A plan of 30% fuel oil saving, proposed by B&W in 1975, with a low speed propeller driven by a low speed diesel engine through a reduction transmission has strongly excited an interest of people of shipping business and shipbuilding.
Two kinds of transmissions using electromagnetic couplings are respectively proposed as the above transmission. One is a combination of an electromagnetic coupling with a planetary gear, and the other is an electromagnetic gear composed of an electromagnetic coupling with a synchronous motor.
This paper introduces, at first, test results of a 16, 000 ps electromagnetic gear manufactured for trial in case of having the reduction ratio of 7=430/61.4 rpm, in order to compare the case of reduction ratio 7 with that of 4, and secondarily, test results of 600 KW/600 rpm electromagnetic coupling supplied with AC electric power and driven by a 1, 200 KW/ 1, 200 rpm driving machine, in order to confirm a feasibility of the system combined with a gear.
Some noteworthy conclusions base on these tests are as follows:
(a) The favourable reduction ratio of the electromagnetic gear may be between 1 and 4. Therefore, it is suitable to couple the electromagnetic gear with a low speed engine of 100 rpm or so in case of driving a low speed propeller of 50 rpm or so.
(b) An electromagnetic coupling supplied with AC power can be used as a part of a favourable transmission when used with a planetary gear, because it is easy to manufacture a planetary gear of reduction ratio more than 3.

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On the pressure fluctuation caused by shaft vibration in chambers between seal rings of the stern tube sealing, which has a direct influence on the sealing performance, we described its causes and countermeasures in the previous report. In these experiments, we found further-more that, if air remains in chambers between seal rings, pressure fluctuation in these chambers remarkably increases under the influence of the air. We made an experimental study to clarify this phenomenon and obtained the following results.
When air remains in chambers between the seal rings, the air and the oil form a mass-spring vibratory system, as elastic-element and inertia-element, respectively.
Because of this, in some conditions, remaining of, air in chambers between seal rings causes resonance phenomenon and pressure fluctuation increases remarkably, compared with oil replete condition. And these phenomena leads to deterioration of sealing performance.

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The maintenance works for marine engine plants could be classified into inspecting action, preventive-, precautionary-, emergency-maintenances, sweep action and administrating work from the basis of failure reports and maintenance ones. Then the following four indices could be evaluated from about 8300 failure data and 55000 maintenance ones submitted from about 60 diesel ships and turbine ones during about 60×10⁴propelling hours and 11×10⁴ones.
Mean occurring rate of inspecting action, preventive-, precautionary-, and emergency-maintenance were estimated to be in the ratios of 8: 60: 10: 1, mean man-hour per occurrence 1: 1: 2: 7, mean manning index 1: 9: 3: 1, percentage of repair recovery on board 86: 89: 83: 85.

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