Workboat Annual
Marine Fuels and Engines
By Chris Townsend, E.I. Naval Architect, Guido Perla & Associates, Inc.
Marine propulsion starts at the prime mover and ends at the propeller. In this, the second article in our series of marine propulsion systems, we will discuss the most common types of marine prime movers and the different fuels that they use. Many factors go into deciding which prime mover best fits a given vessel. These factors include the intended service of the vessel, as well as the weight, size, regulatory compliance, and cost of the prime mover. Cost considerations typically include the initial cost of the engine, lifetime maintenance expenses, and fuel cost. Optimization of fuel costs can be achieved one of two ways: choosing an engine that burns the cheapest fuel possible, or choosing an engine that is particularly fuel-efficient. A combination
of these factors can also be cost-effective over the life of the engine. One of the flaws in choosing an engine that burns the cheapest fuel available is the unpredictable nature of both global and local marine fuel markets. Prices could go up, prices could go down, or regulations could limit or prohibit the use of certain types of fuel.
Fuels
The selection of a primary fuel can be influenced by other factors, such as storage arrangements and auxiliary systems associated with the chosen fuel type. Consider briefly the major types of marine fuel in use today:
Heavy Fuel Oil (HFO)
Historically the least expensive of inuse marine fuels, heavy fuel oil is used extensively in the low-speed reciprocating engines that power many of the
world's largest commercial vessels. Though the cost of the fuel is low, the use of heavy fuel oil for marine propulsion requires a cleaning system to remove excess impurities, as well as a heating system to lower the viscosity for efficient combustion. The energy required to deliver the fuel to the engine ready for combustion is quite high. The space and weight required for the heating and treatment systems associated with HFO make using this type of fuel impractical for smaller vessels. Ever growing emissions standards are also making the primary use of HFO more expensive and less practical. New regulations allow for the creation of Sulfur Emission Control Areas (SECA), in which levels of sulfur emissions must be below those achievable when burning currently available HFO. This requires that a vessel be rerouted around the SECA, install a scrubber sys-
About the Authors
By Chris Townsend, E.I., Naval Architect, Guido Perla & Associates, Inc.
tem to remove sulfur from emissions, or switch to a more expensive low-sulfur distillate fuel while transiting the SECA. Reports from refiners indicate that there is little interest in developing
SeaNG Rendering One of three Compressed Natural Gas (CNG) carrier versions designed by Guido Perla & Associates, Inc. This 118-meter vessel carries 50 mmsCF of CNG in 16 coselles and features a dual-fuel mechanical drive propulsion system.
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