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

-----------------------------------------


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 :D

[TarJak]

:up:Great explanation Joe!

There is another very simple no calculation way of doing this:

ID and range find your target
Select the torpedo depth, speed and pistol settings before raising the scope for the shot.
Open all tubes
Raise the scope and range find again. I like to be within 800m if possible.
Wait for the target's bow and the first mast to cross your reticle. Fire one.
Wait ten seconds. Fire two.
Wait ten seconds. Fire three.
Wait ten seconds. Fire four.

If the target is moving too fast for a 30 second spread adjust your reticle towards the direction of travel between shots.

If it's too small for this many torps just fire two or three rather than all four.

[abel29a]

My prefered method is to simply use the angle indicators in the scope. Point the scope at the front of the vessel, and see what bearing this gives you (e.g. 340).

Then quickly point the scope at the stern and read the bearing once more. (e.g. 335).

Using the examples above the vessel is covering a 15DEG arch - if firing a two torpedo salvo I would then choose a spread of 8-10 deg to get good separation.

I usually go for two torp spreads, and then I aim for the forward torpedo to impact somewhere around the bow, while the rearmost torpedo impact in the engine or boilerroom.

[BelegDraug]

When needed, I usually uses the "auto-spread" in TDC, but with a very small angle, just 2 or 3 degrees, firing 2 or 3 torps. That's gives me, in general terms, a good explosion, speially on thos big juicy tankers. Sometimes, the last topr goes by, but that's part of the game, isn't it?

[joegrundman]

When i posted this spread angle calculation, the last part of it was cut off. I've now restored the rest of the calculation. :)

@Tarjak. Yes, you do the longitudinal spread (as the Americans call it) too, and it is by far my preferred spread technique, but doesn't use the spread control dial at all. Wanting to finally use that effectively was what motivated me to convert the equation to the metric system;)

In terms of analysing the advantages and disadvantages, i could say that the longitudinal spread has the enormous advantage of requiring no calcualtion, and being very simple to implement. It's disadvatage is that if a ship detects the attack and attempts an evasion, then if it can evade the first torp, the chances are great that it can evade all the torps. This is not the case for a true fan shot. However, even when using steamers against destroyers I don't think i can recall a single successful detection-evasion manoever except in the case of a stationary target suddenly accelerating.

The more realistic disadvantage of a longitudinal, or indeed any manual spread over a programmed spread, is the longer periscope exposure required to make the spread, unless you are prepared to shoot blind for some of the shots.

That notwithstanding, i don't think this technique is going to be your number one choice. Still, give it a go. I got the courageous with three out of four on the first attempt :)