Calculating Spread Angle

[joegrundman]

Because it's so easy, I almost always manually form my spreads without using the automatic spread feature.

There are two reasons why, one is that if you have a mixed loadout, for a long time T1's are stacked in tubes 1 and 2 while T3's are stacked in tubes 3 and 4. Unfortunately the spread selector doesn't allow for firing tubes 1 and 2 or 3 and 4 togther....

The second reason is the difficulty of determining the correct spread angle for a comprehensive blasting of the target.

I have nothing to say about the first problem other than manually reorder your tube loadout while in base, however there is a way to determine reasonable spread angles:

The spread angle can be calculated by a metric conversion of the spread angle calculation which i obtained from the indispensible US submarine fire control manual

http://www.hnsa.org/doc/attack/index.htm

OK here it is in a form that the mildly mathematically capable Kaleun can manage in a few seconds once familiar with the equation- practice a few times on paper to get the hang of it, it's pretty easy:

Spread angle= (target length/100) x (%coverage/100) x (6000/range at time of firing) x Sin of torpedo track angle

Spread Angle
------------

this is then put into the TDC

Target Length is obtained from the recogntion manual, but make life easy for yourself! Round off the number to an easily calculated figure.
E.g.
armed trawler - 50m
small freighter=75m
medium and large freighters=150m
T3 Tanker and battleships = 200m

%Coverage= The percentage of the ship's length you wish to cover by the spread.
-----------
E.g
100% = the full length.
75% = If you are pretty sure of hitting the thing with all torps, but just want to make sure it goes down with the minimum of fuss and scope exposure
150% = if you are more uncertain of your solution and just want to increase your odds of hitting it with something and hope to get lucky with a cripple or a kill. you will certainly miss with 1 or more torps in this case.
200% = as above only more so.

Note for coverage of more than 100%, be sure not to fire only 2 torps as they could therefore travel either side of the target without hitting it.

Range
------

Make life easy for yourself and round off the calculations

250-350m= 250 m ...........6000/250=24
350-750 = 500m.............6000/500=12
750-1250 = 1000m...........6000/1000=6
1250-1750 = 1500m..........6000/1500=4
1750 - 2250 = 2000m........6000/2000=3
2250 - 2750 = 2500m........6000/2500=2.4 (call it 2 and a half)
2750 - 3250 = 3000m.......6000/3000=2
3250 - 3750 = 3500m........6000/3500=1.7 (Call it 1 and three quarters)
3750 - 4250 = 4000m........6000/4000=1.5
4250 - 4750 = 4500m........6000/4500= 1.33 (1 and a third)
4750 - 5500 = 5000m........6000/5000= 1.2 (call it 1 and a quarter)
5500 - 6500 = 6000m........6000/6000 =1
6500 - 7500 = 7000m........6000/7000= 0.85 (call it 1)

Sin of torpedo track angle (tta)
-------------------------

This is the angle at which the torpedo strikes the target. This will generally be close to the AOB, but be aware of situations where it isn't.

Again, make the calculation easy for yourself

tta= 90-60, use Sintta of 1
tta= 45-60, use Sintta of 0.75
tta= 30-45, use Sintta of 0.5
tta= 15-30, use Sintta of 0.25

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OK, most of this calculation can usually be done long in advnace, as soon as you know the likely range to target at time of firing. So if you are interested in trying out a different method, then enjoy it.

Example 1)

Large merchant, length 150m, 100%coverage desired, range 2000m, AOB 90

Spread angle = (150/100) x (100/100) x (6000/2000) x (sin90)
= 1.5 x 1 x 3 x 1
= 4.5 degrees

Example 2)

Battleship Rodney, length 250m, 100%coverage desired, range 2000m, AOB 90

= 250/100 x 100/100 x 6000/2000 x sin90
= 2.5 x 1 x 3 x 1
= 7.5 degrees

Example 3)

Large Tanker, length 190m, 150% coverage, range 3000 m, AOB 90
=200/100 x 150/100 x 6000/3000 x sin90
=2 x 1.5 x 2 x 1
= 6 degrees

but I still think manually setting longitudinal spreads is easiest