Japan Renews Salvage Tug Capacity

While only a limited amount of technical detail is available as yet, Mitsubishi states that the 3,000gt newbuild will offer “one of the highest pulling capacities in Japan”. The current Koyo Maru, which also came from the Shimonoseki Enoura works in June 1998, has a certified bollard pull of 132.5t. The potency of the prospective fleet addition has had to reflect the growth in the size of many types of merchant vessel, notably containerships and vehicle carriers, in the intervening period.

The purpose-designed Koyo Maru will accordingly have the wherewithal to respond to large-scale marine accidents, and particular consideration has been given to the most challenging firefighting scenarios, as reflected in the optimal placement and performance of monitors and other equipment, and in enhanced fixed-point holding capacity.

The open, aft deck and associated deployment gear will enable boarding and use of remotely operated vehicles (ROVs) as and when required.

The march of the years since the present Koyo Maru entered service has seen a step change in environmental requirements, such that her successor has been specified with selective catalytic reduction(SCR) technology. This will allow unfettered operation in areas subject to the strictest NOx emission controls, potentially including coastal waters of North America, the North Sea and Baltic Sea. Handover to Nippon Salvage is scheduled for June 2024.

The hull form, which features a more vertical bow line than the raked stem characteristic of earlier-generation salvage tugs, has been devised to improve propulsion efficiency and seakeeping. Contracted service speed for the Koyo Maru is 14.5 knots. By comparison, the present Koyo Maru can sustain 16.5 knots in good conditions, drawing power from two Daihatsu diesels delivering a combined output of around 7,500kW through twin controllable pitch propellers in Kort nozzles.

A few metres longer, at 86m, than the newbuild, the current tug is somewhat leaner by about 1m, through a beam of 14.5m.