2.16 Stability Assumptions.
The ship was not fully loaded on September 27, 1994. Assume that there were 500 tonnes fuel aboard, a couple of hundreds tons of resh water, 1000 tonnes of cargo (cars, lorries, trailers) and 100 ton passengers and luggage and port trim tank full, 185 tonnes, to balance heavy cargo on starboard side. Then the dead-weight (dwt) is about 2200 tonnes and the draft (d) is about 5.1-5.2 meter. Deck no. 1 below car deck is then below the waterline.
With its large beam (B) 'Estonia' had always good, built in ability. I estimate the metacentric height GoM to be about 2.1 meter, which is confirmed by other people. But see point 4.4. (GoM is a Basure of the 'lever' which together with the ship's displacement ps the vessel upright). 'Estonia' required approximately minimum Mabout 1.8 meter to fulfil the rule requirements of damage stability. ve estimated the lightship weight of 'Estonia's to about 9,000 ton. onia' was a 'two compartment' ship i.e. two watertight partments below the garage could be flooded without the vessel zing or sinking. See also point 5.5.
If water leaks into the car deck (figure 2.16.1), the vessel heels 12° with 600,000 litres on the deck. Fig. 2.16.1B. This water line and fitted with 20 cms high sills. The water is always not flow down to deck no. 1 as the door openings are at the ad on the side of the sloping deck.
You need about 1200 tonnes of water on the car deck 7.62 meter above the keel to list the vessel about 23 to starboard. This water, 1200 tonnes, forms a 2.8 meter high wedge with its base against the starboard side and with a lever about 7.22 meter from centreline, which lists the ship (a fair number of trucks and trailers were parked on the starboard side water filled the space below and beside the trucks and the centre of gravity of the water wedge was pushed inboard). Fig. 2.16.1C. The top of the wedge is many metres from the ship's centreline and almost a meter below the sills of the fire doors, when the ship lists. Some water flows out from the car deck via the existing scuppers. The more water that enters the car deck, the more Estonia' lists, and at a certain angle of heel with a certain amount of water on the car deck she tips upside down (see point 5.5). The reason for this is that the righting arm, GZ, becomes 0 at abt. 34° heel, fig. 2.16.1D, and the vessel then is unstable. The vessel cannot float with list 90°, fig 2.16.1E, which is an unstable position. Then the vessel is on its way of turning turtle with the whole superstructure flooded, fig. 2.16.1F. When 'Estonia's was turning upside down, she should have floated with the centreline (and the openings down to deck 1) three, four metres above the waterline, fig. 2.16.1E. Very little water could during that time flow down to spaces below the garage.
The volume below the car deck is abt. 18,000 m³, and that air cannot leak out when the ship is upside down. As the lightship was only 9000 tonnes and the dead-weight 2200 tonnes, there was plenty of buoyancy left inside the ship (abt. 7000 tonnes), so that the 'Estonia' should in the end have floated up side down, if she had capsized with water in the garage fig. 2.16.1F. But she did not do that. She sank!
It does not matter if there are errors in the weight assumptions, le. if the ship and the cargo, etc. were lighter or heavier, or if the stability was better or worse or the levers were longer or shorter, because the principal result is always the same. You need substantial amounts of water on the car deck to heel the ship 18°, and you need about 2000 tonnes of water on the car deck to heel the ship about 34°, where it turns turtle in minutes and floats up side down (see point 5.5).
Water in the garage does not only heel the vessel. The water also trims the vessel either on the bow or on the stern. The water always collects at the lowest point on the car deck, which shifts position when the ship heels and trims. With 1200 tonnes of water in the garage the ship trims about one meter either on the stern (1200 tonnes water aft the opening in the bow moves up several metres above the waterline and makes further water entry more difficult or on
few minutes the bow (1200 tonnes forward) which means that the car deck almost below the waterline forward and facilitates water entry. In the latter case you would expect that the 'Estonia' had turned turtle in a as Herald of Free Enterprise outside Zeebrügge 1987 (but 'Herald of Free Enterprise' only ended up on the side as the water depth was 8-9 metres where she capsized, i.e. she never sank below the water surface but rested on the bottom with the side above water see point 4.16).
It took about 33 minutes for the 'Estonia' to list to 70° after she had first suddenly listed to 15° (witnessed by several survivors). It means that about one hundred tonnes of water per minute should have leaked into the garage above the waterline during 30 minutes. It seems quite strange. We know that if the inner ramp was completely open and if the ship trimmed on the bow and if there was speed forward, that the vessel would have turned turtle in a few minutes, alternatively if the water ended up in the stern, that the bow opening would have been about 2-3 metres above the waterline and no or little water could get in. My conclusion is that there was no water in the garage.
If a watertight compartment below deck no. 1 below the car deck of 'Estonia' is flooded (figure 2.16.2) with abt. 1000 tonnes of water the stability, the metacentric height GoM, is reduced by 0.8 meter due to free water surfaces (loss of inertia to prevent the vessel to list). If two compartments are flooded (fig. 2.16.2B) the metacentric height is reduced 1.6 metres and there remains only 0.5 meter of GoM. It means that the ship is still stable, but that she rolls slower. This is the rule requirement. Ships shall survive with two flooded compartments.
If three compartments are flooded (>2200 tonnes) the initial stability becomes negative and the ship may suddenly list 50°. But because it is only 2200 tonnes of water in the ship, it becomes stable again, when it has listed a certain angle fig. 2.16.2D, because the free water surfaces are reduced by the heeling, when the water is pushed up against the watertight car deck. Open watertight doors are temporarily on the dry and no water spreads. Also the righting lever (GZ) is positive at larger angles of heel.
the night of the accident is clear. The watertight doors between all six That three or more spaces could be flooded on 'Estonia' during watertight compartments on deck no. 1 forward of the engine room were open. The following probably happened. First (at abt. 00.40) one or two compartments (the sauna (11)) on deck 0 were flooded due to a shell damage, and the vessel was still stable fig. 2.16.2B. When the water reached deck no. 1 (at abt. 00.50) it spilled out there (fig.2.16.2C), which was observed by many passengers on deck no. 1 who complained at the reception, which in turn informed the bridge (00.54) by telephone. SL was sent to check! While a large number of passengers on deck no. 1 started to evacuate their cabins and doors on deck no. 1, and filled other spaces on and below deck climb to deck no. 7, the water spread through open watertight no. 1. The result was that the initial stability (GOM) became zero and that the ship listed to starboard at 01.02 (fig. 2.16.2D). Then the ship became temporarily stable, when the water could not spread through the watertight doors and the free surfaces were reduced. But water continued to flow in fig. 2.16.2E, water could again spread through the open watertight doors and the superstructure was flooded, so that the ship heeled more and more 70° at 01.35 - and sank 01.55. -
-That the ship finally sank (01.55) and did not, e.g. tip over up side down, was due to the fact that there was a hole below waterline fig. 2.16.2F and plenty of water (weight) below the car deck, which stabilised the ship. All air in the ship below the car deck and forward of the engine room escaped through the ventilation system while the angle of heel was less than 90° and the buoyancy was reduced to <12000 tonnes. The engine room was still dry, but its buoyancy was maybe only 5000 tonnes, so 'Estonia' could not float on that. Thus she sank, probably with the bow first.
