TEMPERA Tanker double act

The Yokosuka shipyard of Sumitomo Heavy Industries in Japan has handed over the first of two double acting tankers to Finland?s Fortum Oil and Gas. The 106,200 dwt Aframax tanker, delivered at the end of August and called Tempera, features a stern form designed to break ice, an extended double hull, twin wheelhouses and diesel-electric pod propulsion.

The Double Acting Tanker (DAT) design is a product of Kvaerner Masa-Yards, the Finnish shipbuilding group, which has a patent on it. This is the first time it has been used on new tankers. A second ship, to be called Mastera, is scheduled for delivery in a few months.

The DAT principle essentially involves the ship travelling ahead in open water and astern in heavy ice. In this latter operating profile, the stern form breaks the ice while a pod propulsion unit creates a lubricating water stream between the ice and the hull. It is claimed the tanker will do three knots travelling astern in one metre thick ice. Fortum says ice this thick was broken in laboratory tests.

Year round supply

Fortum owns two oil refineries in Finland ? one in Porvoo (near Helsinki) and one in Naantali (near Turku). It imports crude oil from places such as the Primorsk oil harbour in Russia. All are above the 60oN parallel meaning its ships are highly likely to encounter heavy ice conditions in the northern hemisphere winter.

Ice and ships are a dangerous mix at the best of times. Throw in some oil and the dangers ? through the potential environmental consequences of a ship colliding with ice ? are heightened still further. Yet Finland needs its oil in winter more than at any other time ? to generate energy for heating and lighting. So Fortum (formerly Neste) tankers have to traverse through icy waters.

Ice strengthened

The DAT crude oil carriers are 1 A super ice strengthened. They have a specially reinforced double hull ? with a fatigue life of 40 years ? protecting the cargo tanks, double skin cofferdams protecting the bunker tanks and a double bottom protecting the pump room. Fortum specified an extension of the ice strengthening in some areas of the bow and stern based on its experience and recommendations from Kvaerner Masa-Yards.

The hydrodynamic form of the hull is intended to combine maximum efficiency in open sea (travelling forward) with the ability to maintain a supply line when harbours are ice bound (travelling astern).

Electric propulsion

Propulsion drive is supplied by a single 360 deg.-rotating ABB Azipod unit with a maximum continuous output of 16MW (nominal rating 15MW). The pod is located outside the hull and contains the electric motor and a fp propeller.

Five Wärtsilä diesel generators, comprising two 6MW 9L38B diesel engines, two 4MW 6L38B diesel engines and one 1.7MW 6L26A diesel engine, each produce a 6.6kV AC current at 60Hz. The current is fed into a switchboard and on to a cycloconverter propulsion system, which ultimately contains the pod motor. Transformers and frequency converters direct power, as required, to the bow thruster motors and the pump motors. ABB supplied the ships? complete electric propulsion system.

System redundancy

Fortum recognises that in the event of total pod failure the ships and their cargo of oil would be left without propulsion power and only the manoeuvrability potential of the bow thruster. It says great attention has therefore been paid to system redundancy and reliability. This started with a Failure Modes and Effects Analysis (FMEA) of the complete diesel-electric Azipod propulsion system carried out by Lloyd?s Register at the design stage.

“Power plant and power supply (main switchboard, cable routes, couplings etc) have been doubled all the way until the propulsion motor in the pod,” explains Olli Kaljala, Fortum?s project manager for the newbuildings. “In the propulsion motor stator winding and rotor have been doubled.”

The pod still has only one shaft and propeller, so damage to these or mechanical failure of the steering gear could cause the vessel to lose propulsion. “This kind of serious damage to the propulsion unit is very unlikely and could be caused only, for example, from grounding,” says Kaljala, who adds in support of this argument the 15 years cumulative operational experience Fortum has of Azipod propulsion with Lunni and Uikku.

