The influence of grounding events on maritime industry.
Varsami, Anastasia Elena ; Popescu, Corina ; Dumitrache, Cosmin Laurentiu 等
Abstract: In the shipping business ships' grounding have
always represented an important topic when talking about accidental
loads due especially due to their impact on the marine environment.
Taking this into consideration, we must also keep in mind that ship
structures include various types of constructions like fast vessels
built of front edge technology materials to very large commercial ships
built according to traditional procedures. Groundings are considered to
be accidental loads and it is clear that the field of ship structures
with respect for accidental loads could focus on highly varying topics.
The purpose of the present paper is to contribute to the understanding
of ship grounding events and how they changed the maritime industry and
their major consequences regarding marine environment pollution.
Key words: ship, grounding, maritime industry, pollution
1. INTRODUCTION
Over the past decades there has been a continuous increase in the
public concern about general risk issues. The consequence of this trend
is that whenever a catastrophic accident occurs and receives the proper
media coverage there is an immediate political and public demand for
actions to prevent the same type of catastrophe in the future.
Examples of this pattern are seen in connection with the grounding
of the Exxon Valdez and the following requirements for double hulls and
in connection with the loss of the Estonia with the following
reformulations of requirements for ferry design and operation.
Many of the past improvements in safety of marine structure have
been triggered by disasters but there is a change in this trend.
The maritime society is beginning, albeit slowly, to think and work
in terms of safety assessment of individual ships instead of the much
generalized prescriptive regulations which have evolved over the past
150 years.
In line of these aspects it is clear that rational procedures for
evaluating the consequences of accidental loads are highly desirable,
not to say necessary.
Accidents like the grounding of Exxon Valdez or Braer or the loss
of both Estonia and Titanic demonstrated the potential seriousness and
fatality of marine accidental loads.
Yet, although the public, the governmental bodies and the
marine society have long recognized the danger of accidental loads,
it has been noticed the need for further work.
A fundamental problem with rational consideration of grounding and
collision in rules is that there are no simple measures of a ships
defense against these loads.
An idea would be to consider the correlation between major design
changes and the amount of oil spilled but the amount of oil spilled
seems to be a random process and this is the main reason for which it is
impossible to draw cause and effect conclusions.
2. CHANGES IN SHIPS' CONSTRUCTION DUE TO GROUNDINGS
Accidents like the grounding of Exxon Valdez or Braer or the loss
of both Estonia and Titanic demonstrated the potential seriousness and
fatality of marine accidental loads. Yet, although the public, the
governmental bodies and the marine society have long recognized the
danger of accidental loads, statistics demonstrate the need for further
work.
A fundamental problem with rational consideration of groundings in
rules is that there are no simple measures of a ships defense against
these loads. An idea would be to consider the statistical correlation
between major design changes and the amount of oil spilled but it has
been noticed that the amount of oil spilled seems to be a random
process. Within a reasonable time span this makes it impossible to draw
cause and effect conclusions from statistics alone and attempts of doing
so would most likely be highly reactionary with questionable
effectiveness.
There is a methodology which takes into account the high level of
uncertainty and randomness of groundings. Inside this methodology there
are three steps to take into consideration:
* Hazard identification, meaning what could go wrong and what are
the consequences. For example this could be oil spill due to grounding
of a tanker in a certain geographic area.
* Scenario identification, meaning what are the steps leading to
the hazard and what is the probability of a given hazard.
* Risk assessment from the two analyses above calculates the
product of consequence and probability.
As an example, the result of the analysis above could be that the
probability of up to 1000 tons of oil spilled along a certain coast line
in one year is 10-3. Now with the risk quantified it would be up to
governments, and international regulatory bodies to set up acceptance
criteria.
Risks cannot be eliminated but it can be reduced to a level
acceptable to society. There are no universally acceptable risks so
decision-makers have to identify levels of risk that are tolerable.
3. WHAT A GROUNDED SHIP MEANS
3.1 Definition of a Grounded Ship
A grounded ship is in a position not intended by her designers,
builders, or operators, and is subject to very different forces and
conditions than when in normal service. The ship is more like a poorly
designed, inadequately protected, and usually inappropriately placed
breakwater than a ship at sea. Part of a grounded ship's weight is
supported by the surrounding water, part by the ground. The portion of
the ship's weight supported by the ground is ground reaction (R),
or tons aground; it is equal to the lost buoyancy. The ground reaction
distribution is uneven and unpredictable. There are four major effects
of ground reaction:
* The loss of buoyancy alters hydrostatic characteristics and hull
girder loading.
* The upward force of ground reaction at the keel causes a virtual
rise in the center of gravity.
* Extremely high local loading with damage or penetration of the
hull can occur, particularly on rocky bottoms.
* Ground reaction holds the ship stationary; she cannot respond to
or fall away from disturbing forces, such as waves, as she does when
afloat.
The conditions of a grounding event are seldom fully defined in the
beginning and often are not completely defined during the salvage
operation. The grounding condition and the environment are the principal
sources of forces on a grounded ship.
