The help content in the second sea-searching experiment
The green ‘help’ buttons on the right of
the lower half of the screen will cause
more information to be displayed about how
this simulation and interface work, etc.
If you are a beginner, please start by reading
How to Use the Help Screens, and Beginners' Introduction.
See the appropriate section for instructions on how to
start, stop and replay.
Your actions will be recorded for posterity
in the interests of scientific enquiry,
though your identity will be kept confidential!
How to Use the help screens
How to use the help screens provided here.
Each of the buttons on the right provides a (textual)
piece of help on the subject indicated on the button label,
which appear in the same space as this text is now
appearing. If there is more text than will fit
onto one screen, you may move through it using the
blue buttons on the left of the lower half of the
screen. If a move is
impossible, you will be beeped at, but nothing
more serious will happen.
If pressing one of the green buttons results in a beep,
this means that the file for that piece of help text
is not available. If this happens, or if there is
anything which you think should be explained,
or you would like to be clarified, that is not,
please inform the program author.
It is not possible to see the help screens while in the
middle of a run, as this would interfere with the realism of
time pressure in decision making. However, when you stop
the run, you may continue to page through the help until
you start your next run, or quit from the program.
If you have not studied the other screens already,
the suggested order is:
- the Beginner's Introduction;
- Interface Principles;
- Click Response;
- the Ship and General Display (then try it out);
- the ROV, Cable and Sea-bed (then try);
- the Game Object, Targets and Scoring
(and try getting close to a target).
This is the explanation for beginners, which you should read
if you are unfamiliar with the task of mine hunting.
You will need to study all
the help information at some point,
otherwise you will probably assume something incorrectly.
This is simply an overview.
You are in command of a mission to sweep an area of sea bed
and dispose of any mines you find. At your disposal are
- a ship;
- a “remotely operated vehicle”, or ROV for short, which is
a small unmanned submarine attached by an umbilical cable to
the bottom of the centre of the ship. It starts docked
inside the ship.
How it is done
First you look for a suspicious target. Having found one,
you manoeuvre the ship to a position between 100 (red circle)
and 200 (green circle) metres away,
and bring the speed down so that the ship won't drift
away while your mind is on other things. Next, you put out
the ROV, and fly it towards the target until it appears
properly on your camera view, so that you can identify it.
If the target is an old oil-drum, you can just leave it at
that, and bring the ROV back in. If it is a mine, you now
have to disable it.
You are responsible for flying the ROV to a position where
an explosive charge can be attached to it. How this is done
is not part of the game, but you are told when it has been
done. Then you get away from the mine, and when clear you
can detonate it. Job done. Then see if there are any more.
The cable is fairly strong, and you can pull the ROV
back toward the ship by reeling in the cable.
How to start learning
Read the sections on how to use the help screens,
and on the interface and the response
to clicks. To get as far as reading this you have
already discovered most of the essentials.
While learning the task, ignore the cost of information,
turn all the sensors on until you have a good idea of
how you are going to perform the task.
Then you will need to get a
feel for the controls of the ship.
Read the sections of help about the ship, and about the
general display, and without bothering at all about mines
or the score for the moment, manoeuvre the ship around,
and experiment with the display changes, stopping when you like.
You could also replay the ship demo run.
When you are fairly happy with that,
try the ROV. Read the sections of help about the ROV,
the cable, and the sea bed. Perhaps look at the ROV
demo run. Try it, and have a good look from all
sides at how it responds to your controls. Then read
the section on the targets, and see if you can
manoeuvre the ROV close to one.
Then you will be ready for the full game. Read the sections
on the game object and scoring, and have a go. Good luck!
- Be patient! This is deliberately not an easy task, and
may well take several hours of study and trial before you
feel you've ‘got the hang of it’. When you do, however, it
feels correspondingly satisfying!
- In my research, I wish to study the different ways that
people go about this task. Please do not consult with others
(keep your clever ideas to yourself). There will be a chance
later to do that if you wish.
The object of the game
After starting the game, when you reduce the
scale of the plan, you will see a red-bordered rectangle,
(to the North-West) which defines the area which you are to
check over and clear of mines. You start inside a green
rectangle, and you must return to this after sweeping
in order to complete the task.
