STERN THRUSTER

Technical field

The present invention relates to a stern thruster for mounting on the transom plate of a boat. More precisely the invention relates to a stern thruster for being arranged outboard on the transom plate of a boat, or outboard on the stern frame of the boat if the boat does not have a generally plane transom plate.

Problem to be solved

The clearing between the stem of the motor and the transom plate is quite small when stern drives or outboard motors with a stem and a gearbox are arranged outside the transom plate of the boat. It is quite common to arrange two stern drives, one on either side of the vertical centreline of the transom plate.

It is well known to arrange a stern thruster comprising a transversal thruster tunnel with a thruster propeller working in the lateral direction on a T-gearbox arranged on a thruster stem extending through the transom plate, where the thruster stem holds the transversal thruster tunnel and the T-gearbox, while the thruster stem comprises an axially arranged drive shaft extending through the transom plate and connected to a thruster motor, most commonly an electric motor.

Further it is common to arrange the stern thruster in line with the centreline of the transom plate so that the stern thruster can be arranged as low as possible on the transom plate due to the fact that the transom plate is generally V-shaped tapered towards the bottom of the boat. An example of such an arrangement of stem thrusters is illustrated in CA2419669, Fig. 8.

It is a problem that the electrical thruster motor arranged inboard may create sparks during its operation or upon activation and deactivation of electrical relays. Further, it is a problem when arranging a stern thruster according to background art, there has to be made a small hole for the drive shaft between the motor and the gearbox, and then the thruster stem with the thruster tunnel are mounted outboard and the motor has to be connected from the inside of the hull and be mounted inboard. Then electrical cables connecting a power supply to the motor relays for the thruster motor are wired. Such a solution is difficult to make explosion proof. Sparks from the electric motor or relays may

ignite gases aboard the vessel, e.g. petrol gas, oil vapour or propane.

CA2419669 further shows, in Fig. 7, laterally arranged starboard and port convex shaped covers arranged for guiding the outwardly directed jet of water downwards. In this way sending the jet of water directly into the stem of the stern drive has been avoided. The concave shaped cover of the opposite inlet of the stern thruster has a lower horizontal edge about the inlet of the cover to avoid air from entering the inlet. Thus cavitation within the side thruster is avoided. However, it may be a problem that an outlet according to CA2419669 to a large degree guides the water downwards and thus is unable to provide the desired lateral force for turning or lateral manoeuvring. Another problem related to CA2419669 may be that the jet of water is sent more or less directly into the cavitation plate of the gearbox, either on starboard or port side of the stern thruster and lateral thrust is thereby lost.

US5016553 shows a stern thruster for a boat where the stern thruster is arranged on the transom plate when an inboard motor is used, and integrated in the stern drive when a single stem drive is used. The thruster motor is driven by hydraulic fluid pressure from the main propulsion motor.

US6579133 shows a thruster integrated in a single outboard motor for a boat.

Short summary of the invention

The present invention solves several of the abovementioned problems related to safety, mounting and operation.

The invention pertains to a stern thruster for a boat with one or more stem drives or outboard motors wherein the stern thruster comprises an outboard thruster housing. The outboard thruster housing comprises;

- an electric motor, and

- a transversal thruster tunnel with at least one thruster propeller operating mainly in the transverse direction of the boat, wherein the thruster propeller is driven by the motor, and

- the thruster tunnel being arranged mainly on the outside of a transom plate of the boat, and

- wherein the thruster tunnel comprises a central portion with at least a port and a starboard guide channel forming port, respectively starboard inlet/outlet from the thruster tunnel, and

- wherein the guide channel constitutes a transition between a mainly circular cross- section at an inner connection portion connected to a mainly circular cross-section of the central portion of the thruster tunnel, to a non-circular cross-section at the outer inlet/outlet towards the sea,

- the guide channel is arranged for guiding a jet of water of the stern thruster through a gap formed by the transom plate and the one or more stern drives or outboard motors to improve the steering impact on the boat.

Additional features of the invention can be found in the dependent claims in the attached set of claims.

According to an embodiment of the invention there will be no spark generating components on the inside of the transom plate, only electrical cables inboard the vessel with gas-tight, explosion proof bushing or seal arrangements to an outboard arranged electrical motor.

