2.15 Impact Loads on the Fore Ship above the
In 1971 the writer worked for Lloyd's Register of
Shipping and was asked to investigate a number of damages to
bow structure above waterline on tankers and bulk carriers -
plastic deformation of plates and stiffeners. It was found
that transient and random impact forces on structure above
waterline, similar to slamming forces on the bottom of the
ship, were to blame. These impact forces increased in number
and amplitude, when the angle between the bow shell and
waterline (flare angle) was reduced and when the shell plate
was flatter (less rounded). The impact pressure, the impact
was produced by compressed air that was trapped between the
water and the hull, could be ten times bigger than a
periodic and hydrodynamic external wave load but of much
shorter duration and over a much smaller area. The high
pressure could cause local plastic deformation of shell
plates and stiffeners. When 'Estonia' listed >34 degrees
to starboard the effective flair angle was almost zero
degree and therefore an impact load could develop sideways,
when that side hit the water surface. The Commission has
never considered that the visor was struck off sideways in
Actually - in retrospect - the following could have
happened. The visor on the 'Estonia' was not well
maintained. The bottom lock was probably not locked
3.7 - it may have been
damaged earlier. Only the side locks were in use.
After the sudden listing at 01.02 hrs the visor was
still attached, but when the angle of list increased, the
side locks and the port deck hinge were damaged, when the
visor was subject to an impact load - high pressure -
sideways at say 01.16 hrs.
However, the starboard deck hinge held and the visor was
still attached to the ship by it, when it sank. The visor
was apparently later removed from the wreck under water
2.16 The Stability of the Estonia' and how the Listing
Chapter 3.7.3 of the Final Report (5) states
that a new trim and stability booklet was developed
and approved by the Bureau Veritas in connection
with the change of flag (January 93) (it is not
included in the supplement of the Final Report).
However chapter 3.6.2 of the Final report states
that only temporary certificates PSSC and LL were
issued in June and September 1994, as another (sic)
new trim and stability booklet was developed. No
correct stability book is included in the Final
Nevertheless - to load a ferry is not difficult
and the stability is seldom critical in part loaded
conditions (and the ship was not fully loaded on
September 27, 1994). Assume that there were 500
tons of fuel aboard in various tanks of the hull, a
couple of hundreds tons of fresh water, 1 000 tons
of cargo (cars, lorries, trailers) on deck 2 (the
car deck) inside the superstructure and 100
tons of passengers and luggage and port trim tank
full, 185 tonnes, to balance (?) heavy cargo on
starboard side. Then the deadweight (dwt) is about
2 200 tonnes and the draft (d) is about 5.1-5.2
meter. Deck 1 below the car deck (deck 2) is then
below the waterline. The car deck, the
bottom of the superstructure, is 2,5 meters
above the waterline: 2.17
for a detailed loading condition. There was also a
stern trim. Full deadweight was >3 000 tons, so
you could have loaded another 800 tons (of fixed
cargo) on the ship (e.g. on the car deck) without
overloading it. Extra fixed cargo on the car deck
would in fact be loaded below the ship's
centre of gravity, G, and would have
increased the stability.
Let's assume that the bow ramp of the
superstructure is open and that water flows into
the superstructure due to forward speed of
the ship and pitching up/down of the bow and that
the water does not flow out through the opening.
Evidently as soon the ship stops all water flows
out again when the ship pitches and trims on the
bow. Note that the hull is undamaged and that the
ship floats normally. The inflowing water is only
extra weight being 'loaded' on the ferry.
The vessel heels about 10 degrees with 600 000
litres of water loaded on deck 2 - figure 2.16.1B.
The water does not flow down to deck 1 as the door
openings are at the centreline and fitted with 20
cms high sills. The water is always trapped on the
side of the sloping deck 2 - or with stern trim it
ends up at the stern, increasing the
With its large beam (B) 'Estonia' had always
good, built in stability. You need about 1 200 tons
of water 'loaded' on the car deck, (deck 2) 7.62
meter above the keel to list the vessel about 20
degrees to starboard. This free water, 1 200 tons,
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) - see figure
2.16.1C above. 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. All water should of course
flow out through the bow opening, when the ship
stops! But we assume that the water does not flow
The more water that is loaded on the car
deck, the more the 'Estonia' lists as all water is
in the side, and at a certain angle of heel, with a
certain amount of water on the car deck, she tips
upside down - CAPSIZE! Then she floats upside
The reason for capsize is that the righting
arm, GZ, becomes 0 at about 34 degrees heel,
figure 2.16.1D, and the vessel then is
unstable. The vessel cannot float on the
undamaged hull with a list 90 degrees, see figure
2.16.1E above, which is an unstable
position. The vessel then capsizes - turns up side
down ... and floats upside down.
