©1990, 1995 General contents
Chapter 8 Appendix B

Appendix A
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:

  1. the Beginner's Introduction;
  2. Interface Principles;
  3. Click Response;
  4. the Ship and General Display (then try it out);
  5. the ROV, Cable and Sea-bed (then try);
  6. the Game Object, Targets and Scoring (and try getting close to a target).

Beginners' Introduction

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
  1. a ship;
  2. 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! Two requests.

  1. 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!
  2. 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.

Game Object

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

  1. to examine all targets that are potentially dangerous (see ‘targets’), and identify them using the appropriate buttons;
  2. 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;
  3. 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);
  4. and complying with safety regulations, which means not navigating the ship within 100 metres of a mine or unidentified target.
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 lose points.

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 mines. 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 and challenging.

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.

Interface Principles

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 ‘presentation’ level.

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.

General Display

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 tried. 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.

Click Response

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.

  1. 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.
  2. Nothing at all happens. Firstly, if you are replaying a previous run, no mouse interaction is possible at all. Wait until the replay has finished. 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.
  3. 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.

Sea Bed

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.


The targets

In the area to be swept, you may find two kinds of target.

  1. 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.
  2. 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.
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.

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 turning!).

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 saliently.

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 ROV.
Control Hints.
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 seen.

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 section (UMB). 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 simulator.) 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 model!). 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.


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.
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.
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 (submarine).
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.
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 propellers.
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.

Next Appendix B
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