A Spill Risk Assessment of the Enbridge Northern Gateway Project

Hoffman 2010 p. 5-­‐49). However, a report prepared for Enbridge by FORCE
Technology entitled Maneuvering Study of Escorted Tankers to and from Kitimat:
Real-­‐time Simulations of Escorted Tankers for a Terminal at Kitimat clearly
determines distinct differences among VLCC, Suezmax, and Aframax tankers for
several maneuverability characteristics including steering ability, turning ability,
and stopping ability. In terms of steering ability, FORCE determines that VLCCs
require over one and a half times the distance to conduct a zigzag test 20 than
Aframax tankers with both vessels in laden condition (see Figure 4-­‐1 in FORCE
2010). Similarly, for the turning ability test 21 for laden tankers, results show a
considerably larger area required to turn VLCCs than both Suezmax and Aframax
tankers when at full sea speed and at 10 knots (See Figures 4-­‐2 and 4-­‐2 in FORCE
2010). Finally, in terms of stopping ability, loaded VLCCs require nearly one and a
half times the stop distance compared to Aframax tankers and nearly twice the
distance than Suezmax tankers at 10 knots when the engines are running astern at
full power (Figure 4-­‐5 in FORCE 2010).
Based on the detailed findings in the report submitted by FORCE, there are indeed
very different maneuverability characteristics among VLCCs, Suezmax, and
Aframax tankers navigating shipping routes. Thus, DNV’s assumption of
uniformity among the three tanker classes fails to incorporate any of the distinct
handling capabilities of each tanker that could affect incident rates. Depending on
the nature of the LRFP data, the uniformity assumption potentially results in an
underestimate of particular incident occurrences for VLCCs compared to Suezmax
and Aframax tankers if VLCCs have a higher incident frequency and the LRFP
incident data largely consist of incident frequencies for Suezmax and Aframax
tankers. DNV’s failure to include proprietary LRFP data prevents any verification
of incident occurrence rates for the various tanker classes, however Eliopoulou
and Papanikolaou (2007) found that tanker incidents with serious consequences
or total losses and spillage rates between 1990 and 2003 were highest for VLCCs
compared to Aframax and Suezmax tankers.
A second consideration is the relative incident frequencies among different age
classes of tankers. A recent study from Eliopoulou et al. (2011) examines the
relationship between tanker age and accidents in tanker casualty data from the
LRFP database after the Oil Pollution Act of 1990. The authors determine that
incident rates for non-­‐accidental structural failure, or what DNV refers to as
foundering, vary significantly depending on the age of the double-­‐hull tanker.
Indeed, non-­‐accidental structural failure tanker incidents for double-­‐hull tankers
20 According to FORCE, tankers perform the zigzag test by “…commanding the rudder 10 deg. to port. When
the ship has changed its course 10 deg. from its initial course, the rudder is commanded 10 deg. to starboard.
When the ship has changed its course 10 deg. to starboard from its original course, the rudder is again
commanded 10 deg. to port.” (FORCE 2010 p. 19). The test completes after two zigzags.
21 Tankers perform the turning ability test by “…commanding the rudder 35 deg. to starboard while the
engine is running at the maximum load. As the ship starts to turn, a great part of the ship’s longitudinal speed
is transferred into a transverse (drift) speed that due to the great resistance reduces the longitudinal speed
significantly.” (FORCE 2010 p. 20).
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