Topic:

THE EFFECT OFCOLLISION ON

VESSELS

APPROVAL PAGE

DEDICATION

TABLE OF CONTENT

APPROVAL PAGE

DEDICATION

TABLE OF CONTENT

ABSTRACT

SECTION ONE

1.0 Introduction1.1 Vessel Collision And Materials1.2 Aims And Objectives1.3 Statement Of Problems1.4 Ship Collision1.5 Collision

SECTION TWO

2.0 Literature Review2.1 Overview2.2 Effect Of Ship Structure And Size On Grounding And

Collision Damage Distributions2.3 Collisions Between Vessels And Marine Animals2.4 Materials And Methods

2.4.1 Study Location And Facilities2.4.2 Hydrodynamic Scaling

2.5 Types Of Collisions2.6 Allision

SECTION THREE

3.0 Collisions Analyses3.1 Examples Of Collisions That Can Be Solved

Analytically3.1.1 Billiards3.1.2 Perfectly Inelastic Collision

3.2 Examples Of Collisions Analyzed Numerically3.2.1 Animal Locomotion

3.3 Collisions Used As An Experimental Tool3.3.1 Space Exploration3.3.2 Mathematical Description Of Molecular

Collisions3.4 Attack By Means Of A Deliberate Collision3.5 Whale-Watching Vessels And Ship Strikes3.6 Fast Ferries And Ship Strikes

SECTION FOUR

4.0 Collision Model4.1 General4.2 Collision Friendly Design

4.2.1 Mono Pile4.2.2 Steel Tripod4.2.3 Jacket4.2.4 Gravity Based Foundation

4.3 Reasons For Collisions4.3.1 Vessel Factors

4.3.1.1 Vessel Speed

4.3.1.2 Type And Size Of Vessel:4.3.1.3 Visibility:

4.4 Cetacean-Related Factors4.4.1 Species Differences4.4.2 Population Differences4.4.3 Swim Speed:4.4.4 Time At The Surface:

4.5 Geographical Factors4.5.1 Hotspots:

SECTION FIVE

5.0 Summary, Conclusion And Recommendation5.1 Summary And Conclusion

5.1.1 Assessing The Extent Of The Collision Problem

5.2 Recommendation

REFERENCES

ABSTRACT

A collision is an event in which two or more bodies

exert forces on each other for a relatively short time.

Although the most common colloquial use of the word

"collision" refers to accidents in which two or more objects

collide, the scientific use of the word "collision" implies

nothing about the magnitude of the forces.

Collisions with vessels (or “ship strikes”) can result

in injury and death in a number of marine vertebrate taxa,

including large whales (Laist et al., 2001; Jensen and

Silber, 2003; Glass et al., 2009), sirenians (i.e., manatees

and dugongs) (U.S. Fish and Wildlife Service, 2001;

Greenland and Limpus, 2006; Lightsey et al., 2006), and

turtles (Hazel and Gyuris, 2006;Hazel et al., 2007).

A collision between an OSV and an offshore installation

is defined as an accidental limit state (ALS) by regulatory

authorities but it is relevant for the maritime sector as

well to documents safety principles. The offshore standards

specify a minimum amount of impact energy that the unit has

to be capable of dissipating without jeopardising the

overall safety, with respect to stability, residual strength

and pollution.

Significance should be given to the percentage of

collisions that don’t come to light, as for each collision

reported, many will go undiscovered. Others may be witnessed

but may still not be reported. However, there are many

things that can be done to improve the current situation and

a major step forward will be the collection of as much

information as possible.

SECTION ONE

6.0 INTRODUCTION

6.1 VESSEL COLLISION AND MATERIALS

Collisions with vessels (or “ship strikes”) can result

in injury and death in a number of marine vertebrate taxa,

including large whales (Laist et al., 2001; Jensen and

Silber, 2003; Glass et al., 2009), sirenians (i.e., manatees

and dugongs) (U.S. Fish and Wildlife Service, 2001;

Greenland and Limpus, 2006; Lightsey et al., 2006), and

turtles (Hazel and Gyuris, 2006;Hazel et al., 2007). All

endangered large whale species are vulnerable to collisions

with ships.

Several reports provided summations of records of ship

strikes, accounting for nearly 300 incidents through 2002

(Laist et al., 2001; Jensen and Silber, 2003) and over 750

incidents through 2007 (Van Waerebeek and Leaper, 2008).

These numbers are certainly minima as many other strikes

likely go undetected or unreported, some collisions do not

leave external evidence of collision, and in the case of

some recovered carcasses, the cause of death could not be

determined (Glass et al., 2009) due, for example, to

advanced decomposition. Observed injuries resulting from

whale/ship collisions can include, for example, broken

bones, hemorrhaging, other evidence of blunt trauma, and

severe propeller cuts (Knowlton and Kraus, 2001; Moore et

al., 2005; Campbell-Malone, 2007); and on occasion a vessel

may arrive in port with a whale carcass pinned to its bow or

riding atop the bulbous bow.

One critically endangered species, the North Atlantic

right whale (Eubalaena glacialis), appears to be more prone,

on a per-capita basis, to vessel collisions than other large

whale species (Vanderlaan and Taggart, 2007) and ship

strikes are considered a significant threat to recovery of

the species (National Marine Fisheries Service, 2005). In a

population estimated to contain only 300–400 individuals,

there were 50 confirmed right whale deaths between 1986 and

2005, 38% of which have been attributed to ship collisions

(Kraus et al., 2005). An average of 2.2 known North Atlantic

right whale deaths and serious injuries from ship strikes

occurred annually between 2003 and 2007 (Glass et al.,

2009). Ocean-going and coastal vessels are increasing in

number, size, and speed to keep pace with waterborne

commercial, industrial, and recreational activities. The

number of commercial vessels engaged in maritime commerce

has tripled in the last 50 years with most of the growth

occurring in the 1970s (Vanderlaan et al., 2007), and

continued growth of global freight transport is projected at

a rate of 4% or more at least thorough 2020 (Corbett and

Winebrake, 2007).

6.2 AIMS AND OBJECTIVES

A collision between an OSV and an offshore installation

is defined as an accidental limit state (ALS) by regulatory

authorities but it is relevant for the maritime sector as

well to documents safety principles. The offshore standards

specify a minimum amount of impact energy that the unit has

to be capable of dissipating without jeopardising the

overall safety, with respect to stability, residual strength

and pollution.

