International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 5

Number 2

June 2011

261

1 INTRODUCTION

The manoeuvre of ships turning is one of the most

frequently executed port manoeuvres. It is executed

every time during the ships port call. Simultaneous-

ly, it is comparatively little examined manoeuvre.

Place, where the ship’s turning manoeuvres are

executed, is called the turning basin. It can be under-

stood as a two different meanings. First as the

manoeuvring area appointed by the ships, place

needed for a ship to execute turning. Second mean-

ing is the hydro-technical building artificial or natu-

ral with suitable horizontal and vertical dimensions,

where the considerable alterations of the course of

the ship are executed. Shortly, it is the hydro-

technical construction, part of the port waters. Cer-

tainly due to safety, the turning basin as the hydro

technical building always has to be larger in all di-

mensions than the manoeuvre area to avoid the colli-

sion with bottom or bank (Kornacki & Galor 2007).

Figure 1. The ships turning manoeuvre with using of two tug-

boats.

The main parameter describing the turning basin

is a size of the turning basin and size of manoeu-

vring area needed to execute manoeuvre. The influ-

ences on the size of turning basin during the ma-

noeuvre have the large quantity of factors.

The ship’s turning manoeuvres in a practice are

„in the place”. This should be understand as the

changing (alternation) of the ship’s course whose

longitudinal velocities, during the manoeuvre, are

close to zero (Kornacki 2007).

Turning the ship over the place is done on the

turning basin as a result of the planned tactics of

manoeuvring and can be done by the ships itself or

in co-operation with tugs or use of anchors or lines

(springs).

To be able to describe the practical realization of

the manoeuvre in the quantitative way, the factors

and the ways of the assessment of the manoeuvre

will be introduced. The attempt at the exact assess-

ment of manoeuvres will not be undertaken. The

“operator” executing manoeuvre puts the actions to

continuous evaluation of the correctness and the ad-

visability of the next steps during of his work.

The acquaintance of the phenomenon of the in-

stantaneous pivot point is important during execut-

ing the ship’s turning manoeuvres. The existence of

this phenomenon in ship manoeuvring is known to

navigators. The recognizing of the instantaneous

pivot point’s location on a ship during ship’s turning

manoeuvres is causing some problems. It is im-

portant to be well-informed about location.

Ship’s Turning in the Navigational Practice

J. Kornacki

Szczecin Maritime University, Szczecin, Poland

ABSTRACT: The turning-basin is a special part of the port waters area. During every port's call ship need to

be turned. The paper presents the analysis of the ship’s turning in the navigational practice. The paper is based

on the practical experience.

262

In the last part, the assay of the presentation of

the practical view of the realization of the manoeu-

vres of the ship’s turning will be undertaken. The at-

tempt at presenting will be undertaken as the deci-

sion process proceeding and as the decision transfers

on the realization of the manoeuvre.

2 THE ASSESSMENT OF THE SHIPS TURNING

MANOEUVRE

Wanting to evaluate the realization of the manoeu-

vres of the turning, the methodologies of such as-

sessment should be known.

The opinion, that the manoeuvre has to be exe-

cuted effectively and safely, is repeated during the

various conferences and discussion on the subject of

the skill on shiphandling generally and shiphandling

on the simulators. One can show on three elements

which are very essential for the statement the cor-

rectness’s of the realization of the manoeuvre on the

basis of the convention STCW’78 with later correc-

tions and experience from led trainings on the

shiphandling simulator (Artyszuk 2002). The ele-

ments of assessment of such manoeuvres should be

the statement that the manoeuvre was executed:

− safely

− effectively

− according to the principles of the manoeuvring

practice

The assessment basis on this opinion can be pro-

posed as the sum of these elements (Kornacki &

Kozioł 2006):

ZEBO ++≈

(1)

where:

- the assessment of the manoeuvres,

- safety of the manoeuvres,

- effectiveness of the manoeuvres,

- compatibility with the principles of the manoeu-

vring practice.

One can propose the following division the crite-

ria, which will have the influence on the assessment

of the realization of the given element, and in the ef-

fect of the whole manoeuvre.

The element of the safety of the manoeuvre is es-

timated on the basis of following criteria:

− the size of the area of manoeuvring the ship dur-

ing the of executing the manoeuvre,

− appearing the contact with different individual or

navigational obstacle during the of executing the

manoeuvre,

− the energy of the collision with bottom, underwa-

ter slope, bank (it is sometimes admissible such

contact depending on the accepted tactics of the

manoeuvre).

