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Abstract In order to improve the performance of an evacuating system it is important to understand the processes in-volved in both the evacuating system itself as well as factors such as the motion of the ship and the wave climate close to the ship. The objectives of this paper are to study the process of launching evacuation equip-ment from a drifting ship in a seaway and to study the influence of the wave climate and drift on the evacuat-ing process by using experimental model tests. The wave climate close to the ship was examined by meas-uring the waves at different distances from the ship on both the leeward and the windward side for regular waves. The influence of drift on the wave climate was also studied. Model tests of three evacuation systems, a conventional lifeboat, a “fall” system and a chute sys-tem, have been performed. 58503
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The results are compared to previous studies where the ship had no drift. Keywords Evacuation; passenger ship; wave climate; drift; life-boat; chute; model test. Introduction Today most evacuation equipment for passenger ships can only be used safely in calm water. As it is consid-ered too dangerous to perform real exercises in realistic situations at sea, the requirements are only put on func-tional tests in harbours. During the Estonia accident it was evident that a damaged passenger ship in rough weather in cold northern waters easily can lead to catas-trophically losses of lives using today’s standards of equipment. The wave system close to a ship highly influence the possibilities to perform a safe evacuation of a ship. The ship motions affect the launching situation for the evacuating equipment and the relative motion between the wave and the ships hull is a limiting factor for life-boat, chutes and slides. It is therefore important to also investigate the wave climate when examining evacua-tion operations. The relative and absolute amplitudes have been numerically investigated (Ekman 2003), but the complexity of the situation also requires experimen-tal investigations. In Ekman (2004) an experimental study of absolute and relative wave amplitudes is pre-sented and discussed. In the present paper the wave appearance is further discussed and the connection be-tween the wave system and the evacuation operations are discussed. Previous work on evacuation system evaluation using model tests have been reported by Simões and Veitch (2000) and Simões, Veitch and Pelley (2002) for off-shore structures and Werenskiold and Scarpa (2003) for ships. Experimental investigations studying the behavior of evacuation equipment for ships in waves without drift has been performed by Tsychkova and Rutgersson (2001 a,b,c). The objectives of the present tests are to study the ap-pearance of the wave climate around a drifting ship in a seaway and its influence on using evacuating equip-ment. The purpose is also to study the dynamics in the processes involved when launching and operating dif-ferent types of equipment in this environment.
The results from the present tests will be used to create databases to evaluate future evacuation processes. Test Facilities, Models and Model Test Setup The tests were performed in the seakeeping basin at Canal de Experiencias Hidrodinámicas de El Pardo in Madrid, Spain which has dimensions of 150 by 30 by 5 meters. The basin is composed of three main compo-nents, the basin itself, a wave maker and a computerized planar motion carriage. The carriage is able to run in the longitudinal and transversal directions as well as rotat-ing around its vertical axis. However, since the tests presented in this paper investigated the situation when a ship with no forward speed was exposed to beam seas, the model was fixed in surge, yaw and pitch but free to move in heave, sway and roll (Marón, Tsychkova, Ek- man, Prieto, Gutiérrez and Taboada, 2003). The choice of scale factor in the present case was the result of a compromise, which was reached between a sufficient size of the models and the possibility to gen-erate adequate waves in the towing tank. In the present study the scale factor was 30, which was sufficient to make waves with necessary height and period, and to investigate evacuation system behaviour as a whole. “Mother” Ship Model The launching of evacuation equipment is most com-monly discussed when a traditional RoRo ferry needs to be evacuated. Therefore the ship chosen as prototype for the present study was a conventional RoRo ferry with length Lpp=160 m, breadth B=30.4 m and draught T=6.6 m, see Table 1 and Fig. 1. The scale of the ship model was 1:30, i.e. the model had a length of Lpp=5.3 m, breadth B=1.0 m and draught T=0.2 m. Table 1: Specifications of the RoRo ferry. Lpp B T KG GM Roll period 160 m 30.4 m 6.6 m 14.2 m 2.6 m 14.2 s Fig. 1: RoRo ferry of length Lpp=160 m. Models of the Lifeboats and Davit Today four types of lifeboats are in use, namely: open lifeboats, partially enclosed lifeboats, self-righting par-tially enclosed lifeboats and totally enclosed lifeboats. On passenger ships open lifeboats and partially enclosed lifeboats are mainly used. A partially enclosed lifeboat with a capacity of 150 persons, lowered vertically from winches on two cables, was chosen as prototype of the lifeboat system. No specific davit system was modelled, but the con-struction of the davit model provides a possibility to change parameters such as the distance between the lifeboat and the mother ship, launching height, launch-ing speed and acceleration in the parameter ranges nec-essary for this investigation. “On-load” release mecha-nisms have been modelled in the present tests by using electromagnets. The other lifeboat system, which was tested, was a “fall” system. The idea of a “fall” system was conceived (Tsychkova and Rutgersson, 2001c) as an improvement of the lifeboat system. The “fall” system is a compro-mise between the lifeboat/davit system and the tradi-tional free fall system in order to combine positive fea-tures from both systems. β=45°β≈9°”On-load”releaseConventionalpartially enclosedlifeboatShape of totallyenclosed lifeboat,suggested for the“fall” evacuationtxzylzl Fig. 2: Suggested “fall” system. The following modifications of the lifeboat/davit system was suggested in Tsychkova (2001c) (Fig. 2): • change of the lifeboat shape; • specially designed seats for passengers with back support and belts; • possibility to increase the davit arm length; • possibility to increase the launching speed; • use of “on-load” release mechanism; • direct boarding arrangement where the people can embark the lifeboat directly from a protected mus-tering station. The capacity of the “fall” lifeboat is about 20% lower than the capacity of the conventional lifeboat with the same length. Model of the Chute System The chute system is one of the latest contenders in the search for the best method for passenger evacuation and is therefore also investigated in the present study. The main advantages of the chute system are: • low cost; • more space efficient onboard; • one launching device can be used for many life rafts; • the risk for serious accidents is low during training and use in calm environment because only one person at a time is using the chute. The main disadvantages of this system are: • a close position of the platform and the life rafts to the “mother” ship; • large exposure to wind, waves and cold weather; • may be difficult to use for child, elderly and dis-able people; • small possibilities to choose “weather windows”. As a prototype for the chute system a 10m chute with a diameter of about 1 m, a platform fixed to the chute and a life raft was chosen (Fig. 3). The boarding platform and the life raft have a circular form. In full scale the platform and the life raft have a diameter of 6 meter and a capacity of 50 occupants (for more details see Tsychkova and Rutgersson, 2001b). L Life rafts Chute Platform Fig. 3: Chute system (L=10 meter). The chute (Fig. 3) was fixed to the “mother” ship and to the platform. The platform was fixed to the mother ship by elastic bands. The chute was able to change its length by the action of forces from the “mother” ship and the platform, although there were no arrangements to stretch the chute and to prevent deformations of the chute form. The platform was fixed to the mother ship by elastic bands. Arrangements for Wave Measurements The tests were designed so that the wave climate close to the ship model could be analyzed. This was accom-plished by using resistive wave probes to measure abso-lute wave amplitudes and relative amplitudes between the ship and the surrounding wave elevation. In order to measure the relative amplitudes three wave meters were attached to the ship on the windward side (see Fig. 4). One meter was placed approximately amidships (11 meters fore of LOA /2 in full scale), one placed fore (43 meters fore of LOA /2 in full scale) and one meter placed aft (59 meters aft of LOA /2 in full scale). On the leeward side one meter was used to measure relative amplitudes. This meter was placed amidships at the same longitudi-nal position as the meter on the windward side. +