WO2010110703A1

WO2010110703A1 - Propulsion unit for a boat

Info

Publication number: WO2010110703A1
Application number: PCT/SE2009/000162
Authority: WO
Inventors: Magnus Eriksson
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-03-27
Filing date: 2009-03-27
Publication date: 2010-09-30
Anticipated expiration: 2011-09-27

Abstract

The present invention relates to an electrical propulsion unit for a fast boat (13), specifically a planning or semi-planning boat, where the propulsion unit is attached to the stern and includes en outboard arranged electrical propulsion motor (1) in a water protective housing (2) which via a an outgoing transmission shaft is attached to a surface piercing propulsor (3). The propulsion unit is provided with a vertically adjustable drive unit (8, 9, 10; 8, 9, 11, 12) which moves the unit vertically without changing the propulsor's angle to the boat, a trim system (6) which around a horizontal axis (5) changes the propulsor's angle to the boat and a steering mechanism (7, 14) which around a vertical axis (4) unlimited, up to 360 degrees, changes the propulsor's angle to the boat.

Description

Propulsion unit for a boat

The present invention relates to an electrical propulsion unit for a boat, specifically a planning or semi-planning boat.

There are many advantages with the possibility of moving the centre of the propulsor, i.e. propeller or propelling device, vertically without changing its angle to the hull. It is also further advantageous if it is possible to control the propulsor's interaction with the water without any restrictions in 3 dimensions. By doing so it is possible to optimize the running conditions for both the propulsor and the hull. This is not possible with known boat motor- and propulsor units.

Drive units of conventional type include two main types, outboard motors, where the motor is rigidly attached to the upper end of the rig, and stern drive units, where the propeller drive unit is mounted on the outside of the stern and mechanically attached to an inboard mounted engine. In both cases it is possible to change the trim of the rig around a horizontal axis attached to the stern in so the angle between the rig and stern can be adjusted. The propeller cannot however be translated in parallel in the vertical plane. The mechanical power transmission in the stern drive case makes such a movement impossible.

The rig's yaw center, i.e. the vertical axis around which the drive unit turns, is also positioned close to the stern in all known drive units. It is however more beneficial if the yaw center could be positioned further back closer to the hydrodynamical pivot center of the rig. When the underwater part of the rig is moving through the water during turns a torque proportional to the distance between the pivot center and the yaw center is created. This torque will tend to stabilise or destabilise the rig depending on if the yaw center is upstream or downstream of the pivot center. The smaller the distance the smaller is the acting torque and thus the smaller and less powerful actuators can be used to turn the rig. To minimise the power consumed for actuators this distance should be minimised.

The faster a boat travels through the water the higher the added resistance will be from those underwater parts, appendages like propeller and propeller hub, that are submerged. To reduce this effect one can use surface piercing propellers where the hub is partly or completely above the water and only the propeller blades are cutting through the water. This technique will reduce the resistance for the high speed applications. To further reduce the resistance the running trim of the boat should be increased. With a conventional surface piercing unit it is impossible to maximise the trim due to the fact that the propellers will be lifted out of the water, and thus the thrust effect and trimming torque will be reduced, for a completely submerged drive unit the trimming angle can be higher but the resistance will also increase compared to the surface piercing unit. These two embodiments thus have their own benefits and disadvantages.

The present invention solves the conflicting behaviour of the known drive units and admits a vertical movement of the propulsor without changing its angle to the stern, and that the propulsor's interaction with the water can, without restrictions, be arbitrary manoeuvred in 3 dimensions.

The invention will be described in more detail in the following with reference to the accompanying drawing, in which

fig. 1 shows a first embodiment of the invention with the drive motor housed in a submerged pod with a conventional hydraulic steering mechanism, fig. 2 shows a second embodiment of the invention with the drive motor vertically arranged above the water and with an electrical steering mechanism, fig. 3 shows another view of the invention in fig. 2 showing the vertical adjustable drive unit moved via electrically driven chains and fig. 4 shows the inventions in fig. 2 with the vertical adjustable drive unit replaced with one using linear electrical actuators.

The basis for the invention and what solves the described problems in a way that no previous drive systems have done, is an electrical motor 1 housed in a waterproof pod 2 mounted on the stern of a boat 13 in such a way that the complete drive unit including propulsor 3 can be vertically moved without changing the angle to the stern. For stern drives the propeller angle to the hull can normally be controlled around a vertical axis 4 to turn the boat and turned around a horizontal axis 5 for trimming with hydraulic actuators 6 of the boats running trim. A mechanical power transmission where the motor is mounted inboard and the propeller mounted on the outside can not vertically adjust in parallel the height of the propeller. Since the electrical propulsion creates the possibilities to trim the rig inward and outward and at the same time adjust the rig vertically the resistance can be minimised by minimising the wet surface of the rig whilst at the same time creating the desired retrimming torque to get the optimal hull running trim.

