Groundbreaking PSV design wins Offshore Support Journal Support Vessel of the Year Award 2015 sponsored by DNV GL

This year the Offshore Support Journal Support Vessel of the Year Award, sponsored by DNV GL, was awarded to Juanita - built by Kleven Verft AS, owned by Ugland Marine and designed by Salt Ship Design

With its innovative propulsion system using contra-rotating propellers and permanent magnet technology and hydraulically driven submerged cargo pumps with an especially flexible tank arrangement, Juanita is a genuinely groundbreaking vessel. Named on 20 May 2014, Juanita started work on a two-year charter (with options) with Statoil.

The platform supply vessel (PSV) is the first example of the SALT 100 design. With a length of 88.9m and a breadth of 20m, Ugland’s new vessel has a deck area of 1,035m2. Externally, at least, it is not dissimilar to many other PSVs, with DNV GL’s DEICE (Winterized) class notation, NOFO 2009 and NMD standby rescue capability for 225 people, whilst being prepared for FiFi 1 and a Triplex gantry crane/cargo rail cranes and DEICE-C, if required, but below the waterline, the vessel has contra-rotating propellers, with each propeller driven by a permanent magnet motor – a world first for an offshore vessel.

Internally, the vessel also differs from any other PSV and has an especially flexible cargo-handling arrangement with Framo deepwell pumps in all of the mud, brine and special product tanks and the ability to transport low flash liquids (LFLs) and LFL* classified mud/brine and other noxious chemicals in no less than eight tanks.

As Tor Vestbostad, Salt Ship Design’s sales director, explained, a new tank plan has also been developed for the vessel that utilises the space available more efficiently. It allows for a larger volume of cargo to be carried by the vessel and eliminates the need for a pump room whilst ensuring optimal cargo tank layout for efficient handling of all types of liquid cargoes, including oil emulsion.

The innovative propulsion system, the result of collaboration between Scana-Volda and Inpower (who developed the permanent magnet motor concept), has resulted in a particularly robust power train with no gears and a direct-drive arrangement with quintuple gensets (three large and two smaller units), with a selective catalytic reduction system to further reduce emissions. Each propeller in the contra-rotating arrangement is independently driven by a permanent magnet motor. The propellers are protected against damage, being on the ship’s centreline with the tip of the propellers >0.8m above baseline with a heel arm mounted below.

This configuration confers an extremely high level of fuel efficiency on the vessel. At 12 knots, says Salt Ship Design, this equates to a reduction in fuel consumption of greater than 20 per cent compared to a conventional hull with conventional azimuth thrusters.

“Contra-rotating propellers are, by their nature, more efficient than conventional propellers,” said a spokesperson for Inpower. “Motors directly connected to the propellers mean there are fewer components, and improved energy conversion makes this solution more efficient and safer than the alternatives.”

“The contra-rotating propeller system was a big effort for us in terms of innovation and implementation,” said Scana Propulsion’s CEO Kristian Sætre, highlighting the role played by Inpower and its expertise with permanent magnet motors. As he noted, permanent magnet motors are an accepted, proven technology used in propulsion solutions for modern hybrid cars and in the automation industry, wind energy and hydropower. Inpower has long experience with permanent magnet technology and established collaboration with leading manufacturers of permanent magnet machines, which enable it to tailor a propulsion solution to meet the needs of the vessel.

“Propulsion systems based on permanent magnet technology offer unique capacity, efficiency and operating economics,” says Geir Larsen, CEO of Inpower. “The properties of directly connected permanent magnetic motors perfectly suit contra-rotating propellers for several reasons, including their high efficiency at nominal revolutions and over the full revolution range. Electric motors are also slow-running machines, and directly connected to the propeller shaft, they help to avoid energy losses through reduction gears. They also save considerable space, and with a compact propeller permitting a more efficient stern configuration, this adds up to substantially better efficiency with lower fuel use and reduced emissions.”

Juanita’s unique cargo-handling system is based around the use of Framo submerged pumps from Frank Mohn in Norway. Framo pumps have been refitted to supply vessels before, Mr Vestbostad explained, but the tank arrangement and the use of submerged deepwell pumps from the outset, in such large numbers, is unique and makes for an especially flexible arrangement that was of particular interest to Statoil, Norway’s state oil company, which is using an ever greater range of chemicals and products that need to be transported to and from its offshore oil fields.

