Coastline speed limit could drop emissions 70%
Setting a speed limit on cargo ships sailing near ports and coastlines could cut their emission of air pollutants by as much as 70 percent, according to an analysis in the American Chemical Society's journal Environmental Science & Technology, Ship & Bunker reports.
The paper found that, because fuel consumption and emissions increase exponentially with speed, slowing container ships from between 25 and 29 miles per hour (mph) down to 14 mph, or 44 to 52 percent, reduced carbon dioxide emissions by about 60 percent, nitrogen oxides by 55 percent, and soot by 70 percent.
Imposing speed limits on ships operating near land, something the California Air Resources Board (CARB)has proposed, could protect the health of people living nearby, the analysis suggests.
The conclusions of the study were released last month, and come from emissions testing performed during three trips from San Pedro Bay to the Port of Oakland.
Two of the trips, completed in July and August of 2009, involved the same 5,000 twenty-foot equivalent unit (TEU) Panamax class vessel, with the third trip in September 2010 involving a post-Panamax vessel described as having up to 10,000 TEU capacity.
The study said it used Marine gas oil (MGO) with a sulfur content of 0.00065%, 0.00942%, and 0.1657% within appropriately regulated waters, and HFO bunkers with a 3.14%, 2.15%, and 2.5% sulfur content by weight were used in non-regulated waters for the three trips respectively.
California Air Resources Board and the U.S. Environmental Protection Agency both helped to fund the study.
Even without an official speed limit, many ship operators are already embracing slow steaming as a method of reducing fuel costs as well as emissions.
Cargill Inc. said recently that it will reduce vessel speeds 18 percent to 9 knots (10.4 mph) to reduce bunker costs, and Maersk Tankers has previously said it has been able to reduce bunker costs 50 percent by dropping speeds from 14-16 knots down to 8.5 knots.
