Croatia on a high with recent deliveries

Croatian shipbuilders have built up a healthy backlog of orders since the end of the Balkan conflict. The four main players ? 3 Maj, Brodosplit, Trogir and Uljanik ? have been particularly successful in the handymax oil tanker market, including products and chemical carriers. It is this specific ship type that is the focus of this article, which features the recently delivered Tarantella and Maritea. Although superficially both designs are similar, one, Tarantella, is configured for a specific trade while Maritea is destined for worldwide service.

Tarantella; first of Trogir sextet

As the first ship to be delivered according to DNV?s tough new ?Plus-2? notation, the advanced products tanker Tarantella represents an important development for Laurin Maritime, one of the leading clean oil product and large-parcel chemical carriers in the US Gulf. Built by Trogir Shipyard of Croatia, the recently delivered newbuilding is the lead ship in a series of six identical vessels based on a design to meet Laurin?s requirements and refined in close cooperation with the yard.

Owned by Anglo-Atlantic Steamship Company, based in the Isle of Man, with Laurin Maritime as agents, the 46,764 dwt IMO II newbuilding will service the trade that Laurin has developed in recent years in the chemical and the clean oil product markets. Its ships carry full cargoes of clean petroleum products and full or part cargoes of easy chemicals such as caustic soda, styrene, cumene and BTX (Benzene, Toluene, Xylene).

The six new ships will be referred to as the ?T-class? since all the names will begin with the letter ?T? and are related to dance and music. The T-class represents a step towards shipping more chemicals without aiming at the parcel trade and, as such, has several important features in respect of cargo handling and propulsion.

The 182.9m long ship is a double hull oil/chemical tanker with centreline longitudinal bulkhead, bulbous bow, transom stern and forecastle and complies in full with the revised Marpol Rule 13G.

Cargo handling

The most common type of ship used in the pure chemical parcel trade today is a chemical parcel tanker with 18 tanks or more, all of which are below 3,000m3 capacity in order to meet the requirements of IMO II class cargoes. Most of these ships have stainless steel tanks but some are epoxy or zinc coated. This design with many small tanks has, however, a number of disadvantages such as higher building costs (especially if stainless steel tanks), slower loading and discharging due to more hose connections, more expensive and time-consuming tank cleaning and larger tank coating areas to maintain and eventually replace.

The T-class ships are designed to combine the carrying capabilities of costly chemical tankers and the less sophisticated oil product tankers. To optimise Laurin?s shipping capabilities in this trade, these ships have eight tanks of 3,000m3 each and six tanks of 5,000m3 each (plus two slop tanks) and can thus be switched between carriage of clean petroleum products and chemicals.

The mix of size has been tailored for the trade as IMO II cargoes are combined with caustic soda, MTBE (a fuel additive), vegetable oils and clean petroleum products, which are not IMO II and therefore not restricted to a maximum tank size. A number of tanks have been reinforced to carry heavy cargoes like caustic soda, while all tanks are strengthened for light cargoes with high vapour pressure such as Penhex-Naphtha. The decks of the tanks are reinforced and P/V (pressure/vacuum) valves installed up to a Reid Vapour Pressure of 17.5 PSI.

The design incorporates a Marflex electrically driven submerged centrifugal cargo pump in each tank allowing eight grades of cargo to be loaded or discharged simultaneously at a rate of 3,500m3 per hour. The electric pumps, it is claimed, give several advantages over hydraulic pumps such as higher pumping efficiency, reduced risk of cargo contamination by hydraulic oil and less maintenance than a complicated hydraulic power and pipe system.

Additionally, noise is almost eliminated. This can prove important when performing cargo operations in terminals close to cities. It also helps enhance crew comfort. It is environmentally safe since there is no risk of hydraulic oil spills while leaks on the main supply line or the return lines can cause the entire system to be shut down for repairs.

Stainless steel heat exchangers are fitted in each of the 14 tanks enabling the temperature of cargoes to be increased from 44oC to 66oC in 96 hours. Tank washing is effected by means of two fixed Scan-Jet single nozzle machines for hot and cold washing in each cargo tank and a 557m3 fresh water double bottom tank is dedicated for this purpose.

