Finding the range the hard way.

Telemon · 12-28-10, 10:22 AM

Trying to do it the hard way I’m reading the method of determining range from The Submarine Torpedo Fire Control Manual found in Sub Skipper's Bag of Tricks-Techniques, tactics, tutorials, videos, in the forum and am somewhat puzzled.
The manual is reputed to be an official document and I am surprised that it seemingly contains errors. These errors are confusing me and I hope some one will clarify things for me.
From the Manual, page 5-2. The details of the periscopes states that the optical length of the Type II ‘scope is 40ft and that of the type IV 36ft. No other lengths are given.
The next paragraph states’ …examination of the tables reveals that …we have had to sacrifice about 6ft of periscope depth’. I have examined the tables but can only see a change of depth of 4ft! Where is the other 2ft?

Page 5-3. Reading the first paragraph on the page we are told in the figure (Plate II?) the target subtends 5 divisions (of the reticule) in high power and 1¼ divisions in low power. The Manual goes on to state ‘That it is known that at 1000yds 17 ½ yards or 52.5 ft subtends an angle of 1 degree’. It then says that ‘Using this information we can deduce the following formulas(sic):
The formulae given are. R(range) = (19.1h)/n
R(range) = (76.2h)/N

Where R = range in yards.
h = height in feet.
n = number scale divisions in low power.
N = number scale divisions in high power.

From the information given can some one explain to me how the figures 19.1 and 76.2 are derived and how they are related to 17.5 and 52.5?

Finally the figures referred to in Plate II.
The two worked examples.

(a) For the upper diagram; Range = 76.2 x 120 /5 = 1840 yards.

(b) For the lower diagram; Range = 120 x 19.1h/1.25 = 1840 yards.

Both answers are incorrect!

Upper dia. Range = 76.2 x 120 /5 = 1828.8 yards (rounded up would give 1830 yards)
Lower dia. Range = 120 x 19.1/1.25 = 1833.6 yards (rounded down would give 1830 yards)

Again can some one explain the discrepancy please or point out where I am misreading?

12-28-10, 10:22 AM	#1
Telemon Helmsman Join Date: Nov 2008 Posts: 103 Downloads: 288 Uploads: 0	Finding the range the hard way. Trying to do it the hard way I’m reading the method of determining range from The Submarine Torpedo Fire Control Manual found in Sub Skipper's Bag of Tricks-Techniques, tactics, tutorials, videos, in the forum and am somewhat puzzled. The manual is reputed to be an official document and I am surprised that it seemingly contains errors. These errors are confusing me and I hope some one will clarify things for me. From the Manual, page 5-2. The details of the periscopes states that the optical length of the Type II ‘scope is 40ft and that of the type IV 36ft. No other lengths are given. The next paragraph states’ …examination of the tables reveals that …we have had to sacrifice about 6ft of periscope depth’. I have examined the tables but can only see a change of depth of 4ft! Where is the other 2ft? Page 5-3. Reading the first paragraph on the page we are told in the figure (Plate II?) the target subtends 5 divisions (of the reticule) in high power and 1¼ divisions in low power. The Manual goes on to state ‘That it is known that at 1000yds 17 ½ yards or 52.5 ft subtends an angle of 1 degree’. It then says that ‘Using this information we can deduce the following formulas(sic): The formulae given are. R(range) = (19.1h)/n R(range) = (76.2h)/N Where R = range in yards. h = height in feet. n = number scale divisions in low power. N = number scale divisions in high power. From the information given can some one explain to me how the figures 19.1 and 76.2 are derived and how they are related to 17.5 and 52.5? Finally the figures referred to in Plate II. The two worked examples. (a) For the upper diagram; Range = 76.2 x 120 /5 = 1840 yards. (b) For the lower diagram; Range = 120 x 19.1h/1.25 = 1840 yards. Both answers are incorrect! Upper dia. Range = 76.2 x 120 /5 = 1828.8 yards (rounded up would give 1830 yards) Lower dia. Range = 120 x 19.1/1.25 = 1833.6 yards (rounded down would give 1830 yards) Again can some one explain the discrepancy please or point out where I am misreading?