Inside the red rectangle,
the task is
The first two parts of the task are essential, i.e., you
cannot complete the task without doing these. The others are
secondary, in that you may complete the task but you will
- to examine all targets that are potentially
dangerous (see ‘targets’), and identify them using the
- to disable all mines, which means flying the ROV to
within 5 metres at under 0.2m/s, clearing the danger area,
and detonating the mine;
- to avoid damage to ship, ROV or cable, principally by not
being within 100 metres when a mine explodes
(mines explode either if they are run into,
or if there is too much engine noise close by);
- and complying with safety regulations, which means not
navigating the ship within 100 metres of a mine or
After you have become reasonably skilled at the game,
getting a high score becomes the priority.
To achieve the best score, you will have to use only
the information you need, by turning off what you do not
need at any time.
Speed and caution are not easily compatible, and you will
have to decide how to trade off the different objectives,
in the light of the scoring system (q.v., which defines
the relative priorities from the point of view of the
person setting the task).
The scoring system
The main surprising thing about the scoring is that
there is a cost in points for using information.
The purpose of this is that after you feel confident that
you know what is going on, you can turn off the information
that you do not need.
The way the information is priced means that when you are
learning, there will be a large negative score.
You are to ignore the score completely until
you feel happy that you know what is going on well.
Your objective is first to learn how to do the task
(ignoring the scoring absolutely),
and only then to attempt to achieve the highest score you
can by judicious switching off of information.
For completing the task (as described under ‘object’) there
is a bonus of at least 20000.
If there are adverse weather conditions, you may get more.
You cannot get a good score without this.
For each mine that there is, when you detonate it after
priming it you will get a bonus of 500. When you identify
any target by clicking the correct button, you get a
bonus of 500. However, clicking on the wrong identification
will lead to a penalty of 500 under ‘infringements’.
So don't just guess what the target is without looking.
You cannot complete the task without
identifying all the inert targets and detonating all the
If a mine explodes while a vessel is within 100 metres of it,
the vessel will be damaged. How much depends on how near
it was to the explosion, and the penalty for damage is
calculated accordingly. The penalties are large.
If you navigate the (centre of the) ship within the area of
possible damage of a mine or unidentified target, you will be
penalised for breaking safety regulations, at the rate of 10
points per half second, irrespective of whether or not it
is a mine or whether it explodes.
Distances are calculated in 3-D.
The information on the sensors is paid for in points.
The cost of each sensor is shown on it, when that sensor is
off. The total cost per half-second, of all the sensors
that are currently on, is shown on the display, as is the
cumulative total cost of information till now.
Finally, time ticks away steadily, and you lose 1 point for
every half second that you take to complete the task.
The number, type and position of the targets are randomly
allocated whenever you start a new run. The scoring is
designed to allow for this, in that you will take longer if
there are more targets, but you will accumulate more
bonuses. With luck (and a bit of skill) your score should
come out positive in the end, if not first time then
certainly after a few trials!
If you are really curious to know about other people's
scores, look at the scoreboard, which gives each player's
best score to
date. Your own scores (on the current configuration) are
available to you every time you have this help screen.
The purpose of the simulation
This simulation game is intended to provide a semi-complex
task for experiments into matching the presentation of
information to the user with the representation embodied in
the user's ‘mental model’ of the task/system.
The main way in which this is done is by recording what
actions are taken in what situations. The way that the
situations are categorised depends on what information you
use for making your action decisions. This will become
apparent when you have reached a level of competence that
permits you to turn off all the sensors you do not need.
The design of the simulation as a whole
The simulation is intended to bear a resemblance to an actually
possible complex task, and thus be inherently interesting
Not all of the information and controls could be accommodated
onto one screen comfortably. This means that there have to be
some changes in the information and controls displayed over
time. The principle governing the
way in which the task is split up is that the information
most directly relevant to the performance of a control
action is displayed with it. Thus, for example, the control
of the ship's rudders is displayed along with the information
about what the setting is currently (both graphically and
numerically), and what the ship's heading is.
