EP1169223B1

EP1169223B1 - Drive means in a boat

Info

Publication number: EP1169223B1
Application number: EP00917580A
Authority: EP
Inventors: Benny Hedlund
Original assignee: Volvo Penta AB
Current assignee: Volvo Penta AB
Priority date: 1999-03-16
Filing date: 2000-03-16
Publication date: 2006-08-02
Anticipated expiration: 2020-03-16
Also published as: DE60029767T2; ATE334875T1; SE516559C2; WO2000058151A1; SE9900936L; SE9900936D0; DE60029767D1; EP1169223A1

Abstract

Boat propeller drive with an underwater housing which is connected in a fixed manner to a boat hull and has tractor propellers arranged on that side of the housing facing ahead. The underwater housing has a lower, torpedo-like portion, in which the propeller shafts are mounted. The propellers are designed with hubs, the maximum diameter of which is smaller than the maximum diameter of the torpedo-like portion.

Description

Field of the invention

The present invention relates to a drive assembly operable to propel a boat when installed therein, wherein an embodiment of the present invention concerns a propeller drive which is arranged in a fixed manner on an outside of a boat hull and has an at least essentially vertical drive shaft which, via an angle gear enclosed in an underwater housing, drives in a counter-rotating manner a pair of at least essentially horizontal propeller shafts each with their own propeller, and a drive unit which is arranged on an inside of the hull and to which the vertical drive shaft is drivably connected.

Background of the invention

It is a known from a published European patent application no. EP 0 215 758 and from a published German patent application no. DE 35 19 599 that, in fast motor boats, considerably higher overall efficiency can be achieved with an outboard drive with twin counter-rotating propellers coupled to an inboard engine than with an inboard engine coupled to a straight shaft with a single propeller as described in a published European patent application no. EP 0 269 272. Until now, outboard drives in fast boats have with few exceptions been of a type which is suspended steerably as well as trimmably and tiltably in a transom stern of a boat. Such an exception is disclosed and described in a Swedish patent application no. SE 8305066-6, wherein a special embodiment of a drive with a pusher propeller and a tractor propeller is installed in a fixed manner and projects down from a bottom of a hull. An advantage derivable from being able to trim the drive at different angles in relation to the transom stern of the boat is that an associated drive angle can be adapted to a corresponding position of the boat in water, such drive angle being dependent on loading, speed and weather conditions, so that optimum propulsion can be achieved under different operating conditions. Advantages of being able to trim the drive are most apparent in smaller and medium-sized fast-moving boats up to about 40 feet (circa 12 metres). The larger and heavier the boat is, the less its position in water is affected by said factors and the smaller a need to be able to trim the drive. At the same time, the cost of the drive increases considerably, the greater the power that it is to transmit. For these reasons inter alia, outboard drives are seldom used in boats in the size class over 40 feet (circa 12 metres), but in this case engines drive straight propeller shafts with a single propeller via inboard-mounted reversing gears.
From the aforementioned European patent application no. EP 0 269 272 and also from the aforesaid German patent application no. DE 35 19 599, it is known that tractor propellers are capable of providing drive assemblies for boats with enhanced propulsion performance. It is further possible to identify from the German patent application no. DE 35 19 599, by virtue of inclusion of a relatively small cavitation plate in conjunction with a pair of mutually counter-rotating tractor propellers, that propulsion performance can be improved to a range wherein cavitation effects occur in the pair of propellers.
Taking the European patent application no. EP 0 269 272 and the German patent application no. DE 35 19 599 as points of reference, a technical problem that the present invention seeks to address is a manner in which further enhancements to propulsion performance can be provided to drive assemblies for boats. Such further enhancements relate to bringing about not only higher overall efficiency and better performance of such drive assemblies, but also simplified installation and lower installation weight.

Summary of the invention

An object of the invention is to provide more optimal propulsion performance of drive assemblies operable to propel boats when installed thereto.
According to a first aspect of the present invention, there is provided a drive assembly operable to propel a boat when installed therein, the assembly comprising:

(a) a propeller drive enclosed in an underwater housing and operable to drive in a counter-rotating manner a pair of propeller shafts, each shaft being provided with a corresponding propeller, the propellers being operable to function as tractor propellers; and
(b) a drive unit drivably connectable to the drive shaft;
characterized in that
(c) the underwater housing includes an elongate substantially cylindrical portion, the substantially cylindrical portion being of torpedo-like shape, the propeller shafts being mounted in the substantially cylindrical portion; and
(d) the propellers include corresponding hubs at central regions thereof, the hubs having maximum diameters which are smaller than a diameter of a front end of the substantially cylindrical portion adjacent to the propellers, the substantially cylindrical portion being mountable to the boat by way of a wing-like profile of the assembly.

