IWRAP Training Seminar February 2010

The second IWRAP training seminar was held at St.Germain en Laye February 16-18, 2010.

Various aspects of IWRAP were discussed at the seminar, some of which are documented below:

Modelling Apparent Width due to cross current

Issue: (Igor) Can I modify the breadth of the ship? I would like to model the apparent width of a ship due to cross current or side wind.

Discussion: Not possible in the present version of IWRAP.

Lateral Distribution bar width

Issue: (Igor) When establishing a lateral distribution based on AIS data, you would obtain the basic distribution through numerical analysis of AIS data. For this you would need to select a with of each rectangular bar of the distribution, after which you would fit a suitable lateral distribution within the IWRAP tool.

The shape of the (mathematically) fitted distribution will change, depending on the width you select for the numerical analysis...

Should the width of the numerical tabs not be selected carefully, perhaps as a function of the width of the ships passing the passage line?

Discussion: (Erik) Yes, your right, you need to experiment a little with the width of the tabs. If you make them to narrow, you will not get any distribution.

Solo Ship Kollision?

Issue: (Esa) A ship is alone in the world. It sails with a speed of 10 knots back and forth between point A and B which are 10 nautical miles apart. In one year the ship has made 12*365 = 4380 voyages. If this is modelled by one leg, length 10 nautical miles with volume of traffic being 4380 voyages each way, IWRAP yields a number of collisions...... How is this possible since the ship is alone in the world?

Discussion: IWRAP assumes that each voyage is independent of all other voyages, so in the IWRAP world it is possible for the ship to encounter itself going the other way :-)

One possible way to overcome this problem is to use uniform distributions in both directions and make sure there is no overlap between the two distributions. This however only takes care of head-on collisions. Since each ship belongs to a single category of ships, and there is a fixed average speed for this category, the model should not yield any overtaking collisions.

Minor bugs found in Version 2.2.0a

• Result view - On legs using uniformal distribution, the distribution is not rendered in geographic result view.

• Error when entering Zero as the value for Std Deviation of a Normal Distribution - Error msg is given, but the application chrashes (Identified and reported by prof. Knud Benedict)

• When naming project files using accented charecters (Málacca), the models do not save properly. Only an empty model is saved...
• Using Gambel distribution both ways on a leg yields high collision rates. Collision rate seems not to decrease when if you move the gambell distributiond far away from each other..

Input for the IWRAP Wishlist

• Intelligent naming of Legs and Traffic Distributions utilising the knowledge of north/southbound and west/eastbound.
• Wind and Current "Roses" for each leg
• Colour scheme for polygons. The blue scale should be reversed making the deepest polygon the most dark blue shade.
• Colour Scheme for polygons. Transparency shoud be set to 50% as default.
• Colour coding of results should be normalized, i.e. On legs the result should be divided by the length of the leg on polygons, perhaps be divided by the total length of all polygons?
• Using Raster Charts, the identity of the current map is not displayed anywhere. One solution could be to mark the map in use in the list of maps in the map menu item.
• When switching between raster maps, the scale changes. Better to keep the scale of the last map used.
• Important: END Points - There is a grounding contribution from end points of a leg structure.... grounding calc should end at leg points that are not connected to other legs.