Keywords

1 Introduction

It is not possible to build ship power plant (different types and size) in land conditions as well as to conduct an appropriate research on them in order to determine a demand for the electric energy, and simultaneously identify loads, reconstructing real operating conditions (Balcerski 1991, 1992; Balcerski and Bocheński 1991). Hence it is necessary to conduct research on the actual objects in operating conditions. Special measuring team’s occurrence during long-term voyages of sea ships in different operating conditions is hampered and connected both with costs and organizational problems of these type undertakings. In these conditions a collection of appropriate operating data and information about object parameters presents a big problem in research conduction concerning identification of real machinery and marine devices operation as well as layouts of energetic systems. The presented material contains an attempt to describe such a type of research.

From the point of view of the functions fulfilled, it is possible to divide energy receivers on board into four groups (Śmierzchalski 2004; Wojnowski 1992): main propulsion devices, main propulsion auxiliaries, general-ship’s devices, hotel devices and economic equipment.

In most merchant ships the main propulsion is carried out with the use of low or medium speed piston internal-combustion engines, which directly provide the mechanical energy to the propeller.

In the presented material research results of marine power station loads in three different ships were characterized: m/v COSCO Long Beach container ship; m/v Skagica chemical tanker and m/v Navion Clipper oil tanker in different so-called operating states.

The determination of electric energy demand for ship is carried out at the unit design stage. The following factors decide above all about the value of electric energy demand (Śmierzchalski 2004; Wojnowski 1992): ship’s type and size as well as type of transported cargo; type and power of main engine as well as type of applied fuel; considered, given unit characteristic of the load condition (ship’s operating state); electrification and automation ship degree; swimming area; crew and passengers amount.

Assuming that all pumps operating the main engine are electrically powered, and the ship has been equipped with air-conditioning installation, an average daily electric load during sea travel at the maximum continuous output of the main engine can be calculated from a model (Wojnowski 1992):

$$ W = 0.020\;N_{w} + 1.6\;Z + 9\sqrt Z + 80 $$
(1)

where:

W :

average daily electric load [kW]

N w :

maximum continuous output on the shaft [kW]

Z :

number of people on board

Observation of energy systems load in three ships was conducted during their work for the following period of time: 86 days for m/v COSCO Long Beach container ship; 85 days for m/v Skagica chemical tanker; 87 days for m/v Navion Clipper oil tanker.

At that time the accepted following operating ships states were recorded: free swimming (sea voyage), travel by the channel, stop in the port (cargo operation), maneuvers (arrival into the port, departure from the port or dock), stop on the anchorage, storming, drifting. The mentioned states refer to all units. For m/v Navion Clipper ship the concept of the operating state—DP load was implemented.

Free swimming (sea voyage)—it is a state (Wojnowski 1992) in which the unit swims through open sea or ocean. This state is characteristic by constancy power load. Most often one generating set is used then.

Travel by the channel—it is the unit travel through limited water region, river or channel. Increased power plant readiness, and additionally generating set is started is required then.

Stop in the port—it is an operating state, during which the ship stays in the port and cargo operation is conducted. Power load and its changeability depends mainly on the unit type as well as period of its stop in the port. The pumps operating the main engine are turned off in container ship at longer stop, relative load is rather small, and one generating set works. Load value in the oil tanker is greater at unload, then energy is needed to drive cargo pumps; two generating sets usually work. At load one is enough.

Stop at the dock—during the research one of the ships stayed in the shipyard; arrival and departure maneuvers from the dock due to cargo character were categorized on graphs to arrival/departure from the port. Stop of ship at the dock is an operating state characterized by low power load, which uses the energy from shipbuilding power lines or its own generating sets.

Maneuvers—it is a state during arrival or departure from the port or dock, characterized by large electric power loads and their changeability caused above all by a use of bow thrusters. A work of few generating sets is necessary.

