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Floating on air

 

With innovative hull design, use of compressed air and dual-fuel propulsion, Stena Bulk and Stena Teknik are on their way to introduce what could be the most energy efficient and environmentally sustainable tanker ever built.

 

Stena's well-known MAX concept has been introduced in several tanker segments, with the 2002-built, io,000-dwt C-MAXes being the smallest and the 200l-built, 312,000- dwt V-MAXes the largest. The fleet of 65,000-dwt P-MAX MR product car­riers currently consists of six units, with a further two to be delivered later this year.

The current series will be concluded in 2010 when the two last units are delivered. That the market has wel­comed the MAX concept is proved by the fact that long-term time charters nover all P-MAXes, including the four not yet delivered.

And there are new MAXes on the drawing table, one being the 209000­dwt B-MAX that is designed to carry Russian crude through the Baltic Sea.

Although Stena Bulk daims to cur­rently be waiting for the right moment to order a number of B-MAXes, it is highly likely that the next MAX tanker to be ordered will be another one that takes environ-mental performance to a higher level.

Stena's in house skip design team is working intensely on the development of a new 15 ,000-dwt coastal IMO II chemical/products car­rier called E-MAXair, primarily for trade in North European waters.

"Our scope is to design a vessel with a significantly less environmen­tal impact than today's conventional coastal tankers", says Jacob Norrby, Naval Architect and project manager at Stena Teknik.

"We have two major operational limitations; the vessel shall be able to carry 13,500 tons of cargo through Drogden in Oresund to bypass the Danish Belts, and calls at some oil terminals restricts the beam to 23 metres."

The result is a design that incorporates MAX redundancy features such as two engine rooms and double pro­pulsion and manoeuvring systems.

The vessel is slightly longer than a conventional comparable carrier, but due to the operational limitations, the E-MAXair can however not be built with the extreme breadth that characterizes the rest of the MAX family.

The hull design features several new details. The patented forebody is designed with a unique `hammer shark bulbous bow' that will optimize the water flow to a bottom section with a compressed air cavity, which reduces the friction against the water.

"A cautious estimation is that the reduced friction will mean about ten per cent in fuel savings", says Jacob Norrby. When designing a new vessel with the scope to reduce fuel consumption, the first thought is that the hull should have a slender form. The design developed by Stena has however significantly larger fuel savings potential in broader vessels such as the B-MAX and a prospective new P-MAX series.

The air cavity takes up about 25 per cent of the hull's wet surface.

"This is a very promising solution for vessels with a large flat bottom area litre tankers, but today we do not see it as an effective design for vessels with other hull forms, such as ferries and ro-ros", says Jacob Norrby.

The aft section of the vessel has also been given a smarter design with an improved hydrodynamic profile that enables the vessel to be fitted with larger, slow-rotating propellers.

Stena expects the new hull design to save around 4.5-5 tons of fuel oil per day, compared to a conventional tanker of similar size.

Additional savings can be achieved by for instance hull washing once a year and by propeller polishing once every third month. On the other band, the Stena design team is currently somewhat sceptical to the promises from paint manufacturers that their new paint products will reduce fuel consumption.

"We are monitoring the develop­ment closely, and we are conducting our own tests. So far, we have found no scientific evidence that supports the manufacturers' statements", says Jacob Norrby. "If we get more solid proof, we might have reasons to reconsider."

Stena has been in talks with Sky­Sails for about three years to fit the vessels with the German company's kite system.

"We have simulated trips all over the world, the decisive factor is what amounts of wind energy there are on the routes a vessel is expected

 

Through generators, the engines power two electrical motors connect­ed to the shafts. An advantage is the flexibility to choose the propeller's rpm instead of being limited to the engines rpm.

There is however still a question mark concerning costs.

"We have received only limited information yet and lacé firm offers. We know that they are more expen­sive than conventional diesel engines , but not how much", says Jacob Norrby and there is according to him probably a historical aspect that has influenced the price gap.

"The marine dual-fuel engine was initially developed for the large gas carriers. The engine manufacturers could probably raise their prices substantially and shipowners would still make huge savings by switching from very expensive steam turbines."

Dual fuel engines are still favour­able as fuel logistics is a major challenge in the E-MAXair project. Today, availability is limited with few ship bunkering stations around Northern Europe. There are a handful gas powered ferries in Norway, but it is of course easier to supply gas bunkers to vessels with regular calls in a limited number of fixed ports, than it is to secure supply to a tanker in irregular trade.

Stena is looking into a number of possibilities. Using barges is one option; another is to place containerized LNG tanks in key terminals, which are supplied by smaller gas carriers.

Another feature that is rare on tankers of this size is that the E­MAXair will probably be built with a separate pump room. This will house ballast water pumps and the ballast water treatment equipment.

All in all, the new hull design, the compressed air and the gas power, topped by a kite, are estimated to reduce fuel oil consumption by 7 tons per day compared to a conventional tanker of similar size, to 15 tons LNG per day.

The shipbuilding market has gone soft, and that is not only sending newbuilding prices southward. To­day, even South Korean shipyards are interested in specialized, custom made newbuilding projects. Accord­ing to Ulf G. Ryder, CEO of Stena Bulk, there is a possibility that a first E-MAXair order is placed already this autumn.

For the design team, the challenge continues however. There are loads of work to do, problems to solve and an ambitious testing programme to carry out before the first state-of-the-art E­MAXair vessel will sail out on its first voyage.*

 

The MAX fleet to­day consists of: 2 C-MAX tankers, 2 V-MAX tankers, 6 P-MAX tankers with a further 4 P-MAXes on order.