[Redlance88]

mostly it comes down to what other information your using to track and make various solution guesses about the ship that you are tracking. what you need to figure out a ships speed is to know how far it has traveled in a certain amount of time... D/T = speed. for silent hunter distance is in either meters or nautical miles. and time is in seconds ( not very useful) min or hours. knots are nautical miles /per hour. so if you have the ability to accurately locate the ship at two different times, you can measure or calculate the distance traveled for that specific amount of time and get the speed of the ship from that information.
Lost yet? in the game there are several ways to get this information and they vary in how historically accurate they are. but in simplest terms you have to time the ship your tracking and see how far it goes in the time you watch it. now this is where it depends on how you play the game and what information you have to work with. if you can see the contact on the map you can just put a mark on it , hit the u key start the stop watch , and a min later put a mark on where the ship has moved to, and grab the ruler and see how far the ship has moved in 1 min. this distance will be in meters and the time is one min so it will have moved say 154 m in one min. or (154m X 60 Min ) 9240 m / hour. one knot is 1852 m per hour so if you divide 9240 by 1852 you get 4.98... or as close that makes no differance 5 knots / hour. I hope that was more helpful than confusing, but like I said without knowing things like if you have show enemy contacts on the map turned on or things like that I cant be more specific on what your trying to do. other than the basics of speed = distance over time. and that a knot per hour is = to 1852 meters per hour. or about 31 meters per min.