For the invention the steering mechanism 14 that turns the boat and the trim system 6 changing the hull trim can be of known type equal to stern drives. In figure 2 one embodiment of the invention shows the steering mechanism 7 fitted with a gearwheel mounted around the drive motor controlled by a smaller electrical drive motor. The trim system 6 in figure 2 is arranged with single or double acting hydraulic pistons similar to what is normal for stern drives.

The vertical adjustable drive unit shown in figure 4 is designed in the following way. En sleigh 8 is mounted in a glide bearing 9 which in turn is rigidly mounted to the inside of the stern. Alternatively the glide bearing can of course be mounted on the outside of the stern. The sleigh is vertically adjustable via a pair of electrical linear actuators 10 which are fastened to the sleigh 8 at the upper end and fastened at the bottom to the glide bearings 9 outer side. Hydraulic actuators can also be used instead of the electrical ones.

Another embodiment of the vertical adjustment unit is shown in figure 2 and 3. Here the sleigh 8 is moved up and down in the glide bearing 9 via a chain 11 attached to the sleigh 8 and driven by an en electrical motor 12 via a gearwheel.

The propulsion motor in the water protective housing can, as shown in fig 1 , be completely or partly submerged into the water in where the housing 2 then is called a pod. The propulsion motor is then aligned in the direction of travel and has the propulsor 3 mounted on a transmission shaft in front or behind the motor close to the pod. In certain cases it is more advantageous to have the propulsor in front of the pod allowing a larger part of the pod to bed trimmed up and out of the water without lifting the propeller out of the water.

In an alternative constructive design according the figure 2-4 the propulsion motor 1 drives the propulsor 3 via an angular gearwheel. Here the propulsion motor is placed above the water. Certain advantages related to small wetted surface and manoeuvrability can be achieved. At low speeds and when running astern the whole unit can be submerged and turned 360 degrees around steering axis. The propulsor can of course be oriented either at the fore end or at the back end.

The propulsor 3 is in certain applications preferably a so-called pumpjet propulsor, shown in figure 1. The size of the components in contact with the water is directly affecting the hydrodynamic resistance. Size in this context is both total wetted surface and the cross-sectional area for the actual appendage.

For electrical propulsion motor 1 submerged into the water in a pod 2 it is of outmost importance to be able to increase the rpm as much as possible, without loosing too much propulsion efficiency, since the possible power output increases linearly with the rpm of the motor. The net result is that for a given power output a higher rpm means a smaller motor, which in turn reduces the hydrodynamic resistance of the submerged pod and reduces the disturbances in the propeller wake field, the water that flows into the propulsor 3. High rpm is normally something that is avoided in the context of propeller design since it is a cause of cavitation, but a pumpjet with the appropriate design has larger cavitational margin compared to a conventional propeller.

In a conventional arrangement with an inboard mounted combustion engine which mechanically drives a propeller a normal propeller or contra-rotating propellers can be used up to speed of about 35 knots. For speeds above 35 knots a waterjet, pumpjet or a surface piercing propeller be more beneficial.

For certain applications a surface piercing propeller is a suitable propulsor. In contrast to a conventional arrangement with an inboard engine where, according to above, problems with lifting the propeller out of the water when trimming the drive unit outward may arise whilst while using an electrical motor according to the invention an optimal position for the surface piercing propeller can be obtained via the adjustable 3 dimensional drive unit.

In certain applications, and then preferably with a pulling propeller, it is beneficial to have eventual exhaust gases and coolant water released through an outlet at the back end of the pod or propulsor hub. In those applications where a surface piercing propeller is used it can, in some cases, be advantageous to fit a semi-open tunnel covering the essential upper part of the propeller which can act as both a coolant surface and coolant- and exhaust outlet.

If the propulsions system is constructively designed with a bottom mounted fin it can, in addition to the added steering capability of the unit, also act as an integrated heat exchanger for oil or other coolant fluids. Oil cooling plates can also be mounted on the upper part of the pod intended to be washed over with spray originating from a surface piercing propeller.

Claims

Claims:

1. Propulsion unit for a fast boat (13) mounted on the stern of the boat including an electrical propulsion motor (1) in a water protective housing (2) which via an outgoing transmission shaft is attached to a surface piercing propulsor (3), , c h a r a c t e r i s e d in that the propulsion unit is provided with a vertically adjustable drive unit (8,9,10;8,9,11,12) which moves the unit vertically without changing the propulsor's angle to the boat, a trim system (6) which around a horizontal axis (5) changes the propulsor's angle to the boat and a steering mechanism (7, 14) which around a vertical axis (4) unlimited, up to 360 degrees, changes the propulsor's angle to the boat.

2. Propulsion unit according to claim ^c h a r a c t e r i s e d in that the propulsor (3) is a pumpjet propulsor.

3. Propulsion unit according to claim ^c h a r a c t e r i s e d in that the propulsor (3) is a surface piercing propeller.

4. Propulsion unit according to claim 1-3, c h a r a ct e r i s e d in that the propulsor (3) is of a pulling type and attached to a transmission shaft oriented forward in the length direction of the boat (13).