According to another embodiment the installation is simplified as it is not necessary to mount the stem thruster outboard and the electric motor inboard on each side of the transom plate.

According to another embodiment of the invention the lateral outwardly directed jet of water is to a large degree directed towards and through the relatively narrow opening between the transom plate and the stem of the stern drive. By so doing the jet of water will not be hindered by the stem, nor by the cavitation plate of the gearbox.

Brief description of drawings

The attached drawings are only meant to illustrate the invention without limiting its scope, which solely should be limited by the patent claims below.

Fig. 1 shows a partly transparent perspective projection of a stern thruster according to the invention.

Fig. 2 shows a cross-section of a stern of a boat with a view of one or two stern drives

mounted in the boat and a longitudinal cross-section of a stern thruster according to the invention arranged preferably between the stern drives.

Fig. 3a shows a vertical projection of the outboard mountable motor housing and the thruster tunnel according to an embodiment of the invention, where the line A-A (L) is transversal relative the boat, and the line B-B is mainly vertical.

Fig. 3b shows a horizontal projection of the thruster tunnel along the line A-A (L) from Fig. 3a. The line L may be curved towards the transom plate as shown here.

Fig. 3c shows a vertical projection of the motor housing and the thruster tunnel along the line B-B from Fig. 3a and is perpendicular to a section A-A from the same figure. At the top is the motor housing with relays and gas-tight bushings or seal arrangements for electrical cables, and at the bottom is the transversally arranged thruster tunnel with the transversally arranged propeller. An outlet (non-circular, preferably elliptical) for a transversally directed nozzle is stippled inside the section plane.

Fig. 4 shows on the right side the same projection of the motor housing and the thruster tunnel as in Fig. 3a. The section A-A is taken from the connection of the port side channel to the central portion of the thruster channel and has a circular cross-section. B- B and C-C show the cross-sections at successively 1/3 and 2/3 outwards along the side channel along the axis being a straight line in this projection, showing an embodiment where the thruster channel is turning in towards the transom plate. The sections B'-B' and C-C are taken along the line L' curving downwards, and where the thruster side channel is curved downwards towards its end to avoid cavitation.

Fig. 5 shows a stern thruster according to background art.

Embodiments of the invention

When stern drives (101) with a stem (110) and a gearbox (120) arranged outside a transom plate (100) of a boat (1) are in use, there is only a small space between the stem (110) and the front edge of the gearbox (120) and the transom plate (100). It is common practice to arrange two such stern drives (101), one on each side of the vertical centreline (102) of the transom plate (100).

The invention relates to a stern thruster (201) for a boat (1) with one or more stem drives or outboard motors (101), wherein the stern thruster (201) comprises an outboard

thruster housing (240). The outboard thruster housing (240) comprises;

- an electric motor (228), and

- a transversal thruster tunnel (220) with at least one thruster propeller (222) operating mainly in the transverse direction of the boat (1), wherein the thruster propeller (222) is driven by the motor (228), and

- the thruster tunnel (220) being arranged mainly on the outside of a transom plate (100) of the boat (1), and

- wherein the thruster tunnel (220) comprises a central portion (231) with at least a port and a starboard guide channel (230) forming port, respectively starboard inlet/outlet (234) from the thruster tunnel (220), and

- wherein the guide channel (230) constitutes a transition between a mainly circular cross-section at an inner connection portion (232) connected to a mainly circular cross- section of the central portion (231) of the thruster tunnel (220), to a non-circular cross- section at the outer inlet/outlet (234) towards the sea,

- the guide channel (230) is arranged for guiding a jet of water of the stern thruster (201) through a gap formed by the transom plate (100) and the one or more stern drives or outboard motors (101) to improve the steering impact on said boat (1).

The invention renders superfluous a thruster stem that would otherwise extend from the transom plate and where the thruster stem usually holds a transverse thruster tunnel. Likewise the invention renders superfluous an axially arranged drive shaft running through the transom plate and connected to a motor, usually an electric motor on the inside of the transom plate.

In an embodiment the invention the stern thruster is arranged in the centreline (102) of the transom plate (100) to allow the stern thruster to be arranged as low as possible on the transom plate (100) as the transom plate usually is V-shaped tapered towards the bottom (150) of the boat (1).

