacts (no sonar). This is the toughest thing, but a good method would make extreme weather situations easier to deal with.
The one method I have had limited sucsess with is like this:
When you get a hydrophone contact, plot a line on that compass bearing of arbitrary lenght (I do 20 km, you cant really hear farther) and start the stopwatch.
Wait 3 min 15 seconds.
Plot a second line.
Now you have a 'v' on your map.
This is the tricky part, you have to assume the ships speed.. there are several ways to do this, all with certain error...
There are ways to figure out the speed of a target by the screw sounds, but I dont know how. The other is to ask your kind hydrophone op.. He will tell you 'slow, medium, fast, very fast'.
Slow is on average about 7 knots. Fast can be 15-20. Very fast is almost always 25.
Say for example you estimate the ship to be going about 10 knots. Plot a line in your 'v' that is 1 km long, and that fits into the 'v'. This is a very approximate range!
The variables that can mess this up is if the ship is moving towards or away from you, then it will seem like the ship is going slower than it really is. But your hydrophone operator will probably tell you if that is the case.
Repeat the whole process at another point and you can make a very rough course approximation.
I hope this all makes sense!
If anyone else has any methods for approximating courses with just hydrophone contacts, please let me know!
EDIT:
By the way, how can you get an accurate AOB from one visual observation? You would need alot of skill to get good, accurate readings.
I wonder if there is a way to take bearing readings from the bow and stern, and from that (and range readings) calculate the AoB from a known ship length.. Interesting...