Auxiliary Propulsion System
For Two-stroke Engine Plants

Add Propulsion Redundancy,
Operational Safety and Minimize Risk
- in a Very Simple Way

2

Extra margins of safety are dictated by
the transportation and handling of
volatile and flammable liquids and
gases, corrosive chemicals, and similar
hazardous cargoes which may harm
the personnel and the environment.

Therefore Safety First…
Safety precautions on board ships have
constantly been improved throughout
shipping history. Accidents at sea give
rise to such improvements in order to
secure the best possible safety for the
crew, the ship, other vessels and
installations at sea, the environment
and the business as a whole.

Governments, authorities, classification
societies, shipowners and insurance
companies are challenging the manu-
facturers of ships and ships’ equip-
ment to encourage them to improve
their products in relation to reliability
and safety. More than ever before,
safe transportation of oil products,
toxic chemicals and liquefied gases is
a must. This kind of transportation is
an important and growing business,
characterized by high stakes, huge

capital costs, high-value cargoes and
risk management. On the other hand,
environmental fractions, politicians,
the press and the public opinion exert
an increasing pressure for environ-
mental consciousness and safety.

Propulsion Redundancy
In recent years focus has been set on
redundancy of propulsion machinery
as well as on requirements for arran-
gements necessary to restoring and
maintaining availability of the ships’
propulsion power and manoeuvring
capability.

In order to meet this demand, MAN
B&W have developed a new Auxiliary
Propulsion System consisting of:

• Two-stroke propulsion engine
• CP Propeller & Control System
• Tunnel gear with two steps
• El-motor/alternator

- and the Alpha Clutcher

The principle of an auxiliary

propulsion system

Safety of Highest Priority

Photo: Øyvind Hagen, Statoil

3

Proven Elements
The low-speed two-stroke engine it-
self is unique in its simplicity and effici-
ency always securing safe operation.

The long lasting know-how and practi-
cal experience from a vast number of
different ship types and propulsion
applications form the basis for the
very high mechanical quality of our CP
propellers.

The supply of a large number of com-
plete propulsion packages including
tunnel gear and shaft alternator has
accumulated good long-term service
experience.
The design of the Alpha Clutcher is
based on a disconnecting device de-
veloped under the name “Separex”
by Burmeister & Wain in Copenhagen
in 1973.

With the Alpha Clutcher, the main
engine can automatically be clutched
out from the direct-coupled propeller
shaft, and consequently the propulsi-
on power is delivered by the GenSets
to the shaft alternator used as electric
motor, and via the tunnel gear to the
propeller shaft.

Single is Simple
The MAN B&W Auxiliary Propulsion
System (MAN B&W AP System) is a
very simple and cost effective alterna-
tive to, for instance diesel electric pro-
pulsion systems and maintains all the
advantages of a low-speed two-stroke
engine plant. In relation to twin-screw
propulsion installations, the single
screw configuration is usually prefer-
red due to a 10 - 12% higher propul-
sion efficiency and last but not least
due to the obvious cost reasons.

4

4

Advantageous Auxiliary Propulsion Power

Increase the Safety for the Crew
as Well as for the Ship
In case of a failure causing loss of
main propulsion power, the MAN B&W
AP System secures the course and
manoeuvrability as well as safe navi-
gation at reduced speed to the nea-
rest harbour. From the bridge panel
the main engine is stopped and the
Alpha Clutcher is clutched out en-
abling the propeller to be driven by the
PTI-motor on the tunnel gear. Propul-
sion power is retained and the ship
has regained its steering capability at
a service speed of at least seven
knots. Under adverse weather conditi-
ons the ship can maintain its position
until the weather conditions improve
or assistance has arrived.

Reduce the Tug Related Harbour Fees
As a safety precaution, harbour authori-
ties often demand stand-by harbour
tugs alongside ships when loading/dis-
charging critical cargoes. The propulsi-
on system must be ready for take-away
operation and consequently overhaul of
main engine and its auxiliary systems
and equipment is not allowed. With the
auxiliary propulsion system in take-away
mode ready for take-off, the ship fulfils
the demands of the authorities and can
eliminate the costs for stand-by tugs
when immobilizing the main engine.

