TECHNICAL FIELD The present invention relates to electric propulsion devices for vessels, and in particular to a vibration dampening device for interconnecting an electric propulsion device for a vessel and a portion of a hull of the vessel.

BACKGROUND

Electric propulsion devices for propulsion and maneuvering of marine vessels are known in the art. One of the advantages of electric propulsion devices is reduced vibration and acoustic noise, compared to former, non-electric propulsion devices, such as those based on internal combustion engines. However, electric propulsion devices, including their motor and their associated propeller, will still produce vibration and acoustical noise which is to some extent transferred to the vessel’s hull. In particular, electric propulsion devices which include a gear transmission device will produce vibrations and acoustic noise which may be annoying to people onboard the vessel when transferred to the vessel’s hull. Electric propulsion devices may in some cases be constructed without a gear transmission. However, such electric propulsion devices will often result in excessive dimensions of the electric propulsion device, in particular its diameter, which is a disadvantage with respect to the hydrodynamic properties of the electric propulsion device.

Hence, there is a need for a vibration dampening device for interconnecting an electric propulsion device for a vessel and a portion of the hull of the vessel. In particular, there is a need for such a vibration dampening device which also provides a durable and robust interconnection between the electric propulsion device and a portion of the vessel’s hull.

SUMMARY

The invention provides a vibration dampening device for interconnecting an electric propulsion device for a vessel and a hull portion of the vessel, as has been defined in the appended independent claim 1.

Advantageous embodiments and possible further features have been defined in the dependent claims. The disclosed vibration dampening device for interconnecting an electric propulsion device for a vessel and a hull of the vessel results in useful vibration damping and damping of audible acoustic noise.

In addition, the disclosed vibration dampening device provides an additional advantage of galvanic isolation between the electric propulsion device for a vessel and a hull of the vessel. This in turn leads to reduced corrosion problems that may occur over time in traditional, electrically propelled vessels. Also, the disclosed vibration dampening device provides electromagnetic isolation which may positively affect electromagnetic compatibility issues that may be present in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention will be described with reference to the drawings, wherein:

Figure l is a perspective view illustrating an electric propulsion device for a vessel interconnected to a hull portion of the vessel, figure 2 is a perspective sectional view of a vibration dampening device for interconnecting an electric propulsion device for a vessel and a hull portion of the vessel. figure 3 is a perspective exploded view illustrating aspects of a vibration dampening device for interconnecting an electric propulsion device for a vessel and a hull portion of the vessel, figure 4 is a perspective view illustrating aspects of a vibration dampening device of figure 3 in an assembled state, and figure 5 is a perspective sectional view of a double-acting vibration dampening device for interconnecting an electric propulsion device for a vessel and a hull portion of the vessel. figure 6 is a perspective sectional view of an alternative embodiment of a vibration dampening arrangement for interconnecting an electric propulsion device for a vessel and a hull portion of the vessel, figure 7 is a perspective sectional view of an alternative embodiment of a vibration dampening arrangement for interconnecting an electric propulsion device for a vessel and a hull portion of the vessel, figure 8 is a cut through image of an the embodiment according to figure 6

DETAILED DESCRIPTION

Figure l is a perspective view illustrating an electric propulsion device for a vessel interconnected to a hull of the vessel.

In the illustrated example, the electric propulsion device 110 has an upper portion that is connected to a vertical extension element, or a mast 200. The electric propulsion device 110 includes an electric motor and a propeller, which may constitute sources of vibrations and acoustic noise. The electric propulsion device 110 may further include a gear transmission which may be a source for additional, adverse vibrations and acoustic noise. A shaft in the form of a substantially cylindrical tube 180 protrudes vertically down from the underside of the hull of the vessel. The substantially cylindrical tube 180 may be fixed with respect to the hull of the vessel, or it may be rotatable with respect to the vessel, allowing azimuth operation of the electric propulsion device 110. Also, in some configurations, the substantially cylindrical tube 180 may be arranged to be tilted between a lowered, operational position and a raised, non-operational position. In order to reduce the propagation of vibrations and acoustic noise from the electric propulsion device 110 to the vessel's hull, a vibration dampening device 100 has been arranged between the substantially cylindrical tube 180 and the electric propulsion device 110. The vibration dampening device 100 has been partly covered and is held in place by means of, i.a., a locking ring 150. Further disclosure of the vibration damping device has been given below, i.a. with reference to figure 2.

