Measurements and Simplified Estimation Methods of Ship Waves due to Small Vessel
Shigeaki SHIOTANI*, Nobuyuki FUJITOMI**
Katsuhiko SAITO***, Hiroshi ISHIDA***
*Nagasaki University **Hiroshima College of Mercantile Marine *** Maritime University of Kobe
KEYWORD: characteristics of ship waves, experiments of actual small vessel, simplified estimation of ship waves
ABSTRACT
The information of ship waves generated by a small vessel is very important to prevent damage of marine floating structures. This paper deals with the measurements of ship waves generated by two kinds of actual small vessels and investigates the fundamental characteristics of ship waves due to a small vessel passing near the marine structures. The measurements of ship waves due to two kinds of actual small vessels are described. The measurements of ship waves generated by actual small vessels were carried out in two cases varying the distance from the ship's sailing line and the ship speed. And two simplified estimation methods of ship waves are discussed. Comparing the calculated results of ship waves with the experimental ones, they show reasonably good agreement.
1. INTRODUCTION
In the field of naval architects, many researches on ship waves generated by relatively large ships have been developed and many efforts have been made from the standpoint how to reduce wave resistance for ship hull design1)2). These experimental studies have been restricted to model tests of relatively large ship in the towing tank or the circulating water channel in order to estimate accurately the ship wave resistance3).And, the investigation of the characteristics of ship waves propagated to large distances from a ship almost have not been conducted because of out of interesting target. Also the studies on ship-generated waves by relatively small vessel have not been made satisfactorily.
In the field of fishery, the waves generated by a relatively large ship do not always cause severe conditions to marine floating bodies such as the cage for fishing aqua-culture locating far away from the main navigational waterways. Because the ship waves are reduced largely already. Rather than an advancing large ship in waterways, the waves generated by a small vessel passing freely out of waterways at relatively high speed induce unsatisfactory effects, such as large ship motions of the small boat moored in a fishing port or the damage of the marine floating body adjacent to the sailing line.
This paper deals with the measurements of ship waves generated by two kinds of actual small vessel. The two selected small vessels have the ordinary displacement and the high speed types. The purpose of this study is to investigate the fundamental characteristics of ship waves by actual small vessels and to estimate these waves, in order to prevent damage of small marine floating bodies such as the cage for fishing aqua-culture.
The measured results were compared with the calculated ones by two kinds of simplified estimation method of ship waves. The detailed experimental results are shown with the calculated ones.
2. MEASUREMENTS OF SHIP WAVES
One selected ship is a research ship which is the displacement type of Nagasaki University, her displacement is 40 tonnage, her length is 20m, her breadth is 3.9m, her draft is l.3m, her shaft horse power is 430 SHP and her navigational ship speed is 12 knots. Photo. I shows the displacement boat used for the wave experiment. This ship has been used usually to research the marine biology near the coast in Nagasaki Prefecture. The measurements of ship waves generated by this small vessel were carried out in the Nagasaki Bay. During the wave experiment, the wind were very calm and
