No smoke from the OK Coral

Alaskan air quality is set to survive a potential smoke stack choking later this year when Princess Cruises? latest luxury liner Coral Princess, delivered from France?s Chantiers de l?Atlantique last month, arrives in the state in May. The ship, like Holland America Line?s Zuiderdam (see elsewhere in this issue), features a combined diesel and gas turbine (CODAG) electric power generation plant, an arrangement that is being applied for the first time in the cruise industry.

Princess has gone to great lengths over the years to comply with Alaskan air quality legislation. Yet, occasionally, it still falls foul of the regulator. In 2000, for example, the US Environmental Protection Agency (EPA) charged the company over two instances of smoke emissions that violated Alaska?s air quality regulations. Princess attributed the emissions, from the diesel powered Sun Princess and Dawn Princess, to “short-term technical and operational issues”.

Gas turbine

priority

A CODAG ship such as Coral Princess should avoid such short-term issues, as a gas turbine produces no visible smoke, irrespective of load. In the most sensitive areas, such as Alaska?s Glacier Bay where vessels manoeuvre at low speed, the operator plans to use the ship?s single gas turbine as the sole power source, says Richard Vie, technical director at P&O Princess Cruises. Power generation will simply be switched to a ?Gas Turbine Priority? mode, he explains.

Even when either of the ship?s two 16.2MW diesel engines is run to take up variable load beyond the gas turbine?s 25MW capacity (when operating in ?Gas Turbine Priority? mode), the fact that the diesels are fitted with a common rail system, with electronically controlled fuel injection, should limit visible smoke emissions at normally problematic low loads (the engines are also fitted with direct water injection to tackle NOx emissions). Smoke emitted by Coral Princess in Alaska and specifically its visibility should therefore be OK as far as the EPA is concerned.

Normal operation

Despite being fitted with a gas

turbine, the majority of Coral Princess?s time will be spent in ?Diesel Engine Priority? mode. Unequal load sharing with the gas turbine leading will only be used when absolutely necessary.

“Fuel consumption is an issue,” explains Vie. “We will use diesel engines in preference to the gas turbine because of fuel costs.”

In circumstances where the power generated by the two diesels, which burn cheaper heavy fuel oil, is insufficient to cover the ship?s power demand in ?Diesel Engine Priority? mode, the gas turbine, which burns more expensive marine diesel oil, will be used as a top up power source.

It is well catalogued that running a gas turbine at low load is very fuel inefficient. However Vie contends: “It is always more fuel efficient to run the diesels flat out.”

Sea trials

Coral Princess experienced a number of problems with the propulsion system during its sea trials. One involved an overheating tail shaft bearing, which prevented the ship from being taken up to full power. This was resolved by altering the point at which the bearing is lubricated. The ship also experienced some software problems with its power management system, which took some time to debug. The other main problem the ship experienced was a leaking stabiliser seal. Rectifying this required a 24-hour drydock at the SOBRENA repair yard in Brest, just prior to delivery to the owner in December. However the yard and owner both point out that such problems are commonplace on first-in-class ships such as this.

Space creation

The V16 diesel engines are located in the bottom of the ship, while the gas turbine is in a separate engine room on deck 15, under the funnel. The diesel engine room contains just two diesels as opposed to the four or more that are customary on this size of ship, so it is smaller than normal. This and the location and size of the gas turbine allows space traditionally reserved for machinery to be given over to other uses.

However some of the machinery space that other cruise operators are managing to claim back for other uses through the installation of podded propulsors (thus eliminating shaftlines) remains as machinery space on Coral Princess. This is because P&O Princess, at the time of contracting the ship three years ago, was unconvinced of the reliability of pods and therefore did not specify them.

Passenger capacity on the 88,000g panamax ship is 1,970 in 987 cabins, giving a space ratio of 44.7 (Space ratio = gross tonnage (ft3)/passenger). This compares to 46.0 on Holland America Line?s Vista-class, 42.9 on Royal Caribbean?s Radiance-class and 46.7 on Celebrity?s Millennium-class (the latter two have combined gas turbine and steam regeneration electrical (COGES) power plants).

Gas turbine

Efforts have been made to reduce the weight of the gas turbine through redesigning and rationalising the casing and mountings etc. According to the shipyard this has trimmed about 40t from the standard weight of the installation.

The gas turbine?s location, aft of the diesel engines? exhaust gas uptakes, is insulated against noise emission and fire. It sits on a half-deck raised just over a metre from deck 15. The void space is intended to help prevent noise transmission to the public decks below. The walls are noise and fire insulated with foam.

