Two considerations dominate the evolution of cruise vessels today: the size and the complexness of the ships, both of which are increasing every day. This results in a striking increase in the measure of electrical power installed and the number of systems to be controlled. Aside from these prerequisites, others arise, such as environmental issues, safety considerations and matters of economy.
However, both of the aspects mentioned above indicate that approaches in the direction of all electric ships and total ship control are needed, because environmental issues lead to requirements of low emission and restrictions on anchoring; and total ship control will enable a safe and economical control of all installations on board. This article will provide an insight into both of these aspects and highlight the products offered by SMEC Automation that fulfill these requirements.
Ever since the introduction of steam engines and transatlantic challenges such as the Blue Ribbon, cruise ships have grown larger, more refined and increasingly complex and sophisticated, thus presenting an exciting environment to both passengers and crew. However, a number of associated developments have also taken place:
Power consumption, including electric power, has risen dramatically, both at sea (as a result of the propulsion of faster and larger ships) and in port (due to domestic consumption).
Not only has the size of the systems on-board increased, but their number and variety as well, incorporating propulsion, electrical generation, heating, ventilation, air-conditioning, hotel services (many small sanitary units), intra-ship communication systems and many new emergency and IT applications.
Due to the rising costs of crew, a large amount of pressure on a small crew creates the need for a high degree of autonomous automation and remote control and supervision.
Operating costs must be kept at a minimum, requiring very reliable systems with minimal maintenance that can be executed within designated periods of time, due to the ship’s operational profile or, better, its schedule
Environmental attention, both in ports and in delicate and beautiful places (such as Alaska and the tropical reefs) leads to a focus on a ship’s emissions in certain locations and to restrictions with regard to damaging the ocean bed. In order to fulfil the owner’s or operator’s wish for a vessel compliant with all aspects mentioned, the latter must be covered by the ship’s design and build. In the following, the two most relevant aspects will be covered and the resultant requirements on ship’s installations and systems will be indicated.
Maneuverability and Energy Consumption, at Sea and in Harbor
With the increase of a ship’s size and speed, the propulsion power required rises accordingly. At the same time, the internal power consumption becomes substantial and, in certain cases, more than significant in relation to the level of direct propulsion power. Propulsion power may be required simply for propulsion at sea, or be split between propeller power and bow/stern thruster power when maneuvering. The latter means that if each unit (propeller or thruster) had its own (mechanical) power supply (like a diesel engine), the total installed power would have to be at least the sum of all the individual maximum power units. This would result in an enormous installed power base. At the same time, since diesel engines are not at their best on low power, fuel consumption and emission quality at low speeds (maneuvering) will be far from optimal.
This can all be optimized by switching to a system of electrical propulsion and, if this is extended to include domestic users, the result will be an all electric cruise ship. This will lead to an installed base of, for example, four or six large generator sets
An all-electric ship concept as described here will require the following:
A number of (large) generators, controlled by a power management system and propulsion control system
Usually, a medium-voltage distribution system, because of the high power transferred from generators to propellers (or podded drives –PODs) and thrusters
A low-voltage distribution system for other consumers or local distribution
A propulsion system, usually with fixed propellers (either on shafts or on PODs), which are controlled by variable frequency drives
Thruster units controlled in the same way
A dynamic positioning system, connected to propulsion, thrusters and rudders (or PODs)
The resultant system will provide the following advantages in comparison with conventional systems:
Flexibility in ship design and in the allocation of large equipment
Reduced fuel consumption (reductions of up to 8% or more have been measured)
Reduced emissions
Increased total availability and the redundancy of the ship’s prime functions (propulsion and electrical power supply)
Reduced maintenance on prime movers (diesel generators), because they will nearly always run at the correct power rate
In general, maintenance on electrical equipment such as switchboards, frequency drives and associated equipment is very low, so the total maintenance effort is not likely to increase; and together with the data processing system, a very high maneuverability, which may go as far as no tugs being required in harbor, again saving costs.
SMEC Automation has a long-standing experience in this field and can supply all the products mentioned in an integrated approach, resulting in a total system that will fit the bill perfectly.
