VESSEL REVIEW | JMS Sunshine – Hybrid LNG-powered tug for Singapore’s Jurong Marine Services

Sembcorp Marine has taken delivery of the first in a new series of LNG hybrid-powered tugs specially designed for domestic service in Singapore.

Designed by Norway's LMG Marin and classed by ABS, the 30-metre JMS Sunshine will be operated by Jurong Marine Services, a wholly owned subsidiary of Sembcorp Marine. Its area of operations will be within the jurisdiction of the Maritime and Port Authority of Singapore.

"The hull of the tug has been designed to achieve minimum resistance without compromising seakeeping and stability/manoeuvring performance," LMG Marin told Baird Maritime. "Advanced CFD simulations have been conducted and validated with the model tests."

The designer added that the main operational parameter is the bollard pull. JMS described the maximum bollard pull requirement as 65 tonnes, increasing it from 60 tonnes as planned in the beginning.

"For a tug of traditional design, it would mean that the main engines need to be sized to generate enough power to achieve required trust. However, while learning more about the tug's operational profile, we noticed that maximum bollard pull is required only within a short job cycle. Therefore, we decided to downsize the main engines and provide a boost from the onboard energy storage system only when required."

The designer said environmental conditions characterised by high air and seawater temperature associated with extreme humidity levesl also needed to be considered while designing the cooling and HVAC systems.

"The owner was looking for a sustainable solution that will fit within its reduced gas emission targets, and so the tug served as a bridge from diesel to zero-emission fuels. Introducing LNG fuel was one of the objectives without compromising performance parameters or reliability owing to the nature of the vessel's duties."

LMG Marin said the tug had to be designed with particular focus on maximum operability, safety and manoeuvrability, reliability, consumption, and comfort under a range of wave, wind, and weather conditions, all while ensuring a minimal environmental footprint.

The design also called for the incorporation of dedicated high comfort accommodation spaces including two single cabins and three double cabins to house a total of eight crewmembers.

"Ensuring an optimum power train combination with single gas engines and battery hybrid propulsion within a very limited space and meeting all the operational profile requirements was the biggest challenge in the design process," LMG Marin told Baird Maritime. "Accommodating the 50-cubic-metre LNG fuel tank and the battery room for a 900kWh set wasn't easy when it comes to complying with space and class rule limitations. Also, we had to make sure that switching between the different operating modes such as pure electric, mechanical towing, and hybrid mode was to be done intuitively and simply to lessen the burden on the operators."

The ability to switch between the various operating modes is incorporated into the thruster levers, which also control the hybrid operating system.

The designer added that a lack of available outside references for such a tug design compelled the company to further explore the merits of an alternative design. This approach therefore meant that proposed solutions needed to be validated as equally safe as the traditional designs.

"From the technical point of view," added LMG Marin, "the safety aspects related to the location of the battery room within the engine room as well the hybrid control system logic provided us with learning points that we will apply to our future designs, regardless of the type of vessel."

JMS Sunshine runs on pure LNG with a sizable energy storage system based on a lithium-ion battery. This system allows emission-free operation of the tug for up to four hours during idling and low-speed transit. It is also capable of taking over the energy needs if a spike in power is warranted, and comes equipped with a reserve capacity to ensure the safe return of the tug in the event of engine failure.

The propulsion arrangement includes two MTU 16V4000M55RN 1,492kW engines connected via shaft lines to two Schottel SRP430FP 2,000kW azimuthing fixed-pitch propellers.

"The azimuthing thrusters have twin input upper gears," said LMG Marin. "One input is used for the shaft line connection, while the other input is used for the electric motor (PTI)/generator (PTO) connection. The motors draw power from the energy storage system when the engine working load demands it."

Two Marelli Motori B4J400LC6 generators are used to absorb the energy provided by the main engines if the energy cannot be utilised in due time.

"The tug is arranged for handling other vessels with an active winch over the bow and for towing with a towing hook over the stern," LMG Marin told Baird Maritime, explaining the deck equipment setup. The equipment includes a combined electro-hydraulic mooring/towing winch on the forecastle deck and an aft deck towing hook with quick release capability. The quick release can be done either on the hook itself or remotely from the wheelhouse. The remote operation is based on a pneumatic or electric system.

For firefighting, the tug relies on a Jason Engineering pump with a total capacity of 2,700 cubic metres per hour and driven by the port side main engine via a flexible coupling and clutch. The pump is connected to two Jason Engineering foam/water monitors.

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