It should be understood that the vibration dampening device 100 could in an alternative configuration be arranged between the electric propulsion device 110 and the mast 200, or between different mast segments, or in any other configuration that allows the vibration dampening device 200 to be interconnected between the electric propulsion device and the hull of the vessel.

Figure 2 is a perspective view illustrating a sectional view of a vibration dampening device for interconnecting an electric propulsion device for a vessel and a hull of the vessel.

The vibration dampening device 100 interconnects an electric propulsion device 110 for a vessel and a hull portion 120 of the vessel. It should be understood that the hull portion 120 is intended to include a portion of the hull's body or any other element that is structurally in direct mechanical contact with the hull's body. For instance, the hull portion 120 could in some instances be part of a mast that is secured to a bottom part of the hull's body.

A substantially cylindrical tube 130 protrudes vertically down from the underside of the hull portion of the vessel into a substantially cylindrical, vertical recess 140 provided at the upper portion of the electric propulsion device. The vibration dampening device 100 comprises an elastic material that fills the cavity defined by the substantially cylindrical, vertical recess 140 and the substantially cylindrical tube 130. In particular, the elastic material fills the cavity in such a way that the substantially cylindrical tube 130 and the substantially cylindrical, vertical recess 140 are not in direct mechanical contact with each other. There will be a portion of the elastic material between any point on the outer surface of the substantially cylindrical tube 130 and any point on the inner surface of the substantially cylindrical, vertical recess 140.

A locking ring 150 is advantageously secured to the upper part of the substantially cylindrical, vertical recess. The locking ring 150 may be fastened by a number of bolts protruding through a corresponding number of circular bolt holes in the locking ring and into corresponding threaded, vertical bores in a cylindrical, upper part of the electric propulsion device, which surrounds the cylindrical, vertical recess. Advantageously, the locking ring 150 has a central aperture with a diameter which is less that a diameter of the substantially cylindrical, vertical recess. This enables the elastic material to be firmly held in place within the cylindrical, vertical recess.

In order to improve the physical stability and strength of the interconnection between the electric propulsion device and the hull of the vessel, in particular axial (vertical) strength, the substantially cylindrical tube 130 may advantageously include a first annular flange 160 at its lower end. The vibration dampening device made of the elastic material will then include a corresponding first annular recess.

In order to further improve the physical stability and strength of the interconnection between the electric propulsion device and the hull of the vessel, in particular axial (vertical) strength, the substantially cylindrical tube 130 may advantageously include a second annular flange 170 at an upper part of its lower end. The vibration dampening device made of the elastic material will then include a corresponding second annular recess.

In an advantageous embodiment, the substantially cylindrical tube includes an axial bore 180. The bore 180 may serve as a conduit for an electric power cable intended to supply power to a motor included in the electric propulsion device. Further cables, for instance signal and/or data cables, may also be passed through the bore. In a particularly advantageous embodiment, the bore 180 includes a catch line having a first end secured to the vessel and a second end secured to the electric propulsion device. This may lead to the advantage that the electric propulsion device is not completely lost in the case of a break-off in the connection between the hull and the propulsion device.

In order to improve the physical stability and strength of the interconnection between the electric propulsion device and the hull of the vessel, in particular rotational strength, the substantially cylindrical tube may include a plurality of (for instance two, three, or four) outer, radial, longitudinal ridges. In this case the vibration dampening device includes the same number of correspondingly located, inner, radial recesses.

Further in order to improve the physical stability and strength of the interconnection between the electric propulsion device and the hull of the vessel, in particular rotational strength, the substantially cylindrical tube may include a plurality of (for instance two, three, or four) inner, radial, longitudinal ridges. In this case the vibration dampening device includes the same number correspondingly located, outer, radial recesses.

In order to provide a controlled break-off in case of an overload situation, one or more break-off points or weakened links may be arranged in the vibration dampening device or its surrounding arrangement.

The elastic material of the vibration dampening device may advantageously be an electrically non-conductive material, e.g., a rubber material, such as nitrile rubber. The elastic material is advantageously water-tight. The substantially cylindrical tube protruding vertically down from the underside of the hull of the vessel is typically metallic, e.g. made of stainless steel. The upper portion of the electric propulsion device, which has the substantially cylindrical recess that accommodates the vibration dampening device of the elastic material, is likewise typically metallic, e.g. made of stainless steel. The vibration dampening device may e.g. be molded in place, or pre-manufactured as two halves, assembled together, for instance by means of bolts, when installing the electric propulsion device to the vessel. The vibration dampening device may also be casted as two or more individual parts and locked in place at installation, using a self-locking solution.