Nitrogen generators

The cargo tanks have to be inerted before loading petroleum products to eliminate any risk of explosion and this can be achieved by conventional inert gas or by the more expensive nitrogen. The owner has opted to fit his ships with a Smit Sinus nitrogen plant with an hourly capacity of 4,400m3 thus eliminating the need for conventional inert gas generators.

This more expensive arrangement offers several benefits including the ability to provide nitrogen blankets, which is a requirement when carrying certain chemicals. Tank cleaning is reduced to a minimum as there will be no soot and the ship will be ready much quicker to receive cargo, particularly when switching from oil to chemicals. This will lead to the service life of the tank coating being extended due to less cleaning and there is no discoloration of the epoxy coating.

The nitrogen generators will make these ships much more chemical friendly since it is normally the soot from the inert gases which causes long cleaning operations. Also, the vessel is fitted with an efficient cargo stripping system as well as a heated cargo tank ventilation system thus reducing the tank drying time.

Hull strength

As already mentioned, the T-class ships will be the very first vessels to be delivered in compliance with DNV?s class notation ?PLUS-2?. This notation gives a longer hull life for owners who want to provide extra assurance against experiencing fatigue problems in service and is designed to give a service life of 40 years in harsh environments like the North Atlantic and the North Pacific. The normal design as per class requirements is 20 years service life.

The reinforced hulls of these vessels have been designed with about 45t of additional steel distributed primarily in the bottom and side structures which are most susceptible to fatigue. Additionally, the scantlings have been increased and there are improvements in details of construction. The use of high tensile steel has been limited to about 30% of the total hull weight.

Propulsion and Power Generation

Propulsive power is provided by two four-stroke MaK 8M32/48 medium-speed engines each with an output of 3,840kW and driving a 6m diameter four bladed Rolls Royce Kamewa controllable pitch propeller via a single stage Metso reduction gearbox. A large 3,200kW shaft generator provides all the electricity needed on the ship during cargo operations in port and at sea. This reduces the need for running auxiliary engines. To provide a higher than average manoeuvrability, a Becker rudder with an active flap on the trailing edge is fitted which requires less rudder movements and gives faster course corrections thus improving ship speed at sea. The Becker rudder in combination with the controllable pitch propeller produces high side thrusts acting almost like a large stern thruster.

The main reason for choosing the medium speed engines is the sophisticated cargo handling system with electrical pumps and a full capacity nitrogen generator, requiring high electrical capacity during cargo operations. A single slow speed engine arrangement would require three large auxiliary diesel engines whereas the ?T? class ships use the main engines instead of auxiliary engines in port. However, to improve redundancy, two small 628kW MAN B&W 5L23/30H engines are fitted as auxiliary generators together with one 100kW emergency generator.

This results in many advantages, the most important of which are lower investment costs for the complete installation, lower costs for lubricating oil and spare parts over their lifetime and about 32% lower emissions of nitrogen oxide (NOx). This is in addition to redundancy in case of one engine breaking down, easier maintenance with smaller and lighter engine parts.

However, the daily fuel consumption while at sea is expected to be about 1.8t higher compared to a traditional 2-stroke arrangement. This additional cost will, it is claimed, be more than compensated for by the savings.

The ships will be equipped with modern navigation aids such as electronic charts, vessel data recorders, AIS transponders and GPS.

Trade prospects

The Tarantella and her sisters are destined to make a significant contribution to the efficient carriage of US exports and imports of chemicals and clean oil products around the North American Atlantic coast and the US Gulf area. In addition, they will carry transatlantic shipments to and from the continent.

Maritea; coated tanker

Ordered by the Italian shipowner CA.LI.SA. SpA, the 35,000 dwt chemical carrier Maritea was delivered in July from the 3 Maj shipyard and is the first in a two-ship series with the second scheduled for completion in March 2003. Designed to transport oil products and IMO II class chemicals, the vessel is classed and surveyed by RINA and ABS and is a high specification ship complying with the highest standards regarding integrated automation, navigation and cargo handling.

With an overall length of 175.87m and a beam of 29.8m, the double hull tanker is powered by a single slow speed Wärtsilä 6RTA52U diesel engine with an output of 9,000kW at 130 rev/min. This low NOx emission, supercharged, single acting main engine is coupled directly to a 5.4m diameter four-bladed left-handed Kamewa CP propeller giving a service speed of 15 knots. A high degree of manoeuvrability is achieved through a Becker flap type rudder and a 1,000kW Kamewa bow thruster.