The sensors and effectors are grouped together following the
obvious physical, mechanical or functional sub-systems,
rather than having higher-level connections. Thus, the
interface that you see is designed to be the kind of
interface that you might come across for a system that has
not undergone detailed task analysis or analysis of the
user's mental model.
The principles of the interface
As will have already struck you, the screen has four
differently coloured backgrounds. The rationale for this
is simply as follows.
The blue section contains active
buttons that change either what information is displayed, or
the way in which it is displayed; but these buttons do not
affect the simulation itself. They act at the
The next section (black background) provides information in
either a graphic or a verbal form.
The red-backed section provides numerical or verbal
information. The black and red sections respond to
mouse button clicks by toggling the sensors on and off.
If a sensor is off, its cost in points per half second
is displayed in place of the information.
(These are ‘monitors’.)
The green-backed section provides your controls over the
process. As you read this help text, they merely
enable you to select which help text is loaded,
but during a run they cause actual or demanded
values to be set on the various controls.
These values will then appear in the red section,
so you should be able to see that something has
changed as a result of your mouse click.
Two general principles are followed: firstly, if a (legal)
click has no actual effect (e.g., you selected something
that was already the case, or something impossible)
you will receive a beep;
secondly, where possible, information relevant to the state
of some variable is matched in the same row as the control
buttons that allow its change.
The General Position Indicator and its Display Changes
The general position indicator display, on the top half of
the screen, can be manipulated when the game is running by
means of the blue ‘display change’ buttons on its left.
The various ‘fix’ buttons make
what is fixed stay in the same place on the screen
(strictly, the same scale distance away from the centre of
the screen). What is currently fixed is displayed at the
bottom left of the graphic display.
The ‘centre’ buttons bring the named object to
the centre of the screen, but do not affect what is fixed.
The scale buttons alter the scale by a factor of two, either
way. The grid lines remain at 100m intervals, and since you
cannot apply a ruler easily to the screen (nor is there the
time or motivation to do so), the actual value of the scale
is not given. You can work out what it is roughly by
observing the grid lines.
The plan and section buttons will be self-evident when
This graphic display is very useful to give you an idea of
what is going on. This is essential while learning about
the task. However, its use is priced highly, and when you
are reasonable competent at doing the task, you will want to
turn off this display unless you really need it.
How the mouse button clicks operate
The interface is deliberately limited to allow at most
one mouse click every half second. Very rapid clicking is
pointless, since the clicks are not stored up. Here is how
to tell what is happening.
When you press (and hold down) the left or middle
mouse button, one of three things could happen.
- You get an immediate ‘beep’.
This means that the area on which you are clicking is not
currently active. You must choose to click somewhere else.
- Nothing at all happens.
Firstly, if you are replaying a previous run, no mouse
interaction is possible at all. Wait until the replay has
Secondly, in the (short) time between pressing the
mousebutton in an active area, and that area highlighting,
nothing is registered. If you want to get on with your
clicking, click on your next choice as soon as the last
choice is highlighted. If you do this, you will be able to
perform two actions every second. This is the maximum.
- After a short time (up to half a second) the area
is highlighted. This means that the action is allowed.
One of three things may then happen.
Firstly, you may hear a ‘beep’ with the highlighting.
This means that the action you have attempted is not
effective for whatever reason.
Secondly, if the cursor was on a sensor area, that sensor
will toggle between on and off.
Thirdly, an action may be performed.
Whether or not you see any immediate effect depends on
what sensors are active at the time.
If all the sensors are on, at least something in the display
should change in some way.
There is also one kind of action which is not done with the
mouse, but should not concern you until you are well
practiced. If you know exactly what is going on, but you do
not wish to do anything for a considerable time (while the
simulation continues), you may press one of the number keys,
1 to 9. (1 is the only one you are likely to want.) This
causes the simulation to move on by about 10 seconds times
the number you press, without showing any display, in the
shortest time possible. All the scoring continues just as
if you had not pressed anything during that period.
Be warned that this cannot possibly increase your score.
The sea bed
The sea bed, in these waters, is muddy and gently sloping.
