Judging AOB by eye - tutorial

[joegrundman]

Judging AOB by eye tutorial - single ships

It requires two things
a) practice (which on the whole we are not short of)
b) knowing what to look for.

To be sure, there are times when it is hard to judge by eye – at extreme range it is hard, and in the dark at medium range it is hard, and there is a band of AOBs between 20 and 50 that are harder than the others.

This is an extract on the subject from the invaluable USN submarine torpedo fire control manual (1950)

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

Section 803

(b) Estimation of angle on the bow by observation through a periscope is one of the arts peculiar to submarining. An officer's ability to accurately estimate angles on the bow increases directly with his experience in submarines.

It’s not necessarily easy, but once you have the skill it’s by far the fastest way to obtain AOB. If you also have a tool that can rapidly convert AOB to target course for you, such as the Submarine Attack Course Finder (or ISWAS – do a search to find threads on the subject), or the German Attack Disk, or Angriffscheibe, as found in the U-jagd tools mod or the OLC GUI for SH3, then the whole process of visuals to target course, to submarine attack course takes seconds.

I have used SH3 for these shots, but of course it makes no difference what game it is, or even if you are judging AOB in the real world (if you haven’t mentally planned a firing solution at a passing ship while standing on the beach, you are a lightweight!)

There are four things you are looking for, apparent length, the orientation of the masts, the position of the bow wave and the front of the bridge

Apparent length

First is apparent length. It is important to note that the apparent length of the target changes with the sine of the AOB.

This means that from AOB’s 90-60, the apparent length of the target doesn’t change much. This means it can be difficult exactly distinguish between AOBs of this range, but on the plus side it means that a variation in this range has a minimal effect on your torpedo solution.

Then the apparent length changes rapidly between 60 and 15, and then it changes slowly again.

The apparent length at 30 degrees is exactly half the apparent length at 90 degrees. In general this is a big source of confusion before you are acclimatized to visual AOB spotting, as one instinctively tends to see this stage as 45 degrees.

Masts and bow wave

For small AOB's you look at the position of the masts in relation to the funnel. this will help you to distinguish between AOBs of 0,5,10 and 15. The point at which the bow of the ship cuts the visible bow wave is also very useful.

Bridge

At larger AOB's you look at the part of the front of the bridge that you can see. The more of this you can see, the further from an AOB of 90 it is.

AOB 0

This is one of the easiest to recognise, since the view of the ship is symmetrical



in fact you can see that it is not quite symmetrical, there is an AOB of about 1 degree.

If you are really struggling to get an AOB, then one approach is to cut the T of the target ship, and once you see this view, you know the target is on a reciprocal course, then continue and adjust to make the sternshot.

E.g. let's say i am on a heading of 10 degrees, and when i have this view the bearing to target is 220, then true bearing to target is 10+230 = 230. Reciprocal of 230 is 230-180=050. Target course is 050 degrees.

this is particularly useful if you are making a convoy attack from inside the convoy, as you will generally have passed directly in front of one ship or another on your way into position.

AOB 5

Now the bow is not in the center of the apparent bow wave, it is about 3/4 of the way across, and on a longish ship the front masts have moved across a small amount relative to the funnel



AOB 10

At AOB 10, the bow is now almost all the way across to one side, only about 1/7 of the other side of the target is visible around the bow. Also the front masts ahve now "cleared" the funnel.




AOB 15

At AOB 15, it is just no longer possible to see any of the other side of the ship, and all the masts appear to have just become on one side of the funnel or the other.



AOB 20

This is one of the more difficult to identify. The bow wave no longer clearly helps and the masts and bridge are not too helpful either.

Apparent length is not yet half the expected full length. Certainly this is one of the easiest AOBs to overestimate. If it's possible, note that you can still just make out the anchor on the other side




AOB 25

Now the big difference with 25 from 20 is that some of the cranes on the ship appear to meet in the center, and that some of the aft cranes are no longer obscured by any of the bridge, but also note that the ship has lengthened greatly since the AOB 20



To be continued...

[SmokinTep]

Good stuff....thanks.

[joegrundman]

AOB 30

At this AOB, the apparent length of the ship is half the actual length. In addition if you now look at the side of the bridge section, you will see in this ship, the corner is about 1/5 to 1/4 the way across, and in a ship with doubled masts, like this one, a small gap has appeared between the different sets of masts



AOB 35

Nevermind that the picture is smaller! The corner of the bridge is now about 1/4 the way across, and the gap between the mast sets has grown



AOB 40

A ship with masts of this kind now shows an even spacing between all the masts at the AOB, and the corner of the bridge is in line with the funnel (clearly this is not a useful marker with split freighters)

you can however say it is approaching 1/3 the way across




AOB 45

Now i'm getting a bit bored of writing comments! For sure this mid range is the most difficult. The gap between the mast sets has become wider than the gaps between the masts, and the corner of the bridge is now under the funnel. the apparent length of the ship is now 7/10 of its actual length.



