AWT Weather Routing/Routeing: Applied Weather Technology

Routing and Severe Motions Avoidance

by Dr. Thomas Weber

In recent years, vessels have on a seemingly regular basis encountered the phenomena of sudden large roll amplitudes. These severe motions are particularly dangerous for vessels carrying high deck cargo, such as container or heavy lift vessels, and may cause loss of or damage to the cargo.  

AWT assists their clients in predicting  the potential for  severe motions by means of a tool for avoiding roll resonance and wave impact. This feature is valuable for both the strategic voyage planning and the tactical handling of the vessel. The implemented method, as proposed by the International Maritime Organisation (IMO), takes into account the vessel’s roll period, course and speed as well as the encountering wave trains as forecast by AWT. It then calculates the potential for heavy oscillations with high amplitudes, capsizing and sudden course deviations of the vessel. The results are depicted graphically in a polar diagram.

The objective of this method is not to calculate any roll period, but to predict the potential of severe motions. The resonance function does not require any sensors, as the system is based on the physical approach that the vessel is an oscillating system which may be excited at, or in the neighborhood of, resonance frequency. This method is available in the BonVoyage System (BVS), AWT’s onboard software product. The Master can use the polar diagram as a guideline to derive reasonable course and speed adjustments to avoid these dangerous situations, thereby preventing cargo losses and damages. Furthermore, AWT is applying this method  for its shore-based Optimum Ship Routing service to generate severe motion alerts.. This objective evaluation of safety takes Optimum Ship Routing to next level.

AWT is the  first ship routing provider to take into consideration these dangerous phenomena in providing its services..  This contrasts the norm for other ship routing services – simply to point the vessel on the right side of the low.

By means of this method, BVS becomes even more important in trades for which there is limited route selection. The Master now has available the ability to carefully analyse the route ahead and thereby predict potentially dangerous conditions well before they occur, rather than a system which can only provide a warning when the vessel is already encountering dangerous conditions. This long-range strategic approach greatly increases each vessel’s ability to avoid cargo loss and damages.