DIESEL ENGINE PROPULSION UNIT ARRANGEMENT IN A VESSEL SAILING IN OPEN WATERS AND ICE-BREAKING

GROUPE PROPULSEUR A MOTEUR DIESEL POUR NAVIRES NAVIGANT DANS LES EAUX LIBRES ET LES EAUX FERMEES PAR LES GLACES

English Abstract

A b s t r a c t
Two low-speed two-stroke diesel engines (11, 12)
are disposed consecutively in the longitudinal direction
and parallel to the longitudinal axis (10) of the vessel
in the hull (18) per propeller (16) and for direct
propulsion of the propeller (16) are connected to the same
via a common line of shafting (21). A coupling (13) is
disposed in the line (21) between the engines (11, 12).
The direct drive eliminates any transmission losses
between the engines and the propeller and the vessel
running costs are low because of the low specific fuel
consumption of low-speed two-stroke diesel engines.

Claims

The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows:
1. A diesel engine propulsion unit arrangement in a
vessel sailing in open waters and ice-breaking, more
particularly a merchant vessel, comprising at least one
propeller, characterised in that at least two low-speed
two- stroke diesel engines are provided in the hull per
propeller and are disposed consecutively in the
longitudinal direction and parallel to the longitudinal
axis of the vessel and for direct propulsion of the
propeller are connected thereto via a common line of
shafting, and a coupling is disposed in the line of
shafting between the engines.
2. An arrangement according to claim 1,
characterised in that the coupling is so designed as to be
engageable only when the portions of the line of shafting
to be connected by said coupling are in an accurately
defined position.
3. An arrangement according to claim 1 or 2,
characterized in that the propeller has adjustable blades.
4. An arrangement according to any one of claims 1
or 2, characterised in that a thrust bearing secured in
the hull and taking the axial forces of the propeller is
disposed in the line of shafting between the propeller and
the engine nearest the same, and a coupling is provided
between said bearing and axial movements of the shafting
portions connect by said coupling.
5. An arrangement according to claim 1 or 2, wherein
the propeller has adjustable blades and wherein a thrust
bearing secured in the hull and taking the axial forces of
the propeller is disposed in the line of shafting between
the propeller and the engine nearest the same, and a
coupling is provided between said bearing and the said
engine and allows relative axial movement between parts of
said coupling to engage or disengage same.

Description

~22~67~ 1
This invention relates to a diesel engine
propulsion unit arrangement in a vessel sailing in open
waters and ice-breaking, more particularly a merchant
vessel, comprising at least one propeller.
The prior art diesel 0ngine 6ystems use only
medium-speed engines of a speed of about 500 to 600 rpm
and a cylinder power of 500 to 800 hp. Since the maximum
propeller speed is about 170 rpm, an electrical unit
consisting of a generator connect~d to the diesel engine
a~d a low-speed electric motor fed by the generator and
connected to the propeller shaft is provided between the
medium-speed diesel engine and the propeller shaft.
Another known possible method of bridging the
different speeds of the diesel engine and the propeller
shaft is to incorporate a reduction gear.
Propulsion systems of this kind have appreciable
transmission losses because of the need for the electrical
unit or reduction gear. Medium-speed diesel engines have
a relatively high specific ~uel consumption, and this has
an unfavourable effect on the vessel running costs.
Besides, medium-speed diesel engines are not suitable not
only in ice-breaking but also for open water sailing over
relatively long periods. The ice-breaking/open-water
power ratio to be provided by the diesel engine is about
3 : 1 to 2 : 1, the limits being variable depending upon
the vessel operating conditions.
The object of this invention is so to improve a
diesel engine propulsion system of the kind referred to
hereinbefore such that the transmission losses for the
drive and the vessel running costs are reduced so that
economic operation of the diesel engine is obtained both
for ice-breaking and for open-water sailing.
To this end, according to the invention, at least
two low-speed two-stroke diesel engines are provided in

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the hull per propeller and are disposed consecutively in
the longitudinal direction and parallel to the
longitudinal axis of the vessel and for direct propulsion
of the propeller are connected thereto via a co~mon line
of shafting, and a coupling is disposed in the line of
shafting between the engines.
The provision of low-speed t~o-stroke diesel
engines delivering to a common line of shafting on which
the propeller is mounted permits direct propulsion of the
propeller, i~e.7 the speed oE rotation of the engine is
the same as the speed of rotation of the propeller. The
invention thus eliminates any need for an electrical unit
or a reduction gear, so that the power losses are also
eliminated. Since low-speed diesel engines have a lower
specific fuel consumption than medium-speed engines, the
vessel running costs are much lower as well. The use of
two engines enables the propulsion power to be divided,
all the engines being in operation for ice-breaking while
only the engine nearest the propeller is operated for
open-water sailing, for which much less power is required,
the other engine or engines being separated from the
shafting by disengaging the coupling. Economic operation
is thus obtained for each engine~ It has surprisingly
been found that the torque characteristic of low-speed
diesel engines arranged according to the invention is
optimum under the various vessel operating conditions.
One exemplified embodiment of the invention will
be explained in detail in the following description with
reference to the drawingJ which i6 a simplified
diagrammatic illustration of a propulsion unit with two
diesel engines.
The two low-speed diesel engines 11 and 12 are
arranged consecutively and parallel to the longitudinal
axis 10 of the vessel and are conventionally secured in
the hull 18, only a part of the stern of which is shown in
the drawingr The two engines 11 and 12 are of crosshead

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design and are two-stroke engines of identical power and
deliver directly to a common line of shafting 21, At the
bottom end of the line 21 in the drawing there is secured
a ship's propeller 16 with fixed blades to propel the
vessel both ~or icebreaking and for sailing in open wa~ers.
A coupling 13 of known construction is disposed
in the line 21 between the diesel engines 11 and 12. The
coupling is so constructed as to be engageable only when
the line sections to be coupled are in an accurately
de~ined position relative to one another.
The two engines 11 and 12 are each provided in
known manner with a thrust bearing 19, each bearing taking
the axial thrust of the associated cranksha~t. ~ thrust
bearing 15 is also provided for the portion of the shaft
bearing the propeller 16 and is secured in the hull 18 and
takes the much larger axial thrust from the
propeller 16. A coupling 14 is disposed between the
thrust bearing 15 and the engine 12 in the line 21 and is
so designed as to take relative axial movements of the
connected shaft portions.
When the vessel is icebreakiny, the coupling 13
is engaged and the power of the two engines 11 and 12 is
delivered to the propeller 16 via the common line 21. Of
course, as in any other disconnectable couplings, in order
to engage the two halves of the coupling 13, the two
halves have to be either both stationary or have to rotate
in the sa~e direction and at generally the same speed.
Yor open-water sailing, on the other hand, coupling 13 is
disengaged and only the power of engine 12 is delivered to
the propeller 16. The total power of the two engines 11
and 12 and the power of the engine 12 alone are so
balanced that cruising is always possible with the maximum
relative engine power.
The fixed-blade propeller 16 may alternatively be
replaced by an adjustable-blade propeller, thus further
improving the matching of the engine power to the vessel

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speed. Instead of the 1:1 power ratio of the engines
acting on the single line of shafting, a power ratio of
2:1, for example, may be used in which case the more
powerful engine is disposed nearer the propeller.
The invention can also be applied to vessels
propelled by two or ~hree propellers operating in
parallel. In that case, each propeller has its own line
of shafting with two low-speed diesel engines driving it,
with a coupling provided between the engines. More than
two engines may also be provided per line of shafting.