Criteria such as: the size of the manoeuvring area

and the energy of impact (collision) they are applied

in the investigations of Marine Traffic Engineering

to the assessment of safety during port manoeuvres

at present. Can, therefore also use these criteria as

the criteria of the assessment of the skill of manoeu-

vring (Guziewicz & Ślączka 1997).

The element of the realization of the manoeuvre

according to the principles of the manoeuvring prac-

tice should comply following criteria:

− the using of the rudder,

− the using of propulsion,

− the using of maximum sets of propulsion,

− the time of the realization of the manoeuvre,

− the using of the tugboats,

− the using of the anchors,

− the using of the lines.

The element of the effectiveness of the manoeu-

vre is estimated in the moment of the end of ma-

noeuvre on the basis of following criteria:

− final ship’s position on the end of manoeuvre,

− ship’s heading on the end of manoeuvres,

− ship’s speed and yaw velocity on the end of ma-

noeuvres (if it is acceptable for continue with

next manoeuvres),

All of these elements have to be acceptable for

next manoeuvres. Turning manoeuvres are always

between the others.

The element of effectiveness is the assessment of

the last stage of the manoeuvres, when the ship is in

the peaceable area with the aim of the given ma-

noeuvre.

The very reliable criterion for the assessment the

skill is the quantity of given commands in relation to

the last element of the realization of the manoeuvre.

The number of given commands in the reference to

rudder, propulsion, using of the anchors or tugboats

are the objective coefficient acquired the practice of

ship’s manoeuvring. Mostly, the persons manoeu-

vring worst are giving too much commands and so

often and the manoeuvres become less controlled.

The problem of the good manoeuvring practice as

the good seamanship is not simple. The giving of

emotional and incessant commands, often before the

reaching the result of previous is the bad practice.

The regard of the parameter relating pronouncement

of maximum sets is important because of the fact of

the influence of propeller’s streams on the bottom of

the reservoir and quay. However, leaving of the re-

serve of the power during the executing manoeuvres

is the good practice in reference to the principles of

263

manoeuvring, which can turn out indispensable in

emergency situations or sudden influence unforeseen

external conditions.

The assessment of individual elements is execut-

ed in the moment of the end of the manoeuvre.

Taking under considering above mentioned, it

should be added that the assessment of these ele-

ments has to contain their weights.

Analysing the assessment, it can be introduce as

follows (Kornacki & Kozioł 2006):

∑∑∑

===

∗+∗+∗=

111 l

zwewbwO

(2)

where:

- the safety elements’ weight,

- the effectiveness elements’ weight,

- the weight of compatibility with the principles

of the manoeuvring practice,

- the criterions of safety,

- the criterions of effectiveness,

- the criterion of compatibility with the principles

of the manoeuvring practice.

Economical is the additional element which in the

practice will have the influence on the assessment of

every manoeuvre. Also, the manoeuvre has to be op-

timum in relation to economic. For sure, the glaring

abuse of the means will be disqualifying.

Summing up, the problem of the assessment of

the skill of manoeuvring is complex. Executing the

manoeuvre of the turning, the previously suitable

tactics is accepted. During the executing of the ma-

noeuvre of the turning and on the end, the manoeu-

vre is the subject to the assessment by performers on

every stage to improve possible mistakes.

3 PIVOT POINT IN SHIP MANOEUVRING

The acquaintance of the phenomenon of the instan-

taneous pivot point is important during executing the

manoeuvres of the ship’s turning. This phenomenon

existence in ship manoeuvring is well known to nav-

igators. The recognizing of location of the instanta-

neous pivot point on a ship during various manoeu-

vres is causing problems for them. For a ship’s

operator is easier to control just a single motion and

practical role of instantaneous pivot point increase.

The navigators are familiar with apply the pivot

point principles while making various kinds of ma-

noeuvres, either at high or at low forward speed.