However, if the ship stops prior CAPSIZE, all
water flows out again by itself = NO CAPSIZE. Let's
assume capsize takes place.
Why do new
passenger ships suddenly lose stability and roll
(This article is published here
2006 as many Internet users searching about the
subject ends up in chapter 2.16 of my book about
the 'Estonia' stability left).
Recently (2006) anewly built
passenger ship suddenly - in a few seconds without
warning - rolled over >20° in fine weather
and many passengers were hurt losing balance and
being thrown into walls and on decks. All water in
the deck swimming pool flowed out. There was panic.
Then the vessel stabilized itself at abt 15°
angle of list and slowly the vessel became
upright again. Why did this happen?
It has of course happened before! A couple of
years ago (1999) it happened to another
newlybuilt passenger ship at
breakfast time. The ship suddenly rolled over, the
whole breakfast buffet was thrown into the wall and
on the deck and passengers lost balance and were
thrown around. The ship owners quickly blamed the
sudden loll on the rudders (sic)! They had turned
too quickly and the vessel listed.
Do you believe that?
In the latter case the vessel remained
at >15° list even after the rudders were
put back straight. And slowly the vessel became
upright. What actually happened?
The answer why many newly built passenger
ships suddenly rolls over is that they lack
regularly inherent stability or GM. What is GM? It
is very simple.
G is the centre of gravity of all weights
of the vessel and M is a point vertically
above G, through which the buoyancy force of the
vessel underwater hull acts, when the ship is
upright or rolling or listing. Evidently the total
weight of the vessel acting down is the same as the
buoyancy force acting upward (remember Archimedes
328 BC) and the ship floats upright. GM is thus
the positive distance between G and M and a measure
of its intact stability. M is always above G -
otherwise the vessel is not upright. When the
vessel rolls a certain angle, the buoyancy is
shifted a little sideways and a positive righting
lever GZ as a function of GM and the angle of list
develops. It ensures that the buoyancy force of the
intact vessel always uprights the ship at angles of
list up to 50°!
The intact stability represented by GM must be
very good in order for the vessel to survive damage
and flooding of the hull, i.e. two watertight
compartments of the vessel are assumed flooded.
Then the vessel loses buoyancy but still floats.
There are lose liquids inside the hull and point
M for various reasons comes down closer to
G, i.e. GM (and also GZ) are reduced but are still
positive, so that the there is enough stability
also in damaged condition. Evidently there must
also be enough buoyancy, so that the vessel does
Why newly built passenger ships
The reason is simply that the actual intact
GM is too small! And the reason for that is
commercial! The ship owner has simply added extra
cabins and facilities high up in the new vessel to
earn more money. G becomes situated higher
up in the vessel closer to M and GM is
reduced. But GM is still positive and the vessel is
stable and on the outside all appears OK.
Evidently the vessel will not survive the damage
condition (GM then becomes <0) but this is such
an unlikely event so the risk is taken by the
immoral ship owner.
Evidently the ship owner must demonstrate to its
maritime administration that the vessel complies
with the damage stability criteria but it is very
simple to fool the administration with a false
report of G (very few people need, e.g. be bribed).
So on paper all looks OK - vessel's official G is
falsified so that the official GM provides regular
damage and intact stability, even if the actual GM
may only be half the official one!
So what goes wrong then?
G is evidently not constant - it varies
as bunkers and water are consumed or transferred
and when ballast is taken on, etc. Simply speaking
the consumption and transfer of liquids aboard
(often done early in the morning) is similar to a
small damage to the vessel. Liquids are moving
around inside the hull and when this happens M is
affected - it moves down during the transfer of
liquids - and GM and GZ are temporarily reduced. If
the officers in charge of the transfer of liquids
are not informed about the actual G and bases their
calculations on the official, false G (shown in all
official papers), actual GM and GZ may become <0
during such routine transfers. And then the lose
liquids flow to one side, the ship loses its
upright stability condition and rolls over
to a new equilibrium at a certain angle of list.
