International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 1

Number 3

September 2007

319

Some Problems of Berthing of Ships with

Non-conventional Propulsions

W. Koziol & W. Galor

Szczecin Maritime University, Szczecin, Poland

ABSTRACT: The berthing manoeuvre of ship is the last stage of navigation process. The safety of berthing

depends on velocity due impact the quay. In case of ships with non-conventional propulsion (mainly two stern

screws and few thrust propellers) the berthing manoeuvres are different then other ships. The paper presents

an analysis the kind of ships power and their manoeuvrability features in aspect of safety berthing.

The process of navigation consists in the safe and

effective passage of the ship to the port of the

destination. The berthing manoeuvre of the ship to

the pier is the last stage of that passage. Then

dynamic influence of the ship to the berth causing

definite deformations and tensions. The analyses of

the manoeuvring tactics of the ship show that first

contact of the ship is the most critical moment

during berthing. The kinetic energy of the ship in

the large part changes in the work of impact in

the moment of the first contact of the hull with the

berth. It depends on kinetic energy whether mooring

will take place without the damages of ship and

berth construction or not. It concerns all ships

independently from their size, distance done or

the kind of the cargo loaded. Therefore it applies to

large vessels (bulk carriers, tankers) about the

displacement of a few hundred thousands of tons,

how and small barges, tugboats, passenger ships,

the pleasure crafts (boats, motor boats, yachts) and

others as well. In every case the safe end of the trip

consists in berthing to the quay without appearing of

losses (damages). Safe berthing is defined as such

stop of the vessel near the berth so that losses do

not happen. Reduction of the ship’s speed to zero in

the moment of impact to the quay would be

the optimum way to avoid of the breakdown while

berthing. It means that the kinetic energy of moving

vessel is reduced to zero. Impact is the main reason

of losses during berthing where either part or whole

energy gives off in the area of contact ship - berth.

This energy as the work can cause negative

results. It requires special devices with the aim of

the improvement of the safety of berthing operations,

called fenders or fender systems. The protection of

berth construction and the ship when approaching to

the berth or already moored to this construction is

the main task o fenders.

The size of kinetic energy absorbed by the system

berth - fender - ship affects the size of the strengths

of the reaction of the system which decide about the

failure or failure free realization of the given

maneuver. Condition of the safety of the maneuver

while berthing the ship to the quay can be as

follows:

E(t) ≤ E

berth

E(t) ≤ E

ship

where:

E(t)) –

maximum kinetic energy of the ships

impact absorbed by the system berth

–

fender

–

ship [kNm]

320

berth

–

admissible kinetic energy absorbed by

the system berth

–

fender [kNm],

ship

–

admissible kinetic energy, near which

the formed strengths of the reaction of

the system berth – fender do not cause

the durable deformation of the ships hull

yet [kNm].

Factors which have the influence on the size of

the maximum kinetic energy of the ship’s impact

against the berth construction are as follows:

− ship maneuverability (kind and the power of

the propulsion, thrusters),

− hydrometeorological conditions (wind, current),

− tugs service (the number of tugboats, their

power),

− the maneuvering tactics (captain’s skill, pilot’s

skill).

The design process of berth’s constructions where

berths various type of vessels requires the qualifica-

tions of the impact energy of these ships. The main

parameters decisive about the value of energy are

displacement of the ship W and the ship’s speed

while berthing v

, at the same time speed comes in to

the equation of energy in the square.

According to (Mazurkiewicz 2003) the displa-

cement of the berthing ships is qualified from

formula:

W = Ws + Ww [N]

where:

Ws – displacement of loaded ship [N]

Ww – weight of additional mass of water [N]

Parameters Ws i Ww can be determined from

formulas:

= L

· B · T · δ ·ρ

g [N]

= (p T

g)/4 [N]

From here effective (real) energy of the berthing

ship E can be determined from formula:

E = W v

/ 4 g [N*m, J]

Than taking under the attention above mentioned

dependence we can say, that main unknown,

however decisive in essential way about the value of

energy of the berthing ship is speed at the time

contact with berth – v

. Determination of that speed

still encounters very large difficulties particularly if

taking into account fact that tugboats more and more

rarely take part in berthing operations in bringing

the ship to quay or platform. This results that

particularly such ships, as the container ships,

ferries, ro-ro ships and cruising vessels, due to

installation of thrusters and more often non-

conventional propulsion-steering systems approach

to quays or the platforms without tugs. They are able

to make maneuvers in different way and fully

controlling the speed of the approach.

