Transportation Costs - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 250

16.6.1 Improved Efficiency
The costs of operation per kilometer depend on the utilization of the capacity of a ship.
In public transportation, such as ferries, fuel consumption and emissions could be
reduced if it were possible to cancel trips that were under capacity. This measure could
increase flexibility of ship owners in planning routes but reduce passengers' conve-
nience. In similar cases, airlines substitute smaller airplanes for larger ones [ 45 ].
16.6.2 Early Scrapping
New ships are more efficient than old vessels. The life cycle of ships is long. There
are a lot of vessels, which consume more fuel and emit more pollutants and noise
than newer types. Replacing old ships with new efficient models reduces fuel con-
sumption and emissions. However, the early scrapping of ships is a very complex
decision involving a variety of factors such as expected fuel prices, the market
forecast, the liquidity of the shipping company, and the expected capital return [ 46 ].
16.6.3 Costs and Tendencies of Natural Gas Application
as a Marine Fuel
According to SOLAS, products of natural gas or biogenic gases are not allowed to
be used on ship as fuels because the flammability limit is below 608C (1408F).
Applications with gases without a special permission are not allowed because
special tanks are needed for liquified or compressed gas. Although LNG is
currently a cheap energy source, the drawback is that it needs high energy amounts
to be liquid and to be safely stored on-board in the ship. CNG needs twice the tank
volume than LNG.
The main reasons are
- The ship cannot travel far enough on one pressure-tank load; and
- The supply infrastructure is not sufficient.
Therefore, the best possibility to start using gas would be on ferries or vessels
with short voyages according to experiences in Norway. In inland shipping, the use
of LNG will rapidly gain high importance because of less pollution [ 47 ].
On sea, the introduction of gases as fuel is much more difficult, because of the
small energy density of gaseous fuels. Ships have to carry a large amount of CNG
to save the required performance [ 48 ].
LPG is heavier and less flammable than methane and burns at higher temper-
atures than CNG and LNG. The specific density higher than air requires special
safety measures on ships. Additionally, LPG is more expensive and available in
smaller volumes than CNG and LNG [ 49 ].