GB2141085A

GB2141085A - Marine jet propulsion units

Info

Publication number: GB2141085A
Application number: GB08413540A
Authority: GB
Inventors: Philip George Joyner; Peter Henry Knowler
Original assignee: Dowty Hydraulic Units Ltd
Current assignee: Dowty Hydraulic Units Ltd
Priority date: 1983-06-08
Filing date: 1984-05-25
Publication date: 1984-12-12
Also published as: GB8413540D0

Abstract

A marine jet propulsion unit comprising a water intake casing 1, an impeller casing 2 connected to the intake casing, an impeller 3 within the impeller casing and a water outlet casing 4 connected to the impeller casing. A rotatable member 5 is associated with the water outlet casing for controlling the direction of discharge of water from the unit. A normally-closed valve means 6 is operable to introduce gas into the water intake casing. <IMAGE>

Description

SPECIFICATION Marine jet propulsion units This invention relates to marine jet propulsion units and to floating vehicles having marine jet propulsion units.

Marine jet propulsion units comprising a water intake casing, an impeller within an impeller casing and a water outlet casing with a rotatable member for controlling the direction of discharge of the water from the outlet are well known.

Also known is a floating vehicle having two such marine jet propulsion units which are symmetrically arranged, one on one side of the longitudinal axis of the vehicle and the other on the other side of the longitudinal axis of the vehicle. The direction of movement of such a vehicle is determined by the respective positions of the rotatable members.

No problems arise when such a vehicle is caused to change its direction of movement by turning substantially along the arc of a circle. However, when it is necessary for the vehicle not so to turn but to move transversely of its longitudinal axis, a problem does arise.

To obtain transverse movement of the rotatable member of one unit is turned so that water discharging therefrom is directed rearwardly of the vehicle and away from the longitudinal axis of the vehicle, so that the axis of the resultant thrust passes through or very close to the centre of buoyancy of the vehicle.

The rotatable member of the other unit is turned so that water discharging therefrom is directed forwardly of the vehicle and towards the longitudinal axis of the vehicle, so that the axis of the resultant thrust passes through or very close to the centre of buoyancy of the vehicle.

The problem which arises is due to the fact that the efficiency of a unit when its rotatable member has been turned to discharge water forwardly of the vehicle is somewhat less than its efficiency when its rotatable member discharges water rearwardly of the vehicle. Typically, the efficiency in the former case is reduced by about 20%.

Thus when a floating vehicle having two such marine jet propulsion units has to be moved transversely, there is an out-of-balance component which causes the vehicle to move not only transversely but also forwardly.

According to this invention, a marine jet propulsion unit comprises a water intake casing, an impeller within an impeller casing, a water outlet casing with a rotable member for controlling the direction of discharge of water from the outlet casing, and normally-closed means operable to introduce gas into the water intake casing.

Also according to this invention, a floating vehicle has two such marine jet propulsion units symmetrically arranged about its longitudinal axis.

By providing the means for introducing gas into the water intake casing and for varying the amount of gas introduced (which means can be a simple bleed valve), the efficiency of a unit can be decreased in accordance with the amount of gas introduced.

Thus, when two water jet units are fitted symmetrically about the axis of a floating vehicle and their rotatable members are orientated so as to cause the vehicle to move in a direction transverse to the longitudinal axis of the vehicle, the normally-closed means of the unit which discharges water rearwardly and away from the longitudinal axis will be opened so as to introduce gas into the water intake casing. The amount of gas so introduced can be of such amount that the efficiency of the unit is reduced substantially to the efficiency of the other unit. The thrusts of the two units will now be counterbalanced and a desired transverse movement of the vehicle can be obtained.

A marine jet propulsion unit in accordance with one embodiment of the invention is shown in Figs. 1 and 2 of the accompanying drawings of which Figure 1 is an elevational view of the unit; and Figure 2 is a scrap view of its normallyclosed means for introducing air into its water intake casing.

