Diesel electric trend growing for offshore vessels

In Norway the Simek shipyard recently followed up earlier vessels when it delivered the Stril Mariner to Simon Møkster Rederi in Stavanger, Norway.

The Stril Mariner is 78.6m long with a 17.6m beam and a moulded depth to the main deck of 7.7m. With deadweight of 3,755 tonnes the PSV has tankage for 910m³ of fuel oil, 925m³ of fresh water, 1,250m³ drill water and 1,010m³ each of mud, liquid mud and brine. Additional tankage includes 175m³ of methanol, 150m³ of glycol, 315m³ of dry cargo and 1,300 m³ for ORO. The cargo deck is 755m² in area.

Accommodation is provided for 31 people in 11 one-man cabins and 10 two-man cabins. There is also a deck office, a hospital and a conference room. The vessel is certified by ISO 9001:2000 (quality) and ISO 1401:2004 (environmental). Designed by the Havyard firm of naval architects the newbuilding has all tankage installed so that there is no storage of liquids that could harm the environment against the ship’s hull shell.

In addition, the vessel gains its ‘green’ designation as a result of the diesel electric propulsion system. As only the engines required to maintain the task in hand need to be running, the resulting emissions, as well as fuel costs, can be dramatically reduced. To achieve this flexibility in the main propulsion system, the Stril Mariner is fitted with four Cummins KTA50-(D)M engines each of which drive a generator to produce up to 5,164kW of power. The propulsion system consists of two Rolls-Royce Marine Ulstein Aquamaster US 205 CRP azimuthing thrusters for main propulsion in addition to a pair of bow thrusters.

Engines and generators can be shut down when holding position or travelling at reduced speed, thus reducing consumption and emissions. Additionally the main engine exhausts have been fitted with a selective catalytic reduction (SCR) exhaust gas cleaning system, cleaning the environmentally hazardous CO, NO_X and VOC hydrocarbons in the exhaust with ammonia, and the nitrogen oxides of the exhaust gas becomes environmentally neutral water and nitrogen gas, thus reducing the NO_X by about 90%.

As diesel electric and other initiatives to contain operation costs while reducing a ship’s environmental impact proliferate, the vessels become ever more complex. In that context the classification societies have a greater challenge since it is no longer just about hull plating welds and shaft alignment. The Stril Mariner is classed by DNV.