Ship's salvage is time-critical because environmental
conditions may improve or worsen with time, but the condition of a
grounded ship steadily deteriorates. The way the ship lays on the ground
and her position relative to the seafloor and coastline influence the
casualty in two ways:
* The way the ship lies on, and is supported by, the ground is a
principal indicator of the effort required to free her.
* Distribution of the ship's weight between residual buoyancy
and ground reaction affects stability and strength.
The ship's position relative to the shore and underwater
features can either intensify or mitigate environmental effects.
Specific considerations are:
* Magnitude and distribution of ground reaction.
* Changes in list and trim caused by the stranding. * The area of
the ship in contact with the bottom.
* Depth of water under and around the ship.
* Channel depth--depth of water between the ship and unobstructed
deep water.
Position and attitude of the ship relative to the ground and the
shore.
3.2 Types of Groundings
An overall view on groundings categorizes the accidents in two
major groups:
* Grounding on soft sea beds, so-called Soft Groundings. The damage
to the hull in terms of crushing at the point of ground contact is
limited but the hull girder may fail in a global mode due to shear force and bending moment exceeding the hull girder capacity.
* Grounding on hard bottoms so-called Hard Groundings. The primary
concern here is the local crushing and tearing of the ship bottom due to
a cutting rock.
Together with analysis of the damage which can develop during
grounding, it is relevant to consider the residual strength and the
stability of the ship in the post-accident condition.
3.3 Salvage of a Grounded Ship
Ships are built for a wide variety of purposes, but all must meet
certain fundamental requirements. They must have reserve buoyancy to
enable them to carry their designed loads and resist damage, stability
to resist environmental forces or damage, and strength to withstand the
stresses imposed on their structure by their own weight, cargo, stores,
and the sea.
There is a basic difference in the way naval architects and salvage
engineers approach the problems of ship stability and strength. Naval
architects, as designers, divide the subject into examinations of intact
and damage conditions. The stability and strength of a proposed design
is examined in normal operating, or intact, conditions, which must, as
matter of course, include free liquid surfaces in tanks. Damage
stability analysis examines a ship design in various hypothetical
conditions of damage that include breaches in the immersed hull.
The salvage engineer on the other hand, deals with damaged
stability and strength, i.e., ships in conditions of known or
identifiable damage that may or may not include breaches in the immersed
hull.
There is a subtle distinction between damage and damaged stability.
A salvage engineer doesn't really deal with damage stability, or
for that matter, with intact stability either. He deals with damaged
stability, and conditions that can reasonably be attained from the
initial damaged condition. While the salvage engineer also examines
hypothetical conditions, those conditions usually have as a point of
departure an initial damaged condition.
4. CONCLUSION
Ships' groundings can have devastating effects on the marine
environment. Cleaning up after a major grounding event could lead to
enormous amounts of money and even then there is no certainty that the
cleaning process has the best results or even the wanted results.
The society needed these kind of events to truly admit that there
is an increased need for safer ships and also for new requirements in
ships' construction so that these kind of unfortunate events would
not be met again in the future in the maritime business. It is not a
good thing that these requirements are triggered only when there is an
appropriate media attention given to these events. This kind of
requirements should first of all come from the shipbuilders and
afterwards from the ship-owners but due to the high costs involved that
arise from these safety measurements it can be easily understood that it
is not in their interest to raise the expenses in the process of
building a ship.
Also, when talking about salvaging a grounded ship, it is first of
all necessary to fully understand the grounded event that lead the ship
into that position so that the best method for salvaging to be applied.
It is an important demand to establish the appropriate method of
salvaging so that the risk of polluting to be reduced at minimum.
5. REFERENCES
Barsan, E. & Muntean, C. (2010). Combined Complex Maritime
Simulation Scenarios for Reducing Maritime Accidents Caused by Human
Error, Proceedings of the WSEAS 3rd International Conference on Maritime
and Naval Science and Engineering, September 3-5, Constanta, ISSN:
1792-4707 88 ISBN: 978-960-474-222-6, pp. 88-93, Published by WSEAS
Press, Constanta
Cahill, R. A. (1985). Strandings and their causes. Fairplay
Publications, ISBN 0905045602, London
Deboveanu, M. (2002). Tratat de manevra navei, Volume 3, Lumina Lex Publisher, ISBN 973-588-564-6, Bucharest
National Research Council, Committee on Tank Vessel Design (1991).
Tanker Spills: Prevention by Design, National Academy of Sciences,
National Academy Press, ISBN 9780-309-04377-9, Washington D.C.
Novac, I. & Chiotoroiu, L. (2004). Teoria navei. Rezistenta la
Inaintare a Navelor, Ex Ponto Publishing House, ISBN 973-644-7,
Constanta
Simonsen, B. C. (1997). Mechanics of Ship Grounding. Technical
University of Denmark, ISBN 87-89502-34-5, Lyngby