Reduce the Insurance Premium
In comparing two ships - one supplied
with the MAN B&W AP System and
one without - the risk-scenario for the
ship supplied with the system is clear-
ly better and thus directly triggering a
positive effect when fixing the ship’s
insurance premium.

Alpha Clutcher Alternative
For ship types where considerable
electrical power is essential during
stays in harbours, the clutch can be
located on the aft side of the tunnel
gear to enable clutching out of the
propeller from the engine and use of
the main engine as power source for
the shaft alternator in PTO-mode sup-
plying power for large cargo pumps etc.

Main engine

Clutch-C2-disengaged

Clutch-C1-engaged

Shaft alternator G1
motor M1 1800 rpm
PTO load max. 1400 kW

Propeller-120 rpm

2 Speed PTO / PTI gear

120 rpm

Alpha Clutcher engaged

Main engine

Clutch-C2-engaged

Shaft alternator G1
motor M1 1800 rpm
PTI load max. 1400 kW

Propeller-85 rpm

2 Speed PTO / PTI gear

0 rpm

Alpha Clutcher disengaged

Clutch-C1-disengaged

Main engine

Propeller-0 rpm

120 rpm

Clutch-engaged

Shaft alternator G1
motor M1 1800 rpm
PTO load max. 1400 kW

PTO gear

Alpha Clutcher disengaged

• Ordinary Propulsion Mode

• Auxiliary Propulsion Mode

• Harbour Mode

5

Reduce the Maintenance-stress
at Short Stays in Harbour
Punctuality, short stays in harbour and
scheduled maintenance of the main
engine must form a synthesis with the
ship’s charter. During the stay at
quayside, overhaul and maintenance
work can be carried out without
delaying the scheduled departure.

Increased Propulsion Availability
Necessary main engine immobilization
or shut downs for, longer lasting
scheduled checks and inspections
can alternatively be dealt with at sea
at reduced speed without off-hire
jeopardizing the ship’s trading schedule
or charter.

Sailing in Confined Waters
The MAN B&W AP System makes it
possible for the crew to operate safe-
ly at reduced speed in channels, rivers
and straits and simultaneously nurse
the main engine or related auxiliary
equipment.

Boost the Propulsion Power
As a measure for observing the ship’s
transportation schedules, the auxiliary
propulsion system can be supplied
with the possibility to boost electrical

power to the propeller, in addition to
the main engine power and hence
increase the ship’s speed when
necessary.

The Alpha Clutcher is for
All Ship Types
Both safety and economy will benefit
from this concept and it makes the
MAN B&W AP System an obvious
choice for many ship types equipped
with low-speed two-stroke main engi-
nes and CP Propellers.

Time for inspections

and overhauls

App. 2708

4327

W=2538

620

770

1645

2977

3740

917

6117

S=2495

992

1030

D=4900

1380

1

2

3

4

5

6

7

8

0

32

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

15

14

13

12

11

10

9

Compact installation for a 13 500 tdw tanker with a 6S42MC main engine

Maintainability

6

Class Notation for Propulsion Redundancy

Another Stamp of Quality
It is expected that an increasing num-
ber of shipowners in future will speci-
fy their new vessels on the basis of
high quality and ‘green images’ like
crew safety and environmental safety
- rather than exclusively on short-term
economic efficiency. With MAN B&W’s
AP System including:

• Two-stroke propulsion engine
• CP Propeller & Control System
• Tunnel gear with two steps
• El-motor/alternator
• Alpha Clutcher

- ship designers, yards, owners and
operators can obtain a specific class
notation for redundant propulsion and
manoeuvring capability.

The following table is a brief overview
of the present class rules for redundan-
cy, some of them are provisional only:

The Clutcher ready for full load testing

Service Speed in Auxiliary
Propulsion Mode
Calculations and practical experience
show - as an input to evaluation of the
engine power needed, that an electri-
cal shaft alternator/motor correspond-
ing to 20% of the main engine output
is recommended in connection with
two-step gearing in the tunnel gear.

Favourable Investment
Competing clutch systems are avail-
able in the market, at almost twice the
price of the Alpha Clutcher concept.
These systems are also more complex
and more expensive to install.