The invention is of advantage in that a combination of the substantially cylindrical housing, the wing-like profile and implementation of propeller hub diameters favorably in relation to the substantially cylindrical housing is capable of providing the drive assembly with enhanced performance.
Propeller drives with pusher propellers which are arranged behind an underwater housing with a torpedo-like portion usually have propellers with hubs which form an extension to a rear region of the torpedo-like portion. This portion has a diameter which is determined by inter alia a space requirement for gear units and propeller shafts accommodated therein, which thus, together with any exhaust discharge outlet in the hubs, determines diameters of the propeller hubs. Even rubber shock-absorbers present in the hubs influence their hub diameter. The hub diameters in turn influence the overall diameter of the propellers. It is usual for the hub diameters to be roughly 30% of their corresponding overall propeller diameters.
A benefit of tractor propellers instead of pusher propellers on an outboard drive is inter alia that the pusher propellers work in undisturbed water because the underwater housing lies behind the pusher propellers. It has been found that there is then no flow-related reason to dimension hubs of the pusher propellers in such a manner that a smooth transition is achieved between them and the underwater housing, that is to say in the same way as in drive employing pusher propellers. By reducing the hub diameter of the pusher propellers in relation to the diameter of the torpedo-like underwater housing, the overall pusher propeller diameter can be reduced, which is advantageous in a number of respects. On the one hand, mass and mass forces are reduced and, on the other hand, a space requirement under a bottom region of a hull is reduced, which means that the underwater housing can be dimensioned so as to be shorter in a vertical direction and conssquently lighter than if propeller hubs with the same diameter as the torpedo-like portion of the underwater housing were to be used.
Optionally, in the drive assembly, the maximum diameters of the hubs are substantially 20% of their corresponding propeller diameters.
It is previously known from the aforementioned published European patent application no. EP 0215 758 to use a propeller combination of a fore and an aft propeller together with steerable outboard drives, in which combination, at least a higher speeds, the aft propeller works in a cavity-generating manner whereas the fore propeller works in a non-cavity-generating manner. In such a way, it is possible to reduce a grip of the propellers in water slightly during turning, so that a certain sideways sliding occurs, such sliding being essential in smaller boats in order to prevent their hulls tilting outwards. It has, however, proved hydrodynamically advantageous to arrange a twin-propeller combination with a cavity-generating aft propeller together with a fixed outboard drive with pusher propellers in larger boats also, which are not susceptible to tilting during turning.
Optionally, in the drive assembly, the substantially cylindrical portion has an end region facing rearward in operation, the end region including an exhaust discharge outlet for discharging exhaust gases generated by the drive unit in operation.
Optionally, in the drive assembly, the wing-like profile is provided at a rear region thereof with a pivotable rudder blade forming in operation a pivotal extension to the wing-like profile.
Optionally, in the drive assembly, the substantially cylindrical portion has an elongate length which is substantially equal to a sum of lengths of the wing-like profile and the rudder blade.
Optionally, in the drive assembly, the exhaust discharge outlet includes a screen at an upper region thereof for promoting removal of exhaust gasses away from the rudder blade.
Optionally, in the drive assembly, the wing-like profile is adapted to be mountable to an underside of a hull of the boat.
Optionally, in the drive assembly, the assembly further includes a cavitation plate disposable in operation between the underwater housing and the boat.
Optionally, in the drive assembly, the propellers include a fore propeller and an aft propeller, such that the propellers have associated blade areas so that, at least under certain operating conditions, the aft propeller is operable to work in a cavity-generating manner, and the fore propeller is operable to work in a cavitation-free manner.
According to a second aspect of the invention, there is provided a drive installation operable to propel a boat when installed therein, the installation including two assemblies according to the first aspect of the invention, the assemblies being disposable in operation substantially next to one another, wherein the assemblies include individually steerable blades in order to steer a direction of travel of the boat.
Optionally, in the installation, the assemblies include corresponding pivotable rudder blades, the rudder blades being susceptible to being steered in mutually opposite directions in operation.

Description of the diagrams

The invention is described in greater detail with reference to exemplary embodiments shown in the appended drawings wherein:

Figure 1: is a diagrammatic partly cut-away side view of an embodiment of a drive assembly according to the invention;
Figure 2: is a plain side view of the drive assembly of Figure 1;
Figure 3: is a perspective view of a drive installation comprising two drive assemblies according to Figures 1 and 2;
Figure 4: is a side view of a second embodiment of a drive assembly according to the invention;
Figure 5: is a perspective view of a drive installation comprising two drive assemblies according to Figure 4;
Figure 6: is a diagram of the overall efficiency of a drive assembly according to the invention compared with a conventional inboard installation; and
Figure 7: is a diagram illustrating the increase in speed of a boat with a drive assembly according to the invention in relation to a boat with a conventional inboard installation.