Similar consideration can be done with regards to

dropped object which can represent a possible hazard when

impacting critical areas on a vessel or offshore platform.

6.3 STATEMENT OF PROBLEMS

Evidence is emerging that collisions between vessels

and whales, dolphins and porpoises (cetaceans) may be

happening more frequently than previously suspected and, in

the case of endangered, endemic or geographically-isolated

cetacean populations in particular, may pose a significant

conservation threat. Studies in recent years indicate that,

for populations in certain areas, up to one third of whales

found dead display signs of having died due to a vessel

strike (Laist et al., 2001).

The problem is even more serious for the critically-

endangered North Atlantic right whale1, which has a remnant

population currently estimated at only 300-325 individuals.

In more than half (10/18) of the post-mortem findings for

right whales that died in the northwest Atlantic between

1970 and 2002 indicated that vessel collisions were a

contributing cause of death (in the cases where presumed

cause of death could be determined) (Moore et al. 2004).

These data are likely to grossly underestimate the actual

number of animals struck, as animals struck but not

recovered, or not thoroughly examined, cannot be accounted

for.

Although fatal collisions are the main focus of these

pages, non-fatal collisions - which can also cause serious

injury - are also of concern. These are likely to negatively

affect the viability, both of the affected individual and

also its social group. There have been many reported

sightings of whales and dolphins with deformed dorsal fins

or flukes and/or wounds suggestive of propeller strike,

indicating the scale of this problem, but also suggesting

that cetaceans can and do survive at least some strikes.

However, some of these injuries may ultimately result

in the death of the cetacean even if it is several years

after the collision. In at least one known case, a pregnant,

adult North Atlantic right whale is believed to have died as

a result of an infection from ship strike wounds she

obtained years earlier as a calf (‘Right Whale News’ May

2005).

6.4 SHIP COLLISION

Ship collision is the structural impact between two ships

or one ship and a floating or still object such as an

iceberg. Ship collisions are ONE of particular importance in

marine accidents. Some reasons for the latter are:

The loss of human life.

The environmental impact of oil spills, especially

where large tanker ships are involved.

Financial consequences to local communities close to

the accident.

The financial consequences to shipowners, due to ship

loss or penalties.

Damage to coastal or off-shore infrastructure, for

example collision with bridges.

As sea lanes are getting more congested and ship speeds

higher, there is a good possibility that a ship may

experience an important accident during her lifetime. Higher

speeds may cause larger operational loads, like slamming, or

excessively severe loads, for example during a collision.

Denser sea routes increase the probability of an accident –

in particular a collision – involving ships or ships and

shore or offshore structures.

6.5 COLLISION

A collision is an event in which two or more bodies

exert forces on each other for a relatively short time.

Although the most common colloquial use of the word

"collision" refers to accidents in which two or more objects

collide, the scientific use of the word "collision" implies

nothing about the magnitude of the forces.

Some examples of physical interactions that scientists

would consider collisions:

An insect touches its antenna to the leaf of a plant.

The antenna is said to collide with leaf.

A cat walks delicately through the grass. Each contact

that its paws make with the ground is a collision. Each

brush of its fur against a blade of grass is a

collision.

Some colloquial uses of the word collision are:

automobile collision , two cars colliding with each

other

mid-air collision , two planes colliding with each other

ship collision , two ships colliding with each other

6.6 limitation of study

SECTION TWO

7.0 LITERATURE REVIEW

7.1 OVERVIEW

Collision is short-duration interaction between two

bodies or more than two bodies simultaneously causing change

in motion of bodies involved due to internal forces acted

between them during this. Collisions involve forces (there

is a change in velocity). The magnitude of the velocity

difference at impact is called the closing speed. All

collisions conserve momentum. What distinguishes different

types of collisions is whether they also conserve kinetic

energy. Line of impact – It is the line which is common

normal for surfaces are closest or in contact during impact.

This is the line along which internal force of collision

acts during impact and Newton's coefficient of restitution

is defined only along this line.

Specifically, collisions can either be elastic, meaning

they conserve both momentum and kinetic energy, or inelastic,

meaning they conserve momentum but not kinetic energy. An

inelastic collision is sometimes also called a plastic collision.

A “perfectly inelastic” collision (also called a

"perfectly plastic" collision) is a limiting case of

inelastic collision in which the two bodies stick together

after impact.

The degree to which a collision is elastic or inelastic

is quantified by the coefficient of restitution, a value

that generally ranges between zero and one. A perfectly

elastic collision has a coefficient of restitution of one; a

perfectly inelastic collision has a coefficient of

restitution of zero.

7.2 EFFECT OF SHIP STRUCTURE AND SIZE ON GROUNDING AND

COLLISION DAMAGE DISTRIBUTIONS

It has been argued that a major shortcoming in the

International Maritime Organization (IMO) Interim Guidelines

for Approval of Alternative Methods of Design and

Construction of Oil Tankers in Collision and Grounding is

that grounding and collision damages normalized by the main

dimensions of the ship have the same probability density

distributions regardless of a particular structural design

and ship size.The present paper explores analytical methods

for assessing the overall effect of structural design on the

damage distributions in accidental grounding and collisions.

The results are expressed in simple expressions

involving structural dimensions and the building material of

the ships. The study shows that the density distribution for

collision and grounding damages normalized by the main

dimensions of the ship depends on the size of the ship. A

larger ship has a higher probability of a larger relative

damage length than that of a smaller ship in grounding

damage.

On the other hand, the damages to the side structure

caused by ship collisions are found to be relatively smaller

for large ships. The main conclusion is that the existing

IMO damage distributions will severely underestimate the

grounding damages to the bottom structure of larger vessels

and to a lesser extent overestimate collision damages to the

side structure of the hull.

7.3 COLLISIONS BETWEEN VESSELS AND MARINE ANIMALS

The movement of ships and boats to and from ports may

potentially have some effect on marine life simply by virtue

of their presence. This is particularly the case with high-

speed leisure craft and in marine SACs designated for their

marine mammals. There have been a number of studies on the

effects of vessel movement on marine mammals.