The electric power plant consists of three MAN B&W 8L23/30H medium speed four stroke diesel generators built by Adriadiesel with an output of 1,280kW each. These power three 400 kVA generators manufactured by Uljanik-Tesu in Croatia. Back up is provided by a 217kW emergency diesel genset.

The engine room is equipped for unattended operation and particular attention has been paid to the ease of access for the maintenance and repair of machinery and the design allows for major dismantling without the need to cut pipes, cables or ventilation trunks. For this purpose, lifting beams with rollers are fitted above the diesel alternator sets, tail and intermediate shaft, as well as in the engineer?s workshop, separator room and hydraulic room. For main engine overhauls, a crane is fitted with a lifting capacity of 25t.

Cargo system

arrangements

The cargo containment consists of 12 tanks arranged in pairs, two slop tanks and one recovery tank. Vertically corrugated bulkheads divide the cargo area along the ship?s centre-line while corrugated transverse bulkheads supported by stools complete the subdivision. Tank sizes very from 4,478 to 2,250m3 and the total carrying capacity is 43,200m3. A double hull, creating six pairs of water ballast tanks and one pair of washing water tanks, protects the entire cargo tank length. For long-term corrosion protection all ballast tanks are coated in a solvent free epoxy coating system while all cargo tanks are protected by phenol epoxy coating system. SIGMA Coatings supplied both.

The ship is arranged for the loading and unloading of chemical and oil products via a midship?s manifold and stern station, as well as through barge connections. Loading and discharging system is arranged with segregated pipeline from two pairs of cargo tanks (SB + PS) and eight cargo tanks arranged as segregated piping. The cargo discharging system consists of high pressure hydraulically driven submerged pumps, one in each tank, delivering to discharge manifolds. The system is able to operate the eight cargo pumps simultaneously and each has a 500m3/h capacity giving a total discharging capacity of 4,000m3/h at 150 mlc (TDH). Cargo operations are performed from cargo control room located in the accommodation.

For cargo heating, engine room and general purpose heating as well as heating cargo tanks washing water, a thermal oil system is provided. The system consists of two 5,000kW oil fired boilers for thermal oil heating, and one economiser for thermal oil heating, capacity 850 kW.

Other features of design

Although Maritea is designed for worldwide service, its primary voyage profile consists of sailing between oil ports/terminals in the Mediterranean Sea. Typical voyage pattern consists of short sea voyages of a similar duration as the time spent in port for loading/discharging cargoes. This gives an average time of four days for one voyage leg and, because of the nature of the coastal voyages and the close proximity of many tourist areas, a lot of attention has been paid in the design to minimise the risk of accidental pollution. This is particularly important since the tight trading schedule does not allow much time for maintenance onboard by the crew.

As a consequence, the newbuilding has a high-spec structural design based on direct calculation (finite element model) including fatigue criteria and has also applied environmental protection class in the design. Another notable feature is the integrated ship control system supplied by Kongsberg Norcontrol offering an alarm and control system incorporating cargo and ballast handling, power management and bridge systems. The latter includes an integrated navigation system with ECDIS connection on both radars.

The wheelhouse is designed for one-man bridge control having all-round windows and CCTV surveillance of important areas of the engine room and upper deck. The standard of crew accommodation easily meets the latest requirements for minimal vibration and noise.

Main particulars ? Maritea

Length overall 175.87m

Length b.p. 169m

Breadth moulded 29.8m

Depth moulded 16.8m

Draught 11m

Deadweight 34,660 dwt

Gross weight 23,500g

Trial speed 15.3 knots at 85% MCR

Main particulars ? Tarantella

Length o.a. 182.9m

Length b.p. 176m

Breadth moulded 32.2m

Depth moulded 17.1m

Draught 12.18m

Deadweight 46,764 dwt

Gross 26,914g

Cargo capacity incl. Slops (98%) 52,940 m3

Main engine: 2 x MaK 8M32/48 medium speed diesel MCR 3,840 kW each

Generator sets: 2 x MAN B&W Holeby 5L23/30H 650kW each

Service speed (loaded): 14.2 knots

Service speed (ballast): 15 knots