[Zyhgar]

Originally Posted by razark

Isn't it supposed to be 3:15 for metric?


(900 meters) / ((3 minutes) + (15 seconds)) = 8.97158997 knots




(100 meters) / ((3 minutes) + (15 seconds)) = 0.996843329 knots





A ship travels (approximately) 100 meters per knot in 3 minutes 15 seconds.
So, mark the position of the target, start the stopwatch. When it reaches 3:15, mark the position again. Measure the distance, divide by 100, and the answer is the speed in knots, reasonably close enough to get a hit. 900 meters, 9 knots. 850 meters, 850 knots. 2100 meters, 21 knots. You never need to divide by seconds or minutes.



For imperial, it's 100 yards per knot in 3 minutes.


(100 yards) / (3 minutes) = 0.987473002 knots

I got the 3.25 from this old post when I googled.
https://www.subsim.com/radioroom/sho...%20get%20speed.