According to Jørgen Brandt Theodorsen, who is responsible for sales and projects at Frank Mohn, more than 400 chemicals are in use offshore today, and as many as 80 different chemicals need to be transported in bulk. These chemicals used to be transported in tank containers on deck, a solution that was inefficient and impractical as the number of chemicals used grew. At the same time, the Norwegian Maritime Directorate has issued stricter guidelines about how chemicals should be handled, and fewer exceptions are accepted that would have enabled them to be carried in a less than optimum way. Stricter rules are also due to come into force at IMO.

Mr Brandt Theodorsen explained that Framo hydraulically driven submerged cargo pumps can handle almost any type of liquid cargo and are of robust construction. They are designed to empty a cargo tank containing the heaviest, most viscous or aggressive cargoes without risk of heat build-up and have a fail-safe design in which the pump motor and bearings are constantly lubricated and cooled by the hydraulic oil driving medium.

A Framo pump is a vertical, single-stage centrifugal pump powered by a hydraulic motor, with a built-in hydraulic motor connected to the impeller by a short independent shaft. The motor, shaft and bearings are lubricated and cooled by the hydraulic driving oil. The pumps are also designed to be easy to operate. It is impossible to overload or to overspeed the pumps, which have a speed torque control valve that automatically regulates the oil pressure and flow to the hydraulic motor. The pumps are also designed to allow for operation with a minimum of liquid in the tank, which saves time spent for drainage and tank cleaning, and pumps have a built-in stripping system.

“The concept adopted on Juanita includes one submerged pump in each cargo tank, with the possibility for arranging full segregation of the cargoes at the manifold,” Mr Brandt Theodorsen explained. “This gives the shipowner a very flexible vessel/tank arrangement in which any cargo/chemical can be loaded in any tank and a very much simplified piping and valve arrangement under deck. The cargo pump room is eliminated altogether.”

The pumps for Juanita have been modified to enable them to handle all of the cargoes typically carried on a PSV. Juanita has a total of 18 of them, one installed in each tank. Twelve of the pumps are of a new specially developed type, the SD150 Mud, which is designed to handle all kinds of mud and mud return in addition to any kind of chemical. The special product tanks on the vessel are fitted with SD100 chemical pumps. This pumping system can handle any cargo supplied off shore, in addition to recovered oil/emulsion, and the vessel is designed in such a way that any cargo can be loaded into any tank, as is the case with the stainless steel tanks on chemical tankers.

The submerged cargo pumps are installed close to the centreline of the vessel. Each pump is resiliently mounted. All of the connections are via the pump’s top plate. Cargo lines are routed from the pump’s top plate to the cargo rails. Tank hatches, cargo heaters, drop lines and recirculation lines are located in the cargo rail area. An access tunnel through the vessel is arranged in the centre of the vessel beneath the main deck.

Frank Mohn says hydraulic drive provides the most flexible and safe power transmission for a cargo-pumping system for an offshore support vessel carrying cargoes with a wide range of viscosities and specific gravities. The company’s scope of supply on Juanita included the pumps, hydraulic power unit, piping system and control unit, which is integrated into the vessel’s computers. The hydraulic system is prepared to meet the requirements of NOFO 2009 and ready to receive a Framo TransRec 150 oil skimmer.

In addition to the benefits outlined above, Frank Mohn cites a number of other advantages that flow from using the submerged hydraulic-driven pumps. These include enhanced safety – eliminating the pump room means there are no electric motors and a reduced number of valves and electric armatures in the cargo area. The cargo tanks are not penetrated below cargo level, and there is no cargo piping in the bottom of the hull, reducing risk of leakage. Eliminating the pump room frees up extra space for cargo. In addition, the Framo cargo-pumping solution can handle all liquids identified by operators in the IBC Code Chapter 17, and the cargo-pumping system is designed to meet the requirements for future chemical code/handling on offshore vessels. As highlighted above, the hydraulics are prepared for powering a Framo TransRec oil recovery system, and the pumps are designed according to NOFO 2009 offloading requirements. 2016's Annual Offshore Support Journal conference, awards & exhibition will take place a week earlier than usual, running from the 2nd to the 4th February. More details can be found on this page.