Feature 2 | RO-RO TECHNOLOGY Car deck drainage procedures required
Safety concerns persist over car deck drainage in the ro-ro sector, writes Rolf C Imstøl*, Bergen University College, Norway, while doors at the bulkhead deck should not be used for supplementary drainage.
T
he Al Salam Boccaccio 98 disaster, where 1069 passengers and crew lost their lives in February 2006,
highlighted the drainage problems of ro-ro ferries and a number of modifications of SOLAS are now being discussed by IMO in order to improve the situation. Te disaster furthermore indicated that pilot-doors were considered as useable for drainage at a time of peril [1]. (Te sources studied merely state that such use was discussed by ship command. Whether or not any such doors were open, at time of disaster, is unknown.) Te rear ramp of the Estonia-wreck was
found slightly ajar, and drainage by doors at the bulkhead deck was indeed discussed some 10 years ago. The problem was raised again last summer when a scenario, suggesting the pilot door of Estonia might have been used for drainage, was presented at the 9th International Ship Stability Workshop in Hamburg. In fact, the Al Salam Boccaccio 98
disaster was to an extent foreseen by Danish authorities who addressed IMO on the subject in 2005 [2]. Te background for the Danish concern was an incident where a Danish ro-ro vessel nearly capsized due to the presence of a plastic bag during a routine sprinkler test. While naval architects may consider ro-
ro ship designs to be perfectly in accordance with some kind of rule or regulation, this may be considered awkward by others. Officers of the merchant navy may, in particular, be entitled to have other
* Rolf C Imstøl is a master of nautical science and a former merchant officer. He presently holds the position of head of the marine technical department at Bergen University College. He furthermore acts as a nautical and marine technical consultant for solicitors representing many bereaved in the Al Salam Boccaccio 98 as well as the Rocknes cases. He has previously published a set of papers regarding ship disasters where ship stability has been of main concern [7].
36
Al Salam Boccaccio 98. Some 1069 passengers and crew lost their lives in February 2006, highlighting the drainage problems of ro-ro ferries.
expectations since the rules of the road, which they have to learn by heart, are not open to any folly regarding safety at sea. ‘In construing and complying with these Rules due regard shall be had at all dangers of navigation and collision and to any other special circumstances….’[3]. Troughout the previously mentioned
Danish routine sprinkler test, the ship in question was presumably located in calm waters undisturbed by waves. When a ship is actuated by waves, the trapped water is likely to distribute itself over a huge deck area as long as the ship’s behaviour is governed by the ship’s natural roll frequency. Aſter some time, however, the ship may be expected to become thoroughly unstable while the list continues to be zero. Sooner or later the Free Surface Moment (FSM) will overwhelm the wave excitement. Te ship is then likely to roll heavily, by the natural frequency of the FSM, for some periods until it finds its new equilibrium, at one side or the other. Thereafter the ship must be expected to roll by its natural
frequency with some list. Such behaviour of a ship in peril may cause panic and it should consequently be avoided. At present, with scuppers only along
the ship’s sides, the best operational option might be to force the ship to heel when the sprinkler system is started. Such handling should of course be analysed in advance, since it is important that the officers have proper knowledge. Pre-prepared procedures are furthermore likely to improve the ship command’s authority, if it is forced to initiate actions that might cause alarm, at time of peril. The prevailing controversy regarding
the Estonia disaster seems to be due to the fact that the official scenario (Estonia scooped water by way of an open bow ramp) seems physically insupportable. She would, according to known simulations of such scenarios, not sink but capsize and remain afloat buoyed up by the trapped air. A new scenario, suggesting that a pilot- door was opened to drain water from the car deck, was presented last summer. Te
The Naval Architect April 2008
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72