Storming—a state in which the unit swims through opened sea at not-supporting weather conditions (strong wind, rough sea). During storming, the power station is usually maintained on alert by attaching an additional generating set.

Stop at the anchorage—it is a unit operating condition with a use of an anchor during the stop. Electric power load is usually constant, except of raising or lowering the anchor.

Drifting—a state in which the unit is on an opened sea, and the main engine is turned off or adjustable screw propeller is on zero position. Loads and their character depend on whether the unit use bow thrusters and whether the readiness to start the main engine is maintained.

DP load—a state which refers to the unit working in the dynamic positioning system (DP). Cargo operation on a sea area by the unit storing petroleum is conducted. During cargo operation the main engine (control pitch propeller is on zero position) and three thrusters work. Loads height and their changeable character requires a use of four generating sets (the fifth remains in reserve).

As it is seen from the operating states analysis, electric power loads largely depend on conditions in which the unit works and on the task performed. In some states a demand for electric energy requires independent work of one generating set, in others a parallel work of two or more sets is necessary.

2 Studied Characteristics of the Ships Power Plants

The power plant of m/v Skagica chemical tanker built in 1977 in Germany by shipyard O&K Orenstein & Koppel AG in Luebeck was the first analyzed object. The ship apart from liquid chemicals can transport petroleum products. The unit has 26 cargo tanks with the total capacity of 7,546 m3. During the research the ship transported ethanol on the route Brazil–Cuba–Guatemala–Spain in summer period.

The power plant of m/v Skagica consisted of medium speed four-stroke engine MaK 6MU551AK about power 2,942 kW driving by elastic clutch and reduction gear four-bladed solid propeller. At the main engine speed 425 rpm, the propeller speed amounts 160 rpm. Ship power station has four generating sets consisting of diesel engines Volvo Penta driving by elastic clutches synchronous generators. Two sets consisted of engines about power 207 kW and generators about power 205 kVA; remained two engines about power 247 kW and generators power 279 kVA. In the system an emergency generating set was not installed. In case of black-out, the generating set no 4 is started automatically with an electric starter from the battery (remained sets are started by means of compressed air starters).

The power plant of the m/v COSCO Long Beach container ship, built in 2004 in South Korea by shipyard Hyundai Heavy Industries in Ulsan was a next analyzed object. The ship has eight cargo holds and can transport 7,455 containers, out of which 500 containers can be reefer containers. During marine electric power system load observations the unit swam on the route China–United States in summer period.

The power plant of the container ship created a low speed main engine—Sulzer 12RTA96C about power 68,640 kW directly driving six-bladed solid propeller and power station consisting of four generating sets.

Container ship m/v COSCO Long Beach was adapted to transport 500 reefer containers. By such load state, these containers would constitute the biggest receiver of electric energy about load 3,500 kW. However, such state did not appear, because their number during the research period did not exceed 100.

The second receiver about large electric energy consumption was a bow thruster, placed in the cylindrical tunnel perpendicular to ship’s pivot, about maximum power consumption of 2,500 kW (it required the use of three generating sets). Due to the effectiveness of the bow thruster at small ship speeds, it was used only during unit maneuvers.

Relatively high power of the electric energy was absorbed by electric motors of the following pumps: the main engine lubricating oil pumps—2 × 400 kW; fresh water cooling system pumps—2 × 200 kW; ballast pumps—2 × 110 kW; sea water pumps—2 × 100 kW; steering gear pumps—2 × 160 kW. Two main engine blowers required 370 kW.

The third research object was power plant of m/v Navion Clipper oil tanker, built in 1993 in Japan by shipyard Mitsui Engineering & Shipbuilding in Tamano. Its task is to transport petroleum from drilling rigs and other units storing oil to port terminals. Cargo can be transported in 12 tanks about the total capacity of 82,015 m3. During the research the unit navigation area included North Sea, Atlantic Ocean and Gulf of Mexico in the summer period.

