Invention relates propulsion unit of a marine vessel according to
the preamble of claim 1 in which the propulsion unit includes a rudder device connected
to the hull of the vessel by a support structure, first propeller unit provided
in front the rudder device and assembled to first shaft arrangement, which is in
connection with a power unit arranged in the vessel, and second propeller unit arranged
behind the first propeller unit.
Propulsion of ship has traditionally been accomplished by using one
or several rotating propellers and steering by making use of rudders in connection
with a propeller. Contra rotating propellers (CRP) are known to offer some benefits
over conventional single propeller. The load is distributed onto the blade area
of two propellers instead of one, and the rotational energy of the slip stream of
the first propeller may be more efficiently recovered, just to mention a few.
The most common solution of providing a CRP system is making use of
two concentric shafts, hollow outer shaft and inner shaft inside the outer shaft.
In this kind of solution the first, front propeller is connected to the outer shaft
and the second, rear propeller is connected to the inner shaft, which extends through
the first propeller hub. US 4,963,108 may be regarded as an example of this kind
of a solution. This arrangement requires substantially complicated shafting and
gear devices. In practise also sealing is prone to be problematic to arrange.
As an alternative, a combination of a traditional shaft driven single
propeller and a CRP pod as rear propeller has also been suggested. With this solution
it is possible avoid the complicated shafting and gear devices of conventional CRP
system making use of two concentric shafts. However, this solution requires substantially
large gap between the propellers, because the pod must be able to turn behind the
front propeller. This in turn decreases the efficiency of the solution.
It is an object of the invention to provide a propulsion unit of a
marine vessel, which minimises the problems of prior art. It is a specific object
of the invention to provide a propulsion unit of a marine vessel, which is additionally
capable of steering action.
Above and other objects of the invention are met substantially as
is disclosed in the claim 1 and as is more clearly disclosed in the other claims.
In this specification the terms "after", "behind", "rear", "in front
of" or alike expressions in connection with describing a location of an element,
are to be understood in relation to direction from bow to stern in the vessel.
According to an advantageous embodiment of the invention a propulsion
unit of a marine vessel includes a rudder device supported on the hull of the vessel
by a support structure, first propeller unit provided in front the rudder device
and assembled to first shaft arrangement, which is in connection with a power unit
arranged in the vessel, and second propeller unit arranged behind the first propeller
unit. It is characteristic to the invention that the second propeller unit is assembled
to a second shaft arrangement, which is arranged in connection with the support
structure of the rudder device. This way the power transmission to the second propeller
unit may be provided through a separate route than within the first shaft arrangement
and additionally the propulsion unit is capable of steering action.
The second shaft arrangement is supported within the support structure
of the rudder device so the synergy of integration different part is maximised.
The support structure of the rudder device includes a torpedo section, which is
arranged behind the first and the second propeller units and includes support means
for the second propeller unit.
The second shaft arrangement comprises a propeller shaft being substantially
parallel to the first shaft arrangement and also a drive shaft being at an angle
to the propeller shaft. Additionally the propeller shaft and the drive shaft are
connected with each other by an angle transmission or alike provided within the
torpedo section. The drive shaft is arranged to extend from the torpedo section
through the support structure inside the vessel.
The first propeller unit includes a first propeller hub, and the second
propeller unit includes a second propeller hub. The first propeller hub, the second
propeller hub and the torpedo section form a substantially streamlined body having
increasing cross-sectional area in aft direction to improve the wake flow and the
wake of the flow into the propellers. The first propeller unit and the second propeller
unit are according to the invention arranged to rotate in contrary direction to
According to another advantageous embodiment of the invention a CRP
(counter rotating propeller) propulsion unit of a marine vessel is provided, which
comprises a front propeller unit being assembled to a shaft extending through the
hull of the vessel, and a rear propeller unit being assembled to a support structure
behind the front propeller. In this embodiment at least one of the propeller units
is provided with that at least one of the propeller units is provided with a pitch
control arrangement. As the CRP propeller units being supported on the hull by,
and the power trains being led through separate structures, the propeller pitch
control may be relatively easily arranged using respective power trains to the propellers.
This results in straightforward manner of providing a propulsion unit with counter
rotating, controllable pitch propellers.
The invention provides several benefits over prior art. Firstly this solution avoids
the problems associated with a propeller being turned for steering action inside
the wake of the forward propeller, which is the case when using pod drive as rear
propeller. Secondly, since the rudder unit is integrated with the rear propeller
construction there is no need for separate, additional rudder. Additionally the
present invention provides a solution, which is clearly more feasible than known
CRP propellers. It also provides improved hydro dynamical efficiency of the whole
assembly owing to the contra rotating propellers and the improved wake originating
from the streamlined body of the propeller hubs and torpedo.
