here are two good ways to get the speed of your target
If your target is approaching your submarine with an AOB of 20-160 use the first method. The closer to AOB 90 the better but we often have to take what we can get.
You must have identified your target ship and know its length in meters.
1. Point your sub just a few degrees ahead of your target
2. Point your periscope at 000. Do not lock the periscope view to the target. Periscope must remain motionless.
3. When bow of the target ship touches the periscope hairline start your stopwatch (I have a real stopwatch, I find it easier to use than the in-game one)
4. Do not move your periscope.
5. When the stern of your target touches the periscope hairline, stop your clock. Note time in seconds that it took for the target to pass "through" the periscope hairline.
6. Lower periscope. We are trying to be sneaky you know.
7 Use this formula
1.94 X (Length of target ship in meters) / (Seconds it took your target ship to pass through the periscope hairline) = Speed in knots
No need to determine range. No need to determine AOB (However the closer to 90 AOB the better. No need to compensate for the speed of your submarine (This is why you are headed straight toward your target)
If your target is approaching your submarine with a large AOB (80-90 degree AOB), there is another technique that is a bit harder to use but pretty useful. Presented with a deep bow of appreciation and gratitude to Hitman for his help in translation.
You must have identified your target ship and know the height of the mast in meters
1. Point your sub either directly toward (bearing 000) or directly away (Bearing 180) from the target ship.
2. Make note of the speed of your submarine and maintain this speed.
3. Lock the scope to the target and note how many marks on the vertical scale cover the target ship from the water line to the top of the mast. For example, the number of vertical marks from the water line to the mast of your target is 2 marks. With this method, it is more likely you would be using the low power setting on the scope.
4. Start your stopwatch.
5. When the target ship “Doubles” its height on the vertical scale (for example: started out covering 2 marks and now covers 4 marks), stop your clock and note the time in MINUTES.
6. Use this formula
(Mast height in meters) x 10 / (time it took the target to “double” in minutes) x 0.03 = relative speed in knots. But we are not done yet. Take this answer and
A. Subtract your own speed if you are approaching the target (bearing 000)
B. Add your own speed if you are headed away from the target (bearing 180)
Now you have the speed of your target. Note this method works IF the vertical scale is in 1/10 of a degree. If you use any mod that changes this scale, the formula will be inaccurate.
This second method works best if your target is approaching your sub with an AOB of 000. The further off from AOB 000 the more inaccurate, but remember that you can be off on the speed of your target and still get good hits.
Hitman did I get this right?
Hitman’s explanation is way more clear than mine.
http://www.subsim.com/radioroom/show...+height+1%2F16
Good hunting!