In marine application the medium speed diesel engine requires gears to adapt its operational speed to the speed with which the propeller performs highest efficiency. There are many configurations of marine gears. They depend on kind and number of engines as well as on the engine room installation. Reverse reduction gears of very different design, single input reduction gears, vertical or horizontal offset or coaxial, twin or multiple input form the main groups of this section of gear designing. The single stage gear unit of today shows very compact design and a high load carrying capacity. This is due to the surface treatment of the tooth flanks by hardening processes. Outstanding experience has been collected with carburised teeth, which have been ground for accuracy achievement. Effective profile modification for the purpose of high bending resistance, protuberance milling to keep the roots of the teeth untouched by the grinding wheel result in utmost resistance against wear and rupture. So the specific loading agreed to by the classification societies are fully justified.
The required accuracy of those gears even at their low circumferential velocity is to compare with the precision of turbine gears manufactured according to BSS 1807. Important are full contact areas between the teeth, this requires careful observation of shaft deflection, bearing clearance, thermal distortions and rigidity of housing, thrust block and foundation in the hull. Another important condition to be observed satisfactory performance of marine gears is the absence of major torsional vibrations producing overload torque or even torque reversal. With diesel engines as power sources excitations of torsional vibrations are very likely to interfere with one or another of the natural ferquencies of the propulsion system. The fundamental connections required to calculate torsional vibration and the rise of torques caused by them are well known. With increasing familiarization of computer technique the calculation procedure has been refined to handle even manifold systems easily and practically reliable.
The necessary over-all-elasticity of the torsional vibrating system thus can be calculated and realised. More and more there are used torsionally elastic couplings to dislocate the natural frequencies to the region of low speed. Good performance showed rubber couplings with metal bonded contact surfaces of special design, which allows a prestressing of the bonded surfaces. Their high torsional elasticity and damping property assures an overcritical operation. At the same time they allow for misalignment without any maintenance trouble. In some cases where it is advisable to avoid the turbulence zone at low speed at all, there are torsional elastic clutches available. They consist of the same elastic rubber elements combined with a clutching device with friction cones and pneumatically operated ring cylinder. Thus, it is possible to engage the whole propulsion system only after having reached the engine service speed. With disengaging and re-engaging the clutch great advantage is obtained during “crashstop”-manouvre, because the time for propeller reversal is much reduced. In any case torsionally elastic clutches are required for twin or multiple engine installations, where they have been applied originally and have proven an ample reputation of reliability. Nowadays, the tedency to install unmanned engine rooms leads to immediate measuring of engine torque : this is relatively easy with highly elastic couplings of linear characteristic, the torsional angles of which are large enough to furnish significant values for the purpose of measurement.
The lecture points out the recent development which has been achieved on the side of Gearing and Couplings adequate to the development of the medium speed diesel engines.

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As for the technics of the electronics for ships in Japan, automatic maneuvering systems and other instruments for ships have been developed as a field of the technical improvement in marine developments. Although the automation and modernization have been made in various directions, their center is “Super automated ships by computor control”.
In recent times the eddy-current coupling has been applied to speed control equipments and buffer equipments of the tortional vibration in marine engines. The generalized formulae by Mr. E. J. Davies are applicable to the construction design in the eddy-current coupling as it is universally known. Nevertheless the equivalent circuits to its physical contents have never been studied enough, and in the speed control system applied to the eddy-current coupling the transfer function showing the relation between the exciting current and the autput torgue has been recognized as the constantK_τ, having no delay time.
In this paper, authors have shown the eddy-current coupling as the simple equivalent circuit, and obtained the relation between the exciting current and the autput torque by the frequency response method. They have also obtained some useful effect that its tranfer function had to be recognized as the delay function, and devised the speed control system, having many excellent merits in efficiency, quick response and dimensions etc.

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