It gives a few, fairly random, echoes to your sonar, which
appear as grey dots on your general position indicator.
This is enough to give you a general visual impression of
where the sea bed is,
when you look at the North-South or West-East sections on
your computer generated display. For accuracy,
however, you must rely on your digital instruments, which
give you vertical measurements of
the sea depth (at the ship), or the height and
depth (of the ROV). In the home area, the sea just happens
to be 50m deep, and in the area to be swept it is close to
this value, sloping only very gently.
The main hazard of the sea bed itself (as opposed to the
targets) is that the ROV may get stuck in the mud. This is
tedious, and wastes time.
In the area to be swept, you may find two kinds of
Having identified these types of mine, your task is to fly
the ROV to a position where someone else will actually do
the job of priming it—how this is done does
not concern us in this game, but it could be the fixing of
a small explosive charge to the mine, using some kind of
robotic arm. What you need to know is that
in order for this priming to be done, you need to bring
the ROV within 5 metres of the mine (range shown on one
of the sensors), at a Ground speed of
less than 0.2m/s. As soon as these conditions are
fulfilled, the priming will be done instantly, and the
word ‘Ready’ will appear in the green ‘detonate’ button on the top
half of the screen. Any time after this, pressing that
button will result in the mine exploding, and your being
credited with points accordingly. Don't do it until both
your vessels are over 100 metres away!
The mines are acoustically set off, but running into them
makes a loud clang which also sets them off.
Type 1 mines explode on contact if the ROV is within 2m,
For type 2 mines this is 1m, but they do more damage.
This will probably result in the ROV being destroyed and
the run ending.
If you use too much motor too close to the mine,
it will go off and you will have
an enormous damage penalty. You are safe using all full
thrusters if you are 5m or more away. Closer than this,
the effect is proportional to distance and to the square of
the revs from each thruster.
- Inert targets. These all look like oil-drums on
their end, i.e., cylindrical. They are close to the sea bed
itself. When you see one like this, you should click on
the appropriate recognition box, (“It's Inert”)
when your score will go up
and that target will disappear from the display.
- Mines. These come in two shapes, with slightly
different behaviour. The mine
type 1 looks like a cube on its face; the mine type 2 looks
like an octagon on its point. Both types of mine have a
tether extending downwards from the centre of the bottom of
the mine to the sea bed, which is some 2 to 3 metres below.
While any target is still either unidentified or
dangerous, two circles will appear on the general display if
the ship is within 400 metres of it. The outer (green) one is
200 metres from the target, the length of the cable. The centre
of the ship has to be within this circle for the ROV to be
able to reach right up to the target. The inner, red one is the
100 metre danger zone. If the centre of the ship goes inside this,
your safety infringement penalty will grow rapidly.
The ship model
The ship is 60 metres long. It has twin propellers that can be
operated independently, and twin rudders that operate only
together. There is also a bow thruster, which gives a
smallish sideways and turning force, most useful and
effective when the ship is moving very slowly through
the water. It takes a fair time for a propeller revolutions
demand to take full effect—the revs only change at a fixed
low rate. Each of the components that can be altered has
five possible demand values: zero; full either way,
and part either way.
The ship is equipped with a sonar that will detect all
suspicious objects (‘targets’) on or near the sea bed, up to
500 metres away from the centre of the ship, in all directions
equally. However, this sonar will not distinguish between
the different types of object. It also picks up other random
echos from the sea bed, within 500 metres or more, and it has a
clever (computer-based!) system integrating information from
sonar and radar, and displaying it in various ways: plan or
section; various scales; various things fixed or centred.
This forms the main display which is always present on the
top half of the screen.
In the ship's own graphic display, there is a diagram of the
ship's heading, speed and rudder position along with a
verbal indication of how each rudder is performing (useful
to know if you're trying to figure out why the ship isn't
The digital sensors include the actual propeller and bow
thruster revolutions, and their demanded values;
the rudder angle and demand; The surge (i.e., forward
speed) and sway (i.e., sideways speed); the heading of the
ship, the heading of the nearest target and the distance to
it; and the depth of the sea at the centre of the ship.
