Nowadays, fuel prices are very expensive. Therefore, reducing the fuel costs has become one of the most important concerns for shipowners. There are some methods to lower the fuel costs of a ship. But improving the performance of the main engine is fundamental. On the other hand, a diesel engine has the highest thermal efficiency among the existing power sources. So that, it is the most suitable power source these days when many efforts to save energy are considered. We are now concentrating our efforts to increase this profit. In order to do this, it is useful to list all factors concerned with the thermal efficiency of a diesel engine and to analyse their abilities.
In this paper, we will report the results of our analysis. At first, we estimated the abilities of many factors including thermodynamic cycle problem, combustion rate of a fuel spray, cooling loss, gas exchange process, mechanical efficiency and heat recovery, respectively. And then we consider the total ability of all factors in combination.
In conclusion, we got 60% as the maximum thermal efficiency of a diesel engine. This value can be realized using a diesel engine, a gas turbine and a Rankine cycle engine in combination. And that this value will be realized with the up-to-date technology or through improvements in existing technology. We will make this 60% value as the next target.

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The energy-saving design of the propulsion plant is very important for the improvement of ship's overall performance. IHI developed a diesel engine and steam turbine combined propulsion plant, the Super Economical Shaft Generator system (SSG system), and delivered in April 1981 a ship equipped with the first SSG system having many energy-saving features. Following this, IHI developed the SSG Mark-II system, an improved version of its precedent. The ship mounted with the first SSG Mark-II system put into service satisfactorily. The SSG Mark-II system ingeniously recovers low-temperature waste heat which has been so far lost, increasing the waste heat recovery rate by 30% to 40% compared with the conventional system. As a result, the recovered turbine output from the waste heat reached about 10% of main engine output at NOR.

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As waste heat recovery system of main engines in motor ships, various turbogenerating systems have recently been proposed by shipbuilders and engine builders with practical applications on board. The Mitsui-ATG system, or Mitsui Advanced Turbo-Generating System, has been developed through the introduction of a new concept of “Parallel temperature difference” in an exhaust gas economizer by putting a low pressure steam generator (LPSG) in the system.
In this paper, the Mitsui-ATG system is presented with its concept, flow diagram, distinctive features, performance, the results of the sea trials and the measurements on the running services on board.

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It will be useful to present calculation method of available energy by van der Waals equation. The model of van der Waals gas is important to bind ideal gas change and existence gas change.
On the other hand, a part of available energy of the system is transposed between available energy and unavailable energy by variation of outer-parameter of surroundings. It is a transposition of available energy by variation of surroundings.
This paper describes a calculation method of available energy and transposition of available energy in van der Waals gas.

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A new digital torsion meter has been developed by Akasaka Diesels Ltd. and Ono Sokki Co. The torsion meter was applied in an actual vessel and it was confirmed that the torsion meter of this type was available for practical use.
This paper describes the results obtained by analyzing the marine propulsion power measured in several Diesel ships. The test records show the change of navigating state clearly. By the steady running test under the calm weather condition, the increase of propulsion power due to the secular change of propulsive performance of vessel may be detected within the accuracy of 1 %.

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For reducing the operating cost of ships, the turbo generator is an effective measure for utilizing the waste heat energy contained in the exhaust gas of the main engine, which generates the electrical power required on board the ship.
The parallel operation of the turbo generator and the shaft generator/motor is applied to utilize this waste heat energy of the main engine to the fullest possible extent. By applying this system, the following merits are obtained.
(1) Using the waste heat energy of main engine as much as possible.
(2) Operating the shaft generator/motor as the shaft motor, reduce the fuel consumption of the main engine.
(3) Operating the shaft generator/motor as the shaft generator, compensate for the shortage electrical power.
The energy saving shaft generator/motor control system introduced in this paper is characterized by stepless operation of the shaft generator/motor by means of the steam control valve lift, making it possible to recover the waste heat energy as much as possible.

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In this paper, the following points are discussed for fuel saving.
-It is effective to optimize turbocharger spec., compression ratio and fuel injection timing, and also to provide such measures as fuel injection system of high injection rate, variable injection timing device, turbocharger by-pass system for charging air and non-cooled turbocharger.
-Some considerations on the de-rating are mentioned.
-At slow steaming, reducing number of working turbocharger, changing turbocharger spec. and slow nozzle are typical measures.
-Introduction of exhaust gas by-pass system is successful measures for utilizing the economizerturbogenerator system.
-Some examples of retrofit application to engines in service for fuel saving are given.

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