In addition to its vibrational dampening or acoustic attenuating effect, the disclosed vibration dampening device 100 provides an additional advantage of galvanic isolation between the electric propulsion device for a vessel and a hull of the vessel. This may in turn lead to reduced corrosion problems that may otherwise occur over time in traditional, electrically propelled vessels. Also, the disclosed vibration dampening device provides electromagnetic isolation which may positively affect electromagnetic compatibility issues that may be present in the prior art. Figure 3 is a perspective exploded view illustrating aspects of an alternative vibration dampening arrangement for interconnecting an electric propulsion device for a vessel and a hull of the vessel. In this embodiment the vibration dampening arrangement includes an elastic vibration dampening device 300 which, when assembled for operational use, is sandwiched between an upper, ring-shaped metal bracket 310 and a lower, ring-shaped metal bracket 320. The upper and the lower ring-shaped brackets each include a plurality (two shown) flanges for cooperation with corresponding recesses in the vibration dampening device 300, improving vertical strength and preventing rotation. The upper bracket 310 may be secured to the portion of the vessel's hull and the lower bracket 320 may be secured to the electric propulsion device of the vessel.

Figure 4 is a perspective view illustrating aspects of the vibration dampening device of figure 3 in an assembled state.

Figure 5 is a perspective sectional view of a double-acting vibration dampening device for interconnecting an electric propulsion device for a vessel and a hull of the vessel. In this embodiment, there are two elastic members interconnected by a metal connection. Hence, the vibrations and acoustic noise will propagate from the electric propulsion device through a first elastic vibration dampening device, which is further connected by a solid-state metal connection to the second elastic vibration dampening device, and finally to the cylindrical tube that protrudes vertically down from the underside of the hull portion of the vessel. This will further improve the effect of dampening vibrations and acoustic noise from the electric propulsion device to the vessel's hull.

Figure 6 is a perspective sectional view of an alternative embodiment of a vibration dampening arrangement for interconnecting an electric propulsion device for a vessel and a hull portion of the vessel. The vibration dampening arrangement is an independent unit that can be connected between the hull of a vessel and the upper part of a propulsion unit. The arrangement can be bolted at both ends to the upper part of the propulsion unit. This allows for an easy way to attach the vibration dampening arrangement. It also makes it easy to change the unit and perform service and maintenance. The vibration dampening arrangement is comprised of a lower metal bracket 603 with a central axial bore. The bore may serve as a conduit for an electric power cable intended to supply power to a motor included in the electric propulsion device. Further cables, for instance signal and/or data cables, may also be passed through the bore. Around the bore there is a vibration dampening device 602. The vibration dampening device 602 can be both cast and vulcanized and can be typically made of a polymer, rubber or polyurethane. The vibration dampening device 602 ensures that the interconnection 601, connecting the hull of the vessel and the propulsion unit, are mechanically separated. In order to improve the physical stability and strength of the interconnection 601 between the electric propulsion device and the hull of the vessel, in particular axial (vertical) strength, the substantially cylindrical tube 130 may advantageously include an annular flange. The vibration dampening device made of the elastic material will then include a corresponding annular recess.

A locking plate 604 is advantageously secured to the upper part of the propulsion unit substantially cylindrical, vertical recess. The locking plate 604 may be fastened by a number of bolts protruding through a corresponding number of circular bolt holes in the locking plate and the lower metal bracket 603 into corresponding threaded, vertical bores in the upper part of the electric propulsion device. The locking plate 604 has an overhanging lip corresponding to the annular flange of the interconnection 601. The locking plate 604 and the interconnection 601 is separated by the vibration dampening device 602.

Figure 7 is a perspective sectional view of an alternative embodiment of the vibration dampening arrangement for connecting an electric propulsion device for a vessel and a hull portion of the vessel from figure 6. As shown here the interconnection 601 is bolted to the substantially cylindrical tube protruding vertically down from the underside of the hull of the vessel. The substantially cylindrical tube is typically metallic, e.g. made of stainless steel.

The elastic material of the vibration dampening device may advantageously be an electrically non-conductive material, e.g., a rubber material, such as nitrile rubber. The elastic material is advantageously water-tight.

Figure 8 is a cut through image of the embodiment according to figure 6. Here it is shown that the vibration dampening arrangement is oval shaped in order to ensure a correct orientation of the vibration dampening arrangement during installation.