These include the Institute of Zoology’s Marine Mammal

Strandings Project (Jepson personal communication 1998), the

Natural History Museum’s stranded whale recording scheme

(Muir personal communication 1998), the work of the Sea

Mammal Research Unit and Durlston Country Park in Dorset

(Browning personal communication 1998) and studies

undertaken in Cardigan Bay (Evans personal communication

1998) and the Firth of Forth (Reid personal communication

1998).

Research has shown that although a rare occurrence in

UK waters, collisions do occur between marine mammals and

ships/boats operating at speed, which may result in fatal

injuries or wounding. However, quantified information on the

occurrence of these incidents is very limited.

Over the past few years, there have been a limited

number of incidents where dead and stranded marine mammals,

often harbour porpoises, have shown evidence of propeller

damage or massive trauma, indicative of ship collisions. In

Scottish waters there have been recent reports of fatal

collisions between vessels and basking sharks, which are a

protected species under the Wildlife and Countryside Act.

Further collision incidents are known to taken place with

seals, however, there is very little information available

on the occurrence of these events (National Seal Sanctuary

personal communication 1998).

Generally, the risk of collisions with marine mammals

is greater for recreational craft and dolphin-watching boats

and guidelines have been developed for minimising the

disturbance to dolphins and porpoises from these activities.

As one would expect, wherever possible, animals will

avoid contact with moving vessels. However this is not

always the case, for example dolphins and porpoises often

actively seek out moving vessels and swim close alongside in

the bow wave which may make them vulnerable to injury from

collision (A. Muir Natural History Museum personal

communication 1998). Many mariners, including yachtsmen,

regularly report the enthusiasm with which dolphins

accompany their vessels, often for relatively long periods

of time before diving away. For example, bottlenose dolphins

in the Moray Firth readily approach vessels, to bow ride or

to accompany them through the narrows (UK CEED 1993).

Research has been undertaken by the Sea Mammal Research

Unit to establish the distribution of seals around UK

waters. Observations show that seals co-exist with shipping

in many areas around the coast. The presence of fishing

vessels may even provide an additional food source as a

result of the practice of discarding unwanted fish

overboard. It is unlikely that other marine animals will be

affected greatly by vessel movements in the UK.

7.4 MATERIALS AND METHODS

7.4.1 STUDY LOCATION AND FACILITIES

We conducted two series of trials at the experimental

flow tank facilities at the Carderock Division of the Naval

Surface Warfare Center, Bethesda, Maryland (David Taylor

Model Basin). The first set of trials, to determine

interaction effects around the hull while the whale model

was stationary at the surface, were conducted in a towing

basin measuring 15×383×3 m with an electro-hydraulically

driven carriage capable of towing a ship or submarine model

at speeds of up to 12 knots (Stahl 1995).

The second set of trials, to determine effects on a

submerged whale model, were conducted in a circulating water

channel with a test section measuring 18.3×6.7×2.7 m in

which the same vessel model was held stationary and water

and whale model were forced past it. The two basins and the

types of techniques used in this study have been employed

for over 60 years to study vessel flow dynamics and to model

the types of relationships described in this paper.

7.4.2 HYDRODYNAMIC SCALING

We used scaled models of both whale and ship to

approximate real world relationships between the two. Well

established scaling rules for hydrodynamic model testing

have been developed over the past century and a half,

allowing for the prediction of full scale responses based on

model scale experiments (Lewis 1988). The physical basis of

modern ship model experimentation was developed in the mid-

19th century by William Froude (Froude 1888).

Froude's experiments determined that the similarity

criterion for the wave patterns involving a ship and a model

varied with the square root of the linear scale ratio λ. p

where V is ship speed, g is the gravitational constant, and

L is a characteristic length, typically taken as length

between perpendiculars for displacement hull vessels. From

this relation, it follows that time also scales as λ1/2.

Mass is related to volume by Archimedes law, and scales as

λ3 for equivalent fluid densities. Because atmospheric

pressure and fluid characteristics such as viscosity and

surface tension are difficult or impossible to vary in a

model experiment, phenomena that depend on these

characteristics will not scale directly. Most notably,

Reynolds Number, describing the relationship between viscous

and inertial forces in a flow, will not be equivalent

between model and ship scale in a typical Froude scaled

experiment.

In the case of a collision between a ship and a whale,

it can be safely assumed that the viscous aspects of the

encounter are less significant than the kinematic or

inertial, allowing us to neglect the difference between

model and full scale Reynolds Number. Dynamic pressure,

defined as p. ρV2, is the same at ship and model scale when

taken relative to a local reference pressure to remove the

effects of atmospheric pressure.

7.5 TYPES OF COLLISIONS

There are two types of collisions between two bodies -

1) Head on collisions or one-dimensional collisions - where

the velocity of each body just before impact is along the

line of impact, and 2) Non-head on collisions, oblique

collisions or two-dimensional collisions - where the

velocity of each body just before impact is not along the

line of impact.

According to the coefficient of restitution, there are

two special cases of any collision as written below:

1. A perfectly elastic collision is defined as one in

which there is no loss of kinetic energy in the

collision. In reality, any macroscopic collision

between objects will convert some kinetic energy to

internal energy and other forms of energy, so no large-

scale impacts are perfectly elastic. However, some

problems are sufficiently close to perfectly elastic

that they can be approximated as such. In this case,

the coefficient of restitution equals one.

2. An inelastic collision is one in which part of the

kinetic energy is changed to some other form of energy

in the collision. Momentum is conserved in inelastic

collisions (as it is for elastic collisions), but one

cannot track the kinetic energy through the collision

since some of it is converted to other forms of energy.

In this case, coefficient of restitution does not equal

one.

In any type of collision there is a phase when for

a moment colliding bodies have the same velocity along

the line of impact.Then the kinetic energy of bodies

reduces to its minimum during this phase and may be

called a maximum deformation phase for which

momentarily the coefficient of restitution becomes one.

Collisions in ideal gases approach perfectly

elastic collisions, as do scattering interactions of

sub-atomic particles which are deflected by the

electromagnetic force. Some large-scale interactions

like the slingshot type gravitational interactions

between satellites and planets are perfectly elastic.

Collisions between hard spheres may be nearly

elastic, so it is useful to calculate the limiting case

of an elastic collision. The assumption of conservation

of momentum as well as the conservation of kinetic

energy makes possible the calculation of the final

velocities in two-body collisions.

