As well known, the screw propeller immersed near the water surface ventilates air through the free surface. This phenomenon itself has been well investigated in the past. However there are few reports which examined the propeller vibratory forces induced by this air ventilation phenomenon. This paper investigates experimentally the propeller bearing forces due to the air ventilation according to the open propeller dynamometer. The experimental results reveal the followings. The manifestation of the air ventilation can be classified into the partial ventilation and the super ventilation. When the former occurs, the bearing forces are induced. The value of the bearing force is influenced by the main factors of immersion depth, slip ratio, and free surface behaviour. As for the slip ratio, the bearing forces are likely to decrease with the decrease of the slip ratio and tend to zero in the region under the critical slip ratio, of which value is 0.3-0.4 for the model screw propellers used in this experiments, where the air ventilation does not occur. It is noticeable that the bearing forces due to the air ventilation are considerably greater than that due to the shear flow of hull wake. Therefore the engineer designing the propeller shaft systems needs to consider the effects of the bearing forces induced by the air ventilation.
The blister which is broken out on sealing rings is the most serious problem to stern tube seals and a study has been carried out to make clear it. Through the investigation and analysis of blisters on sealing rings after the use, the following matters were found; blister is not caused by the defect of material and blister is closely related to the existence of sea water. Then blisters could be successfully broken out in a small test stand and various tests were conducted to examine relations between the blister and test conditions such as temperature, pressure, circumferential speed, environment (existence of water) and shaft eccentricity (repeated stress) . Another tests were also carried out with sealing rings which have the different sectional shape and materials. The generating mechanism of blister was hypothesized and the prevention measures were considered based on the above test results.
In monitoring the oil contents of ballast water being discharged from tankers, sample mixtures extracted from the effluent should be pumped up to oil content meters through the long piping system. Two tankers, existing and newly constructed, are investigated about specifications of the piping systems both for sample mixtures and over board discharge. While, the effects of the specifications on the errors in measuring the oil contents are studied experimentally with a simulating apparatus of the systems. The fluctuations in oil concentration at the outlet of the apparatus rise to 10-200% of the mean concentrations at the inlet especially for highly viscous oils. Measures to reduce the errors being caused by the fluctuations are shown as follows: (1) Increase of the flow velocity through the piping system. (2) Increase of the temperature of the sample mixture. (3) Elimination of stagnant flow, such as that in large strainer, from the system and frequent flushing with fresh water.