The Offshore Wind Installation industry has been responsible for a plethora of interesting and innovative work vessels in recent years. Varieties of customised maintenance, installation and personnel transfer craft are now available for the renewable energy sector in both monohull and multihull forms. Hovercraft are generally not deemed suitable for such work but something that encompasses the benefits of both air cushion technology and a catamaran is now proving itself.

Winds of Change

On 18th October 2013 Umoe Mandal AS signed a contract for the first UM Wave Craft, the next generation offshore wind service vessel. The buyer was Umoe AS with delivery being scheduled for January 2015. The Wave Craft concept is entirely developed by Umoe Mandal and is based on the same Surface Effect Ship (SES) technology that has brought the Oksøy Class minehunters and Skjold (Shield) Class stealth missile craft from Umoe Mandal for the Norwegian Navy. The new idea is to use the same air cushion to reduce wave induced motion when accessing an offshore wind turbine. This allows transfer of personnel and cargo in larger waves than possible with current solutions. The technology also offers a unique high vessel speed, where the air cushion damps motions, providing a very smooth ride. This improves over-all efficiency of turbine maintenance. Some readers may also recall the short-lived Cowes Express ferry service across the Solent between Southampton and Cowes (Isle of Wight) between 1990 and 1992, which used the SES passenger ferries Wight King (Sant Agata), Wight Queen (Virgin Butterfly) and Wight Prince (Royal Schelde). The development of the Umoe Mandal Wave Craft vessel started in 2011 and has been funded by the Carbon Trust’s Offshore Wind Accelerator, the Research Council of Norway under the innovation programme MAROFF, Regionale Forskningsfond Agder (Regional research fund) and Innovation Norway. Performance (both turbine performance, speed and seakeeping) has been demonstrated in an extensive model test program. With confirmed performance for the first vessel Umoe Mandal anticipates a need of more than 5 vessels a year for the European offshore wind market. Located on the southernmost tip of Norway and sheltered by the scenic archipelago that surrounds the city of Mandal can be found Umoe Mandal on the shores of the Gismerøya, a natural harbour. This and neighbouring Kleven are ideal locations for shipbuilders that have provided ships and marine equipment to customers in Norway and abroad. The Mandal yards have over the last 70 years developed and delivered hundreds of various ships to domestic and overseas customers. Aluminium and composites were introduced early on here as a shipbuilding material. Umoe Mandal was established in 1989 under the name Kværner Båtcervice. Its strong maritime heritage and cultural legacy paved the way for a tailor made shipyard for composite production of ships and components. The new Millennium saw the Umoe Group acquire the company. This parent company was founded by Jens Ulltveit-Moe in 1984. Umoe has since grown into one of the largest, privately owned companies in Norway and has four main areas; Umoe Shipping and Energy, Umoe Maritime, Umoe Bioenergy and Umoe Restaurant Group.