7.6 ALLISION

In maritime law, it is occasionally desirable to

distinguish between the situation of a vessel striking a

moving object, and that of it striking a stationary object.

The word "allision" is then used to mean the striking of a

stationary object, while "collision" is used to mean the

striking of a moving object.

SECTION THREE

8.0 COLLISIONS ANALYSES

8.1 EXAMPLES OF COLLISIONS THAT CAN BE SOLVED

ANALYTICALLY

8.1.1 BILLIARDS

Collisions play an important role in cue sports.

Because the collisions between billiard balls are nearly

elastic, and the balls roll on a surface that produces low

rolling friction, their behavior is often used to illustrate

Newton's laws of motion. After a zero-friction collision of

a moving ball with a stationary one of equal mass, the angle

between the directions of the two balls is 90 degrees. This

is an important fact that professional billiards players

take into account, although it assumes the ball is moving

frictionlessly across the table rather than rolling with

friction. Consider an elastic collision in 2 dimensions of

any 2 masses m1 and m2, with respective initial velocities u1

and u2 where u2 = 0, and final velocities V1 and V2.

Conservation of momentum gives m1u1 = m1V1+ m2V2.

Conservation of energy for an elastic collision gives

(1/2)m1|u1|2 = (1/2)m1|V1|2 + (1/2)m2|V2|2. Now consider the

case m1 = m2: we obtain u1=V1+V2 and |u1|2 = |V1|2+|V2|2. Taking

the dot product of each side of the former equation with

itself, |u1|2 = u1•u1 = |V1|2+|V2|2+2V1•V2. Comparing this with

the latter equation gives V1•V2 = 0, so they are

perpendicular unless V1 is the zero vector (which occurs if

and only if the collision is head-on).

8.1.2 PERFECTLY INELASTIC COLLISION

In a perfectly inelastic collision, i.e., a zero

coefficient of restitution, the colliding particles stick

together. It is necessary to consider conservation of

momentum:

Where v is the final velocity, which is hence given by

The reduction of total kinetic energy is equal to the

total kinetic energy before the collision in a center of

momentum frame with respect to the system of two particles,

because in such a frame the kinetic energy after the

collision is zero. In this frame most of the kinetic energy

before the collision is that of the particle with the

smaller mass. In another frame, in addition to the reduction

of kinetic energy there may be a transfer of kinetic energy

from one particle to the other; the fact that this depends

on the frame shows how relative this is.

With time reversed we have the situation of two objects

pushed away from each other, e.g. shooting a projectile, or

a rocket applying thrust (compare the derivation of the

Tsiolkovsky rocket equation).

8.2 EXAMPLES OF COLLISIONS ANALYZED NUMERICALLY

8.2.1 ANIMAL LOCOMOTION

Collisions of an animal's foot or paw with the

underlying substrate are generally termed ground reaction

forces. These collisions are inelastic, as kinetic energy is

not conserved. An important research topic in prosthetics is

quantifying the forces generated during the foot-ground

collisions associated with both disabled and non-disabled

gait. This quantification typically requires subjects to

walk across a force platform (sometimes called a "force

plate") as well as detailed kinematic and dynamic (sometimes

termed kinetic) analysis.

8.3 COLLISIONS USED AS AN EXPERIMENTAL TOOL

Collisions can be used as an experimental technique to

study material properties of objects and other physical

phenomena.

8.3.1 SPACE EXPLORATION

An object may deliberately be made to crash-land on

another celestial body, to do measurements and send them to

Earth before being destroyed, or to allow instruments else

where to observe the effect. See e.g.:

During Apollo 13, Apollo 14, Apollo 15, Apollo 16 and

Apollo 17, the S-IVB (the rocket's third stage) was

crashed into the Moon in order to perform seismic

measurement used for characterizing the lunar core.

Deep Impact

SMART-1 - European Space Agency satellite

Moon impact probe - ISRO probe

8.3.2 MATHEMATICAL DESCRIPTION OF MOLECULAR

COLLISIONS

Let the linear, angular and internal momenta of a

molecule be given by the set of r variables { pi }. The

state of a molecule may then be described by the range δwi =

δp1δp2δp3 ... δpr. There are many such ranges corresponding

to different states; a specific state may be denoted by the

index i. Two molecules undergoing a collision can thus be

denoted by (i, j) (Such an ordered pair is sometimes known as

a constellation.) It is convenient to suppose that two

molecules exert a negligible effect on each other unless

their centre of gravities approach within a critical

distance b.

A collision therefore begins when the respective

centres of gravity arrive at this critical distance, and is

completed when they again reach this critical distance on

their way apart. Under this model, a collision is completely

described by the matrix , which refers to the

constellation (i, j) before the collision, and the (in

general different) constellation (k, l) after the collision.

This notation is convenient in proving Boltzmann's H-theorem

of statistical mechanics.

8.4 ATTACK BY MEANS OF A DELIBERATE COLLISION

Types of attack by means of a deliberate collision

include:

striking with the body: unarmed striking, punching,

kicking

striking with a weapon, such as a sword, club or axe

ramming with an object or vehicle, e.g.:

o a car deliberately crashing into a building to

break into it

o a battering ram, medieval weapon used for breaking

down large doors, also a modern version is used by

police forces during raids

An attacking collision with a distant object can be

achieved by throwing or launching a projectile.

8.5 WHALE-WATCHING VESSELS AND SHIP STRIKES

Several whale species have been killed or fatally

wounded by whale-watching vessels in the recent past,

including minkes, humpbacks and fin whales, Jensen and

Silber (2004). One example of such a fatality is a minke

that was killed in 1998 when a whale-watch vessel was not

actively watching whales but was in transit, on its way back

to port. The whale surfaced about 14m in front of the

vessel’s bow and plunged down quickly. The vessel lurched

and the whale resurfaced immediately behind the vessel with

a deep bleeding gash believed to be fatal Laist et al.

(2001).

In this incident at least one propeller was damaged.

Cetaceans can also be struck and sometimes severely injured

or killed when the whale-watch vessel is actively whale-

watching. Numerous incidences of collisions between whales

and whale-watching vessels during ‘watching time’ are

documented by Laist et al. (2001) and Jensen and Silber

(2004).

