This paper concerns results of model tests and full scale measurements of the propeller designed for inland ship (749 GT chemical tanker) aiming 3% increase of propulsive efficiency comparing with the present conventional propeller.Three concepts, namely (1) small blade area, (2) decrease of hub-vortex, and (3) consideration of ship wake distribution are applied for the propeller design. NHV (Non Hub-Vortex) propeller, of which the blade area was decreased by 20% from the conventional propeller, was designed and towing tank tests (propeller open test and self propulsion test) and cavitation tests (cavitation observation, paint erosion test, and fluctuating pulse measurement) were carried out with the conventional propeller and the SBA-NHV propeller (Small Blade Area NHV propeller). The model test results showed that the propulsive efficiency of SBA-NHV propeller is about 4% higher than that of the conventional propeller and the risk of cavitation erosion and the fluctuating pressure of both propellers are almost equivalent. Finally, sea trial of 749 GT chemical tanker was performed with the SBA-NHV propeller which was newly manufactured. Results of the sea trials and the service performance demonstrated about 4% deduction of engine output without any problem of the ship vibration and cavitation erosion after 15 months operation.
Although “thickness effect” has long been considered to be a weakening factor with respect to fatigue strength, it is still somewhat unclear as to which factors dominate this effect as well as how it is influenced by different structural or joint types and different loading patterns. Using geometric specimens cut from a steel plate, it was confirmed, both through experimentation and the resulting analysis, that not only the stress concentrations but also the stress gradients at weld toes were the dominant factors relevant to thickness effect. These experimental results were verified by fatigue tests of cruciform-welded joints and out-of-plane gusset-welded joints as well as associated analysis (Yamamoto et al. 2012 ). In addition, the thickness effect in large-scale structural models was investigated through structural model fatigue tests and associated analysis, and it was found that the thickness effect in such large models was quite small in comparison to that observed in fatigue tests of small specimens.
Dynamic-scale model tests of a ship anchor chain were conducted to investigate the oscillation of the anchor chain in a chain locker during anchoring. In the tests, the pay-out velocity of the chain was kept constant for a range of speeds 1.0m/s to 2.5m/s. The lateral oscillation and the tension of the ascending chain were measured. The statistical analysis of test data was carried out. Then,resonance phenomena of the chain caused by increasing the pay-out velocity are discussed theoretically. In addition, the effect of the chain pipe length and the upper room height of the chain locker are also described for the purpose of reducing the oscillation. As the results, it is found that the pay-out velocity of the anchor chain, the breadth of the chain locker, the chain pipe length and the upper room height of the chain locker affect lateral oscillation of a chain in a chain locker.
In late years, a demand for the carbon dioxide discharge reduction from a ship and the reduction of the operation cost has been risen more and more. According to these backgrounds, the authors are grappling with establishment of the frictional resistance reduction technology of the ship by means of the air lubrication methods. In the present paper, we carried out confirmation of the air blow condition with a mock-up examination, examination at the wharf, and the numerical computation for investigation of the valve opening rate when air lubrication method is applied to large shallow water ship. After that, we confirmed the energy saving though sea trial test. When the ship was in a horizontal state we confirmed that air was blown uniformly from each small hole, by means of mock-up examination and full-scale examination by use of actual ship at wharf. In addition, through the wharf examination, we confirmed that air was almost uniformly distributed to each branch piping in heeling condition under adequate valve opening. The analytical result of the distribution of flow rate by use of MelTHERFY almost coincides with the estimated flow rate in the heeling condition. Therefore, this method is effective as an analytical technique. Thereafter, when we used air lubrication system at the speed trial test, we confirm an energy saving effect of 12% at the maximum, and the fuel consumption is reduced at the same time.
In recent years, sizes of container ships have been getting larger and larger. The container ships have large hatch openings in the Strength deck by demand of loading / unloading container cargoes. Due to the large cargo opening, thicker steel plates are applied to the longitudinal strength members in the strength deck structures, such as Hatch side coaming, Strength deck, Sheer strake and Uppermost strake of Longitudinal bulkhead. The thickness of these structural members has become thicker and thicker with the trend of enlargement of the container ships, and nowadays extremely thick steel plates over 50mm (sometimes 70mm, 80mm) become to be used.