AOB 50

Now it starts becoming a bit easier again. At 50, you are beginning to see the full length of the ship (actually 3/4 still), and the gap between the mast sets is clearly seen



AOB 55




AOB 60

At this AOB, the corner of the bridge is about half way across the visible bridge



AOB 65



AOB 70

We are now definately seeing more of the side of the bridge than the front, and we are beginning to see the masts "side on"



AOB 75



AOB 80



AOB 85

This is now only very slightly off being exactly perpendicular

[predavolk]

Wow, nice! I ID AOB visually, so these are some handy tips indeed!

[klh]

Well done Joegrundman. I find that I almost always overestimate the AOB with my Mark I eyeball. This will help tremendously!

Have you considered putting this into a pdf? This is something I would love to laminate and keep handy.

[ktrboston]

Great job Joegrundman! this is a help full post. I also use the Submarine Course finder it is an invaluable tool. I always use because it has so many uses. It is a must have for all Captains.

[Laufen zum Ziel]

Great stuff. Many thanks for all the things you have given me and the community.

http://silent-hunter-addict.com

[Sailor Steve]

Thanks, Joe! A great tool. I copied it all and will use it to learn.

[Pikes]

OMG the middle ranges are hard!

Can i add some "references" please that you may consider?

1. Funnel smoke... It trails more at 90 and is straight at 0. In your picture it wasnt so clear but brings me on to...

2. Wake... in the same way you brilliantly identified the bow, the stern appearance shows more and more. Depending on boat of course, but oval hulls give a lot more away after 20 deg. the trailing wake appears around 75 degrees. Unfortunately your images are still and smoke and wake move so not as easy to tell from still, but wakes are awesomely useful for nightime since they glow more.

3. Flat straight surfaces! Search for a flat panel, the most obvious and useful is the highly visible bridge, but also consider cargo containers which are nice and square. You get nice rectangular patterns that your eye can use when looking at the front "face". These are most useful in the lead up to 90 degrees when the ability to see right across the front of the ship gets closer and closer to 90. Its the same as using the masts although i find that unless you know the masts inside-out they can appear so confusing, esp from a distance. (Hands up who hates merchant masts?!)

4. Any protrusions, bilateral differences, distinctive features... For example the bridge on that illustrated ship sticks out either side. That sticky out point is useful at angles closer to 0. Personally i hate any military ships as the superstructures are so complex and there are lots of rounded parts. coupled with the fact that textures dont reflect the light as well as real objects its harder.

5. Finally i had a ponder about 35-55 degrees. I cant think of a single facet that could make this easier. Anyone getting these is either a genius on their ship recog or using the pause button! The one thing you dont have to help is height. As far as i can guess the best way remains with seeing more than one mast and knowing the distance between them. In truth AoB is all about horizontal distances in the same way that range is to vertical distances. If you knew the length of the ship at 90 and measured it at any angle theres some maths that can give you your AoB.

...I r not mathematizian. :p

PS...the maths bit would require very accurate measurement of the length and require very accurate range to convert your measurement from view to real size and would be innaccurate for AoB 0-20 and 70-90 as wouldnt account for the width. It would also be a huge waste of time and completely pointless when you should be getting other things done as AoB changes. :P

[Elmer Kosterman]

You've certainly put some work into this, Joegrundman. Can you say something about how well these tips work on other ships? I haven't really studied it, but I'd have guessed that different ships have different spaces between masts, cranes at diffeent angles, different pilothouse-face-ratios, hull curvatures, etc. This could limit the applicability of some of your tips across different ship-types.

Thanks a lot for the tip about apparent ship-length being one-half at thirty degrees. I always thought it was at forty-five degrees, but you reminded me of high school geometry and tangent 30° = 0.5.

This leads me to questions about AOB when a target is maneuvering evasively. Has anyone noticed if the period of swerves is constant in game, and if so, how long it is? When's the best time to fire a torpedo at a swerving target? So that the programmed AOB matches the actual AOB at torpedo impact? Or maybe so that the programmed AOB matches the average actual AOB while the torpedo is in the water?

[joegrundman]

Thanks Pikes, those are useful additions, although your final point refers to what is known as the aspect ratio. Working with hitman and OLC we constructed the U-jagd tools mod, which OLC incorporated with his GUI. These tools include a tool specifically for calculating the aspect ratio in a few seconds.

It is in the aob range 20-50 that the apsect ratio is particularly strong, because the apaprent length changes so much over this range, for the extremes, using the visual method is better.

@Elmer

well you have to look for clues in every ship, because what you are really trying to do is use small visual clues to construct a 3d orientation in your mind's eye. Once you have teh knack it only gets easier!

As for the evasion pattern, i believe they run on a fixed wavelength, not frequency.