Whale-watching vessels are documented as having caused

injuries to whales on various occasions as a result of

trying to approach too close to the whales. For example, in

1997, a whale-watching vessel attempted to approach a site

where two other boats and four zodiacs were already watching

a humpback whale. The pneumatic, rigid-hulled vessel

subsequently struck the whale when the animal surfaced just

in front of it. The whale then became less active and

appeared injured (Laist et al. 2001).

Other researchers have noted other harmful effects that

whale-watching vessels can have on cetaceans if they do not

follow official guidelines on responsible whale-watching.

For example, Erbe (2002) has documented the potentially

harmful effects of the noise that these vessels produce on

killer whales. The threats posed by marine noise pollution

from vessels and other sources re described in the recently-

updated report Oceans of Noise (available on the WDCS website,

www.wdcs.org).

WDCS has made a series of recommendations on how whale-

watching can be done in a responsible, educational and

exciting way. (See ‘A good whale watch’ under the Whale

Watch section at www.wdcs.org).

8.6 FAST FERRIES AND SHIP STRIKES

A review of worldwide collisions between whales and

fast ferries carried out by Weinrich (2004) noted that out

of 24 collision reports, eleven collisions were with fast

ferries (i.e. travelling at greater than thirty knots).

Laist et al. (2001) also note that the average speed of

vessels operating around whales has increased dramatically

in the past 20 years. High speed ferries were introduced in

the late 1980s.

Since then, their numbers have increased dramatically

and, in 2006, there were over 2000 in use (FFI, 2006).

Weinrich (2004), reviewing earlier reports, notes that the

speed of the vessel may significantly increase the risk of

serious injury or fatality to the whales. The records of

fast ferry whale strikes seem to indicate that many of the

whale species that are struck by other vessels are also

struck by fast ferries. Of the eleven (out of twenty four)

strikes recorded by Weinrich (2004), nine were of fin whales

being struck in the Mediterranean. In November 2005, there

was a joint ACCOBAMS / PELAGOS (www.accobams.org) workshop

on fin whales and collisions. Due to under-reporting of

ferry strike incidents, it is not possible to accurately

gauge the threat to cetacean populations in particular

regions.

However, there are strong concerns for the endangered

humpback population in Hawaiian waters, as reported by

Lammers et al. (2003), who recorded 22 collisions between

vessels and cetaceans between 1975 and 2003. Japanese waters

are another region of concern for collisions between whales

and ferries, not least because strikes are likely under-

reported.

SECTION FOUR

9.0 COLLISION MODEL

9.1 GENERAL

The aspect of collision safety is mostly treated in

connection with the design of tankers. For this type of

vessels, there is an international binding agreement (MARPOL

73/78 Annex I, Directive 13F), which determines the minimum

dimensions of double bottoms and double hulls. Additionally,

the European Union decided to phase out single hull tankers

more quickly to reduce the environmental impact of

collisions with tankers. The state of the art in simulating

collision and grounding events were enhanced by scientific

projects, which were initiated after the spectacular tanker

wreckings of “Exxon Valdez” and “Braer” and set forth e. g.

in connection with the construction of the Great–Belt–

Crossing. In these projects, both, empirical, analytical,

and numerical methods were applied and many experiments were

executed. Several experiments and analyses are described in

Zhang’s dissertation, which also features an extensive

reference list on the field of collision analysis. Between

1995 and 1999 two projects were conducted at Germanischer

Lloyd and Hamburg University of Technology (TUHH) that dealt

with the safety of double hull tankers concerning collision

and grounding. Apart from this, there is a worldwide

interest in the limitation of risks in collisions. An

overview on the actual state can be found in the ICCGS

conference proceedings.

Numerical analysis of ship to OWT-collisions basically

is an extension of the calculation of ship to ship-

collisions. When considering ship bow to ship side

collisions, the bow of the colliding ship can be assumed to

be rigid [3]. Both structures in a ship to OWT collision are

to be considered deformable. Additionally, the interaction

of the support structure and the foundation soil is to be

taken into consideration.

The numerical model for the collision analyses consists

of two main parts:

1. the OWT comprising machinery and support structure

including soil-foundation interaction,

2. The colliding ship including the surrounding water.

Only side impacts of the ship with the OWT were taken

into account due to two reasons. Firstly the ship side is of

lower strength and stiffness and thus more vulnerable

compared to the bow.

Secondly it is more likely that the colliding ship is a

drifting ship and thus ramming the OWT sideways. Motions

(rotations) of the ship around the OWT were not considered.

These are conservative assumptions leading to more severe

damages than in reality.

9.2 COLLISION FRIENDLY DESIGN

9.2.1 MONO PILE

Mono pile foundations exhibit lowest risk in case of

collisions. Only local buckling occurs without rupture of

the ship hull. Much of the impact energy is transformed into

deformation at the mono pile.

9.2.2 STEEL TRIPOD

If a ship hits the diagonal chord and the central joint

of the tripod severe consequences may occur. To minimize

this risk the central joint of a tripod should be located

lower than the maximum draught of a ship that travels

regularly in the area.

9.2.3 JACKET

The work of the collision force can be transformed into

large deformations within the jacket structure as far as the

structure is able to withstand the ship long enough without

being torn off the foundation piles.

Local damage in the model caused by the jacket’s joints

should not lead to widely damaged areas of the ship’s hull.

As the joints were modeled very stiff this condition leads

to higher damage to the ship as it would probably occur in a

real collision.

Although large damaged areas at the ship hull in the

contact zone are unlikely, it is possible that the wind

turbine falls towards the ship, since the damaged jacket

structure acts like a plastic hinge.

9.2.4 GRAVITY BASED FOUNDATION

This foundation type is set onto the soil without piles

or other types of anchors. Horizontal forces have to be

transmitted by friction only. Moments can lead to rotation

of the whole foundation including separation of parts of the

interface between concrete and soil.

Thus a ship impact may lead to failure of the friction

interface and the foundation is pushed away provided the

contact zone is high enough.

Two effects seem to be dominant for gravity based

structures:

1. In case the central column is made of concrete, this

will lead to a more rigid behavior of the support

structure and thus lower the amount of absorbed

collision energy within the first second of contact.

2. Impact energy can be transformed into sliding energy.

The foundation tilts and is pushed away after some

“activation time”.