If you encounter non-calm weather conditions, you
will find the graphic display most helpful. You can easily
figure out what most of the signs represent when you alter
the weather conditions. The red line is the ship's velocity
relative to the water, the green the water's velocity
relative to the ground, and the yellow is the ship's
velocity relative to the ground, which is the thing you are
most interested in. This explains why it is drawn most
The model is a simplification of a model, previously held at
YARD, of a Mine Counter-Measures Vessel (MCMV).
The chief simplification is in restricting the motion of the
vessel to three, rather than the full six, degrees of
freedom, namely: surge (forward), sway (side), and yaw
(rotation about a vertical axis). Heave (vertical motion),
roll (about a fore–aft axis), and pitch (about a lateral
axis) are set to zero at all times.
Within the bounds of this simplification, the modelling of
the hydrodynamics and other factors has stayed fairly closely
to the earlier model, with the main exception of the rudder,
which is less true to life (due to its potential analytical
complexity). The maximum speed is around 8.5m/s (c. 17kt.)
which is reduced very slightly when towing the cable and
Stopping the ship is difficult, since it has so much
momentum. If you are going ahead, put both propellers full
astern, and when you reach about 1.1 metres per second
“surge” speed, stop the propellers. The time it takes for
the propellers to stop will be roughly equal to the time it
takes the ship to finish stopping.
The ROV model
ROV stands for Remotely Operated Vehicle, and it is
a small unmanned submarine used to approach potentially
dangerous objects, to examine them and perform any necessary
operations. It is attached to the ship by an umbilical cable
(q.v.) which carries instructions and information.
The ROV is carried in the ship while not in use, and
while it is in, its controls cannot be used nor its display
The model of the remotely-operated vehicle is largely the
author's own invention. It has two main horizontal thrusters,
which can operate independently, and one vertical thruster,
located in the centre of the vehicle.
There is no rudder, and the directional controls
use the main thrusters differentially.
These are driven electrically and respond quite quickly.
The shape of the ROV may be imagined as based on
an oblate spheroid (smartie shape).
The main sensor is a camera which has a range (optimistic) of 15m
in the underwater conditions. This is tiltable up and down,
up to plus or minus 1 radian (about 60 degrees).
It cannot pan, but always points
towards the front of the vehicle. The camera view is
integrated with information from the ship, showing the
position of targets that are still out of sight as
conventional symbols, irrespective of the type of target.
The ROV graphic display also gives a visual indication of
direction and camera tilt, in the form of imaginary vertical
lines at each of 16 points around the compass. This also
gives a good graphical impression of turning.
Note that when the ROV is in (i.e., not deployed) it is
an error to select the ROV display and controls. To deploy the
ROV, you must use the control to be found in the cable
Other sensors show the demanded turn;
the depth below the surface and height above the
sea-bed; the speed through the water forwards (surge),
sideways (sway) and downwards (heave); the heading
of the ROV, and the heading and
range of the nearest target that has not been dealt with,
if within 500m.
As far as possible, the sensors that relate to each other
have been placed close: thus, the heave sensor is
in the next row to the controls of the down thruster.
The model keeps roll and pitch always at zero. The remaining
four degrees of freedom are modelled very simply, with no
hydrodynamic cross terms, only simple drag.
(This is quite unlike the YARD ROV model in the mockup
The ROV can reach a speed of over 6m/s unhindered, but in
practice the umbilical cable (q.v.) restricts this severely.
The ROV sticks in the muddy sea bed very easily, and can be
difficult to extract. You may have to give it a tug with the
umbilical cable (which fortunately is quite strong in this
Currently, collision with the ship is not modelled, and they
are capable of passing through each other obliviously.
The umbilical cable
The umbilical cable is 200 metres long, neutrally buoyant and,
in this version, fairly strong and elastic—the force
needed to snap it is 10kN (about 1 ton force) and
it will stretch by 10% of its length before breaking.
You can break it by violently mishandling
the controls of the ship and ROV.
The cable is not without water resistance:
it can be very noticeable at times.
Controls and sensors.
