MOL leads the way with aerodynamic PCTC

The design of the car carrier, other than in terms of sheer size, has altered very little in recent decades but all this has changed with the latest pure car truck carrier (PCTC) recently delivered to the Japanese shipowner Mitsui OSK Lines (MOL). In an evolutionary step to improve efficiency of the design of the conventional PCTC, MOL decided to build a new six-ship series of specially designed energy-saving vessels. With their high slab-sided hulls, PCTC ship types are susceptible to wind-resistance and suffer from excessive leeway forces particularly in high winds. To mitigate this problem, MOL has come up with a new design incorporating improved aerodynamics, which reduces the impact of the wind while improving fuel economy.

Built at the domestic yard of Minaminippon, the 57,500g Courageous Ace is the lead vessel. This new design was jointly developed with Universal Shipbuilding Corporation (the merged NKK and Hitachi Zosen organisation) and features a bow which is aerodynamically rounded and beveled by 38 deg. to help reduce pressure from head winds by about 20 per cent, resulting in a projected 4 per cent improvement in fuel economy. The most efficient angle is 45 deg., but MOL adopted the 38 deg. bevel to maximise loading capacity.

In addition, the garage deck, situated on the upper deck, has a longitudinal cut designed in such a way that the wind can pass through to reduce by 19 per cent the influence of side winds which cause leeway and adversely affect the ship?s speed due to the resultant increase in underwater resistance. This is expected to add another 6 per cent in fuel efficiency.

Wind resistance is particularly noticeable at slow speeds when manoeuvring in port. The new design is expected to prevent accidents from collisions or groundings. Improved fuel efficiency, in turn, contributes to energy conservation and helps reduce vessel emissions of CO2, NOx, and SOx per unit load.

The combined impact of these design measures will lead to a speed increase of 1 knot depending on the direction of the wind. MOL says it has also had no negative impact on stowage capacity, with the reverse in fact being the case. It explains that capacity is 6 per cent greater than the standard design (about 300 cars up) because an extra garage deck, a little set in from the full breadth, is included on top of the original deck to accommodate the aerodynamics of the ship. Also, the clear height of each of the 12 car decks is reduced by 0-20cm to maintain stability.

The newbuilding is powered by a Mitsubishi two stroke 8UEC60LS diesel engine with an output of 14,160kW driving a single 6.55m diameter 5-bladed FP propeller fitted with PBCF (propeller boss cap fins). The service speed is about 20 knots. This PBCF system was developed and designed by MOL in the late 1980s and is claimed to enhance propeller efficiency by 4 to 5 per cent.

Auxiliary plant consists of three Daihatsu medium speed 5DK-26 diesel gensets each producing 1,070kW at 720 rpm. To help slow-speed manoeuvring, a 1,040 kW bow-thruster is fitted.

With a carrying capacity of 6,400 vehicles, rapid discharge/ loading is ensured by a starboard side ramp measuring 17m long and 4.5m while a large stern ramp is also installed measuring 30m long by 7m wide. Each cargo deck is fitted with two ramps, one forward and one aft, allowing cargo to be stowed and discharged simultaneously at any deck level. In addition, there are two sets of folding ramps on car decks number 4 and 6 to provide a bypass facility and two hoistable decks. Decks 5 and 7 are strengthened for heavy cargoes while 90 per cent of cargo decks have a minimum height of 1.9m.

Two further units in the series will be delivered from Minaminippon in June and September this year while the remaining three units are slated for delivery from Shin Kurushima Dockyard in September and November 2003, and January 2004. The last three units will be equipped with high expansion foam fire fighting systems supplied by Kashiwa and electrically driven windlasses to prevent oil pollution.