9.3 REASONS FOR COLLISIONS

There are conflicting studies regarding the response of

certain large whale species to vessels (Baker and Herman,

1989, Peterson, 2001). Researchers have found that some

larger whale species, such as the humpback, bowhead or grey

whale, can detect and change course to avoid a vessel over

relatively large distances, sometimes several kilometres

from the approaching vessel.

Conversely, whales may (consciously or unwittingly)

allow vessels to approach very closely before they react,

particularly when they are feeding or socialising -

behaviours necessary for their survival.

Collisions, self-evidently, happen when either whales

or vessels (or both) fail to detect the other in time to

take avoidance action. Research suggests that there are

several variables which, singly or in combination, may

either make a collision more likely, or may influence

whether a collision is likely to inflict fatal or severe

injuries. These may be broadly divided into vessel-related

factors, cetacean-related factors, and geographical factors.

9.3.1 VESSEL FACTORS

9.3.1.1 VESSEL SPEED

Historically, the first accounts of collisions fatal to

whales began to appear in the late nineteenth century. While

there may be an historical reporting bias, it is worth

considering that, at this time, ships began to reach speeds

of 13-15 knots (24-28 km/hr). For example, one of the

earliest collision accounts, dated 1885, involved a pilot

vessel travelling at around 13 knots.

The number and speed of larger vessels (over 100 gross

tons) registered with Lloyds Register of Shipping increased

rapidly between about 1950-1980, as did the number of

documented ship strikes, and likely, reporting effort.

Currently, there are around 80,000 registered vessels over

100 tons travelling the world’s oceans. Operators are likely

to have less opportunity to detect and try to avoid whales

when travelling at higher speeds. Research on the

probability of sighting an animal during vessel cruises

conducted for the purpose of obtaining cetacean abundance

estimates can be examined. These studies indicate that

whales are more likely to be spotted if the vessel is moving

at a relatively slower speed (Asmutis-Silvia, 1999).

Additionally, the probability of a collision causing fatal

or serious injury to the struck whale obviously becomes more

likely as speed increases. Limited information on

whale/vessel collisions has shown increased severity of the

strike based on speed.

Additionally, Butterworth et al. (1982) tested the

impact of vessel speed and whale detection during a Southern

Hemisphere minke whale cruise. Best (1982) summarized the

Butterworth study stating "The chances of all the animals on

a survey track line being seen (one of the critical

assumptions of line transect theory) are therefore dependent

on the speed of the surveying vehicle and the frequency with

which the whales surface to breathe. Clearly, the faster the

vehicle moves, and the more infrequently the whale surfaces,

the greater the chances that not all of the animals on the

track line will be detected."

9.3.1.2 TYPE AND SIZE OF VESSEL:

Almost all vessel sizes and classes have been involved

in collisions with cetaceans, including cargo ships, ferries

(particularly the newer models of high-speed ferry), cruise

liners, navy ships, recreational vessels, fishing boats,

whale-watch vessels and research vessels. In recent years,

there have also been reports of wet bikes (jet-skis) being

involved in collisions. If not handled with care, these

high-speed watercraft can present a real threat to

cetaceans, since they are extremely fast, highly-

manoeuvrable and also noisy (above the water at least):

these factors can combine to startle and panic cetaceans,

and the frequent changes of direction made by wet bikes

means that cetaceans are often unable to escape.

Non-motorised vessels can also pose a threat. In July,

2005, a sailing vessel reported striking a

criticallyendangered North Atlantic right whale while

transiting the waters off Cape Cod during the night. It is

often assumed that collisions involving sailing vessels are

less likely to be fatal than those involving motorized

vessels. However, there are reports of significant injuries

caused by collisions with racing yachts, which are capable

of reaching speeds of around 30 knots (Laist et al. 2001).

There may be several reasons that smaller vessels

appear to be less of a risk regarding collisions with

cetaceans. First, there may be a reporting bias. In the U.S.

and some other countries, military vessels have an

obligation to report whale collisions. Carrying passenger

vessels, such as commercial whale watch vessels, are also

more likely to report due to the high number of witnesses on

board. However, smaller vessels may not report because they

are unaware of the reporting protocols, or fear fines may be

imposed as a result of reporting. Secondly, smaller vessels

(e.g. <20m), as long as they are not travelling at excessive

speed, generally are:

1. More vulnerable to bad weather and night operation

and are, therefore, more likely to operate in

clear conditions, giving a better chance of

sighting a whale in the vessel’s path;

2. They are closer to the water and have better

visibility all round their vessel - although, for

the same reason, they are unable to see whales at

a distance;

3. As compared to a large ship, they tend to be more

manoeuvrable, may be more likely to be able to

avoid striking a whale or dolphin in their path.

9.3.1.3 VISIBILITY:

By contrast, the sheer size and bulk of the very large

vessels (for example, those over 100m in length) and the

fact that the bridge tends to be towards the back of the

boat, means that visibility close to the bow of the vessel

is more likely to be limited. The long reaction time needed

to change course means that the boat may be unable to avoid

striking a whale – it may, quite literally, be stuck on a

‘collision course’. In 93% of collision accounts examined by

Laist et al. (2001), whales were either not seen beforehand,

or were seen too late to be avoided.

Also, the greater mass of these larger vessels would

absorb much of the impact of a strike, so that a collision

with even quite a sizeable whale might go unnoticed and

unreported. Indeed, as discussed in the case studies

section, for crew-members on the larger ships, the first

indication that their vessel has struck a whale may be when

the ship arrives in port with a whale draped upon its bow.

We already know that the vast majority of reported fatal

collisions are caused by larger vessels, but given this last

point, it is quite likely that a number of collisions with

larger vessels go unreported, as seems likely for smaller

classes of vessels.

9.4 CETACEAN-RELATED FACTORS

Generally speaking, cetaceans are difficult to locate.

They spend the majority of their lives under the surface of

the water giving us only a brief glimpse into their lives.

This makes them a particularly difficult species to observe

and, in this case, avoid.