Fuel consumption

The four largest engines (W38s) burn HFO. When the ship is loaded and travelling at 13.5 knots they consume 56t/day of 380 cSt HFO. When the ship is in travelling at this service speed in ballast they consume 40t/day of 380 cSt HFO. These engines are also used during offload operations in harbour, which takes about 12 hours and requires about 17t of fuel. The ship has tank capacity for 2,890m3 of heavy fuel oil.

The smaller engine burns MDO. It is principally used in harbour, during the inerting of the cargo tanks and loading. Inerting takes 12 hours and requires 15t fuel. Loading takes 10 hours and requires 3.5t. Tank capacity for MDO is 308.2m3. Lub oil capacity is 63.2m3.

Cargo handling

There are three electric-driven cargo oil pumps, which each have a pumping rate of 3,500m3/h. These are backed up by a single cargo stripping pump, which has a pumping rate of 300m3/h. These four pumps are sited in a pump room located between the engine room and slop tanks, toward the aft of the vessel.

The vessel?s 12 cargo tanks and 2 slop tanks have a 98% capacity of 121,158.2m3. The cargo tanks are divided by a longitudinal centre bulkhead and are partly epoxy coated. The slop tanks are fully coated. An inert gas system is provided for the cargo and slop tanks. The cargo manifold system is 124m from the bow, 118m from the stern, 4.7m from the ship?s rail and 1.9m above deck. It contains three manifolds. A deck crane for hose handling, with a 15t SWL, has a maximum outreach at the manifold of about 8m.

The pump room also contains two electric-powered ballast water pumps, one with a pumping rate of 2,500m3/h at 35m T.H. and the other with a pumping rate of 3,000m3/h at 70m T.H. The ship has 16 segregated ballast tanks, with a total ballast water capacity of 46,922.4m3.

The ballast water tanks are located in combined side and double bottom tanks. These are divided by the longitudinal centre bulkhead. There are 12 ballast tanks around the cargo tanks, two fore peak ballast tanks and two aft peak ballast tanks. All the ballast tanks are fully epoxy coated.

Three fresh water tanks (for technical water, fresh water and drinking water) are located on the starboard side. They have a combined holding capacity of 342.3m3.

The ballast tanks, the pump room and the cargo piping can be inerted by removable connections. It is possible to carry out an emergency cargo transfer to the double hull tanks.

The cargo and slop tanks have steam heating coils. To produce steam, there are two sets of oil-fired, two-drum, water-tube type auxiliary boilers. These have a rated evaporation of 12,500kg/h and produce saturated 0.88 MpaG steam. There is also an exhaust gas economiser system of the forced-circulation, fin type. This comprises two sets of boilers with a rated evaporation of 1,050kg/h and two sets of boilers with a rated evaporation of 700kg/h. All produce saturated 0.88 MpaG steam.

Steam is delivered to cargo tanks by insulated pipes through six sheltered steam delivery boxes on the upper deck.

Each cargo tank has two deck-mounted tank cleaning machines. Each slop tank has one. There are also separate tank cleaning holes for portable tank cleaning machines in the cargo tanks, slop tanks and ballast tanks. Two heat exchangers can heat the water used for tank cleaning.

Fore and aft navigation

As the vessel can travel in both the conventional aft first mode and the ice-breaking stern first mode, it has two wheelhouses (one aft facing, one stern facing). Each has its own steering and control equipment. For example there are two identical ECDIS systems, two radars and an integrated bridge control system.

The bridge is classified for one-man operation. Lloyd?s Register of Shipping is the class society for the vessels.

ABB?s structured finance division structured and arranged the financing of the two newbuilds. A sub-division, ABB Credit, leases the vessels to Fortum.

“Finnish expertise and technology played a key role in the design of these tankers. Special attention has been paid to manoeuvrability, decreasing environmental emissions, as well as safety,” says Jukka Laaksovirta, senior vice president of Fortum?s logistics department. “Due to their flexibility in icy conditions, they can transport crude oil to Fortum?s refineries throughout the year.”