ABS

GL

DNV

LRS

RINA

Restored
propulsion
power

N/A

N/A

50%

50%

N/A

Time to
restore the
propulsion
power

max 2 min

N/A

N/A

N/A

N/A

Speed with
restored
propulsion
power

7 knots/ 1/2

of design

speed

(whichever

is less)

7 knots/ 1/2

of design

speed

(whichever

is less)

6 knots

7 knots

6 knots/

7 knots

(TakeHome/

Alternative

Propulsion)

Time /
distance

36 hours

72 hours

72 hours

N/A

1000 miles/

2000 miles

Weather
conditions

Wind:17 m/s

(33 knots)

Waves:

4.5 m (15 ft)

Wind and

waves: BF 8

(Beaufort

scale)

Wind and

waves: BF 8

(Beaufort

scale)

N/A

N/A

Obtainable
notations

R1 R1+

R1-S R1-S+

RP1 x%

–

–

THS

APS(p/v/m)

Propulsion Redundancy Class Requirements and Notations

Normal speed

Vs design

in knots

Auxiliary speed

PTI power

= 20% of ME

12
13
14
15
16
17
18

7.0
7.6
8.2
8.8
9.4
9.9

10.5

Knots

7

Alpha Clutcher Characteristics

Description
The MAN B&W AP System is based
on the “Power Take-In” principle in-
cluding the Alpha Clutcher, for clutch-
ing out the main engine from the pro-
peller shaft in PTI-mode.

The prototype of the Alpha Clutcher
was produced in the spring of ‘99. The
clutch function is controlled by
hydraulic oil added through an oil
distributor ring similar to that of the
CP Propellers.

No Foundation Required
The propeller shaft is connected to an
intermediate shaft passing through
the tunnel gear. The Alpha Clutcher is
installed on this intermediate shaft.

A short intermediate shaft is installed
between the Clutcher and the main
engine. The tunnel gear is connected
to the Clutcher via a flexible coupling.
A single bearing supports the shaftline
and the tunnel gear has a normal
foundation seating in the ship.

The Alpha Clutcher has internal bea-
rings and does therefore not need an
expensive thrust transmitting founda-
tion.

Conical Bolts
The cone bolt connection instead of
gearwheels is chosen in order to avoid
clearance problems and hence ham-
mering in-between the load transmit-
ting surfaces. It may be critical to use
gearwheels in the shaftline of a two-
stroke engine because of torsional
vibrations.

The principle consists of two radially
split shaft flanges with a number of
cone holes, a part of each in the outer
flange and a part of each in the inner
flange. When the cones are pressed
into the holes, the flanges are locked
together. When the cones are out of
the holes, the flanges are free to rota-
te independently of each other.

The cone bolt connection

and the split flanges

Tugs´ assistance during

berthing and mooring

8

Perfect Fit Connection
To align the two flange parts for a per-
fect fit between the cone holes and the
cones, a ring is pressed against the
flanges opposite the cones. This ring is
controlled by studs and tightened by
nuts on these to the backside of the
cones. Tension in the studs presses the
cones into the cone holes and ensures
alignment of the flanges. This ensures
a perfect fit connection, which prevents
hammering in-between the connection
surfaces like an ordinary fitted bolt.

When the nuts are loosened, the
cones and the ring are free to move
and the flanges are free to rotate
because the studs are placed outside
the split diameter.

In the Alpha Clutcher the stay bolts do
not pass inside the cones, but in-
between them. The cones and the
studs are moved by servo pistons to
enable hydraulic remote control.

Patented Locking Principle
Instead of tightening a nut on each
stud, a locking ring locks all cone
bolts at one time. When hydraulic pres-
sure is added, the studs are stretched
and the ring is turned into locked posi-
tion. The pressure is then released
and the cone bolts are mechanically
locked. To unlock the cone bolt con-
nection, “clutch-in pressure” has to be
added to be able to turn the locking
ring, and after this pressure is added
for clutching out.

The principle of the locking ring

Auxiliary Propulsion Mode
Clutching out the Alpha Clutcher is
done remotely from the bridge. Auxili-
ary propulsion mode is established in
less than two minutes. When clutch-
ing in, the Clutcher is remotely con-
trolled from a panel in the engine
room.