As a rule of thumb, cetaceans may be more likely to be

hit if they are:

young or sick

slow swimmers

distracted by feeding or mating activities

habituated to vessels (or otherwise fail to sense and

react to vessel approach)

congregated in an area for feeding or breeding (risk

may be density dependent)

9.4.1 SPECIES DIFFERENCES

Whilst there are formal reports of vessel strikes

affecting around a quarter of the 80-plus cetacean species,

the likelihood is that most, if not all, species of cetacean

(particularly in those populations living close to areas of

high vessel density or activity) will be involved in

collisions with vessels at some time, and that incidents may

be under-recorded. The most comprehensive reviews, such as

that conducted by Laist et al. 2001, have tended to focus on

ship strikes involving great whales (the baleen whales, plus

sperm whales), but there also accounts of collisions

involving pilot whales, beaked whales, bottlenose dolphins,

striped dolphins, orcas (killer whales), river dolphins and

harbour porpoises, amongst other species.

Unfortunately, there is no way to account for the

number of animals that are lost at sea, especially those

that are unlikely to float and, therefore, be detected, such

as minke whales. Furthermore, unless a carcass has a

necropsy performed on it the possibility of ship strike as a

cause of death may not be ascertained. In other words, the

body may have suffered internal injuries but there may be no

visible external sign of a strike.

9.4.2 POPULATION DIFFERENCES

Cetaceans are divided into discrete (although often

poorly characterised) biological populations. Some such

populations are known to be genetically distinct. Damage to

a single population thus needs to be seen in the context of

the potential loss of a discrete biological entity as well

as having implications for a wider species unit. Moreover, a

local population of whales is an important component of its

ecosystem and damage to this component may have implications

for other species and habitats.

Pesante et al. (2000) believe that the reproductive

segregation of Mediterranean fin whales from the North

Atlantic stocks, and the small population size of the

Mediterranean fin whales (ca 3,500: Tethys, unpublished)

mean that the level of dead/injured whales (due to

collisions) is a source of concern.

9.4.3 SWIM SPEED:

There are some accounts of whales displaying a ‘last-

second flight response’ prior to being struck by a vessel

and one might expect a threatened animal to try to avoid a

collision by desperately speeding away. For example, the US

Coastguard (1991) reported an incident where two large

whales may have dived to avoid collision but were

subsequently struck by the coastguard vessel.

Collisions occur with those species known for swimming

relatively swiftly, particularly when large ships are

involved. Depending on where the whale is in proximity to

the ship, the hydrodynamic forces may pull the whale toward

the hull, or repel the animal. The issue was recently summed

up as follows in a review of boat harassment: “It might be

assumed that dolphins and other cetaceans can easily outpace

vessels or dive deep underwater to safety.

This notion is predicated on their first perceiving the

presence of the vessel and then acting in good time in an

appropriate manner to avoid it. ...In fact, dolphins cannot

attain the speed of many vessels and have to come to the

surface every few minutes to breathe…” (Simmonds, 2000)

9.4.4 TIME AT THE SURFACE:

The amount of time spent at or near the surface is an

important factor when assessing the probability of an

individual whale or dolphin being struck by a ship. Surface

time may be dictated by prey density such. Studies by

Baumgartner et al. (2003) indicate that the vertical

migration of plankton results in dense patches of copepods

at, or near, the surface at night. Right whales may be more

susceptible to ship strikes at night as a result of spending

more time at, or near, the surface as well as they are less

likely to be detected by passing vessels in the dark.

As already noted, mothers with newborn calves, older

calves and juveniles are obliged to spend a greater

proportion of their time at the surface and so are

particularly vulnerable, as are sick or entangled whales.

Some species, such as the sperm whale, spend a great deal of

time at the surface, resting and socialising, and hence,

although renowned for their lengthy deep dives, sperm whales

may be frequent victims of vessel strike.

9.5 GEOGRAPHICAL FACTORS

9.5.1 HOTSPOTS:

Most collisions occur on the continental shelf,

reflecting high usage by both vessels and cetaceans. Of 58

collision accounts examined by Laist et al. (2001), over 90%

of incidents (53 accounts) occurred either on the

continental shelf or shelf slope. In general, the cetacean

populations which are most frequently-struck are those

living on or near busy vessel routes (particularly shipping

or ferry routes); or where there is an unusual concentration

of vessels in a shallow, confined area.

This is the case for the North Atlantic right whale off

the east coast of the US and for sperm whales in the Canary

Islands (Andre 1998). Calving and nursery areas are

particularly vulnerable.

SECTION FIVE

10.0 SUMMARY, CONCLUSION AND RECOMMENDATION

10.1 SUMMARY AND CONCLUSION

5.1.1 ASSESSING THE EXTENT OF THE COLLISION PROBLEM

Global cooperation and information gathering

Significance should be given to the percentage of

collisions that don’t come to light, as for each collision

reported, many will go undiscovered. Others may be witnessed

but may still not be reported. However, there are many

things that can be done to improve the current situation and

a major step forward will be the collection of as much

information as possible.

Co-operation between all parties involved

In order to make progress, all stakeholders (users of

the marine environment, scientists, conservation non-

governmental organizations and relevant government

departments) must communicate regularly.

Collisions workshops have been held in Europe and the

US to collate available information and to strategise

possible solutions. Many workshops have also been held in

the US to aid in the protection of the North Atlantic right

whale. A workshop should also aim to educate and improve

awareness of the issue, and to assist in the collection and

dissemination of information.

The ‘Co-operation Protocol on the conservation of the

cetaceans of the Canarian Archipelago’ was signed in 2000.

Actions planned under the Protocol include the financing of

studies, the modification of the maritime route and

navigation speed near the areas where the cetaceans are

concentrated, and the development of education and social

awareness campaigns and the training in the field of biology

and ethology of the personnel steering the ships (Econews

2000).

Dedicated studies of cetacean distribution and populations

WDCS considers that the lack of cetacean distribution

and population data available for much of the world to be a

considerable obstacle in the assessment of impacts of

collisions. Detailed studies of cetacean population

distribution and abundance will help to identify general

movements, and particularly, areas of biological

significance to populations. Increased efforts to understand

cetacean ecological and physiological needs will be an

important first step to offering protection from individual

and cumulative potential threats. Prey distribution and

availability is also an important factor.

