Abstract
This study proposes an estimation method for allowable wave heights for ship loading and unloading and evaluation of effective working days, considering moored ship motion that is affected by ship sizes, mooring conditions, and wave periods and directions. The method’s validity was examined with wave field data at pier 8th in Pohang New Harbor. The wave field data, obtained when downtimes had occurred, indicated wave heights of 0.10‒0.75 m and wave periods of 7‒13 s for ship sizes ranging between 800‒35,000 ton in weight. On the other hand, the estimated results for allowable wave heights for ship loading and unloading using this method yielded wave heights of 0.19–0.50 m and wave periods of 8‒12 s for ship sizes of 5,000, 10,000 and 30,000 ton in weight. Thus, this method reproduced well the field data responses of ships of various sizes and at different wave periods. But the allowable wave heights proposed by Korea’s technical standard are did not respond to various the ship sizes and wave periods. And the results of this method tended to decrease in 16–62 percent when have considered long wave, and it is decreased in 0‒46 percent when did not consider long wave than Korea’s technical standards in case of the ship sizes of 5,000‒30,000 ton, wave period of 12 s and wave angle of 75 degree. The allowable wave heights for ship loading and unloading proposed by Korea’s technical standards have indicated that overestimated for ships smaller than 10,000 ton in weight. On the other hand, the percentage rate of effective working days accounting for ship motion at pier 8th in Pohang New Harbor was 6.5 percent less compared to the corresponding results that did not consider ship motion.
Highlights
Korea’s technical standards for ship loading and unloading regulate that the effective working day rate in a harbor is kept over 97.5 percent per year, and that the allowable wave height is under 0.3 m for small ships, 0.5 m for middle and large ships, and 0.7‒1.5 m for mega ships
In the case of a ship with size of 10,000 ton in weight, the allowable wave height for short and long waves varies between 0.22‒0.35 m at a wave period 12 s, whereas the corresponding result when short waves only are considered, varies between 0.33‒0.42 m at a wave period of 12 s
For a ship that weighs 30,000 ton, the corresponding wave height accounting for short and long waves ranges between 0.42‒0.50 m at a wave period of 12 s; but the result accounting for short waves only becomes greater than the technical standard for all wave periods studied
Summary
Korea’s technical standards for ship loading and unloading regulate that the effective working day rate in a harbor is kept over 97.5 percent per year, and that the allowable wave height is under 0.3 m for small ships, 0.5 m for middle and large ships, and 0.7‒1.5 m for mega ships. The allowable wave height refers to the wave height at the front of the berth; when exceeded, the loading and unloading of the ship becomes impossible This wave height is used as a reference value for estimation of the ship’s effective working days in a harbor, and it varies with ship types and sizes, and incident wave conditions. The validity of the estimated allowable wave height was examined through comparisons with actual field data, during loading and unloading downtimes. This estimation method was applied to Pier No 8 at Pohang New Harbor, and was used to compare the effective working days against Korea’s technical standards
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