Inside the ship, the cable is wound round a drum or capstan, over which
it can slip. This means that we have control of two quantities:
1) the tension at which the cable slips over the drum,
and therefore is payed out if there is any spare, and
2) the speed at which the drum is turning,
which dictates the speed at which the cable
is being taken in, if is it not slipping.
You can tell whether the cable is slipping, by
comparing the set payout tension with the tension of the
cable at the ship (displayed adjacently).
If the tension at the ship reaches the payout value
(even if momentarily) the cable will slip.
The tension and speed can operate together: i.e., the cable
can be set to be winding in if the tension is less than the
fixed amount, and paying out if it is over that amount.
Pulling in the ROV can be quickly done by setting
maximum tension and take in speed together.
In addition, the total length of cable out,
and the actual distance between the ship and the ROV,
are displayed, which allows an easy estimation
of how straight the cable is.
Placed with these are the controls to put out or take
in the ROV from its dock in the centre of the ship.
Taking in can only be done when the cable length
out is at the minimum value of 3m. Winding in the
cable automatically stops at this length.
Also, here are the numerical versions of the weather
parameters, in case these are not easy to see on the ship
graphic display. The directions are in degrees clockwise
from North, like vessel headings, the speeds are
in metres per second, and length and height in metres.
Start, Stop and Replay
How to start, stop and replay
Starting a new run
This is simple.
Click on the “Start” button in the upper half screen.
All the variables are re-initialised.
When you start, all the sensors and graphic information is turned off.
To see what is going on, you will have to turn
some of the sensors on by clicking the mouse buttons
when the cursor is in a graphic or sensor area.
Replaying an old run
The run to be replayed will be the one indicated in the red section
in the lower half screen, just to the right of this.
You may choose which one you want by using the buttons
“Select Next Run” and “Select Run Before”.
Having chosen the run you want, click on the Replay button
in the upper half screen.
To stop a new run, click on the “Stop” button in the top half screen.
During a replay, no buttons are active.
You must use the ESC key if you want to stop a replay.
- ASTN = ASTERN
- The front of the ship.
- The umbilical cable that connects the ship and the ROV.
- The state of a rudder when the water from the ship's motion
and the water from the propeller are coming at it from
opposite directions: the rudder loses its turning effect.
- Most of the controls are activated via servo mechanisms,
rather than direct mechanical couplings. The demand is the
value you want to get: it is set straight away, but it
takes a short time for the
actual value to reach the demanded value.
- HEAD = HEADING
- The angle, measured in degrees clockwise from North,
of the line joining the bow and stern of the ship,
or two other points.
- (Of ROV) Speed (m/s) down (+) or up (-).
(Of Ship) Ignored; always zero.
- Rotation about the port/starboard axis. Not modelled
for either vessel in this simulation; assumed zero.
- PROP = PROPELLER
- Applies force ahead or astern. These are heavy, cumbersome
things that take a considerable time to change speed.
- Rotation about the ahead/astern axis. Not modelled for
either vessel in this simulation; assumed zero.
- Remotely Operated Vehicle: a kind of unmanned submersible
- The equipment at the stern of the ship for controlling
direction. Port rudder makes the ship turn anticlockwise if
it is going ahead, clockwise if it going astern.
- Each square on the position indicator is 100 metres, hence
about 18 squares make a nautical mile, and a cable is just
under two squares.
- As with a wing, a rudder loses its ‘lift’ and turning power
when the water comes at it from an angle too far away from
the angle at which it is pointing.
- STBD = STARBOARD
- The rear end of the ship.
- (Ship and ROV) Speed (m/s) ahead (+) or astern (-).
- (Ship and ROV) Speed (m/s) to port (-) or starboard (+).
- Small blades inside a duct, applying force whichever way
they are pointing. They respond much quicker than
- SI units are used throughout the calculation and display.
Speeds are in m/s: 1m/s = 2kt. Distances are in metres: A
nautical mile is about 1800 metres. (Grid shows 100 metre squares.)
- (Ship and ROV) Rotation about a vertical axis;
leads to change of heading.
Please inform the program author if there is any other term
you do not understand.