Port navigation risk assessment



Brad Judson, BSc, MA, MNI, BMT Fleet Technology Ltd.


The dynamics of navigation, shiphandling and collision avoidance intrinsically link a master, bridge team and their vessel with a port’s safety support structures in the context of the tides, currents, wind, hazards and other vessels in confined waters.

On the bridge, there is a heightened level of readiness to meet the increased level of external threats, the vessel is made ready for immediate manoeuvre or  emergency anchoring, the workload is shared and a pilot is embarked. The port entry passage plan is executed and adjustments are made for actual conditions encountered.

Passage planning is risk management

Just as a master prepares a passage plan for a harbour approach, understanding the safety environment and the navigation hazards managed by mariners is key to identifying appropriate aids to navigation, channel dimensions, and traffic management systems to minimise the likelihood of vessel grounding and collision.

Channel design is well supported by guidance such as that provided by PIANC internationally or WHAMS in the United States. Manoeuvring assessment is also in hand through the use of technology such as BMT SeaTech’s PC Rembrandt. Traffic flow and collision risk can be analysed using WebStat by GateHouse, Voyage Traffic Planning and Simulation System by SimPlus or other Geographic Information System based products.

BMT Fleet Technology’s Buoy Ranging Software enables the selection and placement of buoys and the estimation of serviceability. However, it is only recently that the analysis of an appropriate level of aids to navigation and traffic services is advancing to the same level of sophistication. This was made possible by modeling navigation risk on how a master plans and executes a passage in restricted waters.

Risk-based aids to navigation design

As vessel designs and traffic characteristics change, the port must consider the appropr iateness of existing navigation constraints and more precisely assess if support is sufficient or restr ictions are excessive. Navigation hazards in port approaches have successfully been assessed from the vessel and master perspective with the support of software that provides a measure of positioning quality for different combinations of aids to navigation.

The Excel spreadsheet method, design minimal de sécur ité or DMS, developed by Brad Judson, Stéphane Julien and others demonstrates navigation risk for each planned track for a design vessel in various environmental conditions. Limiting factors such as wind, depth, vessel speed and draught become obvious.

The concept of assessing navigation risk in DMS is similar to that of determining an anchor swinging circle and safety margin. The swinging circle of a vessel at anchor is a function of the scope of cable, depth of water, height of tide, wind and current. The safety margin extends this area depending upon risk and one of the factors is the ability to accurately position the vessel by visual aids to navigation, radar and GPS.

The safety margin is not just a function of the manoeuvring capability of the vessel and the master; nor is it just the stated accuracy of GPS or ECDIS, it also a function of the quality of positioning with confirmation by a secondary method and the proximity to shoals. A high quality position might be the visual reference to transit ranges showing the vessel to be on track and confirmation by radar or ECDIS that a master is on the correct set of ranges, for example.

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