This is what happened to
the newly built passenger ships quoted
above. When you stop or finish the
transfer of liquids, M moves up again and
the vessel becomes more stable and uprights. It
evidently only happens to newly built
passenger vessels, where all officers are not
informed about the false G. After the first
incident routines are changed to avoid mishaps,
etc, but the false G remains. The only serious
solution is to remove the extra top weight to bring
the vessel into compliance with the rules
but this never happens - the owner will lose plenty
money and the officers aboard will lose their jobs.
Easier to bribe a few civil servants (and some
Many new passenger ships do not comply with all
the rules anyway. If you are a passenger on such
ships, have a look yourself in the lower decks. You
may find watertight doors there and they are
open. But they should not be there at all. The
passenger ferry 'Estonia' is another sad example.
She didn't comply with any essential safety rules
at all ... and sank like a stone due to a small
hull leakage. Read the full story Disasterinvestigation!
But there are many other examples!
(Translation of Swedish text
in figure 2.16.1 above - Water on car deck.
1A. Initial position.
1B. 600 tons of water on the car deck above the heeled
waterline. No water flows down to deck 1.
1C. 1 200 tons of water on the car deck, which is still
above the heeled waterline. 20 degrees list.
1D. 2 000 tons of water on the car deck, now below the
heeled waterline. 34 degrees list. Water on decks 4 and
5. Righting lever GZ=0. The ship turns upside
1E. 90 degrees list at instable capsize. The ship turns
upside down in seconds. Centre of gravity G outside
centre of buoyancy B!
1F. Final condition. Ship floats upside down on the
undamaged, tight hull).
Then the vessel is on its way of turning turtle
with the whole deckhouse flooded, figure
When the 'Estonia' was turning upside down, she
should have floated with the centreline and the
openings on the car deck down to deck 1 three, four
metres above the waterline, figures 2.16.1E and
2.16.3C. Very little water could during that time
flow down to hull spaces below the garage. One
minute later she floats upside down - figures
2.16.1F above and 2.16.3D right below. Strathclyde
University has simulated the above and produced
some video pictures shown right. Figure 2.16.3A
right shows what the water inside the
superstructure would have looked like seen
from the bow.
2.16.3A - Water on the car deck
There are >2 000 tons of water on the car
deck, the list is >40 degrees and the water
reaches the underside of deck 4. Figure 2.16.3B
shows the outside situation. Nobody can walk on any
decks and the condition is completely unstable. A
few moments later the list is 90 degrees - figure
2.16.3C - and soon after - when the deck house is
flooded - the ship floats upside down - figure
2.16.3D. The whole sequence would take a few
minutes. But it never happened to the
The 'Estonia' floats on the
Deck House and the Water does not flow out through
the Bow Opening
2.16.3B - >40 degrees list
The Swedish NMA (director general Jan-Olof
Selén and director of safety at sea Johan
Franson) has commented upon the above in a letter
dated 2000-12-15 reference 0799-0036172 to the
Swedish ministry of Economy (and Transport) -
minister Ms Mona Sahlin:
(Swedish) NMA will underline that, when
calculating damage stability, you are not
permitted to allow for the buoyancy in a
deckhouse unless it is watertight. On ferries
the deckhouse is not
watertight because there are doors which are
easy to open and windows that cannot resist
water pressure. The situation that you from
safety point of view are not permitted to assume
and to calculate with the buoyancy of a
deckhouse, does not exclude that such a bouyancy
actually exists. It exists and therefore the
sequence of events as described by the
Commission is very likely'.
2.16.3C - On the side
The Commission however clearly showed that the deck
house (decks 4-7) was not watertight, because the
Commission stated that the deck house was flooded
with 7 000 ton/min of water in two minutes,
nineteen minutes after the loss of the visor
but twenty minutes before the ship finally
sank, but that this sudden inflow then stopped -
how is not explained - so that the ship floated for
another twenty minutes on a watertight part
of the deck house, and the Swedish NMA
(Franson/Selén) also thinks that there is an
unaccounted buoyancy force in the deck
house, which prevented the 'Estonia' to capsize.
The 'Estonia' was from stability point of view not
really damaged - the water on the car deck was just
'extra', un-fixed cargo being 'loaded' - or loading
itself on the lowest point on the deck 2 inside the
superstructure! Why the un-fixed, lose, extra water
didn't flow out through the bow opening, when the
ship stopped, is a mystery.
