Abstract : Numerical simulation of maneuvering of "Naniwa-maru" was performed to clarify the maneuver characteristics at wearing and tacking operation. "Naniwa-maru" is a reconstruction of a sailing trader in the 18^th to the mid-19^th century in Japan The rig is simple; single mast with a huge square sail. It is of totally wooden construction in a genuine Japanese manner and weighs 150 tons. The sailing trial was performed in July and August of 1999. The steady sailing performance was measured and compared with the results of the VPP based upon tank tests and wind tunnel studies. The present paper shows first the numerical simulation of her wearing operation, and the results compared with the measured data. The equations of motion dealt with coupled ship motions of surge, sway, roll and yaw. The numerical simulation calculates ship response to the measured rudder angle, and shows the ship trajectory and the sailing state parameters. The calculated results coincided well with the measured data. Then, the numerical simulation of tacking operation was performed in order to investigate the tacking maneuver of this ship. The simulated results showed the difficulty of tacking operation of this ship.

　

　

 "Naniwa-maru" is a reconstruction of a sailing trader that used to ply between Osaka and Edo, today's Tokyo, in the 18^th to the mid-19^th century in Japan. "Naniwa maru" belongs to a type called Higaki-kaisen, and the Higaki-kaisen is a type of the more generic class of vessels named "Bezai-ship". The rig was simple; single mast with a huge square sail. It was of totally wooden construction in a genuine Japanese manner. The sailing trial was performed in July of 1999. The steady sailing performance was measured and compared with the results of the VPP based upon tank tests and wind tunnel studies, which were mentioned in the reference [1]. According to the trial the ship could reach as high as 70 degrees to weather on her track and the speed then was some 30% of the true wind velocity in a fair sailing breeze. She was swiftest on a broad reach, achieving more than 40% of the wind speed. The prediction matched the test results fairly well.

　

 Bezai-ship has a single large square sail and relatively shallow center keel, so that it does not perform as well to windward as modern sailing yachts. Consequently it is believed that Bezai-ship normally have used "wearing operation," instead of "tacking operation" when changing her tack. During the sailing trial period of the Naniwa-maru, several wearing operations were performed and the trajectory and sailing parameters were measured. This report first shows the comparison between these measured data and simulated results. Then, in order to clarify the possibility of tacking operation of this ship, the tacking simulation was also performed using the sail performance obtained by the wind tunnel tests and the numerical calculation by means of the Vortex Lattice Method.

　

2.1 Principal Dimensions in Trial Condition

　

 Principal dimensions of Naniwa-maru in trial condition are shown in Table 1, and the general arrangements are in Figure 1 . Figure 2 shows the lines of this ship. Figure 3 shows the deck arrangement and the diagonal design on the topsides of the ship. This diagonal design is the symbol of the Higaki-Kaisen. "Higaki" is the name of a guild of traders in Osaka in those days, and the word means a diagonal designed fence. Therefore their ship had this design as the symbol. It should be noted that the mast is stepped relatively aft than the midship. Hence, in upwind condition, although the yaw moment generated by the sail tends to leeward around the mast it acts as to windward moment around the center of gravity of the ship. Therefore this ship showed slight tendency of weather helm in upwind sailing. Figure 4 shows the sailing trial condition.

　

Table 1 Principal Dimensions of "Naniwa-maru" in trial condition

　

Length overall:　29.9m

Water line Length on trial (L):　23.0 m

Breadth moulded (Bm):　7.4m

Depth moulded (Dm):　2.4m

Draft (D):　2.1m

Light Weight (hull, sailing rig and rudder):　88 tons

Ballast (blocks and chain, ab.75% loading):　56 tons

Crew, Instruments, etc:　3 tons

Displacement on trial(Δ):　147 tons

Sail Area (SA):　380m²

　

2.2 Data Acquisition System

　

 In order to measure accurate trajectory of the ship, several GPS systems were employed for both the Naniwa-maru and the chase boat. The units were HDGPS units with ±1m accuracy and Kinematic GPS (KGPS) units with ±2cm accuracy. The heading of Naniwa-maru was measured by Moving-Base RTK (MRTK) unit, while that of the chase boat was measured by a TANS Vector unit, both of which are based on the GPS technology. The accuracies of both units have been within one degree. Flux gate compasses were also used as backups.

　

　

　

　

 The chase boat was a 10.1m long overall sailing yacht, always following the ship under power without sail. The chase boat has a fin keel of almost the same draft as the ship, therefore it can be considered that both of two vessels are riding on the same sea current so that current effect is cancelled by taking the difference of the two measurements. Moreover, the chase boat can run without leeway, so that the leeway angle of the Naniwa-maru is obtainable simply by the difference between headings of the two vessels. The attitude angles of Naniwa-maru and their changing rates were measured by an optical-fiber gyroscope. The rudder angle was measured by a system of line and pulleys, and a rotary encoder. The direction and the speed of apparent wind were measured at the masthead of the chase boat and at the top of a six-meter-long pole on the quarterdeck of Naniwa-maru using the conventional combination of a vane and a cup speedometer. The speed-over-water of the chase boat was measured by a paddle wheel sensor.