AOB by Eye Manual

8/9/2019 AOB by Eye Manual

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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

Quote:

(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 estimateangles 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 coursefor 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 ofvisuals 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 alightweight!)

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.


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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. Themore 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 reciprocalcourse, 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 of230 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 anotheron 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


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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 ahvenow "cleared" the funnel.

AOB 15

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


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AOB 20

This is one of the more difficult to identify. The bow wave no longer clearly helpsand 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 outthe 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


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To be continued...

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 aship 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


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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.


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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


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AOB 65

AOB 70

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

AOB 75

AOB 80


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AOB 85

This is now only very slightly off being exactly perpendicular

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:


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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:


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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)


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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.


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

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