Description of embodiments of the Invention

In Figure 1, a reference number 1 designates generally a drive unit consisting of an engine 1 a and a reversing gear mechanism 1b which are fixed to an inner surface 2 on a bottom 4 of a boat hull. An underwater housing 5 has a fastening plate 7 which is fastened to an outer surface 8 on the bottom 4. The engine 1a drives, via an angle gear in a reversing gear of the gear mechanism 1b, an output shaft 9 which in turn drives, via an angle gear comprising conical gearwheels 10, 11 and 12, a pair of propeller shafts 13 and 14, of which the shaft 14 is a hollow shaft, through which the shaft 13 extends. The shaft 13 bears a propeller 15 with a hub 15a and blades 15b, and the shaft 14 bears a propeller 16 with a hub 16a and blades 16b.
The propeller shafts 13 and 14 are mounted in a torpedo-like part 20 of the underwater housing 5. A housing part 21 between the torpedo 20 and the fastening plate 7 has a wing-like profile with slightly domed side surfaces on both sides of a vertical plane of symmetry. On the aft side of the housing part 21, a rudder flap 22 is mounted for pivoting about a vertical pivoting axis. The front end portion 23 of the rudder flap 22 has a semi-circular cross section and projects into a semi-circular channel 24, as shown most clearly in Fig. 3, where the starboard drive assembly is shown with the rudder blade removed. The side surfaces of the rudder flap lie, at the front edge, in the same plane as the rear edge of the side surfaces of the housing part 21, so that a smooth transition is obtained between the housing part 21 and the rudder flap 22. Together, these two extend over the entire length of the torpedo 20.
At its aft end, the torpedo 20 has a discharge opening 25, in which an exhaust pipe 26 opens, which runs from the engine 1a and through the underwater housing 5. As a result, the propellers will work in completely undisturbed water, on the one hand on account of their being positioned in front of the underwater housing and on the other hand on account of the positioning of the exhaust discharge outlet, which moreover, on account of the ejector effect which arises during motion, contributes to minimum exhaust back-pressure. As can be seen from the figures, the torpedo is at its rear edge designed with a screen 27 towards the rudder flap 22 in order to screen the rudder blade from the exhaust gas flow. By virtue of the fact that the exhaust gases are conveyed out through the underwater housing and not through the propeller hubs 15a and 16a, the diameter of the hubs and thus the diameter of the propeller as a whole can be reduced. In steerable outboard drives with pusher propellers, the maximum diameter of the hubs is normally the same as the maximum diameter of the adjacent part of the underwater housing, whereas the maximum hub diameter of the propellers 15 and 16 shown in Figs 2-5 is roughly 60-65% of the maximum diameter of the torpedo 20 in the portion adjacent to the propellers. As the propellers require a certain minimum distance from the surface of the bottom of the boat above, the length of the underwater housing in the vertical direction is also affected by the propeller diameter, which means that the smaller the propeller diameter is, the shorter the underwater housing needs to be in the vertical direction.
Fig. 2 shows a propeller drive of the type described in connection with Fig. 1, that is to say a drive with an underwater housing 5 which is fixed directly to the bottom surface of the boat hull by its fastening plate 7. The drive has two propellers 15 and 16, of which the fore propeller has three blades whereas the aft propeller has four blades, which is known per se in steerable outboard drives. In a preferred embodiment, moreover, the blade areas of the propellers are adapted to one another in such a manner that, within a predetermined upper speed range, the aft propeller works in a cavity-generating manner whereas the fore propeller works in a non-cavity-generating manner.
The propeller drive in Fig. 2 is mounted on one side of and at a distance from the centre line 30 of the bottom. A corresponding propeller drive is mounted on the other side of the centre line, as shown in greater detail in Fig. 3. As mentioned above, the rudder flap of the right-hand drive has been removed in order to illustrate the design of the wing-like part 21 of the underwater housing 5. With twin-mounted drives, means (not shown) can advantageously be arranged, which make it possible to disconnect the normal synchronous operation of the rudder blades and instead steer the rudder blades in a mirror-inverted manner, that is to say in such a manner that a given deflection of one rudder to, for example, port leads to a corresponding deflection of the other to starboard. In this way, the steering deflections cancel each other out and the rudders instead function as brake flaps without any steering effect.
Fig. 4 shows an embodiment of a propeller drive according to the invention, which differs from that described above in that the underwater housing 5 is connected to a housing 32 which is mounted against the transom stern 31 of the hull and contains an angle gear and a reversing gear mechanism with an output shaft connected to the shaft 9 (Fig. 1). In the transition between the housing 32 and the underwater housing 5, the latter is designed with a cavitation plate 33 which extends up to the transom stern 31. The front edge of the cavitation plate 33 is sealed against the surface of the transom stern, so that the cavitation plate 33 forms an extension of the bottom of the boat. Like the drive in Figs 1-3, the drive in Fig. 4 has a three-bladed fore propeller and a four-bladed aft propeller which is preferably, within a given upper speed range, a cavity-generating propeller. Fig. 5 shows a boat hull with two drives of the type shown in Fig. 4 mounted on the transom stern at an equal distance from the centre line 30.
The diagram in Fig. 6 illustrates the overall efficiency as a function of the speed of the boat for one and the same boat type with on the one hand a conventional inboard installation, that is to say straight shafts and a single propeller (broken line), and on the other hand the drive assemblies according to the invention described above (solid line). As can be seen from the diagram, the difference at, for example, 38 knots is as much as 20 percentage units, in other words an increase in overall efficiency of no less than roughly 40% is obtained with the installation according to the invention compared with a conventional inboard installation. The diagram in Fig. 7 illustrates in a corresponding manner the increase in speed of a boat with a drive assembly according to the invention in relation to the same boat with a conventional inboard installation. It can be seen from the diagram, for example, that if the top speed of a boat with a drive assembly according to the invention is 40 knots when equipped with a given engine, the top speed of the same boat and engine with a conventional inboard installation is roughly 35 knots.

