Specifying a Model
Introduction
This page describes how individual elements of a model can be entered into the project.
When defining the model of the waterway in question, the user specifies:
- a number of route legs
- Traffic Lateral Distribution on each leg and in each sailing direction
- Traffic Volume Distribution (i.e. number of ships and types of ships) for each leg in each direction
- Causation Probability factors for each leg in each direction and for each type of incident
- a number of polygons defining grounds and hazards, defining their depth
For junction waypoints (i.e. waypoints to which more than two legs are adjacent) the proportion of ships sailing from one leg to the other must also be specified.
Routes, Waypoints and Legs
A new Leg is entered by selecting the Leg tool 
from the menu bar and clicking the left mouse button at the location where you want the leg to start.
Then move the cursor to the location where you want the Leg to end, and click the left mouse button again. The Leg end points are waypoints and are drawn as blue dots.
If you want to draw a new Leg that is connected to a specific Waypoint, just move the cursor over the waypoint and observe that it changes shape from an arrow to a finger 
.
Click the left mouse button to start the new Leg, move the cursor where you want this leg to end and press the button again.
Fig. A - Entering a new Leg
Fig. B - Connected Legs
If you want to move a Waypoint/Leg, select the Pointer tool
from the menu bar and drag the Waypoint dots.
Alternatively you may double-click (left mouse button) and edit the latitude and longitude coordinates of the node directly.
The displaying of Leg numbers and distributions graphics can be turned on/off by pressing the 
button located below the zoom slider.
Deleting an object
To delete an object chose the Recycle Bin Tool 
.
Once the Recycle Bin Tool has been selected, click on the objects you wish to delete.
Defining Traffic Lateral Distribution
For each leg a Traffic Lateral Distribution must be entered.
Specification of the traffic distribution requires specification of the traffic spread across the waterway and specification of the traffic composition and the intensity.
Note that a ferry travelling between two ports can theoretically collide with itself in IWRAP. To remedy this change the causation factors.
Select the Pointer Tool from the menu bar and double-click on the relevant leg. This opens the Leg Editor.
When selecting the Distribution tab, the window shown in figure D below, appears. Here the distribution in each direction can be given.
The traffic distribution will always be shown as "North" and then "South", as apparent in figure D below or, alternatively “West” and “East”, depending on the orientation of the route.
The traffic distribution may be composed by a weighted sum of a series of standardised probability distributions.
Distributions are added by pressing the “Add” button and selecting a distribution from the look-up list that appears.
The method for specifying the parameters of the distribution may be selected from the scroll-bar “Input method”.
Definition of the traffic distribution at least requires specification of the mean value and the standard deviation of the probability distribution and specification of the (relative) weight of this distribution in the combination.
In the example the north bound traffic is a combined normal and uniform distribution, where the normal distribution is weighted 64% and the uniform distribution is weighted 36%.
Fig. C
Fig. D - Leg Editor, Distribution Tab selected
Fig. E - Leg Editor, Traffic Tab selected
Entering Traffic Volume Distributions on a Leg
By selecting the Traffic tab in the Leg Editor (fig. E above) and pressing the "Edit" button will invoke the "Traffic Volume Distribution Editor" (fig. F).
The traffic distribution is defined as the annual number of ships operating on the leg.
The annual number of ships operating on the route is specified as a function of ship type and length in meter. There are 14 ship types and each has different properties as to breadth, draught, speed etc.
If the user is not interested in these finer aspects, all tankers could be classified as for instance Crude oil tankers and all cargo ship as general cargo ships etc. or they could even be pooled into one single class.
Notice data can be copied and pasted to and from the table, by right clicking the mouse.
By pressing the share bottom, you can share the entered Traffic Volume Distributionwith other legs.
By pressing the Copy button you can copy the Traffic Volume Distribution from another leg to this leg.
When sharing the traffic with another leg, you just have to change the traffic in one leg and the change will affect the other shared legs.
Fig. F - Entering Number of Ships and Ship Types
Fig. G - Entering Ship Speeds
The vessel traffic distribution may also be assessed by selecting the traffic distribution editor 
from the menu bar.
By choosing “Average Speed” located in the Data Item combo box in the upper left of the window, the window in fig. G appears. Here the average speed of each ship can be given. The values in parenthesis are the default values.
Notice that when you point the cursor to a cell, all the properties are displayed.
Only cells with frequencies larger than 0 are activated.
If the average speed is not specified, i.e. it is zero, then IWRAP (GRISK) will use a representative speed for each class based on the build-in world wide statistics, the value in parenthesis.
The data item "Causation reduction factor" is used to adjust the causation factor for a specific ship category. The reduction factor will in general be larger than one and acts as a division factor to the overall causation factor for the leg.
The causation reduction factor can be set for an individual ship, or for an entire class of ship. For instance, most passenger ships will have two navigators on the bridge, which will result in a much higher awareness on the bridge, compared to ships having only one navigator on the bridge. It could be evaluated that two navigators may result in a reduction in the probability of not detecting a possible treat by a factor of 20. Hence, in this situation the causation reduction factor is 20.
Causation Probability Factors
The causation factor specifies the probability that the officer on the watch will fail to react in time given that the vessel is on collision course with another vessel.
For a thorough description of the causation factor reference is left to the Theory part of this Wiki.
Fig. H shows the list of global default value setting of the causation factors. It is seen that several causation factors are involved in the analysis. The global value setting may be overwritten at the individual legs and waypoints to take account of special implemented navigational precautions, such as presence of traffic separation, VTS-center, special waterway arrangements at leg crossings, etc.
