When a commercial ship is disabled and drifting offshore an effective emergency response requires towing assets with sufficient capabilities to be able to render useful assistance. The emergency towing vessel (ETV) must be able to arrive on scene in a timely manner, successfully attach a tow line, and have sufficient power to tow the disabled ship to a safe location for assessment and repair.
This study assesses emergency towing vessel needs for different types of large, high windage ships. Clear Seas Centre for Responsible Marine Shipping commissioned Vard Marine Inc. to examine the capabilities which a single ETV should have to be able to render assistance to a disabled ship drifting onto Canada’s Pacific coast. The analysis, part of Clear Seas’ Marine Transportation Corridors project, is intended to inform decision makers, response professionals and the public regarding the extensive capabilities that are required to be able to respond to emergency towing scenarios.
Seven large ships were selected to represent container ships, LNG carriers, vehicle carriers, passenger ships (cruise ships), bulk carriers and oil tankers. These ships either operate in Canadian coastal waters or are expected to do so in the future. The analysis used wind and wave data with various levels of severity for Canada’s Pacific coast to identify towing vessel needs.
Emergency towing worst-case scenarios result from severe weather conditions combined with ships with large windage (ship area above water) as analysis indicates that the load placed on a drifting ship by wind has the most impact on its speed and trajectory. Ships with high windage are therefore the most susceptible to accelerated drift rates and potential grounding if disabled. Their size and profiles also make them more difficult to take and maneuver under tow.
The report describes desirable characteristics for ETVs capable of open ocean operations, concluding large and powerful ETVs are needed to cope with the difficult conditions off the Pacific coast. It goes beyond propulsion power and bollard pull needs to highlight other characteristics such as ship attachment points, vessel reach and endurance, and human factors.
The results presented in this report are drawn from traffic transiting Canada’s Pacific coast, but the conclusions are relevant elsewhere, as similar types of ships encounter comparable wind and wave conditions in Canada’s Atlantic region.
Published September 13, 2018