Preferably the motor for the stern thruster (201) is an electric motor (228). Further the thruster housing constitutes a splash proof, preferably waterproof and gas tight encapsulation of the motor (228).

A driveshaft (221) is arranged through a waterproof bushing or seal arrangement (223) in the thruster housing (240) between the motor (228) and the thruster propeller (222). The drive shaft of the motor (228) may be connected to a gearbox (224) with a propeller axis (225) or be directly connected to the propeller axis (225).

The stern thruster (201) according to the invention may be arranged for the thruster tunnel (220) to comprise a central portion (231) with at least a port or a starboard guide channel (230) constituting port, respectively starboard outlets (234) from the thruster tunnel (220), to guide water into and through the central portion (231). The guide channel (230) usually also constitutes the port inlet from the sea to the thruster tunnel (220), but the inlet for water may be arranged differently.

The guide channel (230) constitutes in an embodiment of the invention a transition from a mainly circular cross-section at an inner connection portion (232) connected to a mainly circular cross-section of said central portion (231), to a non-circular cross-section at the outer inlet/outlet towards the sea, as illustrated in Fig. 4. The section A-A in Fig. 4 shows the circular cross-section in the central portion (231) and the outlet/inlet (234). The section B-B is located further out on the guide channel (230), and the section C-C is located close to the outlet/inlet (234). The horizontal projection shown to the right in Fig. 4 has a mainly horizontally curved axis (L) through the central portion (231). The axis (L) curves gently towards the transom plate (see Fig. 3c) at the starboard and port inlet/outlet (234SB, 234BB). In an embodiment of the invention the starboard and port inlet/outlet (234SB, 234BB) in addition curves gently downwards along an axis (L ¹ ) to avoid cavitation, see Fig. 4. In another embodiment of the invention the inlet/outlet (234) may have a very narrow (short) and extended (high) shape. The port/starboard outer inlet/outlet of the guide channel (230) are arranged to be arranged lower than the central portion (231) of the thruster tunnel (220) to reduce the risk of cavitation. The longitudinal axis (234L) of the non-circular or elliptical cross-section of the outlet (234) of the guide channel (230) may be arranged for being arranged mainly in parallel with the plane of the transom plate (100) to guide the jet of water between the transom plate and the stern thruster. The stem thruster is arranged for being positioned next to a stern drive (101) or between two stern drives (101), see Fig. 2, and where the longitudinal axis (234L) of the non-circular or elliptical cross-section of the outlet (234) is arranged for being positioned mainly in parallel with the direction of the stem (110) of the stern drive (101) in operational position. Usually the stem of the stern drive (101) has a direction approximating the angle of the transom plate (100).

The thruster housing (240) may in an embodiment of the invention comprise a back plate (241), see Fig. 3b, arranged for resting against the outside of the transom plate (100), thereby requiring only a small opening in the transom plate (100) for letting cables through from the already gas tight thruster housing (240). The complete package with the thruster housing (240) comprising thruster tunnel (220), gearbox (224), motor (228) and back plate (241) is thereby arranged for fastening directly onto the transom plate (100). Only a smaller box (247) and wiring of the cables inside the transom plate (100) is required. Alternatively, the fastening may be obtained by a flange around the thruster housing (240).

The thruster housing (240) may in an embodiment of the invention comprise a back plate (241) arranged for being positioned on the inside of an opening in the transom plate (100), where the opening has an edge in the transom plate (100) arranged for being covered by and for fastening by a flange on the thruster housing (240). An opening corresponding to the shape of the flange may then be cut in the transom plate (100) and the complete package including the thruster housing (240) comprising thruster tunnel (220), gearbox (224), motor (228), back plate (241) and electrical power cables (280) may thus be put directly into the opening and fastened by the flange on the edge.

The stern thruster may comprise power cables (280) to the motor (228) and potentially control cables (281), primarily electrical cables (281) and electrical relay control cables (281) for electrical relays (242) between the power cables (280) and the electric motor (228). The power cables (280) are arranged with a gas tight bushing or sleeve (229) through the thruster housing (240), preferably through the box (247) in the back plate (241).