The first three causation factors in the list (merging, crossing, and bend) relate to collisions occurring at or near a waypoint. The two following (head-on and overtaking) relates to collisions occurring along the leg. For the calculation of the grounding frequency, two factors are used: one is the grounding causation factor and the other is the mean time between checks.
The first factor defines the probability that the navigator do not make a turn when he is supposed to.
The mean time between checks defines the conditional checking frequency (conditional on a turn was not made) with which the navigator performs the checking. Since the navigator has not performed the turn the mean checking time is expected to be high. Here it is set to 3 minutes.
Fig. H - Global Causation Probability Factors
Fig. I - Causation Reduction Factors for each Leg
Further, it is apparent that a default setting of the causation reduction factor of 20 has been selected for all passenger ships and fast ferries. These two classes of ships both will have at least two navigators on the bridge and most likely also dual engines and improved navigational equipment. This adds additional safety, and it is judged that this will imply a general reduction of the causation factors of a factor of 20.
The user may modify the values and save these in a specific file that can be used in other projects. An important element of the BaSSy FSA-toolbox [see the BaSSy-project] is in the learning and guidance of setting this set of causation factors for different navigational route layouts.
At each leg there are three causation factors in each direction: one for head-on collisions, one for overtaking and one for grounding. These may all individually be adjusted.
To specify the causation factors click on the ”Causation factors” tab and a window like Figure 11 appears. Hear a causation reduction factor can be set. The global causation factor is divided by this factor. The global values can be set by pressing the button ‘Global settings’.
The causation factor acts as a thinning probability on the calculated number of blind navigation collisions. In the specification of the causation factor it should be considered if navigators exhibit extraordinary awareness; possible because of two navigators being present on the bridge.
For ferry routes, as already mentioned, it is typically the case that the causation factor is significant lower than the average, due to the navigators increased situation awareness and that two navigators are present on the bridge.
Junctions and Leg to Leg Distributions
A junction is a Waypoint which is connected to more than two other waypoints. For junction waypoints it is possible to specify the amount of traffic going from one Leg to another.
If you provide no information about the traffic flow, then IWRAP will divide leg to leg traffic equally among the legs.
Fig. J- Waypoint editor
Select the Pointer tool and double click on a junction Waypoint. As seen in fig. J, four methods are available when given the traffic going from one leg to another. The first is the simplest, where the overall percentage is given. The fourth is the most time consuming where the percentage is specified for each ship type and length category. Remember to fill out all leg-leg combinations by selecting From Leg and To Leg in the two combo boxes.
Each junction point has three causation factors: One for merging, one for crossing and one for turning. These can also be set globally as for the legs.
Depth curves and grounds
To calculate the frequencies of grounding, depth curves must be defined. Select the Polygon tool 
. Pick a point on the map and release the mouse button. Now choose the same point while holding down the mouse button. Drag the new point to its position. Release the mouse button. Pick the point again and drag a new point. This way a polygon with as many points as necessary is defined, see Fig. K.
Fig. K - Defining grounds or depths curves with the polygon tool.
Fig. L - The Area Editor comes up when the pointer tool double click on a polygon point
Notice that the big island to the left (Samsø) has been defined by a polygon with 0 m depth.
To assign the depth and colour of the ground, choose the Pointer tool and double click on one of the points in the polygon. This brings up the Area Editor in which the name, depth and colour of the ground can be specified. In the colour window custom colours can be defined representing different depth intervals. The “Alpha channel” sets the transparency of the colour. Remember to define the land contour with a 0 m polygon.
IWRAP uses the polygon depths to identify which ships may ground on the individual grounds.
Creating depth curves using Google Earth(TM)
It is possible to create polygons using Google Earth and import these to IWRAP. Open Google EarthTM and add a new folder to My Places (fig. M).
Add an Image Overlay containing a chart to the folder. Drag the chart, so that it fits the land contours. Use the transparency slider to see the land below the chart. (Fig. M)
Fig. M - Add a new folder where the polygons are to be located
Fig. N - A chart added to Google EarthTM. Use the transparency slider to fit the chart.
Fig. O - A polygon representing a curve of 2m.
Fig. P - Polygons created in Google Earth(TM) and shown in IWRAP
Now add polygons representing the depth curves:
The name of the polygon must contain '?m' i.e. information about the polygon depth in metres. For example "Reef 6m curve". During the import into IWRAP, the depth information is extracted from the Google Earth(TM) kml file.
To see the polygons the altitude mode should be set to 'absolute' or 'relative' (fig. O).
When drawing the polygon, you should add plenty of points as it is difficult to insert points later (There seems to be a bug in Google EarthTM, when inserting new points). The polygons can be given different colours to reflect the depth. These colours are however not imported into IWRAP.
When all polygons have been added the folder can be saved. This is done by right-clicking the mouse on the folder containing the polygons. Save it as a kml file. To import the kml file into Grisk, select 'Import KML' from the File menu.
Grounding due to Drifting
A model for calculating the frequency for drifting grounding has been implemented. The black out frequencies and repair times are given by the user. Also the dominant drift directions are given. In the model it is assumed that the vessel will start immediately to drift with the drift speed.
Fig. Q
Fig. R
Area traffic
To account for collision with traffic that is not on defined routes (Pleasure crafts and fishing vessels) this model is implemented.
The user specifies the density of pleasure crafts and fishing vessels.
The difference between the two categories is that fishing ships are larger than pleasure crafts. This feature has not been validated.