2.16.3D - Floating upside down
The 'Estonia' floats upright or upside
down on the Hull
The volume of the hull below the car deck is
about 18 000 m3 in 14 water/airtight compartments
and that air cannot leak out, when the ship is upside down.
As the lightship was only 9 000 tonnes and the dead-weight 2
200 tonnes, there was plenty of buoyancy left inside
the ship (about 13 000 m3 of slightly compressed
air and >4 000 m3 of buoyant material in hull,
superstructure and deckhouse), so that the 'Estonia' should
in the end have floated upside down, if she had capsized
with water in the superstructure on deck 2 - figures 2.16.1F
and 2.16.3D, the latter made by University of Strathclyde.
But she did not do that. She sank at once!
It does not matter if there are errors in the weight
assumptions, i.e. if the ship and the cargo, etc. were
lighter or heavier, or if the stability was better or worse
or the heeling/righting levers were longer or shorter,
because the principal result is
always the same. You need substantial amounts of
water on the car deck in the superstructure to heel
the ship 18 degrees, and you need about 2 000 tonnes of
water on the car deck to heel the ship about 34 degrees,
where it turns turtle in a very short time and floats up
side down. There are many examples of this. Of course, if
there is not sufficient air left inside the hull and the
remaining buoyancy is less than the weight, it sinks at once
with pockets of air inside the hull.
Why didn't the 'Estonia'
Water in the superstructure does not only heel the ferry.
The water also trims the vessel either on the bow or on the
stern. 1 200 - 2000 tons of water inside a superstructure is
a very big, moving weight.
The water always collects at the lowest point on the
car deck, which shifts position, when the ship heels and
trims due to the water.
With 1 200 tonnes of water on deck 2 in the
superstructure (a very large moving weight - as stated!) the
ship trims about one meter either on the stern (1 200 tonnes
water aft - the opening in the superstructure bow moves up
several metres above the waterline and makes further water
entry more difficult - or on the bow (1 200 tonnes forward)
- which means that the deck 2 is almost below the waterline
forward and facilitates water entry with speed forward -
BUT - all water flows out, when the ship stops!
In both cases (assuming no water flows out) you would
expect that the 'Estonia' had turned turtle in a very short
time - as 'Herald of Free Enterprise' outside Zeebrügge
The 'Herald of Free Enterprise' however only ended up on
the side, as the water depth was 12-13 metres where she
capsized, i.e. she never sank below the water surface but
rested on the bottom with the side above water. It went very
fast - all passengers inside cabins of the port side drowned
immediately, all passengers in cabins on the starboard side
- above water - were thrown into the wall, that became a
floor and where they could await beings rescued. Passengers
in the full breadth saloons ended up in water between the
floor and ceiling, where the former starboard side bulkhead
with windows and doors became a new roof high above. They
were caught in a 'swimming pool' with 10 meters high sides!
In the garage all vehicles were pushed to port and smashed
to pieces. There was no - zero - time for evacuation.
Evidently the 'Estonia' did not capsize like the 'Herald of
According to the Final Report (5) it took about 20
minutes for the 'Estonia' to list 90 degrees (at 01.35 hrs)
after a sudden list 15 degrees at 01.15 hrs 1.9.
Then it took another 19 minutes to sink at 01.54 hrs. We
know that this scenario is a falsification based on
manipulated calculations of (a) inflow of water through the
bow opening, (b) stability, angles of heel and amount of
trim and (c) that the water does not flow out when the ship
stops. We also know that the Commission has never explained
how the hull below deck 2 was water filled, so that the ship
would have sunk. The Swedish government desperately asked
its Board of Psychological Defence, SPF, on 19 April 2001 to
prepare one example how the 'Estonia' could have sunk,
without capsizing 1.49
due to 2 000 tons of water inside the superstructure but the
SPF has not been able to do it. The task is of course
impossible. As soon as the ship stops and has not capsized,
all water flows out and the ship is safe!
We know that if the inner ramp was completely open and if
there was 15 knots speed forward, that the vessel would have
turned turtle in a few minutes due to a very large inflow of
water Appendix 4. We know
that that scenario of the Commission is 100% false, because
it never happened. So let's study how a ship normally
If a watertight compartment below deck 1 below the car
deck of the 'Estonia' is flooded (figure 2.16.2) with water,
i.e. the ship hull is leaking, the stability, the
metacentric height GoM, is reduced due to free water
surfaces (loss of inertia to prevent the vessel to list). If
two compartments are flooded (figure 2.16.2B), the
metacentric height is further reduced and there remains only
minimal inherent stability. It means that the ship is still
stable, but that she rolls slower. This is the rule
requirement. Passenger ships, but not cargo ships, shall
survive with two flooded compartments due to leakage.
