In recent, a number of coastal ferries have high-speed catamaran hull forms, and the waterjet propulsions are widely used for the catamarans for high propulsion efficiency at high forward speeds. Catamarans with large spaces on the deck can transport many passengers and vehicles. And they have good stabilities, compared with mono-hull type vessels. But, passenger ferries should have excellent seakeeping performance for the safe and comfort of passengers on board. So it is required to improve hull form and verify its hydrodynamic performance in order to reduce motions of the catamaran in waves.
In this study, free-running seakeeping tests are performed for a designed high-speed catamaran, and the motion characteristics of the full-scale vessel in actual sea are predicted. Full-scale vessel has the length of 50 meter, and a 1/15 scaled model ship is constructed. Free-running model tests are carried out in a large towing tank and an ocean basin. Irregular waves are generated up to Sea state 4, the wave directions are varied in the range of 0 to 180 degrees with the interval of 45 degrees. Ship speeds are changed between 20 knots to the full-scale maximum speed of 40 knots. A pair of horizontal fixed fins are attached between two hulls for the reduction of pitch motions, the fin effects were confirmed by the model tests.
Running trims of the vessel are changed depending on the fins, so the seakeeping behaviors are analyzed with consideration of ship attitude. RMS values of pitch, roll motions and vertical, lateral accelerations at the bridge are compared with the operating criteria for the fast small vessels or passenger ships.
Motions of a ship in a seaway have great influence on the cargo and persons on board. In particular, motions and acceleration characteristics of ferry are very important factors in comfort of passenger, so should be thoroughly investigated at the design stage for the safe operation.
In this study, a 50 meter high-speed ferry is designed and its seakeeping performances are investigated by free-running model tests.
Tests are performed in multi-directional irregular waves up to Sea state 4, and ship speeds are varied from 20 to 40 knots in full-scale.