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In-depth | DAMAGE STABILITY


by the watch officer of the ship Mariella, which went to the aid of survivors, between 01.30 and 01.36 hrs and proper records were kept. Mr Björkman also cites the information


given by passenger Carl Övberg who was in a cabin on deck 1, marked in yellow (see figure 1 below), it is evidence that water had penetrated the Estonia’s hull. “When the sudden list occurred Carl Övberg escaped using the green path to the stairway, he stopped and turned in the stairwell and saw water flowing out onto deck 1 from an air pipe with a swan neck in the centre corridor.” A possible cause of the shell failure,


according to Mr Björkman, was the shallow swimming pool forward of the sewage room. “Te swimming pool room was insulated at the sides (the outside water was less than10°C six months per year). Te whole space was a rust trap of unbelievable proportions. Pool water oſten flowed out and behind the insulation and corroded the shell plate and frames. “There were also reports that the


sauna space forward of the pool - very oſten heated to 100°C - was frequently flooded, which resulted in wetting the side insulation and corrosion. It is possible that the hull leak sinking the Estonia started in these rusty compartments,” writes Mr Björkman.


SOLAS II-1.15.9.1 An added and very significant factor to the loss of the vessel was that the watertight doors within the hull, which should have been closed, were open. Te Final report (5) does not describe the watertight bulkheads and doors in the hull of the ship; numbers, positions and how they close and open, and how the doors are remotely indicated/controlled,” writes Mr Björkman. “Tis”, he says, “is a serious fault, as it is


very important to know, if the watertight doors/bulkheads are closed and are preventing water to spread, when a ship is sinking”. He goes on to point out that: “If the


watertight doors had been closed, and if Estonia were only leaking into one or two hull compartments, the ship may have listed, but should not have sunk as a result of the leakage (or water on the car deck in


32 The Naval Architect September 2010


the superstructure above the hull).” As any naval architect will accept a


ro-ro ferry with the watertight doors in its hull closed should float even if it capsizes. According to Mr Björkman Estonia should have had an airtight space of around 18,000m3


never know, when a collision will take place, so the watertight doors must be closed (SOLAS II-1.15.9.1).” Furthermore, SOLAS rules state that:


below the waterline which


would have been sufficient for the vessel to float even with one or two damaged compartments in the hull. “Estonia was correctly protected


according to SOLAS rules by 13 watertight bulkheads, which divided the ferry into 12 watertight compartments between the aſt peak and tanks forward and the forepeak tank. Tese are simple rules dating back up to 50 years that govern the design of ro-ro ferries,” explained Mr Björkman. According to the naval architect “the


risk of collision is always there, but in most collisions, about 70%, you only rupture the hull between two bulkheads, i.e. no bulkhead is damaged and only one compartment is flooded. No problem - the ship floats. In more severe collisions, say 29%, you may damage one watertight bulkhead and two compartments are flooded. No problem again - all passenger ships above a certain size are designed to survive with two watertight compartments full of water. If two watertight bulkheads - a fair distance apart - are damaged in one collision - a very rare occurrence (


“the watertight doors in all the bulkheads must be closed at any time at sea. You


“the number of openings in watertight bulkheads shall be reduced to a minimum depending on the design of the ship ...; satisfactory means to close the openings shall be provided’ (SOLAS II-1.15.1). In engine compartments you cannot have more than one door in each bulkhead except in special cases” (not applicable to Estonia). “A normal interpretation of these


regulations is that there are no watertight doors at all in the bulkheads except between engine rooms (for escape and emergency purposes). Watertight doors between passenger


and/or crew spaces in the hull are not permitted. Any passenger or crewmember must


take the stairs up to the bulkhead deck and down again to reach an adjacent compartment,” said Mr Björkman. Estonia did not comply with these rules.


Te engine control room (ECR) on deck 1 was itself fitted with two watertight doors - one leading into the engine room itself, one leading into the passenger accommodation forward. On deck 0 below the ECR the same bulkheads were also fitted with watertight doors. This arrangement contravened the


regulations and should have caused sufficient concern for the authorities in any one of Sweden, Finland or Estonia to revoke the vessel’s licence to operate. A


Figure 2: Estonia’s control panel for watertight doors.


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