This is the essence of the kinematics of the turn

of the ship that certain lateral velocity of the ship’s

centre of gravity always accompanies the angular

velocity. It is directed in the external board in the re-

lation to the centre of the circulation. During the

turn, local lateral velocities on the stern and the bow

of the ship are different from this existing in the cen-

tre of gravity. The lateral speed is larger on the stern,

on the bow meanwhile smaller. It results from this,

that on the stern the local lateral velocity coming

from the rotational movement adds to the fine lateral

movement, while it is on the bow inversely. The

point in which the local lateral velocities reduce to

zero is the instantaneous pivot point. The complex

movement of the ship, being in the generality con-

nection of three movements i.e. longitudinal, lateral

and rotational movements in relation to the centre of

gravity can replace with two movements consisting

from the longitudinal and rotational movement in re-

lation to the instantaneous pivot point.

At high speed applying the stern rudder will in-

volve the rudder lateral force as developed on a con-

stant arm. The ship’s lateral motion strongly corre-

lated with simultaneous turning is generated,

consequently the instantaneous pivot point, in cer-

tain time, lies somewhere close to the bow and usu-

ally changes but in a rather narrow limit. Practically,

the pivot point can be considered steady location.

3.1 The position of instantaneous pivot point

It is well known from rigid body mechanics that in-

stantaneous arbitrary ship planar motions can be

uniquely decomposed into a combination of transla-

tional motion of the point of origin and angular mo-

tion of the whole body around this origin. Both mo-

tions are defined by the linear velocity vector of the

origin and the angular velocity vector. Such an in-

stantaneous state of motion is equivalent to a sole

angular motion around the instantaneous pivot point.

The pivot point is a point on the body or can be even

outside the body physical extents, in which the linear

velocity disappears. The pivot point position instan-

taneously changes because of the ships linear and

angular velocities are time dependent.

The position of instantaneous pivot point refer-

ence to the centre of gravity or amidships is quali-

fied exact kinematic dependence (Artyszuk 2009):

−

and

(3)

or non-dimensionally - divided by ship’s length L:

264

−

and

(4)

where:

- the longitudinal coordinate of pivot point,

- the longitudinal non-dimensional coordinate

of pivot point,

- the lateral coordinate of pivot point,

- the lateral non-dimensional coordinate of

pivot point,

- the longitudinal velocity,

- the lateral velocity,

- the angular velocity,

- the length of the ship.

The dimensionless values relating to any linear

dimension of the ship is much more useful also in

the shiphandling practice. The tips are universal for

any ship size and ship visual positioning against ex-

ternal objects is also easier in relative units.

The instantaneous pivot point lies mostly oppo-

site the side of the place of applying steering forces.

During manoeuvres with the stern rudder or as a re-

sult of the lateral effect of the propeller during active

stopping the ship, it is placed to the bow from amid-

ships. The position of instantaneous pivot point is

more-less steady for the given individual ship, alt-

hough it is able to change in certain borders. The po-

sition of the instantaneous pivot point is comprises

in range of 0.3 ÷ 0.5 L counted from amidships (or 0

÷ 0.2 L counted from bow). Often, the literature tells

about average values of this position for the ships in

range of 0.25 ÷ 0.3 L counted from a bow, it should

be treat rather for orientation and the current values

should be accepted according to the parameters of

the circulation settled e.g. (Artyszuk 2009).

Figure 2. The ship with lateral force generating turn.

Often, it is very convenient for a short prediction

period, as dominating in shiphandling practice, to

disregard the lateral non-dimensional coordinate of

pivot point and, instead of, to rotate a ship around

the pivot point projected on the ship’s centre line to-

gether with its simultaneous translation in the direc-

tion of heading according to the forward speed.

It is two other aspects of position of instantaneous

pivot point. First is a position of it during turning of

the ship in spot. Second is position of it during

astern movement.

3.2 The position of instantaneous pivot point during

ship turning in spot

Typical situation of ship turning at spot is while the

longitudinal velocity is nearly zero, the instantane-

ous pivot point is located on the ship’s centre line

and the constant yaw velocity is requested. This kind

of manoeuvres happens in turning basins.

To realize turning a ship at spot, the following

steady phase motion equations shall be (Artyszuk

2010):

( ) ( )

( )











=+=+

=++=

2211

zHz

yHy

zymx

vmcmF

(5)

where:

- virtual masses [kg], [kg], [kg m

- surge, sway and yaw velocity [m/s],

[m/s], [1/s],

- external total surge, sway forces and

yaw moment [N], [N], [Nm],

The ship with all elements important during ships turn

PP – pivot point

G – centre of gravity

M – amidships, geometrical centre of the ship

– the angular velocity

265

- hull sway forces and hull yaw moment

[N], [Nm],

In case of application of two independent parallel

forces, like using of two (or more) tugboats, such

forces and moments can be defined by:











2211

FyFyz

yyy

xFxFM

FFF

(6)

This should solve the problem of discrete attach-

ment points for tugs.

