It is fast, economical and environmentally virtuous. It is called Wavecraft and as Selwyn Parker reports, when it comes to transferring crews between shore and open-sea platforms, helicopter may no longer be the only option
Any vessel with a top speed of 55 knots and a range of 700 nautical miles (nm) is bound to attract attention. When you throw in fuel-sipping propulsion, the economies get even more interesting.
Launched earlier this year, the Voyager 38X is the top-of-the-line version of Wavecraft. “Voyager 38X implements intelligent design and state-of-the-art technology to offer a new standard for offshore crew transfer,” says Umoe Mandal vice-president of sales and marketing Are Soreng. “It directly competes with helicopters on levels of safety, comfort, fuel efficiency and overall reduced cost of offshore logistics.”
The vessel is also clean and green. Equipped with the latest developments in high-speed diesel engines and selective catalytic reduction (SCR) emissions-reduction technologies, the Voyager 38X complies with the USA Coastguard’s EPA Tier4 requirements, an important attribute if the vessel is to appeal to the North American industry.
Launched in early 2018, this new offshore support craft is attracting attention from the windfarm and oil and gas industries. In fact, it was these industries that encouraged the group to develop Wavecraft in the first place.
The Umoe Mandal shipyard is based on an island near the town of Mandal in southern Norway. It was back in 1988 when Umoe Mandal, then known as Kvaerner Batservice, began to specialise in fibre-reinforced plastic composites. The shipyard’s experience and knowledge grew rapidly, resulting in the build of six of the fastest combat ships in the world, the Skjold Class corvettes, for the Royal Norwegian Navy. As well as building ships, the group has supplied composite materials for a variety of applications where durability and lightness are vital, for example in wind turbines.
The development of the Wavecraft Voyager series took three years, starting in 2014. The original inspiration for the vessel came from the Carbon Trust, the not-for-dividend environmental body, which challenged the group to build ships suitable for crews servicing offshore wind turbines. The immediate result was the Sprinter 26 and Commander 27 series, designed for rapid transportation over medium to long range. Two of these vessels are operating in the North Sea. They can ferry between 12 to 24 passengers at speeds of up to 45 knots, consuming around 21 litres of fuel a nautical mile.
The Wavecraft design is based on surface-effect ship (SES) technology. This represents a big advance on the hovercraft system and has been widely deployed in high-speed naval craft. In effect, SES produces a form of skimming and, among considerable other advantages, SES vessels make a lot less noise than hovercraft.
Following this success, several oil and gas companies threw down the gauntlet to Umoe Mandal, requesting a similar kind of offshore support vessel that would ferry crews to platforms located much further offshore than the typical windfarm. The craft had to be faster, have a longer range, and be capable of transporting a lot more people than a helicopter.
In fact, for the purposes of this exercise, the helicopter became the enemy. As Umoe Mandal CEO Tom Svennevig explained, the vessel would have to operate within a similar timeframe as a helicopter as, “you don’t want your crew spending too long in a boat”. It also had to operate at a much lower cost per passenger, so that the economies were compelling by comparison with rotary-winged flight. And of course, the passengers had to be able to get on and off in complete safety, even in heavy seas.
As a result the Wavecraft Voyager series was born. Seating between 60 and 150 passengers in comfort depending on the size of the vessel (up to 10 times more than a helicopter) it can cover 700 nm at a speed of 50 knots. Top speed is 55 knots.
Umoe Mandal says Wavecraft will transport crews “at a fraction of the cost of a helicopter” and while the group does not want to reveal too many numbers, it suggests savings are much higher than 50% over the flight alternative. The longer the journey, the better the economies of scale.
Disembarkation and loading is straightforward. The vessels can be supplied with a gangway and a SeaSpyder system, whereby crews are moved in cabins under a magnetised “passive compensation method” that reduces the load on the wires holding the cabins. According to SeaSpyder, the system allows “any vessel to bring aboard personnel and guests in almost any condition.”
