Eco Friendly Tugs Steer Maritime Green Concept

Marine vessels are deemed to be the most considerable source of air pollution.

Operating within a prosperous, powerful and complex international industry, they are still not affected by emission control regulations. Ports, as the main point of entry for vessels, have been perceived as areas where an extremely high level of pollutants is regularly being detected, however costal parts are also exposed to such a threat. The shipping industry is utterly cut-throat and financially delicate in terms of any disruptions in its operating concepts, thus vessel engines are designed and constructed to be endurable, utilizing the lowest quality fuel available. The competitive concept of the industry imposes the need for increased trade volumes and larger ships with larger engines. These developments affect all efforts of the world wide communities to preserve air and health quality standards.

Vessel owners and operators are gradually starting to acknowledge that economic prospect and environmental protection are not mutually exclusive. Since it is possible to reduce generated emissions, they accept the challenge and responsibility to diminish the air quality consequences of ever increasing trade volumes. Technologies for controlling emissions can be integrated within the initial design or can be equipped onto an existing vessel as a retrofit control device. Taking into consideration all the necessary requirements, it becomes obvious that emission control technology solutions are more acceptable for newbuilds since the retrofit option will depend on the space availability, alignment with other component parts or installation methods what largely depend on vessel types.

Although there is a slow pace in introduction of new emission friendly solutions in an extensive world-wide fleet, particular vessel builders and designers have already realized the importance of and necessity for being more environmentally friendly.

Offshore Ship Designers has been further developing the zero emission Green Tug design by constructing a low emission diesel electric harbor tug for IJmuiden based Iskes Towage & Salvage.

The Azistern 3270 tug will be run by three diesel gensets driving electric motors mounted over azimuthing propellers aft and a Voith in line thruster forward and is anticipated to reduce emissions by 30% compared with conventional, similar sized harbor tugs currently in service. Decisions on final battery size and engine configuration are yet to be decided. The hullform will be redefined using computational fluid dynamics (CFD) to optimize its resistance for transit speeds of 7-l0 knots. It has been estimated that approximately 35% of fuel consumption is used during transit. With the optimized low-resistance hullform, savings of around 15% can be made when compared to a conventional tug hullform. The fully diesel-electric propulsion concept of the Azistern 3270 tug will be more energy efficient than traditional diesel direct drive. There will be no more need for hydraulic transmission in the operation of deck machinery, such as winches, resulting into lower fuel consumption. A high working load is kept on only one engine to contribute to emission reduction. The power needed to produce the maximum 70 ton bollard pull is 4500kW, however only 10% of this power is required to take the tug from one point to another one. While operating, only one engine or the battery will be used for 90-95% of the time, while all three gensets will be running at the same time for only about 5% of the time. For a conventional tug, both main engines run 2000k W at very low load for 95% of the time, generating relatively high emissions.

The two contracted tugs will be built at Damen Shipyards, Hardinxveld. The delivery is expected to take place in the mid of 2013.

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World Maritime News Staff, January 27, 2012; Image: Damen Shipyards