All these facts induce to consider the necessity of

changes existing recommendations for design of port

constructions. Particularly that in last years follows

both the intensive development of the various kind

of fender systems and more installed on ships non-

conventional propulsion-steering systems improving

the safety of the berthing operations.

1 PROPULSION AND STEERING SYSTEMS

1.1 Propulsion systems

The ship’s propulsion systems can be equipped with

one or more propellers. The propellers can be

different type as follows:

1 fixed pitch propeller – called conventional

propeller,

2 controllable pitch propeller,

3 KORT Nozzle.

A conventional, fixed-pitch propeller, when

driven by a high or low speed diesel engine with

reversing reduction gear and shaft, is perhaps the

most economical and mechanically least complex of

the many vessel’s propulsion system. Efficiency of

such conventional systems in the aspect of

maneuvering of the ship at the sea speeds is good

however it worsens maneuverability on small speeds

considerably.

There are variations of the conventional

propulsion system that make it more efficiency to

control ship’s speed. One of the variants is usage of

a controllable pitch propeller system. Presently such

propeller is used more often, because it provides the

operator almost infinite speed variation from nearly

zero thrust to max that is ship’s speed. In both cases

conventional rudder is applied the most often,

sometimes Becker or Schelling rudder.

The considerable improvement of driving efficiency

on small speeds particularly is got by the location of

the screw in a nozzle fixed to the hull – KORT

nozzle. These nozzles are the most often used on

tugboats and fishing ships in the connection with

conventional rudder that is on the vessels with the

small speed. However the use of nozzles on large

and very large ships also confirmed the significant

influence for maneuverability [Nowicki 1999].

The use of movable flaps additionally together with

movable Kort nozzle considerably enlarges the

maneuvering abilities of the ship.

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1.2 Rudders

1 conventional rudder,

2 Schelling rudder,

3 Becker rudder,

4 conventional bow and stern thursters,

5 directional steerable thrusters.

Equipment of conventional propulsion-steering

systems with bow or stern thrusters gives

considerably larger maneuvering possibilities.

Special type of thrusters is steerable thruster which

can direct his thrust in any direction improving

ship’s maneuverability at low speed.

1.3 Propulsion – steering systems

1 Z-Drives / Pods,

2 Cycloidal Drive

3 Water Jet.

Z-Drives

Pods

Z-drives are type of ship’s propulsion in which

the device producing the strength moving the vessel

is propeller fixed under the hull of the ship on

turning around the perpendicular axis the shoulder.

The modern Z-Drive propulsion have very large

influence for the maneuvering properties of the ships

that is why at present are the most popular drive for

the small ships of the type offshore and tugboat.

Z-Drives are available in fixed-pitch or controllable-

pitch propeller versions and with open propellers

or in nozzle. Z-Drives may produce the vector of

the movement in the any direction what creates

the ship with such drive the extremely good in

maneuverability. Conventional rudders are not used

with Z-Drive installations. Such drive is the most

suited to applying on the ships with the system of

dynamic positioning -DP. Z-drives make better

the maneuverability of the vessel in the relation

to maneuverability offered through conventional

rudders. Due to above such ships in harbours do not

need often to use the services of tugboats.

Different kind Z-Drive very similar in the

working is POD-AZIPOD propulsion which from

classic Z-Drive differ in location of the driving

engine. In the POD engine is electrical and located in

POD than directly drives the screw. The electric

engine obtains energy from electric generators being

in the engine room.

Cycloidal Drives

The most famous cycloidal drive is Voith-

-Schneider construction. Such drive possesses

vertically oriented blades which can produce the

vector of the movement in any direction without the

use of rudder. The big disadvantage is that it

increases of ships draught and they are less suitable

for shallow water than some other forms of

propulsion. They are installed on tugboat mainly.

WaterJet

The WaterJet drive is considerably more efficient

from the conventional propulsion specially when the

speeds is more than 25W. Principle of the working

is to put considerable quantity the water inside drive

through the hole in bottom of the ship to the outlet

canal. Water is compressed using the pump then

discharged through the outlet, being in the aft part of

the canal. WaterJet with fixed reversing buckets

allows to do any maneuvers.

Mostly WaterJet Drive is installed on small, fast

passenger vessels and also on larger passenger and

other ferries.

