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



AOB 30

The sine of 30 is 0.5, so this is one of the magic AOBs with one distinctive feature: the apparent length is half the actual length





To be continued...

[Meridian]

The last pic looks more like 45 rather than 25.

[joegrundman]

Originally Posted by Meridian

The last pic looks more like 45 rather than 25.

exactly, and this is why i'm doing this tutorial. It's 25, not 45 and i can mathematically prove it too, but the fact is, until one has trained oneself what to look for, it is natural to overestimate aob.

Also from the Submarine Torpedo Fire Control Manual, section 803

(c) The most common error in estimation of angles on the bow is that of over-estimation which often can be ascribed to one or more of the following reasons:

(1) Lack of appreciation that the effective length of the target varies with the sine of the angle on the bow. Half of the target length is seen with a 300 angle on the bow, seven tenths with a 45 degrees angle on the bow and nine tenths with a 60 degrees angle on the bow.


(2) Lack of depth perception when using a monocular periscope.

(3) The illusion that a target is changing course away; this is very marked at short ranges caused by the high relative angular motion of the target across the line of sight.

(4) The illusion of a target being on a steady course when viewed at short ranges during a change of course of a target towards e. submarine. This illusion is created by a partial or total cancellation of the apparent relative motion of the target across the line of sight by the course change of the target toward the submarine.

(5) Clever camouflaging may also increase the difficulties of angle on the bow estimation.
(6) Determination of target course by angle on the bow estimation is much more difficult with large angles on the bow (over 30) than with small angles on the bow.

I love and use the AOB Aspect Ratio Method.

It's simple, precise and realistic in its use.

Snip from Hitmans Simplified Manual Targeting manual available here: http://www.subsim.com/radioroom/show...t+ratio+method


<B>

AOB (ASPECT RATIO METHOD)

</B>

Each ship has her own “Aspect ratio”, which means the difference of its length

versus its heigth. For example, a 100 yards long ship with a mast of 33 yards
has an aspect ratio of 3,33:1. Now, because what you can see of the ship’s
height remains constantly proportional (The mast) at any given distance, while
the length you can see will change also proportionally depending on the AOB,
you can read from your scope or TBT the new Aspect Ratio the ship shows you,
and by comparing it with the standard aspect ratio at 90º, get the AOB directly.
You just have to do this:

1.- Note the target’s Standard Aspect Ratio (F.e. 4.6 in our Large Old Split
Freighter). You can get it from the recognition manual (length 135.6 metres
divided by a heigth of 29.5 metres) and have it listed already for faster
consulting.

2.- Pause the game (You are now a Tracking Party member), and count the
scope marks until the top of her mast, and the marks from her bow to her stern
(Hint: The scope locks at the exact centre, so just count from the centre to the
bow fairwater and multiply by two). It is easier to do if you raise the reticle to
align the horizontal division with the mast top, like the next image shows.

Important note: The first long mark you see horizontally from the scope centre is

in fact the fourth in the count! The marks 1 to 3 are not drawn to keep a clear

image in the centre, so the first mark you see is the 4

th.

Divide the number of lentgh marks by the number of heigth marks, directly (No

need to convert them to anything else). In our example, we see aprox 6.5 marks
to the stern (13 marks total length of the ship) and some 4.25 marks to mast
top. Dividing it, the resulting value is 3.05

3.- Use following formula to determine the percentual variation of the aspect
ratio:

New Aspect Ratio (3,05 in this case) x 100
Variation = _____________________________________
Old Aspect Ratio (4.6 in this case)

Variation in this case would be 66.4 %

4.- Use this ruler (It is simply a Sinus scale) to determine the AOB:



In this case, 66% in the lower scale represents a 42º AOB, as you can see in
the upper scale. Easy, isn’t it?

I can warmly recomend the above method - it works all the time. You dont even need the correct shiplenghts in the Rec. Manual OR in the game. Just take your Rec.Manual (or what ever source your using - im using the real ONI manuals) and measure the ships up in length and height with a ruler and calculate the Standard Aspect Ratio.

[joegrundman]

I know about the aspect ratio method that Hitman described. I worked with him on the U-jagd tools mod for SH3, which incorporates an aobfinder that solves the aspect ratio problem in seconds.

It was from using the aspect ratio method day-in day-out that helped me to realise what the visual orientation of the ship looked like, and from there be able to just "see" the aob. I hardly ever use any other method now.

Anyway, there are two areas of weakness with using the aspect ratio method that are not present in the visual method, and two areas of weakness in the visual that are not present in the aspect ration method.

The two methods complement each other, and the complete commander would seek to have mastered all these methods.

The weaknesses of the visual method is that firstly, it takes a while to get the hang of it, and secondly, accuracy is difficult in the aob range where the aspect ratio changes rapidly - ie between 20 and 50 degrees. It's also not very easy at long ranges where all you have is a sillhouette.

The weaknesses of the aspect ratio method is that it cannot accurately differentiate between aobs at the extremes (0 - 15, and 60-90) but it is very good in the middle range, and secondly, in conditions of rough weather, if it becomes very difficult to get accurate measurements (I'm sure you don't use pause or stabliise view) then the visual system is quite a lot more accurate.

Finally, while the U-boats used aspect ratio a lot, US skippers were more inclined to practice using Captain's eye, and often used the reverse of the aspect ratio in order to calcualte true length of target based on visual AOB and apparent length.

[joegrundman]

Let's recap by repeating AOB 30

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

[Rockin Robbins]

But wouldn't most of those pointers with cranes and masts only apply to a narrow category of ships? Of course, that is precisely the type of ships you should be shooting at except for tankers. So this could just be an opening for a lecture from you on "don't shoot the warships." It likely would have little effect on a submariner with a fat, juicy BB or CV in his sights.

Some would say that this is my time to hawk Dick O'Kane targeting. NO IT'S NOT! If you check the turorial, there is one secret to being wildly successful in submarines: learn and know ALL the techniques you can. Work especially hard on the ones you aren't good at yet. You should be fitting the appropriate attack tactic to the situation you find yourself in, not trying to stuff every attack into the Dick O'Kane box. Many situations just won't fit!

Estimating AoB by eye is one I am not good at. I'll be working on it! Thanks for all the great screenies.