The turning with particular value of position of

instantaneous pivot point can be completed with a

single external force positioned between the ship’s

bow and stern (Artyszuk 2010):

x ='

(7)

The use of tugs (one or more) for large vessels as

to generate the required external force is limiting the

arms of external forces like technically possible con-

tact points around the ship’s hull for tugboats, like in

pushing mode, where tugs are allowed in specially

marked places contact with the hull or in pulling

mode, where tug operation is restrained by the ar-

rangement of ship’s fairleads.

3.3 The position of instantaneous pivot point during

astern movement

The ship’s propeller working astern generates a side

effect called also “wheel effect”. This phenomenon

is mainly joined with the inflow the reverted propel-

ler race to the ship’s stern and pressure characteristic

of water medium generating lateral trust. Propeller

generate twisted slipstream attacking various sec-

tions of ship’s stern. As long as ship’s positive speed

is remaining the pivot point stay forward of amid-

ships. It is proceeding independently from the astern

throttle. While a ship starts a sternway the pivot

point location changes astern of amidships. The piv-

ot point location sign is changing from a positive to

a negative one. This behaviour is not fully ex-

plained. Because of the propeller lateral force con-

tinues to keep its direction and generate the accom-

panied ship’s lateral velocity, the ship’s centrifugal

force seems to be primarily reason of this behaviour.

Anyway, this shifting of the pivot point from for-

ward to stern because of continued propeller astern

trust together with astern velocity and lateral veloci-

ty base on observation. For sure, the suitably large

external force on the ship’s hull will cause new mov-

ing the pivot point in dependence from the point of

applying and size of the applied force.

4 THE TECHNIQUE OF MANOEUVRING

Turning manoeuvres of the ship could be systema-

tized in relation to the aim of executed manoeuvres

(which is not relevant), the conditions for manoeu-

vre (hydro-meteorological conditions, bathymetric

conditions, legal aspect) that affect the realization of

the manoeuvre, and most important, way of execu-

tion of manoeuvre, which can be further divided into

independent manoeuvres and manoeuvres with tug-

boats assists. During the ship’s turning manoeuvres

is an important use of available propellers, anchors,

ropes or tugs to manoeuvre was executed an ma-

noeuvre area as small as possible while the use of

the propellers, tugs, etc. was the most optimal in dif-

ferent ways.

In the practice, time of realization of such ma-

noeuvre amounts from a few to more than ten

minutes in dependence from accessible propellers

and propulsions, the possibility of the use of the ac-

cepted tactics of manoeuvring, the ship’s condition,

hydro-metrological conditions and bathymetric con-

ditions.

4.1 The independent ship’s turning maneuvers

Independent manoeuvres can be executed using:

− only screw propeller and stern rudder,

− the bow thrusters and screw propeller and stern

rudder,

− the bow and stern thrusters and screw propeller

and stern rudder,

− anchor and the bow thrusters (if available) and

screw propeller and stern rudder,

− lines (springs) and the bow thrusters (if available)

and screw propeller and stern rudder.

The instantaneous pivot point moves from the ex-

treme position in the bow area (during ahead propel-

ler’s mode) to the position in the stern area (while

astern movement) during independent executing the

turning manoeuvre (Rowe 1996). This changeability

of the position of the instantaneous pivot point dur-

ing the manoeuvre is effective on larger manoeu-

vring area of the ship’s turning. The occurrence of

the longitudinal velocity alternating forward and

astern is additional factor influencing the increase of

the manoeuvring area.

The use additionally anchors or lines (springs)

does not cause considerable decrease of the sizes of

the manoeuvring area. What is the aim of their ap-

plying? Simply, it would not be able to execute suc-

cessfully such manoeuvre in many situations. It

seems that use of anchors or lines should influence

266

considerably of the size of the manoeuvring area.

