# Project Overview

## What OMRAT does

OMRAT takes three kinds of input and produces one kind of output.

Inputs:

1. A shipping route – one or more polyline segments on a map.

2. Traffic per segment – how many ships of each type pass per year, their speed, draught, beam, and height above waterline.

3. Obstacles – depth polygons (bathymetry) and structure polygons (bridges, wind turbines, piers).

Output: expected annual frequency for each accident type.

Accident type | When it occurs
--- | ---
Drifting grounding | A ship loses propulsion, drifts with wind/current, grounds on a shallow depth polygon before the crew can restart the engine.
Drifting allision | Same but the drifting ship hits a structure.
Drifting anchoring | The drifting ship successfully anchors before it grounds.
Powered grounding | A ship under power fails to turn at a bend, continues straight, grounds on shallower water ahead.
Powered allision | Same but hits a structure.
Head-on collision | Two ships on the same leg travelling in opposite directions.
Overtaking collision | Same leg, same direction, different speeds.
Crossing collision | Two legs share a waypoint at a non-trivial angle.
Bend collision | Same leg, one ship fails to turn at a bend.

## Who OMRAT is for

- Port / fairway designers doing quantitative risk assessments.

- Environmental authorities estimating baseline risk for a sea area before permitting new infrastructure.

- Researchers comparing IWRAP-style methodology outputs against historical accident data.

- IWRAP users who want an open-source alternative and can already import / export XML.

OMRAT is not a routing or navigation tool. It does not simulate individual ship movements. It is a statistical tool: for a given traffic pattern it returns how often each accident type is expected.

## The methodology in one paragraph

OMRAT implements the IWRAP framework (Friis-Hansen 2008, Pedersen 1995): every accident frequency is decomposed into a geometric candidate count (how often could an accident happen based only on geometry and traffic) multiplied by a causation factor (how often does an accident actually happen given a candidate encounter).

\[F_\mathrm{accident} = N_A \cdot P_C\]

\(N_A\) is derived from the route, traffic, and obstacles. \(P_C\) comes from published tables (defaults: Fujii 1974, IALA IWRAP manual). See Theory (what is calculated) for the full reference table and Drifting Risk Calculations / Ship-Ship Collision Calculations / Powered Grounding and Allision for each accident type’s derivation.

## Background and funding

OMRAT has been developed with funding from:

- Naturvardsverket – Swedish Environmental Protection Agency.

- RISE – Research Institutes of Sweden.

It is licensed under GPL v2+. The source is at https://github.com/axelande/OMRAT.

The mathematical foundations come from:

- Pedersen, P.T. (1995). Collision and Grounding Mechanics. WEMT’95.

- Friis-Hansen, P. (2008). IWRAP MK II - Basic Modelling Principles for Prediction of Collision and Grounding Frequencies. Technical University of Denmark.

- Fujii, Y. et al. (1974). Some factors affecting the frequency of accidents in marine traffic. Journal of Navigation, 27.

## What’s next

- Never installed OMRAT? -> Installation.

- Installed and curious what a first run looks like? -> Quickstart.

- Want to know what a “leg” is? -> Concepts.

- Ready to build your own project? -> User Guide.