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Old 06-02-2016, 07:13 PM   #35
Growing Old Disgracefully
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Default How To Calculate A Targets Speed By Using The Periscope Cross Hair

How To Calculate A Targets Speed By Using The Periscope Cross Hair.

Count the number of Seconds it takes for the > Targets Bow and Stern to pass across the > Periscope Cross Hair.
Time taken = metres per second.
Multiply the number of seconds taken by 3,600 (number of seconds in an hour)
Divide the total by 1.85 (To convert KPH to Knots)

Length of the Target is needed from the Recognition Manual.

Target > Small Merchant 1,700 tonnes.
Length > 78.3 metres.
Number of seconds taken > 25.
Length 78.3 divided by 25 seconds = 3.13 metres per second.
3.13 metres per second x 3,600 seconds in an hour = 11,268 metres (11.2km).
11,2km divide by 1.85 to convert Kilometres Per Hour (KPH) to Knots = 6.05, or 6 knots.
Target is traveling at approximately 6 knots.

Picture 1 > Start the Stopwatch as the Cross Hair touches the Bow.

Picture 2 > Stop the Stopwatch at the end of the Stern.

Picture 3 > TDC Speed Calculation > 6 knots.

Last edited by THEBERBSTER; 05-09-2018 at 04:01 PM.
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