The invention will be described with the reference to the accompanying
schematic drawings in which
- Figure 1 illustrates a preferred embodiment of the invention, and
- Figure 2 illustrates another preferred embodiment of the invention.
Figure 1 shows a stern section of a marine vessel 2. The vessel 2
includes a rudder device 3 supported behind a first propeller unit 6. The rudder
device 3 is supported by a support structure 5 i.e. rudder horn, which is attached
to a hull 4 of the vessel 2. The rudder device 3 include the support structure 5
rigidly attached to the hull 4 of the vessel 2 and a steering part 14, which is
pivoted to the support structure 5 of the rudder device 3. For controlling the steering
effect of the rudder device 3 it is provided with steering device 15, which may
be controlled and operated in a manner known as such.
The first propeller unit 6 is connected to a first shaft arrangement
7 in conventional manner. The first shaft arrangement 7 includes a power unit 8,
which drives the first propeller unit 6. The power unit 8 may be any suitable device
for production power, such as, piston engine, gas turbine or electric motor. After
the first propeller unit 6 there is a second propeller unit 9. The first and the
second propeller unit are adapted as so called contra rotating propellers (CRP).
This arrangement offers improved propulsion efficiency compared to conventional
single screw arrangement. The propellers are positioned relatively near to each
other so that there is only a small gap between the propellers. The second propeller
unit 9 is assembled to a second shaft arrangement 10, which is connected to a power
unit 13 respectively.
According to the invention the second shaft arrangement 10 is arranged
in connection with the support structure 5 of the rudder device 3, so the shaft
and power transmission for the second propeller unit 9 may be led inside the structure
5 and also supported by it. This way power train of both the propeller units may
be engineered to be separate from each other hence avoiding the problems relating
to e.g. co-axial shafts in conventional solutions.
The support structure 5 i.e. the rudder horn of the rudder device
3 is provided with a torpedo section 11 arranged behind the first and the second
propeller units 6,9. Within the torpedo section 11 there is the shaft arrangement
and support means 12 for the second propeller unit 9. The support means 12 comprise
bearings and/or other power transmission and support devices. The second shaft arrangement
10 comprises a propeller shaft 10.1, which is parallel to the first shaft arrangement
7. In practise it is desirable to arrange the shaft 10.1 and the first shaft arrangement
7 aligned with each other. The second shaft arrangement 10 comprises also a drive
shaft 10.2 which coupled to the propeller shaft 10.1 by an angle transmission or
alike 10.3, which is also within the torpedo section 11. The drive shaft 10.2 extends
from the torpedo section 11 through the support structure 5 of the rudder device
3 inside the vessel hull 4. There may further be an additional angle transmission/clutch
10.4 through which the drive shaft 10.2 is in connection with the power unit 13.
It is also possible to connect shaft 10.2. directly to a power unit. Generally according
to the invention it is possible to use readily available commercial z-drive units
for providing power transmission between the second propeller unit 9 and its power
The first propeller unit 6 includes a first propeller hub 6.1. Respectively
the second propeller unit 9 includes a second propeller hub 9.1. According to a
feature of the invention the first propeller hub 6.1, the second propeller hub 9.1
and the torpedo section 11 form a substantially streamlined body having increasing
cross-sectional area in aft direction. This way the efficiency of the whole assembly,
contra rotating propeller and integrated rudder device (CRP Rudder), may be maximised.
Now, turning to the Figure 2, in which corresponding reference numbers
to those of Figure 1 are used, another embodiment of the invention will be described.
In addition to showing a CRP propulsion unit 1 as shown in Figure 1, the embodiment
is provided with propeller angle controlling facility 14. Thus it shows a propulsion
unit 1 with counter rotating, controllable pitch (CP) propeller units 6,9. In the
figure 2 there is shown that both of the propeller units 6,9 are provided with controllable
pitch propeller but it is possible, depending on the power source, to use fixed
pitch (FP) propellers for example in rear propeller unit 9. Using fixed pitch propeller
in rear propeller unit would be beneficial particularly if the power source is an
In practise the realising the pitch control is accomplished e.g. by
hydraulically actuated control system being arranged in connection with a drive
shaft of propulsion unit. The assembly comprising counter rotating propellers and
having the pitch control facility in at least one of the propeller units provides
better propulsion control and allows more unconfined selection of power unit for
The invention is not limited to the embodiments shown but several
modifications of the invention are reasonable within the scope of the attached claims.
For example, the embodiment of the propulsion unit with counter rotating, controllable
pitch propeller units may be considered to be adapted in a concept utilising a combination
of a shaft driven front CP propeller and a podded rear FP propeller drive unit.