VESSEL REVIEW | COS Master – Coastwise Offshore Services’ new windfarm crewboat with secondary survey and civil works capabilities

Dutch operator Coastwise Offshore Services (COS) recently took delivery of a new aluminium crewboat from local builder Next Generation Shipyards (NG Shipyards).

Designed by NG Shipyards in cooperation with local naval architects Van Dorresteijn Design, the Bureau Veritas-classed COS Master will be operated in support of the Dutch offshore wind market. It is the first crewboat in a planned series of four, and each vessel in the series will have a length of 27 metres, a cruising speed of 27 knots, and capacity for 30 passengers and five crewmembers plus up to 15 tonnes of deck cargo.

"We wanted a vessel with a loadline length of just under 24 metres in addition to being fuel efficient, comfortable, and compliant with the new Dutch flag rules covering the transport of more than 12 industrial personnel," COS told Baird Maritime.

To accommodate the range of requirements, the vessel features a monomaran design that combines the improved stability (even in significant wave heights of up to 2.5 metres), the greater deadweight, and the lower resistance of a catamaran with the speed, the fuel efficiency, and the reduced roll guaranteed by a monohull. The monomaran hull design consists of three hulls – one centre hull and two side supporting hulls – and a cross structure.

Compared to other fast crewboats, another advantage offered by a monomaran design includes the ability to sail at higher speeds without any increase in the total installed power.

"Reduction in fuel consumption was another goal that we hoped to achieve with the monomaran design," added COS. "This was done through the combination of a lightweight, CFD-optimised hull, engines with optimal power/weight ratio, and interceptors."

The owner said that when the vessel is transporting 30 passengers, the fuel consumption per passenger is around 15 to 20 per cent lower compared to similarly-sized crewboats with capacities of 24 passengers each.

The engines are IMO Tier III-compliant and are also fitted with exhaust gas aftertreatment and SCR systems. The main and auxiliary engines may run on hydrotreated vegetable oil (HVO) as a more sustainable alternative to conventional fuels. COS said the use of HVO will result in CO2 emissions reductions of as much as 90 per cent while emissions of SOx, NOx, and particulate matter are also considerably lower. A heat recovery system is also installed.

The propulsion units consist of two highly efficient Servogear controllable-pitch propellers.

"These propellers guarantee reduced noise and vibrations while ensuring the vessel is capable of high speed and superb acceleration as well as ample bollard pull," said COS.

The crewboat is also fitted with buoyant flexible high abrasion-resistant surface fendering to maximise grip and durability, which are key attributes when supporting the offshore wind industry. COS said the increased fender height provides significant performance benefits, creating a wider operational window.

The main cabin was primarily designed to provide seating for up to 30 technicians, though the interior may be configured to accommodate conferences or a first aid area. Amenities include a coffee bar, a video system, and wifi connectivity while the electronics include main switchboards from Global Electrical Solutions.

"Besides being used for windfarm crew transfer duties," COS told Baird Maritime, "the vessel may also take on other roles in the oil and gas and civil works industries. These duties include route surveys of pipelines and cables, seabed mapping, inspection, and dredging support."

The owner added that these other duties can be accomplished without sacrificing the vessel's crew transfer capacity. For survey roles, the bridge also comes with a dedicated workstation for two survey technicians and the passenger space in the main cabin can be reconfigured accordingly.

COS Master also has an integrated moonpool with a diameter of 700 millimetres. As an option, the crewboat may be fitted with an A-frame on the stern to expand its offshore support capability.