[brett25]

hey guys,

heres a .pdf version of that torpedo manual:

http://files.filefront.com/Torpedo+A.../fileinfo.html

Also the submarine commanders handbook .pdf

http://files.filefront.com/The+Subma.../fileinfo.html

[Tomcattwo]

Well done, JoeGrundmann!

Here are some other useful tidbits (from someone who used to do this stuff for real):

Mental math: You can do a lot of the target calculations right in your head if you use a few simple thumbrules. Here's some:

Mental Sine Table (to get the sine of any angle from 0-90):
For angles from 0 to 40 = Angle/60 (for example: Sin(10) = 10/60 = 1/6 = .16)
Sin (40) to Sin (50) = 0.7 (At 45 degrees, it's really .7071)
Sin (50) to Sin (60) = 0.8 (Sin (60) = .866)
Sin 60 to Sin 70 = 0.9
Sin 70 to Sin 90 = 1.0

To get the sin of an angle >90 but less than 180, subtract your angle from 180. Ex:

Sin 150 = Sin (180-150) = Sin 30 = 30/60 = 0.5

To find a reciprocal bearing: Take your bearing, add/subtract 200, then subtract or add 20. Example: Find the reciprocal of 346:

346...246...146...166 BINGO! Takes less than a second in your head.

To find distance to track: Distance to Track = Range x Sin (AOB). Example: Freighter is 3200 yards away, Stbd 15 AOB. What is Dist to track:

3200 x sin(15) = 3200 x 15/60 = 800 yards

Here is the basic Line of sight picture:




The basic Line of Sight (LOS) picture shows your boat at the bottom, the target at the top, and shows a vector diagram of speed for both and angle for both. The vertical line represents the TRUE bearing to the target (i.e., the bearing to the target measured clockwise form 0-360 degrees from TRUE NORTH). The relative bearing to the target is the angle between the front of your U-Boat and the line of sight to the target, measured from 0-360 degrees.

So, to find the true bearing, just remember:

RELATIVE + SHIP's HEAD = TRUE

For instance: target bears 346 relative. You are on course 200. What is true bearing to the target?

200 + 346 = 546 (- 360) = 184 degrees true.

What does the LOS picture look like:

Target is (360-346) = 14 degrees off your port bow:




Here are the 3 basic types of LOS:



If you want to plot a course to collide with the target (basically this is what your fire control system does to get your torpedo to hit the target), match your speed across the LOS to target speed across LOS in the same direction.

In the above example, what is target speed across the LOS if target is doing 10 knots?

xGz = Tgt speed x Sin (AOB) = 10 x Sin (30) = 10 x 30/60 = 5 knots.

So what course do we need to be on to collide with target if our speed is 17 knots?

xGu = Uboot Speed x Sin (Rel Bearing)

5 = 17 x Sin (Rel Bearing)

5/17 = Sin (Rel Bearing)

5/17 is about 1/3 (a little less than that but close enough). From mental sin tables, 1/3 is about 20/60. so the Relative Bearing we need to put him on is about 20 degrees starboard (so we are going in same direction to match Speed across LOS). For you purists, the exact answer is about 17.6 degrees. 20 is close enough for Government work.

That means I need to come left about 34 degrees (14 + 20). My current course is 200, so that means I need to be on course 200-34 = 166 degrees true at 17 knots to collide with the target.

It's all about basic trignometry:

If I want to close the range to a target, I need to INCREASE my Speed IN the LOS TOWARD the target.

If I want to open the range to a target I need to increase my speed IN the LOS AWAY from the target.

If I want to make the bearing rate go left (become smaller) I need to make my speed ACROSS the LOS to the RIGHT get bigger.

If I want the bearing rate to go right (become larger), I need to make my speed ACROSS the LOS to the RIGHT get smaller.

I can do that by changing course, speed or both.

Some speed things:

3 minute rule:
In 3 minutes, I travel: speed in knots x 100 yards. Example: at 12 knots, I cover 1200 yards in 3 minutes.

6 minute rule:
In 6 minutes: I travel: speed in knots/10 nautical miles (NM). Example: at 12 knots, I cover 1.2 nautical miles in 6 minutes

You can rapidly figure out almost any time/speed/distance equation in your head with just these two thumbrules - at least get a close estimate.

1 NM = 2000 yards. It's pretty close in meters - not enough difference to worry about for most situations. So mostly: yards = meters

I need to close 5400 meters at 10 knots. How long will it take me to get there?

Using 3 minute rule, I travel 1000 yards in 3 min. so that's 5 x 1000 plus 4/10

5 x 3 = 15 min. .4 x 3 min = 1.2 min approx. Total: 16.2 min.

The more you practice doing this kind of mental math, the easier it is to do.

More to come later.
R/
TC2

[brett25]

joegrundman, tomcattwo

I hope you dont mind, but I made a .PDF version of your excellent tutorial to help me study it better. I will post it here for others unless you have any objections

http://files.filefront.com/AOBpdf/;9.../fileinfo.html

[Sailor Steve]

Those are cool, Brett! Thanks!