The power plant of the m/v Navion Clipper oil tanker creates a low speed main engine MAN B&W 6S60MC about power 10,590 kW directly driving four-bladed control pitch propeller and power station consisting of five generating sets with four-stroke diesel engines Bergen KRG 8 type about power 1,325 kW each and five synchronous generators about power 1,550 kVA each. Emergency source of electric energy constitutes a set compound of the engine Yanmar 6 HAL-HTH type about power 225 kW and generator about power 250 kVA.

The structure of the marine power plant results from its work character. During ship’s cargo operation at drilling rig, the most important task is to keep it at a specific position, and responsible for that is dynamic positioning (DP2). Three thrusters (two bow thrusters and one stern thruster) are the main elements of DP system. During cargo operation the work of the main engine as well as thrusters is necessary.

The biggest receivers of electric energy are three identical thrusters placed in cylindrical channels, two in bow part, one in aft part of the vessel. Each of thrusters is powered by an electric motor about power 1,100 kW. To other electric energy receivers with considerable power consumption must rank electric motors of the following pumps: ballast pumps—2 × 150 kW; main engine lubricating oil pumps—2 × 75 kW; fire and general service pumps—2 × 75 kW; sea water pumps—3 × 37 kW; LT cooling water pumps—2 × 37 kW.

3 Electric Power Loads Comparison of the Examined Units

The basis for analysis of the marine electric power systems loads in the examined units was its loads registration in all sorts of operating states. Exceptionally laborious work in case of computer loads register lack was used to conduct collation of collective loads for individual configurations of attached electric energy sources (Kijewska and Nicewicz 2004a, b; Kijewska et al. 2006; Matuszak and Nicewicz 2007; Nicewicz 2003). Collations were carried out for all appearing operating states and in the presented material only a collective collation was described for medium loads of the researched ships power station (Fig. 1) and average value of relative loads of the researched ships power stations (Fig. 2).

Fig. 1
figure 1

Setting-up of examined marine electric power plants mean loads

Full size image
Fig. 2
figure 2

Setting-up of examined marine electric power plants relative mean loads

Full size image

From the collation on Fig. 1 follows the obvious information that the ship with the greatest tonnage has a large power plant and its demand for the electric energy is the greatest in each of the appearing operating states.

Collation presented on Fig. 2 is more meaningful. It says that the biggest loads appeared for m/v Navion Clipper oil tanker during maneuvers; and for m/v Skagica chemical tanker a maneuvers period is a time of the smallest loads (it is possible to explain it by the fact that central hydraulic system deals with the drive of the biggest energy receivers).

4 Final Remarks

The presented research, called identification of marine electric power systems loads was conducted on different unit types with transport function in the process of their operation by foreign and national shipping enterprises. Above very modest and trimmed results of the research were quoted. The research was carried out in the years 2002–2007 registering loads of the marine electric power systems in ever typical for the given unit, so-called in shipbuilding, operation states as well as in different climatic-weather conditions. The ships were built in the years 1977–2005. Units were built in shipyards in Bulgaria, China, France, Germany, Japan, Norway, Poland, South Korea, Taiwan and Yugoslavia. A detailed analysis was provided on ships the age of which did not exceed 30 years. 14 ships types include six different size of container ships (7500 TEU–1100 TEU), two types of semi-container ships, 3 types of bulk carriers and one type of general cargo ship, DP2 oil tanker and chemical tanker/tanker.

A detailed database concerning loads of marine electric power systems, which rose as a result of identification research, is used for different purposes. One of them is to estimate emissions by ships in ports, which was carried out in the Mechanical Department of Maritime University in Szczecin as part of the international project realization: BSR InnoShip: Baltic Sea cooperation for reducing ship and port emissions through knowledge and innovation. Knowledge of the actual operational ship’s power station loads, including individual generating sets, in all operating states has a great importance at estimating the exhaust emission by ships. The results of the research were used among others at works (Borkowski et al. 2012; Nicewicz and Tarnapowicz 2012), providing a new view for methodology to determine emissions.