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I'm goin' down · 11-19-11, 06:59 PM

stop your boat. If the target is closing and its bearing is between 300 degrees and 60 degrees on the periscope, use the chronometer to measure how long it takes for the target to cross the periscope bearing. Divide by 3 to derive speed per second. (I am using the imperial measurement). Multiply by 180 seconds (i.e. 3 minutes) You have derived the speed is knots.

Hypo. Target length is 425 feet. It's bow crosses the periscope bearing at 57 degrees. Start the chronometer. It takes 30 seconds for the target to cross the bearing. 425 ft./30 sec. = 14.16 ft. per second/3 (no. of feet in one yard) = target's speed is 4.72 (yds. per second) x 180 seconds (180 seconds equals 3 minutes) = 8.49 kts. (target speed using the 3 minute rule.)

Why measure speed between 300 degrees and 60 degrees on the scope? Because Kasmaronznew (mod developer for UBoats in SH4 in the ATO forum) said that measuring speed between those bearings will give you the most accurate reading to calculate speed. I use his method. It works.

11-19-11, 06:59 PM	#10
I'm goin' down Ocean Warrior Join Date: Sep 2008 Location: Notify command we have entered the Grass Sea Posts: 2,822 Downloads: 813 Uploads: 0	speed with map contacts disabled stop your boat. If the target is closing and its bearing is between 300 degrees and 60 degrees on the periscope, use the chronometer to measure how long it takes for the target to cross the periscope bearing. Divide by 3 to derive speed per second. (I am using the imperial measurement). Multiply by 180 seconds (i.e. 3 minutes) You have derived the speed is knots. Hypo. Target length is 425 feet. It's bow crosses the periscope bearing at 57 degrees. Start the chronometer. It takes 30 seconds for the target to cross the bearing. 425 ft./30 sec. = 14.16 ft. per second/3 (no. of feet in one yard) = target's speed is 4.72 (yds. per second) x 180 seconds (180 seconds equals 3 minutes) = 8.49 kts. (target speed using the 3 minute rule.) Why measure speed between 300 degrees and 60 degrees on the scope? Because Kasmaronznew (mod developer for UBoats in SH4 in the ATO forum) said that measuring speed between those bearings will give you the most accurate reading to calculate speed. I use his method. It works. Last edited by I'm goin' down; 11-19-11 at 10:25 PM.