For example, as mentioned previously, Baumgartner et

al. (2003) show that copepod levels may be denser near the

surface at night due to vertical migration, so, if right

whales feed at night, they may be more susceptible to

strikes at night than previously considered. The location

and the scale of the threat to different cetacean species

will only be realised where basic information on the

population is available. Only in areas where detailed

population studies have been conducted, or where collisions

incidents are regular, have we been able to start to

quantify the significance of a problem to date. In those

areas where a problem has been identified, funding of

independent studies may be supported by industries that wish

to be proactive in finding a solution - and even in those

areas, it is important to remember that carcasses are likely

lost at sea, or not thoroughly necropsied, and what is known

should be considered a minimum estimate of the problem.

10.2 RECOMMENDATION

Dedicated observers

In areas where repeated incidences of collisions with

specific vessel and cetacean types occur, speed restrictions

and trained observers may be useful on board vessels to

alert crew when cetaceans are in the area, in order to help

prevent collisions, although of course the preferred outcome

would be not to operate where cetaceans are in the vicinity.

Training the crew in the identification and biology of the

animals is likely to be valuable but should not be

considered an alternative to using independent, trained

observers.

The Coast Guard in the US requires a specially-trained

marine mammal lookout on all its vessels transiting

designated critical habitats or within 20 nautical miles of

shore (NMFS, 1998). However, while trained observers are

considered to be beneficial, they should not be considered

as a sole mitigation method. Even the most highly trained

observer is limited in their ability to detect whales

depending on environmental conditions and vessel speed.

Legislation and voluntary guidelines

In a few countries, legislative requirements are in

place for the protection of marine mammals. However, it is

often difficult to assess the impacts of incidental

collisions. Legislation is most likely to reflect those

industries whose target is interactions with cetaceans (e.g.

whale watching), rather than those whose interactions are

incidental. Legislation might also be more likely to cater

to the general impacts of shipping, for example the combined

impacts of noise and chemical pollution (including oil

spills) and consideration of collisions is likely to be rare

except in well-documented circumstances where evidence of

repeated collisions exist. Other countries may have

voluntary or legislated guidelines for interactions between

cetaceans and whale watch vessels.

Often there are no procedures for other types of

commercial vessels or recreational vessels, and for

incidental interactions, which are just as likely to be the

cause of a collision. Regional agreements also exist to

protect cetaceans in some areas. Each agreement is specific

to the region, but there is potential to offer protection

from collisions, and also from the cumulative impacts of

collisions, noise pollution from vessels and other threats

that they may face.

REFERENCES

1. Zhang, S: The Mechanics of Ship Collisions. PhD Thesis,

Technical University of Denmark, Department of Naval

Architecture and Offshore Engineering, Lyngby, 1999

2. Kulzep, A; Peschmann, J: Grounding of Double Hull

Tankers [Grundberührung von Doppelhüllentankern], Final

Report of Life Cycle Design, Part D2, Hamburg

University of Technology, 1998

3. Kulzep A, Peschmann, J: Side Collision of Double Hull

Tankers [Seitenkollision von Doppelhüllenschiffen],

Final Report of Life Cycle Design, Part D2A, Hamburg

University of Technology, 1999

4. 2nd International Conference on Collision and Grounding

of Ships, Proceedings, Copenhagen, 2001

5. Institut für Seeverkehrswirtschaft und Logistik :

Statistische Daten zu Schiffsverkehren in Nord- und

Ostsee, Bremen, 2000

6. Le Sourne , H et al.: External Dynamics of Ship-

Submarine Collisions. Preprints of 2nd International

Conference on Collision and Grounding of

Ships,Copenhagen, 2001

7. Germanischer Lloyd: "Richtlinie zur Erstellung von

technischen Risikoanalysen für Offshore-Windparks",

Hamburg, 2002

8. Bundesministerium für Verkehr-, Bau und Wohnungswesen:

Genehmigungsrelevante Richtwerte für Offshore-

Windparks, Bericht einer Arbeitsgruppe, Bonn,

14.03.2004

9. den Boon,H., Just, H., Hansen, P.F., Ravn, E.S.,

Frouws, K., Otto, S., Dalhoff, P., Stein, J., van der

Tak, C., van Rooij, J.: Reduction of Ship Collision

Risks for Offshore Wind Farms – SAFESHIP, EWEC London,

2004

10. Biehl, F., Lehmann, E.: Collisions of Ships and

Offshore Wind Turbines: Calculation and Risk

Evaluation, to be published in: Accompanying Ecological

Research on Offshore Wind Power Generation, Springer

Verlag, 2005

11. ACCOBAMS. ‘Fins’ Newsletter of ACCOBAMS (Agreement

on the Conservation of Cetaceans of the Black Sea,

Mediterranean Sea and Contiguous Atlantic Area). Ship

strike special feature. Vol 3 (1): 12-19, August 2006.

12. ACCOBAMS (cf

http://www.iwcoffice.org/_documents/sci_com/SC58docs/sc

58docs.htm)

13. Andre, M. & Potter, J.R. 2000. Fast-ferry acoustic

and direct physical impact on cetaceans: evidence,

trends and potential mitigation. Proceedings of the

fifth European Conference on Underwater Acoustics.

European Commission Community Research. ISBN92-828-

9531-9.

14. Andre, M. 1998. The conservation status of

cetaceans: A case study in the Canary Islands.

Proceedings of the Morecambe Seminar, Theme II: Key

Scientific Issues.

15. Curry, W., 2004 . Testimony to the Senate

Committee on Commerce, Science and Transportation.

http://www.whoi.edu/institutes/occi/currenttopics/abrup

tclimate_curry_testim.html

16. Dotinga, H.M; Oude Elferink, A.G. 2000. Acoustic

Pollution in the Oceans; The Search for Legal

Standards. Ocean Development and International Law, 31:

151-182 Econews, 2000.

http://www2.ncsu.edu/grad/econ_grad_pgm/econews2000.htm

l

17. Erbe, C. 2002. Underwater noise of whale-watching

boats and potential effects on killer whales (Orcinus

orca), based on an acoustic impact models. Marine

Mammal Science, 18 (2): 394-418. ‘Fast Ferry

International’ magazine, 2006. Available via

http://www.fastferryinfo.com/

18. Félix, F; Waerebeek WV; 2005. Whale mortality from

ship collisions underreported, case studies from

Ecuador and West Africa. Report to the Scientific

Committee of the International Whaling Commission.

SC/57/BC1.