When operating in auxiliary propulsion
mode, the shaft alternator is used as
electric motor. This motor delivers
power via the tunnel gear to the pro-
peller shaft. When the Alpha Clutcher
is clutched out, the main engine is
disconnected from the propeller shaft
and stopped. In this mode, however,
the Alpha Clucher will transmit the
propeller thrust to the thrust bearing
of the main engine.

To obtain the best possible propulsion
efficiency in auxiliary propulsion mode
at limited electrical power, it is neces-
sary to reduce the rate of speed of the
propeller to match this limited power
with the power absorption of the pro-
peller. Therefore the tunnel gear incor-
porates a two-step gearing. One
‘step-up’ ratio for the ordinary propul-
sion mode with shaft alternator, and a
larger ‘step-down’ ratio for the PTI
auxiliary propulsion mode.

The Clutcher
housing

9

Ordinary Propulsion Mode
When operating in ordinary propulsion
mode, the main engine delivers the
propulsion power directly to the propel-
ler shaft via the clutched-in Alpha
Clutcher. PTO-power is delivered from
the shaft via the flexible coupling to the
tunnel gearbox and the shaft alternator.

When switching from auxiliary propul-
sion mode, ordinary operation mode
is re-established in five minutes. The
main engine and the shaft alternator
have to be stopped, when the Alpha
Clutcher is activated for clutching in.

When the ship operates in ordinary
propulsion mode, the Alpha Clutcher
is mechanically locked. No parts are
moving and the Clutcher is not expo-
sed to internal wear of any kind. No
hydraulic systems including back-up
systems are required to maintain the
Clutcher in position. No additional
power consumption.

Easy Installation
The Clutcher is easily installed with a
traditional hydraulic shrink-fitted coup-
ling to the fore end of the intermediate
shaft through the tunnel gear.

The connection to the intermediate
shaft at the engine side is made by
hydraulically operated fit and tie bolts.

Alignment Instructions
For easy alignment of the propulsion
plant, alignment calculations are made
and instructions are supplied to the
shipyard. The alignment instructions
ensure the right load distributions on
the stern tube bearings and shaft line
bearings. In this connection the Clutc-
her is seen as an intermediate shaft
integrated with the CP Propeller system
and is therefore easy to fit and align.

Clutch Oil System
Lubricating oil and hydraulic operating
oil are supplied via the Hydra Pack tank
unit for the propeller system. This tank
unit is always assembled and factory-
tested prior to delivery in order to faci-
litate the yard’s installation work.

Operating Manuals
An operating manual will provide the
operating crew with a clear guidance
on the redundancy features of the
system. The manuals cover all details
including a general description of the
complete propulsion system, operat-
ing instructions and procedures for
dealing with the situations identified in
the class required Failure Mode and
Effect Analysis, FMEA-report.

Test and Trials
Class approval of the Alpha Clutcher
will be obtained in our workshop prior
to delivery. During quay and sea trials
the functionality of the Alpha Clutcher
will be tested - and the capability of
the Auxiliary Propulsion System to
secure the right speed and manoeu-
vrability will be demonstrated.

Remote
Control
System
The el-motor/
alternator and
clutch control
system is inte-
grated with the
CP Propeller
and main engi-
ne system.

The automatic PTI start-up sequence
includes, eg interlocks for ‘main engi-
ne stopped’, ‘Clutcher in clutched-out
position’, ‘el-motor/alternator clutched
out’, gearing in the tunnel gear ‘chan-
ged to the PTI step-down ratio’, ‘pro-
peller pitch adjusted to zero-position’.
And then follows the transformer-start
of the el-motor and the clutching in at
the tunnel gear. In auxiliary propulsion
mode the power absorption of the CP
Propeller is controlled to stay within
the load range of the el-motor. All
electrical circuits of the control system
are monitored by the alarm system.

Factory test of the Hydra Pack tank unit with pumps, filters,
thermostatic valve, cooler, servo valves and instrumentation

10

Alpha Clutcher Range for Two-stroke MC Engines

Four Clutcher series - CB1 to CB4 -
have been designed to match auxiliary
propulsion systems for two-stroke
engine plants up to and including the
60-bore MC series. This engine range
corresponds to the power range of the
MAN B&W CP Propellers, which again
covers a wide range of modern chemi-
cal, gas and product tanker designs.

