Cooperation eases the path for gas powered tugs

This is in spite of this system being ground-breaking technology for the towage industry.

Sanmar’s project director, Ali Gurin explained: “Cooperation between the shipyard team, the owners and designers Bukser og Berging (B&B), the classification society DNV and the Norwegian Maritime Authority is proceeding well. Some 90% of the steel construction is already finished and the critical process of installing the LNG tanks and engines has been completed successfully without any hitches. The rest of the outfitting continues as planned. Furthermore, we do not anticipate any slippage of the original delivery schedule despite the learning curve.”

Both vessels will be in service by the end of this year at the Kaarstoe terminal on long term charter to the international energy company Statoil ASA and Gassco, the operator of the gas transportation network off the Norwegian coast.

The LNG system has been designed by AGA Cryo and integrated with the ‘lean burn’ gas engines of the Rolls-Royce Marine propulsion system. The system comprises an 80m3 LNG tank, two cold boxes and the bunkering system. This single tank system has full gas redundancy, meaning that no diesel back-up is required. The vessels will also be equipped with two Rolls-Royce fully azimuthing propulsion units.

The environmental benefits offered by the spark ignition gas engines incorporated in the new design include a 92% reduction in NOx emissions, 17% reduction in greenhouse gas emissions, 98-100% reduction in SOx emissions, and 98% reduction in particulates. The system is fully compliant with Tier III regulations. A cleaner engine room, less waste oil and no switch-over problems are among the operational benefits of a gas fuelled propulsion system.

Developed by B&B, the vessels will measure 38m in length and 14.5m beam and have accommodation for five persons. The hull design and layout has been optimised for the installation of the nine cylinder gas engines to give a static bollard pull of 70 tonnes, with about 20% greater efficiency than that of standard tug designs. A predicted DNV Class notation for a steering-force of 120 tonnes at 10 knots will have considerable appeal in the escort tug market.