But what happens if the seas get rough? Wavecraft is an air-cushioned catamaran using well-established SES technology. Half catamaran and half hovercraft, the vessel sits on a layer of trapped, pressurised air that lifts it partly out of the water, greatly reducing friction between hull and sea. Because the air cushion functions like a giant shock absorber, the vessel is not thrown around as much as would be the case for a deeper-sitting, single-hulled craft constructed in steel or aluminium.
Combined with a ‘heave-compensation’ system that reduces the effect of vertical waves, Umoe Mandal claim the vessel can make relatively light work of even heavy conditions.
To make life aboard even more comfortable, Wavecraft is equipped with fully-automated, proprietary motion control technology, known as ride control system (RCS) and boarding control system (BCS). The skipper can switch between both, according to whether the vessel is in transit or boarding. For instance, when the skippers are approaching a turbine, they would activate BCS. This greatly reduces heave and pitch motion, so passengers can step more easily onto the installation.
When BCS is engaged, the pressure of the air cushion on which Wavecraft sits is adjusted by ventilation valves that counteract the forces of the waves. When the buoyancy of the hulls is increased, the air is ventilated from the cushion and the pressure is reduced, like air being let out of a tyre. But when the buoyancy of the hulls is decreased, air pressure is increased to compensate.
Secrets of success
While Wavecraft is the sum of many parts, it embodies three crucial technologies. First, it is made of strong and lightweight materials that have been developed by Umoe Mandal. Second, it is a catamaran with narrow sea-kindly floats, which create much less drag through the water than a single-hulled craft. And third, the patented lift fans that control the cushion have taken the SES concept a step further.
Returning to the bespoke materials used in Wavecraft’s construction, Umoe Mandal is a specialist in composite sandwich materials, which give enormous strength and endurance. The group has a lot of experience in constructing warships out of composites, including menacing-looking stealth vessels. Because of its light construction, Wavecraft boasts a low displacement, which is where many of its advantages stem from, including the fact that it leaves a small wake in shallow waters, even travelling at speed.
More space equals more comfort
Although it can have bouncy characteristics, the catamaran design provides a big platform. According to Umoe Mandal’s calculations, the advantages of an air-cushioned catamaran over a monohull design are indisputable. The engine can be half the capacity (making the vessel lighter), fuel consumption is between 50% and 70% lower at high speed, and range is therefore greater. The larger capacity allows for extra crew amenities so the Wavecraft fleet can be fitted with suspension and reclining seats, entertainment systems and other modern comforts.
As Umoe Mandal explains: “Unlike a hovercraft, SES vessels do not depend on speed to rise in the water. Even at a complete standstill, large fans create a cushion, or pocket, of air inside the enclosure formed between the twin hulls by flexible skirts fore and aft. Rubber finger-type seals in the bow, and a bag seal in the stern, maintain an air-tight pocket. The air cushion is pressurised using air flow effectors; these are typically centrifugal lift fans, which can reduce draft significantly.” Hence the skimming effect.
Tried and tested
The SES concept is far from new. In fact, the US Navy started experimenting with it in the 1960s, producing impressive early results. But early SES designs suffered from the so-called “cobblestone effect” – bouncing, in so many words. This happened at high speed in relatively flat seas. Scientifically speaking, the ‘cobblestone’ phenomenon is a resonance reaction, arising from the compressibility of air in the pocket. Seasickness was an unfortunate result, but today’s RCS system largely mitigates this.
So while Wavecraft offers a new concept in offshore ferrying, its fundamental technologies have been thoroughly tried and tested in other vessels.
In economic terms, Wavecraft cannot compete with standard, shorter-range, lower-capacity fast ferries. Rather, it comes into its own on longer trips and there are discussions being held about Wavecraft operating as a kind of offshore bus, delivering and picking up from a number of platforms, probably far apart, under a timetable.
Mr Soreng is confident the Voyager series will catch on. “The market has been waiting for this,” he said shortly after it was launched. “Any operator that is shuttling crew by helicopter today is thinking about reducing their use. Not only can we offer a commercially viable alternative to helicopters, Wavecraft Voyager really does not have an equivalent vessel in the market for comparison.”
Time will tell as to whether Wavecraft does indeed re-shape the offshore transit industry, but it certainly looks promising.