for NoMan: Puster Bill very kindly did this diagrame for me with notes on ' how to..'
OK, it really isn't that hard.
I don't happen to have any graph paper right now, but you don't *HAVE* to use graph paper, it just makes it a bit easier.
Excuse the crappy webcam picture, by the way.
First, we draw a vertical line representing our course. On graph paper, you can use one of the lines already there.
We first observe our target at 55 degrees off the starboard bow, at a distance of 3,250 meters. So using the protractor we make a line 55 degrees from the vertical, and extend it out to 3,250 (I used 3.25 inches in this case, so an inch = 1000 yards).
I marked that contact 'Y'.
I take another sighting in 3 minutes and 15 seconds (to take advantage of the 3:15 rule). Since I am travelling at about 7.5 knots, I put a mark on my line .75 inches above 'A', and call it 'B'. My observation from there is the target is at 56 degrees and 2,500 yards.
Using the protractor, I make a line from 'B' that is 56 degrees from the vertical and 2.5 inches long. I mark the end of it 'Z'.
I now draw a line between Y and Z, and extend it all the way to where it crosses my course. I measure the angle at Z - This is the Angle on Bow (AOB). In this case, it is 62.5 degrees.
I then measure the distance between Y and Z. The distance between Y and Z is .625 inches (which in our scale is 625 meters), meaning the target is moving at 6.25 knots.
hope this helps to clear the way.... i have since printed it off and added it to my sh3 file