Passenger ships shall not sink due to leakage!
(Translation of Swedish text
in figure 2.16.2 above - Water below car deck.
2A. Initial position.
2B. Underwater hull damaged. 300 tons of water in one or
two compartments. GoM reduced. 0 degree heel.
2C. 600 tons of water in the ship. Water spreads through
open watertight doors. GoM almost 0. Other compartments
on deck 0 flooded.
2D. Ship has heeled (GoM<0) 15 degrees to a new
equilibrium (GoM>0), where free water surface effects
are smaller. No water on the car deck.
2E. 45 degrees list. Water spreads through open
watertight doors and fills compartments on deck 0. Water
on deck 4 and 5. Stable condition!
2F. 90 degrees list. The ship does not capsize, when
water enters both below and above the car deck. STABLE
If three compartments are partly flooded on deck 0, the
initial stability becomes negative and the passenger ship
may suddenly list 50 degrees assisted by rolling. Because it
is only a certain, small amount of water on deck 0, the ship
will become stable again, when it has listed a certain angle
- figure 2.16.2D, because the free water surfaces are
reduced by the heeling, when the water is pushed up against
e.g. a watertight car deck (deck 2) from below - the
case of the 'Estonia. Open watertight doors are temporarily
'on the dry' and no water spreads. Also the righting lever
(GZ) is positive at larger angles of heel: 2.17
for detailed calculations. When more water flows in, she
That three or more spaces could be flooded on 'Estonia'
during the night of the accident is clear. The watertight
doors between all six watertight compartments on deck 1
forward of the engine room were open. The following probably
First (at about 00.55 hrs) one or two compartments
(including maybe the swimmingpool (11)) on deck 0 were
flooded due to a shell damage caused by, e.g. a collision,
and the vessel was still stable - figure 2.16.2B. Sillaste
was called to assist unless he was already in the engine
room - start the bilge pumps 2.1.
When the water reached deck 1 (at about 00.57 hrs), it
spilled out there (figure 2.16.2C) on the starboard side
(the ship had a small permanent starboard list), which was
observed by many passengers on deck 1, who had just heard
the big crashes due to the collision. The bridge was
alerted. Silver Linde was sent to check! While a large
number of passengers on deck 1 started to evacuate their
cabins and climb to deck 7, some watertight doors on deck 0
were opened by the crew checking what was going on and the
water spread on deck 0. The engine crew was standing in
water to the knees.
The result was that the initial stability (GoM and GZ)
became zero and that the ship listed suddenly to starboard
at 01.02 hrs (figure 2.16.2D). This was noted by all
Then the ship again became temporarily stable
(GZ>0), when the water could not spread through
the watertight doors temporarily in a dry position at the
centreline and when the free surfaces were reduced.
But water continued to flow in - figure 2.16.2E. This
water made the ship temporarily more stable, it uprighted a
little, but the water could soon after spread through the
open watertight doors at centre line and the angle of list
Then the deck house was flooded, so that the ship heeled
more and more - 70 degrees at 01.25 hrs, when the car
deck started to flood aft from above via the ventilators on
deck 4 - and sank 01.32-01.36 hrs. There is a
possibility that the starboard pilot door of the
superstructure 1.16 was
open and that water started to flood the superstructure
(decks 2-3) already at 15 degrees list - see figure 2.16.2D
above through this opening in the side of the superstructure
that then was below water.
The Cause of Sinking - normal Hull
That the ship finally sank (01.36 hrs) and did
not, e.g. tip over up side down, was due to the fact that
there was a damage of the hull below waterline - figure
2.16.2F - and plenty of water (weight) in the hull below
the car deck, which stabilised the ship during the 30
minutes of sinking. All air in the ship below the car deck
and forward of the engine room escaped through the
ventilation system and open watertight doors, while
the angle of heel was less than 90 degrees and the buoyancy
was reduced to <12 000 tons. The engine room was also
flooded, so 'Estonia' could not float on that. Thus she sank
with the stern first.