Unique dual-fuel propulsion installed on Botas escort tugs

Silivri and Sultanhani have a 40 m³ LNG tank fitted aft of the engineroom in a dedicated compartment.

Robert Allan said this was installed transversely for a compact and efficient equipment arrangement, and to ensure associated hazardous zones were physically separate from the accommodation block forward.

“A carefully designed force-ventilated LNG vent mast allows possible vented natural gas from the LNG tank and system to be well dispersed on exit, without the potential for cold vapour collapse,” said the naval architect. “The vent mast locates the outlet well above the working deck and away from any crew areas or ventilation intakes.”

Both tug wheelhouses were designed for 360° visibility for the master and have two control stations (one forward and one aft), each with full functionality.

Deck equipment such as the heavy-duty escort winch and dedicated staple are fully visible from the aft control station, as are the two monitors that are part of the tugs’ FiFi1 class fire-fighting system.

“These small appendages ensure the tug is directionally stable yet still highly manoeuvrable, with very minimal impact to resistance” 

These 900-gt tugs have a moulded beam of 15 m, a moulded depth of 6 m, and capacity to store 164 m³ of diesel fuel and 23 m³ of potable water.

Bureau Veritas classed these tugs with notations for fire-fighting 1 water spraying, escort tugs with automation for unmanned machinery spaces, dual-fuel LNG propulsion, in-water surveys and unrestricted navigation.

Robert Allan said it used extensive computational fluid dynamics (CFD) to design the TRAktor V3900-DF hullform, during which multiple operational parameters were optimised. To ensure excellent tug directional stability, Robert Allan included strake stabilisers at the stern.

“These small appendages ensure the tug is directionally stable yet still highly manoeuvrable, with very minimal impact to resistance,” Robert Allan said. During the design phase, these CFD results were verified in model tests and confirmed in sea trials.

Robert Allan said it incorporated lessons learned and operational feedback from the 10 previous LNG-fuelled tugs it had designed, and it would use these design features as the foundation for future alternatively fuelled tug designs under development.

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