2 PROPULSION-STEERING SYSTEMS

AND MANEUVERING PROPERTIES

OF THE VESSEL

All types of propulsions and rudders mentioned

earlier and various their connection has the use on

the ships of the various size as propulsion-steering

systems. The more systems are different the more

influence on the berthing tactics of the ships they

have. But anyway it allows for very good the control

of their movement. Connection of the conventional

propeller or Z-Drive with bow thrusters allows to

obtain the transverse movement of the ship and

controlling her speed fully what is very important for

size of impact energy. Usage of Z-Drives in example

showed on the figure 1 allows to good controls of

the ship even at the very strong winds.

Fig. 1. Example of usage propulsion-steering systems for

crabbing test: a) ship equipped with PODs and bow thrusters

322

b) ship equipped with two propellers with rudders and bow

thrusters (Serge & Giedo 2002)

Additionally, it became clear that for the

conventional propulsions, the best crabbing results

are found when using almost the complete amount of

installed power. When using pods, only a limited

amount of power is required. For example, some

results show that to obtain about the same transverse

force in combination with a pure sideways motion

(zero yawing moment) about 75% of the installed

power is required for the conventional ship against

about 30% for the ship with pods. This not only

means fuel savings, but also reduces the impact of

the ship on the environment, such as quay erosion.

Very large influence on the maneuverability of

the ship has the use of Schelling or Becker rudder.

On the figure 2 can see the clear influence of the

rudder type and his angle on the diameters of turning

maneuver.

The connection some of propulsions systems

with some of rudders mentioned above cause

that such vessels possess considerably better

manoeuvrabilities from so-called conventional ships.

Fig. 2. Comparison of Turning test Results at Sea Trial (Japan

Steering Systems)

The example of propulsion-steering system

consist of Schilling Rudder and bow-thurster shows

on figure 3 the possibilities of the realization of

the transverse movement (crabbing of the vessel).

Fig. 3. M/V Esso Plymouth equipped with Single Schilling

Rudder provide crabbing ability when used with a bow-thruster

(Japan Steering Systems)

3 CONVENTIONAL VESSEL AND NON-

CONVENTIONAL VESSEL

The presented examples of propulsion-steering

systems have the significant influence on the

maneuvering possibilities of ships. When take notice

of quotes in the literature the most often use of

words conventional or non-nconventional is from the

attention on the kind of drive or rudder

independently as installed on the ship. However in

the aspect of port maneuvers and specially when

berthing opeartion it is good idea to widen means of

words conventional and non-conventional. Considering

the safety of port maneuvers and risk of excessive

impact against berth we can say that we have to deal

with conventional vessels and non-conventional

vessels. Such meaning will be use to describe

maneuvering possibilities of the vessel or all

propulsion-steering system.

Therefore conventional vessel is the ship

equipped in one fixed or controllable propeller and

conventional rudder without thrusters. Maneuvering

possibilities relating to the port maneuvers at low

speed like berthing or turning of the ship are quite

limited.

Therefore non-conventional vessel is the ship

equipped in at least one propeller different than

conventional or more conventional propellers,

rudder and equipped in thruster. Maneuvering

possibilities relating to the port maneuvers are

considerably larger in the reference to the

conventional ship. Such vessel is able to approach

323

the berth under the any angle or even with crabbing

movement to berth what has the essential influence

on the moment of first contact with berth.

Maneuvers can considerably differ from these

possible to the realization through conventional

ships. Not-conventional ship let on more free choice

of maneuvering tactic and her full control even in

bad hydrometeorological conditions.

4 CONCLUSIONS

The propulsion-steering systems applied today

require regards during design of the berth

construction and fender systems with the aim of their

optimizing strength and costs. It is necessary

continuing simulation and real researches relating to

the tactics of maneuvering non-conventional ships

and to determine the berthing velocity. Researches

are very important to execute the verification of

recommendations relating to buildings of the berth

structures. So far all such researches of the berthing

velocity were based on conventional ships and

mainly very large. For such large vessels the

selection of fender systems was the very essential

parameter for the design of quay, mainly because of

very large strengths applied to the berth structure.

However is lack of researches concerning berthing

velocity new types of ships, described in the article

as non-conventional ships. Determination of such

parameters has to be done for clearly specified

hydrometeorological conditions and the type of the

ship.

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