A floating vehicle with two such marine jet propulsion units is shown in Figs. 3, 4 and 5 of the accompanying drawings of which Figure 3 indicates the forces operating when the units are positioned for transverse movement of the vehicle and the two said means shown are closed; Figure 4 indicates the forces operating when the units are positioned for transverse movement of the vehicle and one of the means is partly open; and Figure 5 indicates the forces operating when the units are positioned for transverse movement of the vehicle and one of the means is fully open.

Referring to Figs. 1 and 2 of the drawings, the marine jet propulsion unit comprises a water intake casing 1, an impeller casing 2, an impeller 3 within the casing, a water outlet casing 4 and a rotatable member 5 which can rotate through 360 with respect to the casing 4.

The water intake casing 1 has a normallyclosed valve means 6 by which air can be introduced in varying amounts into that casing. The valve means 6 includes a butterfly closure member 7 which is movable from a closed position to an open position by a Bowden cable 8 and an operating lever 9.

Referring now to Figs. 3, 4 and 5, a floating vehicle 10 is fitted with two marine jet propulsion units 11 and 12, each of which is similar to that described with reference to Figs. 1 and 2. The unit 11 is disposed adjacent a side of and near to the rearward end of the vehicle. The unit 1 2 is disposed adjacent the other side of and near to the rearward end of the vehicle.

When it is necessary for the vehicle to move sideways i.e. transversely, the rotatable member 1 3 of unit 11 is directed rearwardly of the vehicle and away from the longitudinal axis of the vehicle, so that the axis of the resultant thrust passes through or very close to the centre of buoyancy 14 of the vehicle.

The rotatable member 1 5 of unit 1 2 is directed forwardly of the vehicle and towards the longitudinal axis of the vehicle, so that the axis of the resultant thrust passes through or very close to the centre of buoyancy 14 of the vehicle.

Within the valve means 16, 1 7 of both units closed (see Fig. 3), the efficiency of the unit 12 is about 20% less than the efficiency of the unit 11. As a consequence, if A is the horizontal component of the resultant thrust T of unit 11 and 5 is the transverse component of that resultant thrust, the force acting at the centre of buoyancy comprises a transverse component 1.8 S and a forward component 0.2 A. The resulting direction of motion of the vehicle is thus not only transversely but also forwardly.

By opening the valve means 1 6 of unit 11, air is introduced into the water intake casing and this reduces the efficiency of the unit. At a certain opening of the valve means 1 6 (see Fig. 4), the efficiency of unit 11 will be reduced by 20%. With the valve means in that position, the horizontal components of the thrust of the two units balance out and the vehicle moves only in a transverse direction.

By further opening of the valve means 1 6 of the unit 11, the efficiency of unit 11 can be reduced below that of unit 12. The effect of this (see Fig. 5) is to cause the vehicle to move not only transversely, but also rearwardly.

If the vehicle is to move transversely but in the opposite direction to that shown in Figs.

3, 4 and 5, the rotatable member 1 3 of the unit 11 will be directed forwardly of the vehicle and towards the longitudinal axis of the vehicle, and the rotatable member 1 5 of the unit 1 2 will be directed rearwardly of the vehicle and away from the longitudinal axis of the vehicle. In order to obtain a desired transverse movement, the valve means 1 7 will be opened to a position corresponding with the desired transverse movement.

Claims

1. A marine jet propulsion unit comprising a water intake casing, an impeller casing connected to the intake casing, an impeller within the impeller casing, a water outlet casing connected to the impeller casing, a rotatable member associated with the water outlet casing for controlling the direction of discharge of water from the unit, and normally-closed valve means operable to introduce gas into the water intake casing.

2. A floating vehicle having two jet propulsion units according to Claim 1, the units being symmetrically disposed near to the rear of the vehicle with one on one side of the longitudinal axis of the vehicle and the other on the other side of that longitudinal axis.

3. A marine jet propulsion unit substantially as hereinbefore described and with reference to Figs. 1 and 2 of the accompanying drawings.

4. A floating vehicle substantially as hereinbefore described and with reference to the accompanying drawings.