Claims

A drive assembly operable to propel a boat when installed therein, said assembly comprising:
(a) a propeller drive enclosed in an underwater housing (5) and operable to drive in a counter-rotating manner a pair of propeller shafts, each shaft being provided with a corresponding propeller (15, 16), said propellers (15, 16) being operable to function as tractor propellers; and

(b) a drive unit (1) drivably connectable to said drive shaft;
characterized in that

(c) said underwater housing (5) includes an elongate substantially cylindrical portion (20), said substantially cylindrical portion (20) being of torpedo-like shape, said propeller shafts being mounted in said substantially cylindrical portion (20); and

(d) the propellers (15, 16) include corresponding hubs (15a, 16a) at central regions thereof, said hubs (15a, 16a) having maximum diameters which are smaller than a diameter of a front end of the substantially cylindrical portion (20) adjacent to the propellers (15, 16), said substantially cylindrical portion (20) being mountable to said boat by way of a wing-like profile (21) of said assembly.
A drive assembly as claimed in claim 1, wherein the maximum diameters of said hubs (15a, 16a) are substantially 20% of their corresponding propeller (15, 16) diameters.
A drive assembly as claimed in claim 1 or 2, wherein the substantially cylindrical portion (20) has an end region facing rearward in operation, said end region including an exhaust discharge outlet (25) for discharging exhaust gases generated by said drive unit (1) in operation.
A drive assembly as claimed in any one of claims 1 to 3, wherein said wing-like profile (21) is provided at a rear region thereof with a pivotable rudder blade (22) forming in operation a pivotal extension to said wing-like profile (21).
A drive assembly as claimed in claim 4, wherein the substantially cylindrical portion (20) has an elongate length which is substantially equal to a sum of lengths of said wing-like profile (21) and said rudder blade (22).
A drive assembly as claimed in claim 5, wherein said exhaust discharge outlet (25) includes a screen (27) at an upper region thereof for promoting removal of exhaust gasses away from said rudder blade (22).
A drive assembly as claimed in any one of claims 1 to 6, wherein said wing-like profile (21) is adapted to be mountable to an underside of a hull of said boat.
A drive assembly as claimed in any one of claims 1 to 6, wherein said assembly further includes a cavitation plate (33) disposable in operation between said underwater housing (5) and the boat.
A drive assembly as claimed in any one of claims 1 to 8, wherein said propellers (15, 16) include a fore propeller (15) and an aft propeller (16), such that the propellers (15, 16) have associated blade (15b, 16b) areas so that, at least under certain operating conditions, the aft propeller (16) is operable to work in a cavity-generating manner, and the fore propeller (15) is operable to work in a cavitation-free manner.
A drive installation operable to propel a boat when installed therein, said installation including two assemblies according to any one of the preceding claims, said assemblies being disposable in operation substantially next to one another, wherein said assemblies include steerable blades in order to steer a direction of travel of the boat.
An installation as claimed in claim 10, wherein said assemblies include corresponding pivotable rudder blades (22), said rudder blades (22) being susceptible to being steered in mutually opposite directions in operation.