Clear Seas commissioned Nuka Research to characterize both the potential capability and the availability of commercial tugs engaged in usual trade for use as Emergency Towing Vessels (ETVs) in Canada’s Pacific Region. These tugs are referred to as “tugs of opportunity” as they are not dedicated to or necessarily intended for rescue efforts.
Because tug traffic patterns remain relatively consistent from year to year, automatic identification system (AIS) data from 2016 were used to identify the tugs active in Canada’s Pacific Region and represent typical tug activity. Each tug’s location and route were determined from AIS data and its capability was established based on its bollard pull (the force a tug can apply when pulling against a fixed object).
Tugs were divided into four categories for analysis:
|Category||Number of Tugs|
|All tugs present|
|50 metric tonnes (MT) or greater (minimum capability needed for emergency response)|
|70 MT or greater (able to respond in 21 knot winds (93rd percentile conditions)|
|90 MT or greater (most able to provide effective response)|
The proportion of time tugs in each category are likely to be present was determined by frequency of travel in 40 x 40 km grid cells on a map and the frequency with which tugs crossed analytical passage lines drawn on the map of the region. Tugs are most commonly found in near-shore waters from Vancouver to Alaska. Tugs of all sizes follow this general pattern of movement, but larger tugs are present in all areas with less frequency.
Tugs with bollard pull greater than 70 MT were present less than 10% of the time on average within any area. On average, the 35 tugs in this category crossed passage lines with the following frequencies:
- Hecate Strait near Prince Rupert every 1.4 days (34 hours);
- Queen Charlotte Strait near Port Hardy every 1.1 days (26 hours);
- Strait of Juan de Fuca every 2.0 days (48 hours).
When comparing winter and summer, there were only minor seasonal differences in the distribution of tugs with greater than or equal to 70 MT bollard pull.
In 2016, there were no tugs of opportunity able to rescue the largest ships in severe conditions (sustained winds greater than 33 knots or 99th percentile conditions), including large and very large container ships, LNG carriers, passenger ships, and bulk carriers. In less severe conditions, more ship types were rescuable. In sustained winds of 27 knots (95th percentile), tugs of opportunity would have been capable of rescuing all except the large and very large container ships, but it is not known whether any tugs of opportunity would have been available if needed with sufficient time to respond.
This report demonstrates how often tugs of a certain capacity may be available based on historical data but does not assess all factors that would determine the outcome of an incident requiring an emergency tow.
Published July 9, 2019