TYPE

CB 1

CB 2

CB 3 CB 4

Dimensions mm
Lenght [L]

1445

1635

1830

2160

Diameter [D] 1185

1340

1500

1770

Weight* [ton]

14

20

29

44

ENGINE

Cylinder versions

S26MC

4-12

L35MC

4-12

S35MC

4-10

11-12

L42MC

4-7

8-10

10-12

S42MC

4-5

6-7

8-12

S46MC-C

4

5

6-8

L50MC

4

5-6

7-8

S50MC

4-5

6-8

S50MC-C

4

5-7

8

L60MC

4-5

6-8

L60MC-C

4

5-8

S60MC

4

5-7

S60MC-C

4

5-6

* Approx weight incl intermediate shaft

11

Significant Advantages

The Auxiliary Propulsion System with
Alpha Clutcher means:

• Cost-efficient propulsion redundancy
• Simple, reliable and proven techno-

logy

• Safe operation and quick change of

propulsion mode

• Full integration with the CP Propel-

ler system

• Easy handling and installation at

shipyards

• No separate thrust transmitting

foundation required

• No static hydraulic or electric power

consumption

• Maintenance free
• No practical wear
• Free of back-lash

For a very wide range of typical pro-
duct tankers, gas tankers and chemi-
cal tankers the off-hire risk scenario
alone will justify the investment in the
Alpha Clutcher system - even without
adding the value of all the positive
side-effects like, for instance reduced
tug related harbour fees and increa-
sed main engine maintainability.

The Scientific Angle
Extensive studies, recently performed
by Prof Dr C M Gallin, Gallin Marine
Consultants show a clear capital ad-
vantage of a single-screw two-stroke
propulsion plant with the Alpha Clutc-
her Auxiliary Propulsion System - com-
pared to a similar two-stroke propulsi-
on system without propulsion redun-
dancy on the one hand, and a corre-
sponding twin-screw twin-engine two-
stroke propulsion system on the other.
This scientific study was based on all
costs in the fields of Safety, Environ-
ment and Business related to the
cumulative risk for the service life of a
product tanker with the above three
propulsion plant options.

The cumulative risk is calculated from
statistical ‘real life’ figures, based on
accidents and consequences due to
main engine failures, selected and
evaluated from the casualty bank of

Lloyd’s Register in London. The costs
evaluated are for instance: Value of
ship and cargo, repair costs, loss of
hire due to repair time, loss of hire due
to waiting time, loss of hire due to
towing time and the towing costs.

“The 5

th

Product”

- Excellent Project Service
Propulsion know-how, customization,
system integration and service is at
your disposal comprising:

• Lay-out of engine, tunnel gear,

propeller, piping system etc

• Optimizing of propulsion modes
• Selection of the gear ratios for the

tunnel gear

• Alignment analysis and instructions
• Strength and vibration calculations
• Arrangement and installation

drawings

• Instruction books
• Dimension sketches on disks
• Project guides
• Investment/pay back time

calculations

• Operation and maintenance costs

- and much more due to a strong and
flexible toolbox available for such pro-
ject services.

The Genuine Propulsion Package
Since 1989, MAN B&W Diesel’s works
in Frederikshavn, Denmark have manu-
factured and supplied two-stroke
engines of the successful MC-series,
today up to the 8S50MC-C engine.

The MAN B&W CP propeller program-
me has been developed to efficiently
match the MC-engine series up to the
70MC versions.

The Alpha Clutcher is an integrated
part of those propeller systems which
are designed, manufactured and sup-
plied by one company taking full
responsibility for functionality, order
handling, commissioning, warranty
and after-sales service of the comple-
te propulsion system.

Photo:
Øyvind Hagen,
Statoil

MAN B&W Diesel A/S
Alpha Diesel
Niels Juels Vej 15
DK-9900 Frederikshavn
Denmark
Telephone + 45 96 20 41 00
Telecopy

+ 45 96 20 40 30

e-mail:

[e-mail]

http//: www.manbw.dk

653/1.0-GB. Status March ‘01

Copyright

©

MAN B&W Diesel A/S, Alpha Diesel

Reproduction permitted

provided source is given

.

Reg. no. 39 66 13 14