Lateral Speed Method

[Efshapo]

Hi everyone,

This is my first post on this forum. I wanted to share something with you all.

In February, I discovered a new method to acquire data needed to shoot torpedoes. I only tested it on Wolfpack -that's why I post in this section- but it should work on any sub game, and even in real subs.

I searched a bit and so far, I haven't found this technique anywhere else. Maybe some of you could show me sources of what I think I merely rediscovered.

I will try to explain it in a few words:

Usually, one need at least AOB and target speed to shoot. Range is also needed if gyro angle is high.

Once the ship has been identified, range is quite easy to estimate. Speed can be trickier if you're measuring it from an AOB that is far away from 90°. And AOB must be the hardest one since you have to either plot target course, measure width/height ratio, or maneuver to a position where target features are visually aligned (kingpost at AOB 90°, some masts at AOB 45°, target track at AOB 0°...)

With my method, I only use range and lateral speed (perpendicular to the bearing). The point is that you can acquire these data from any AOB. Here is a step-by-step procedure:
- Measure range from target with your preferred method.
- Choose a vertical feature on the target (usually a mast) and measure the time it takes for this feature to cross a certain amount of horizontal graduations (centiradians) on the periscope at 6x magnification, I often use 8.
- Use the following formula to compute lateral speed : lateral_speed (kts) = 0.486 * range (hm) * nb_centirad / time (s)
- Enter 90° for AOB input in TDC (starboard or portside, depending on the direction of traveling of the target).
- Enter lateral speed as speed input in TDC.

Here is a video to illustrate (jump to 3'20s):


This previous method only works for one target. I refined it to work on a whole convoy:
- Choose one representative target among the convoy.
- Measure its lateral speed as seen above.
- Visually estimate its AOB.
- Use this formula to compute target speed estimation: speed = lateral_speed / sin(AOB)
- Enter estimated AOB in TDC.
- Enter estimated target speed as speed input in TDC.

There also is a simple trick to get a good estimation of AOB, using this same refined method:
- Choose one target among the convoy.
- Measure its lateral speed as seen above.
- Also measure its real speed with your preferred method.
- Use the following formula to compute AOB : AOB = asin(lateral_speed / real_speed)
- Enter this AOB input in TDC.
- Enter real target speed as speed input in TDC.

Here is a video to illustrate (jump to 3'30s):


In all these three procedures, the main data from which other are derived is lateral speed, which is actually the one that needs to be accurate for the TDC to yield a good gyro angle.

What do you guys think? Have you seen something similar used elsewhere?

-Efshapo

[Aktungbby]

Efshapo!

[derstosstrupp]

It’s basically Auswanderungsverfahren, which is determining speed by bearing change. It’s nothing new, I’ve done several videos on it, German surface ships did it too (it’s outlined in MDv 304 Torpedo-Schießvorschrift). It’s not exactly like this, but the principle is the same. You can calculate target speed using an estimate of target AOB and an estimate of range, and then a measure of bearing change. The only difference here is that you are using centirad marks versus bearing change which is fine, and you are also setting AOB to 90 and inputting the lateral speed across the LOS into the TDC, which is also fine. Mathematically it’s the same.

Not a primary U-boat method, method of choice in history was simply matching course and speed (“Ausdampfen”), or they plotted (“Koppeln”), and to the extent they couldn’t do that, doing the fixed wire method based on an estimate of target length (“Durchwandernlassen”), or simply estimating speed by bow wake.

[Efshapo]

There are some similarities with the constant bearing method since my technique exploits the same mathematical constant which is lateral_speed = speed * sin(AOB), the gyro angle being directly related to lateral_speed.

In my opinion, the real new trick here is the use of the horizontal centiradians scale which is really faster than maneuvering the sub to get a constant bearing. This is what I haven't seen anywhere else, and would like to know if it had been documented before.

I understand one could do it using direct bearing change but I wonder if bearing measurement is as accurate as the horizontal scale...

[derstosstrupp]

Originally Posted by Efshapo

Yes, there are some similarities with the constant bearing method since my technique exploits the same mathematical constant which is lateral_speed = speed * sin(AOB), the gyro angle being directly related to lateral_speed.

In my opinion, the real new trick here is the use of the horizontal centiradians scale which is really faster than maneuvering the sub to get a constant bearing. This is what I haven't seen anywhere else, and would like to know if it had been documented before.

I’m not referring to the constant bearing method though. Auswanderungsverfahren, as I said, deals with bearing change. Like I said, the only difference between your method and the traditional method, is that you are measuring the bearing change In centiradians and not in degrees of bearing.

I’ve never seen it anywhere else done with centiradians, that part is new, but the overall method is as old as the 1920s when this was developed in between the wars.

Here’s an old video of me doing it with degrees:

[Efshapo]

From TVRE ( http://www.tvre.org/en/acquiring-torpedo-firing-data ):

The main disadvantage of the Ausdampfverfahren method was the relatively long time needed for suppressing changes of target bearing. That's why, on the basis of this method, another procedure was developed, the so called Auswanderungsverfahren method. This procedure was less accurate than Ausdampfverfahren, but required taking only two target bearings 1 minute apart and measuring (or estimating) the distance to the target during the taking of the first bearing.

Yes, thank you! That's indeed really close to what I'm doing.

Again, I guess bearing reading is probably not as accurate as horizontal scale reading but I'm glad someone gives me a document (or rather the name of a procedure) closely related to what I proposed!

We already had the 4- and 3-bearings method, I guess we could call this one the 2-bearings method.

Thanks again.

[Fidd]

There was a little trick I used to use for calculating the amount of cross-wind component when landing an aircraft with a wind, say 45 degrees off the nose. It also used sines, but of course sine-tables and calculators are of limited use when flying an aeroplane!

It worked thus, and all you need is an analogue wrist-watch or just an imagined clockface.

Angular difference of runway to wind's origin. Lets say 45 degrees. You think of that as 45 minutes on your watch and convert that to the proportion of an hour, so in this case 3/4 of the watchface. If the wind is 20 knots, then you have 15 knots (3/4 of 20) cross-wind component, ie the value of wind. pushing the aircraft sideways across the runway. We needed to know this as there were limits on how much crosswind a particular aircraft type could be landed with, before control was lost as it landed and slowed. Which could create disagreeable amounts of paper-work post-incident!

If the angular difference is say 30 degrees, then that's half the watch-face, therefore 1/2 the total windspeed, so if 18 knots, that's 9 knots cross-wind.

This technique is surprisingly accurate for sine values and is a really useful fast and dirty way of calculating the sorts of sums your method requires, whilst you're doing other things and can't be mucking about with calculators etc. With a little practice you can do such sum in your head.