A Wave of Innovation

The Wind Craft built for Umoe Wind AS is the first such vessel built at Umoe Mandal AS and has been chartered by Danish company DONG Energy to serve the Borkum Riffgrund 1 Offshore Wind Farm in the North Sea, 54 kilometres from DONG Energy’s O&M base in Norddeich. Borkum Riffgrund is a major focus area for offshore wind power. The charter was finalised on 17th July 2014. The development of the Wave Craft concept was supported both financially and technically as part of the Carbon Trust’s Offshore Wind Accelerator (OWA) Access Competition. The inception of such vessels will provide significant cost savings to the offshore wind industry and Umoe Wind AS subsequently decided to procure a second Wave Craft vessel from Umoe Mandal AS, the global leader in Surface Effect Ship (SES) technology, to be delivered to Umoe Wind during 2015. The name selected for the first newbuild is Umoe Ventus. So what is a Surface Effect Ship? An SES is lifted by an air cushion enclosed by slender side hulls, a flexible rubber sealing aft (a pressurised lobe bag) and a bow skirt (flexible rubber fingers). The air cushion lifts 80% of the vessel and by utilising this to stabilise heave motion the craft is able to dock with offshore wind turbine structures in higher sea states than conventional mono and multi hull craft being employed on such work. In addition the vessel offers good transit sea keeping and passenger comfort combined with a high service speed. This allows for reaching the offshore installations even when the weather window for safe operation is narrow. Large powerful centrifugal lift fans supply the compressed air to the air cushion with sufficient flow rates to keep the pressure when the craft is subjected to wave induced ship motions and at high speed. The SES is known to have outstanding seakeeping performance in waves with low wave resistance enabling high speeds with low propulsion power. As an example the SES type Skjold Class missile vessel is the fastest operational corvette in the world. The air cushion lifts the hulls out of the water creating a low draught and an unchallenged combination of operational wave height and speed. A service speed of up to 40 knots is possible with the operational threshold being a 2.5 metre significant wave height. The Umoe Ventus is 27.20 metres long with a 10.40 metre beam. The hull draught is 3.00m when the air cushion is not in use and 0.80m when the Surface Effect system is employed. The low draught also increases the ports and regions in which the vessel can operate. The SES technology provides enhanced comfort for the crew and passengers as it acts as a shock absorber coupled with a Ride Control System to damp vessel motions. The ISO standard Motion Sickness Indicator showed the SES vessel as halving the effects of motion sickness compared to rival craft. These benefits assist in reducing the fatigue generated by a rough ride whilst also providing a 25% reduction in fuel consumption compared to alternative vessel types. The ability of the vessel to deliver personnel to a turbine location that are fit for work of course increases the overall efficiency of each duty, not to mention the shortened transit times. The 217gt vessel is powered by a pair of MTU 16V 2000 M72 diesels engines with a 1440kW output. These are coupled to a pair of MJP CSU 650 waterjets. The waterjets operate effectively despite the close presence of the enclosed air cushion to the jet intakes. A separate pair of 360kW diesel engines powers the lift fans installed in the superstructure to provide the air cushion. Only one lift fan is required for normal transit operations but two are installed for both redundancy and use at offshore installations in larger sea states. To increase the operational wave height, Umoe Mandal’s designers have developed a control system to use the air cushion to counteract wave forces. Via this active control the flow in and out of the air cushion is controlled by ventilation valves (visible in the craft’s hulls). This permits the air cushion buoyancy to be varied to match the degree of wave crest and wave trough beneath the craft and thus optimise stability. Tank tests demonstrated that the craft can handle significant wave heights of 2 metres on all headings and 2.5 metres in head and following seas. The general service speed in sea states of both 1 and 2 metre significant wave heights is 35-40 knots and 30-35 knots respectively. The Umoe Ventus is crewed by three persons and can accommodate 12 passengers (wind installation technicians etc) on air dampened seating in the forward section of the deckhouse. Astern of this lounge is a wardrobe area to port and a pantry to starboard. The aft section of the accommodation contains two cabins (one single and one double) for the crew. Above this level is the wheelhouse. The entire deckhouse is placed on dampeners to minimise noise and vibration levels. The Umoe Ventus can cater for 4 tonnes of cargo on the forward deck including in 5’ or 10’ containers. The deckload for cargo is 1 tonne per square metre and a deck cargo crane with an electro-hydraulic SWL of 1 tonne (at 5m outreach) providing a maximum outreach of 9.5m is installed. Naturally the format of the craft does not permit the carriage of heavy cargoes but the design can be adapted in size and capacity to suit the demands of the operator. Among the safety equipment installed is a remotely controlled man overboard recovery system. Although the SES concept is not a new one, the Umoe Mandal SES sits proudly among the 13 shortlisted concepts of initial 450 applications in the Carbon Trust Offshore Wind Accelerator Competition (OWA). The OWA is the Carbon Trust’s flagship collaborative RD&D programme. Set up in 2008, the OWA is a joint industry project, involving offshore wind developers with 72% of the UK’s licensed capacity. Cost reduction is achieved through innovation. Technology challenges are identified and prioritised by the OWA members based on the likely savings and the potential for the OWA to influence the outcomes. Projects are carried out to address these challenges, often using international competitions to inspire innovation and identify the best new ideas. The most promising concepts are developed and commercialised as the OWA works closely with the supply chain throughout the process. The OWA model brings together Carbon Trust’s expertise in delivering innovation and convening industry consortiums with the industrial partners’ technical knowledge and resources. The OWA is two-thirds funded by industry and onethird funded by the UK Department of Energy and Climate Change (DECC) and the Scottish Government.

Sent to Work and Seawork

Umoe’s Offshore Energy sector Umoe Wind AS took delivery of the Umoe Ventus once her sea trials had been undertaken in February 2015. The naming ceremony was performed by Umoe CEO Jens Ulltveit-Moe’s wife on 5th February. Prior to delivery, the Umoe Ventus had secured a charter to DONG Energy to serve the Borkum Riffgrund 1 Offshore Wind Farm and also the Gode Wind site. DONG invested 15m Euro in the construction of this new offshore operations centre and Valling Ship Management ApS in Denmark operates the vessel with Danish crew. The initial charter period, which began on 1st March, is for 8 months with an option to extend by up to 12 months. Being unique in the industry thus far this SES vessel was also showcased at Seawork 2015 in Southampton’s western docks. The Carbon Trust hosted the first UK demonstration on 17th June (the event ran 16th-18th June). The journey to/from Southampton included calls at Dover and Ramsgate. Seawork 2015 was a record-breaking event with exhibition space being a total sell-out six weeks prior to the opening day. Over 600 exhibitors, 7,500 visitors, 65 vessels and over 10,000 products and services were on site, and for three days Seawork was home to international, national and local contingents from the commercial maritime sector. Due to its size the exhibition has outgrown the old Fruit Terminal site so Seawork 2016 (14th-16th June) will relocate to Mayflower Park using the system of pontoons that are sited here each year for the annual Southampton Boat Show. Umoe Wind AS commissioned a second Wave Craft in August 2014 for delivery during 2015. This newbuild will take the name of Umoe Firmus.

Special thanks must go to Are Søreng, Vice President Sales & Marketing at Umoe Mandal AS, and Sarah Hewes for their invaluable assistance with information & images.

Technical Specifications