These elements, in practice, influence directly of the

turning ability and their influence on the size of the

manoeuvring area are not great and grow up together

with the growth of the influence of external (hydro-

meteorological) factors what simulating investiga-

tions confirm. The quantity of applied commands is

significantly decreasing facilitating the realization

and in others time of realization of such manoeuvre

is significantly decreasing. Often, it is the large

meaning on current narrow waters.

Figure 3. The independent ship’s turning.

Thrusters are significant support for the ship’s

turning manoeuvres. They give the possibility the

use constant forces apply in extreme points and af-

fecting in opposite directions. The instantaneous

pivot point does not change the position practically,

and the yaw moment increase significantly. The ad-

ditional using of thrusters helps significantly de-

crease the time, quantity of given commands and the

sizes of the manoeuvring area.

4.2 The ship’s turning maneuvers with tugboats

assists

Tugboats, similarly as thrusters, are a significant

support for the manoeuvres of the turning of the

ship.

Figure 4. The ship’s turning with tugboats assists.

They can work with long towing-hawsers, short

towing-hawsers and as pushers. They give, in the

principle, such advantages and the effects of work-

ing as in case of use of thrusters. The possibility of

use of various directions of working tugboats is the

additional advantage. The only deficiency can be the

sizes of the manoeuvring area caused addition to the

manoeuvring area of ship, the manoeuvring area of

tugboats sometimes.

4.3 The ship’s turning maneuvers with other

advanced propellers solutions

Turning manoeuvres of ships with other advanced

propellers solution signify:

− turning manoeuvres with twin screw propellers

(with or without thrusters accompany),

− turning manoeuvres with advanced rudders,

− turning manoeuvres with azimuth drive,

− turning manoeuvres with Voiht-Schneider drive.

This advanced propellers solutions are applied

mostly on smaller ships. This is the result of the aim

of exploitation and costs. They are combining and

increasing advantages of all independent ship’s turn-

ing and ship’s turning with tugboats assists, simulta-

neously decreasing deficiencies. The forces and yaw

moments are enlarged by multiplying of different

propellers and application more effective rudders.

This kind of propulsions brings great decreasing of

time consumption in ship’s turning. Short time of

manoeuvring transfers to safety of manoeuvring. It

is minimizing the ship’s manoeuvring area.

The independent ship’s turn with screw propeller and

stern rudder

The independent ship’s turn with thrusters, screw pro-

peller and stern rudder

The pivot point is shifting de-

pend of screw propeller’s work-

ing mode (ahead or astern)

267

Figure 5. The ship’s turning with advanced propellers solution

(twin screw propellers, five thrusters).

Appling of advanced propellers solutions brings

some danger of human error in service. Some time,

there are a lot of different elements that could be

regulated. On some of them, to avoid any errors, ad-

vanced steering modules with consoles are installed.

Then operator needs to declare direction and force of

working of the propulsion.

5 CONCLUSIONS

The navigator manoeuvring the ship on the turning

basin has concretely presented the problem which

has to execute with the success. He has the ship with

definite technical solutions and the accessible waters

with known conditions where the task has to be

made.

While executing the manoeuvre the process

which he operates still assesses.

Many factors which concentrate in three groups

consist on the assessment of the ship’s turning ma-

noeuvre. All three elements have to be fulfilled in

the minimum degree to recognise the ship’s turning

manoeuvre correctly executed.

The variety of solutions carries with her the plu-

rality of the possibility of their using.

The direct influence on the realization of the

ship’s turning manoeuvre has position of the instan-

taneous pivot point. The instantaneous pivot point

depends of the way how the operator steers propul-

sion and the accessible solutions of drives.

The techniques of manoeuvring influence the po-

sition of the instantaneous pivot point, longitudinal

velocity and the time of the realization of the ma-

noeuvre. These factors influence the size of the

manoeuvring area. The manoeuvring area influences

the safety of the executed manoeuvre. The operator

can suitably influence the safe realization of the ma-

noeuvre assessing the development of the situation

and suitable action.

In practice, executing the manoeuvre of the ship’s

turning all possible resources are used. This secures

the development of the safety and the certainty of

the realization of the manoeuvre. The plurality of

steerable resources brings with them the develop-

ment of the danger of the pronouncement of the hu-

man error.

The economics influences the manoeuvre of the

turning significantly. For ships execute this manoeu-

vre seldom using of the tugboats assist is more justi-

fied. Better propulsion and steering equipment of the

ship is more appropriate for ships executing this ma-

noeuvre often.

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