The gas turbine can be removed quickly for maintenance or replacement through a door on the starboard side of the gas turbine room.

Power conversion

The two diesels and the gas turbine on Coral Princess supply electrical power at 11,000V to two main switchboards. These feed two 20MW variable speed electric motors (each made of two windings with their own breakers, transformers and converters), which provide drive through two shaft lines to five-fixed-blade propellers. They also feed two groups of three 1,720kW transverse thrusters, one set forward and the other set at the stern, which provide manoeuvrability. A pair of stabilisers tackle roll.

Technical services

A single duct, high pressure, variable volume airflow a/c system is fitted on Coral Princess. Passenger and officer cabins have individual thermostatically controlled electric reheat units. The system is balanced to prevent temperature differentials and air whistling between fire zones.

Up to 1,800t of fresh water is produced each day for onboard use by three ?flash? low-pressure multistage evaporating units. Steam for heating this water and other auxiliary uses is produced at a rate of up to 66.8t/h. Exhaust gas economisers for each of the diesel engines produce up to 5.4t of steam per hour each. An economiser for the gas turbine generates up to 30t/h and two oil-fired boilers produce 13t/h each.

The ship has three fuel oil separators for pre-treating the bunkers burnt in the diesels and the boilers. Two gas oil purifiers pre-treat the fuel burnt in the gas turbine. Other separation and purification equipment includes two lub oil separators, a sludge purifier and a bilge water separator.

Coral Princess has an incinerator system that is able to burn all dry and wet waste, pulped food waste, sludge and waste oil. It comprises two 1,200kW incinerators fitted with a flue gas cleaning system that reduces toxic emission levels. It also has a waste water treatment system that meets regulatory standards and a solid waste treatment system with pulpers and a water press system.

Layout

Unusually for such a vessel, the main restaurants ? which are operated to an open dining policy ? are located midships. The space aft on the lower public decks, normally reserved for a large dining room, is, on Coral Princess, taken up by a multi-purpose lounge (with three revolving stages, projection screens and seating for 421).

This means any natural passenger flows through the casino, between the main dining rooms and an evening show, will rely on the draw of this aft lounge against the main showlounge. The main showlounge is traditionally located at the fore of the ship and is entered from deck 7.

The midships location of the restaurants, on deck 5 and deck 6, means the main galley is located forward of the ship, below the banks of seating of the main showlounge. This also means the main provisions stores are located forward.

There is some passenger accommodation aft of the central four-deck atrium on deck 5, but the bulk of the cabins are on decks 8-12.

Safety outfit

The vessel has a designated safety centre. This contains three terminals for the control and indication of all onboard safety systems (plus one terminal on the bridge and one in the engine control room) and two terminals to operate the ship?s integrated machinery and a/c automation system (there are also six terminals for this in the engine control room and one on the bridge).

An emergency shut down system allows all pumps, fans and valves etc. to be stopped or closed in the event of fire. In addition the whole ship is covered by a high-pressure water-fog fire-fighting system. This includes spot protection for the main diesel engines, incinerators, boilers, purifiers and fuel supply skids. Machinery spaces and the electrical switchboard rooms are also covered by a CO2 fire extinguishing system.

Evacuation is provided for by 10 lifeboats held and launched by stored energy, sliding beam davits. There are also four passenger tenders, two crew tenders and two fast rescue boats. Two self deploying evacuation chutes can handle about 400 people each.

CODAG solutions: Princess vs HAL

The CODAG solution adopted by P&O Princess for the Coral-class of ship is very different to the CODAG solution adopted by Carnival Corporation/Holland America Line for the Vista-class (Zuiderdam and its sisters). While Coral Princess has two high output diesels (with 32 cylinders in total) and a full-rated gas turbine, Zuiderdam has five smaller output diesel engines (72 cylinders) and a single de-rated gas turbine. Total power generative capacity on Coral Princess is 58,600kW; on Zuiderdam it is 65,840kW.

P&O Princess?s solution should give it the benefit of having to maintain and service fewer diesel engines. It is also getting a full 25MW of power from a gas turbine for about the same capital cost as Holland America Line is investing to get 14MW from a gas turbine (due to the latter taking a down-rated model). Holland America Line will though benefit from the flexibility of having more diesels in, for example, situations where one engine is taken down for maintenance. Zuiderdam has pods whereas drive from the electric motors on Coral Princess is directed to the propellers through long shafts.

Both class of ships are built for broadly similar operations focusing on Alaska and other environmentally sensitive areas. Only service experience can truly explain which, if either, solution is the better one.