UZO range estimating to target

[Markus Witt]

Seems that the graticules on the UZO should be used the same way as both periscopes at 6x zoom. I did a little test to confirm. While in port I took the range of a freighter berthed alongside the quay. I used the 6x zoom for both periscopes and counted 12 centirads (120 milirads) on both scopes. With the UZO I also counted 12 marks. Vessel was a N-type freighter with a mastheight of 28 meters. See attached.

Normal zoom is 1.5x, so when zoomed in the marks counted must be divided by 4 (6 / 1.5 = 4) to get the correct number of centirads. So in this example the actual angular height is 12 / 4 = 3 centirads. That gives a range of (28 / 3) * 100 = 933 meters. To confirm the range I fired a torpedo at the freighter, a steam torpedo at slow speed (30 knots) which hit after 61 seconds. Based on torpedo running time the range was 30 * (1852/3600) * 61 = 941 meters.

So to find the range with the UZO count the actual marks (ignore the number 10 next to the scale, this is meaningless) and divide by 4 to get the correct centirads. Range in meters = (mastheight / centirads) * 100.
Or calculate as (mastheight / markings) * 400.