Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
inventory to the U.S. According to the United Nations Framework Convention on
Climate Change (UNFCCC) reporting guidelines, national totals of GHG emissions should
reflect only domestic transport, including the domestic leg of shipments bound for foreign
markets (i.e., operations within 200 miles of the coastline); international aviation and
marine bunker fuel emissions from fuel sold to ships or aircraft engaged in international
transport should be excluded from national totals (UNFCCC, 2006). However,
differentiating domestic and international fuel consumption is often difficult, resulting in
significant year-to-year variations in the official estimates.
The combined GHG benefits that could be anticipated from marine vessel improvements
are estimated as follows. The range of ship design benefits (1-17.9 mmt CO2e) is added to
the range of propulsion system benefits (3.1-7.4 mmt CO2e). While there may be some
overlap between these categories, most of the ship design benefits will be realized for
long-distance ships while propulsion benefits will primarily be realized for ships
operating near-shore. Some additional benefits could be realized through wind and solar
power, but these technologies are still speculative (particularly wind). The combined
benefit is estimated to be 4.1 to 25.3 mmt CO2e in 2050, with about two-thirds of these
benefits realized in 2030 depending upon fleet turnover and phase-in of other
technologies.
Improvements in Ship Design
Overview
In general larger ships provide efficiencies of scale and are capable of transporting more
cargo per gallon of fuel than smaller vessels. This scaling effect has led to an increase in
vessel size of about 4 percent per year for newly constructed vessels, with an increase in
installed power at rates about 10 percent per year. This is more than twice the rate of
growth in seaborne trade and is driven largely by growth in containerized shipping
delivering intermodal cargoes to onroad and railway freight shippers (Corbett, 2007). The
net growth in fuel use and GHGs is nearly proportional to the growth in cargo volumes.
One of the reasons that fuel use trends are not increasing in direct proportion to increased
installed power is that new vessels take advantage of improved hull designs and other
technologies. These changes in hull design include application of ducktails and
interceptor planes which extend the stern of the vessel and enhance propeller efficiency
(Wartsila, 2008; Kanerva, 2006; Jaap, 2005).
Vessel efficiency declines when marine plants and animals accumulate on a ship’s
underwater hull causing fouling. Advances in vessels coatings, such as self-polishing
resin systems based on hydrolysable acrylate polymers, inhibit fouling, and provide a
smoother surface (Royal Caribbean International, 2008; Kiil, 2001). Similarly, vessel
efficiency also can be improved by injecting small amounts of air in the turbulent
boundary layer underneath the ship (Wartsila, 2008; Okada, 2008; Technology Demark,
2007; Katsui, 2003). As a result, drag is reduced through the movement of the air bubbles
and the formation of a thin film of air along the vessel’s hull. This technology has been
3-98