Filed of the invention

This invention relates to a new type of waterjet propuls¬ ive system for high speed boats.

State of art

Today's systems consist of propellers (fixed or vari¬ able), surface piercing propellers, waterjets and air- propellers.

Surface piercing propellers and air-propellers have a good propulsive efficiency at high speed, but are often bad at low speed and manoeuvring. Surface piercing pro¬ pellers also often suffers from vibration problems.

Normal propellers (in particular variable pitch propel¬ lers) give good propulsive efficiency for speeds up to appr. 40 knots. Normally they are not used above 40 knots.

Waterjets are more reliable than propellers and surface piercing propellers, and do not have any vibration prob¬ lems. Waterjets have a lower propulsive efficiency than a surface piercing propeller at high speed, but normally they have better propulsive efficiency and manoeuvring capabilities at low speed.

All above mentioned propulsive systems suffer from the disadvantage of having the rotation 90 degrees to the waterflow.

Applicant is aware of Norwegian patent application no. 913921, WO 93/08075 and GB 1.090.062. These systems make use of paddle wheels or similar, rotating in the same direction as the waterflow.

Summary of the invention

The waterjet, according to the invention, also make use of a paddle wheel, rotating in the same direction as the waterflow, but the paddle wheel is fitted into a closed pump house and acts like an impeller. This makes the sy¬ stem act like a waterjet, which is not the case in the above mentioned systems.

With the waterjet according to the invention, it is pos¬ sible to achieve a propulsive efficiency similar to, or better than, a surface piercing propeller at high speed, and at the same time achieve similar or better reliabili¬ ty, manoeuvrability and propulsive efficiency as today's waterjets at low speed.

With today's systems problems exist in maintaining a high propulsive efficiency over a large speed range. The fact that the paddle wheel, according to the invention, ro- tates in the same direction as the waterflow, makes it possible to keep the relative motion between the water and the paddles approximately constant at all speeds. This enables a high propulsive efficiency to be main¬ tained over a large speed range.

This is achieved, according to the invention, by fitting a paddle wheel into a closed pump house, and use it as an impeller. By doing this the paddle wheel will add pres¬ sure and velocity to the water flowing through the pump house.

Steering can be done by using small rudders changing the direction of the waterflow in the outlet, similar to the systems on today's waterjets.

Reversing can be done by using reverse ducts the same way as is done on ordinary waterjets.

Further advantages and features of the present invention will appear from the following description taken in con- nection with the appended drawings, as well as from the attached patent claims.

Brief disclosure of the drawings

A non-limiting embodiment of an arrangement, specifically a waterjet for propulsion of high speed boats, according to the invention, is shown in Fig.1, 2 and 3.

Fig.1 and Fig.2 show a side view, partly in section, of an embodiment of the present system, Fig.1 illustrating the system in reversing condition, whereas Fig.2 illu¬ strates the system at speed.

Fig.3 shows the system as seen from above.

Disclosure of embodiments

A paddle wheel 1 is fitted into a substantially closed pump house 11, and is acting as an impeller.

The pump house 11 is fitted with a water inlet 8 in the front and a water outlet 4 in the rear. The pump house 11 is formed in such a way that the lower part 2, between the inlet 8 and the outlet 4, is kept close to the paddle wheel 1 and forces the water to change direction and follow the lower part 2 of the house 11 until it is thrown out through the outlet 4.

The fact that the pump house 11 in this lower part 2 is kept in close proximity to the paddle wheel 1 in this area, prevents the water from escaping from the paddles 7, and leads to an increase of pressure and velocity of the water, according to the centrifugal principle.

The upper part 3 of the pump house 11 can be constructed with an appropriate distance to the paddle wheel 1 , as its function is simply to close the pump house 11. Because the pump house is so to say fully closed, except from the inlet 8 and the outlet 4, a vacuum is created in the pump house 11, as the water is thrown out via the outlet 4. This vacuum sucks new water into the pump house 11, through the inlet 8, and then according to the dis- placement principle.

To control the vacuum in the pump house 11, an air inlet is arranged, preferably through the paddle wheel shaft 9 by making it hollow and with holes 10 from the hollow shaft into each chamber between the paddles 7. Air is then allowed to communicate with the system through an adjustable valve, for thereby controlling the vacuum level.

When the boat is laying still or driving at slow speed, it is necessary to increase the vacuum in order to get enough water into the pump house 11. When the boat is driving at high speed, the water is forced into the pump house by the boat's motion through the water, and the vacuum in the pump house can be decreased.

For all combinations of boat speed and engine revolu¬ tions, there will be an optimal vacuum level.

This can be controlled by a computer, using boat speed and engine revolutions as inputs.

The effect achieved by this is very similar to the effect achieved from a variable pitch propeller.

Using a paddle wheel, which is rotating with the water flow, instead of a normal impeller rotating 90 degrees to the water flow, will enable us to avoid the problems created by a 90 degrees rotation.

The waterjet, according to the invention, has no submer- ged parts creating friction. The only friction losses come from the lower part of the pump house and the water outlet.

Calculations and tests have indicated that the waterjet, according to the invention, can be made smaller and ligh¬ ter than today's waterjets. In addition this system is very simple to build and maintain.

In order to avoid cavitation problems, ordinary waterjets has to reduce velocity of the water entering the waterjet during high boat speed. This is done by a water intake formed like a diffusor, and leads to a large water in¬ take. The waterjet, according to the invention, can take the water into the jet at the same velocity as the boat speed. This enables us to use a significant smaller water intake than ordinary waterjets.

The waterjet, according to the invention, can be made of the same materials as today's waterjets.

Size, shape and number of paddles can to be adjusted to various engine and boat sizes, for example in the same way as it is done for ordinary waterjets and propellers.