BACKGROUND Many inflatable or otherwise buoyant devices exist for play by children, some add a safety advantage by supporting children in water. Some mimic boats and have paddle systems to be driven by pedaling.

THE INVENTION The present invention provides a craft for water sport or play, which comprises a body which exhibits buoyancy in water, the body having underwater surfaces and above water surfaces when floating on water, the above water surfaces including surfaces for support of or occupation by a person, mounted on the underwater surfaces a device including a nozzle adapted to provide a propulsive jet of water, characterised in that there is provided a connection from the device to a flexible hose which can supply a source of water under pressure.

The buoyant body can be dimensioned sufficiently to carry, partially or wholly, a child or a person. Alternatively, the craft may be used as a toy, which cannot . carry a person. The above water surfaces may thus be provided with a seat or seat like formations perhaps supporting the child or person entirely above the water or with feet dangling in the water or otherwise as required. The upper surfaces may also have ornamental or other features which are imitative of boats, ships, animals, fantasy objects or the like, for example, in application to children.

In accordance with the invention there is also provided a device for use in a craft according to the invention. The device includes a nozzle and is adapted for convenient attachment to the underside of the buoyant body of the craft.

The device may be provided with passages associated with the nozzle so that the propulsion jet entrains water adjacent the nozzle exit to enhance impulsion by this means. A Venturi effect may be generated by a constriction in the associated passages.

Preferably the connection to the nozzle is adapted to receive a hose, which may be connected to the return of a swimming pool water circulation system.

A preferred design according to the invention provides a curved or arcuate nozzle, with an entrance and exit directed generally in the same direction. This provides that a hose connected to the entrance of the nozzle is pulled rather than pushed as the device moves through the water under impulsion of the jet issuing from the exit of the nozzle. That is convenient and more conducive to a smooth action of the hose, which is flexible.

In accordance with a preferred embodiment of the invention the nozzle is mounted on an upright shaft, which is able to rotate mounted and provided with a steering wheel or handle-bars for a person mounted on the craft or playing with the craft to be able to steer the direction of impulsion given by the nozzle. Alternatively or in addition the nozzle may be fixed and deflection plates or rudder plates can be provided either to serve as steering rudders for the device or as deflectors so as to give a directional control of the impulsive forces and if applicable the entrained water masses.

In accordance with a preferred embodiment of the invention the buoyant body is provided as an inflatable shaped sheet material so that that the body can deflate and collapse as desired. This can be important for economical packaging of the product for purposes of sale and for the transport of the product to locations of sale such as retail outlets.

The inflatable body will have to be suitably reinforced for the mounting of the nozzle and in particular for cases where the nozzle and/or deflection plates or rudders are able to steer.

Preferably the connection provided from the hose will be a swivel connection to allow for compensation through swivelling as the device is steered in the manner of a water-craft in various patterns over a surface of water, for example, in a swimming pool.

The invention will be more fully described by way of an example with reference to the accompanying drawings in which :- figure 1 is a cross sectional side elevation of a nozzle for a device for water sport or play, on section A-A shown n figure 1, figure 2 is an underneath view of half of the device which is symmetrical about the line A-A, figure 3 is a rear elevation of the nozzle, figure 4 is a view of a device in accordance with a preferred embodiment of the invention, figure 5 is a graph of pump performance, figure 6 is a graph of pump performance and nozzle inlet velocity, figure 7 is a perspective"wire"drawing of the nozzle and associated passage, figure 8 is a similar drawing of the nozzle and associated passage in side view, figure 9 is a representation of velocity vectors in the nozzle and associated passage, in use, and figure 10 is a representation of velocity magnitudes in the nozzle and associated passage, in use.

As shown in figures 1 to 3, the nozzle 1 comprises a surface 2 for attachment to the underside of a buoyant body, thus it is submerged when in use. The nozzle has an entrance 3 for water leading via a constricting passage 4 to an exit 5 for a jet of water to issue from the nozzle. Energy for generating the jet is provided by a venturi effect caused by water supplied to a connection 6 which communicates with a passage 7 which narrows and at 8 directs an entraining jet into the passage 4, entraining water in the passage and out of the nozzle 'exit 5. The narrow part 8 of the passage 7 is slot shaped as is the passage 4.

The connection is adapted to accept a swivel connector to a hose or may be provided itself as a swivel connector. The flows of water are indicated by the arrows 9.

Figures 5 and 6 show typical flow rates available from typical swimming pool pumps and hoses, used with the invention.

Figures 7 and 8 show CAD"wire"drawings of the curved nozzle 7 and associated passage 2. The effect of having the associated passage in which water is entrained by the jet issuing from the nozzle is an increase in thrust, which drives the device. The increased thrust provided by the passage associated with the nozzle is defined by the following: Figures 9 and 10 show the flow characteristics in use of the device.

Improvement in design can be achieved in respect of certain detail aspects, within the scope of this invention.

Consider the water ejector nozzle as shown in Figure 4. The force that is exerted on the water in the nozzle (the opposite that is exerted by the water on the nozzle) in the movement direction (x-direction in/figure 3b) is given by the conservation of momentum equation.

Figure 4-Control volume of water ejector nozzle For the control volume in/Figure 4, equation 1 becomes - P in A in COSA + F x=m2V2-(m in(-Vin cos α) + msuctionVsuction (2) , « Fx = m2V2 + m2V2 COS α - msuctionVsuction + Pin Ain Cos a From the conservation of mass, w m2 = min _+ msuction (3) It can be ssen that the contribution of the suction inlet is to increase the mass flux at the outlet, which in turn increases the thrust (Fx) driving the craft. The maximum theoretical thrust (with no losses) with a specified inlet bend angle, a, and inlet area equal to the outlet area, without the venture-suction principle, is Ftheoretical = minVin(1+cosα) + pinAin cosα (4) Comparison with this vale emphasises the amplification factor of the venture.

Applying these equations to a practical example, the following results are shown :- Integrated data The performance of the ejector is measured by its ability to transform the inlet momentum of the pump into a thrust at the outlet through the entrainment of additional fluid through the venture principle. Table 1 lists a number of descriptive parameters for the CFD analysis that can serve as a bench mark for comparison with future designs. Note that the effective horizontal thrust is 123.3N with the current inlet bend angle of a +34° Inlet velocity [m/s] 2.75 Inlet flow rate [m3/hr] 10. 58 Pump head [kPa] at operating point on 32.8 system curve Horizontal thrust at inlet (m inV in+PinAin) 35.9 cos a [Nl Horizontal thrust at outlet (m 2V2) [N] 89.0 Horizontal thrust at suction inlet 1.6 msuctionVsuction [N] Net horizontal thrust of ejector (-F, J [N] 123.3 Theoretical thrust [N] 44.0 Amplification factor 2.8 Minimum pressure in jet throat [kPa]-22. 6 Table 1-Integrated data Figures 9 and 10 show velocity vectors and magnitude contours established during investigations of the nozzle and passage.

The following recommendations can be made: 1. Investigation show the influence of the jet exit slot width and alignment on the effective thrust at the outlet. This implies that the jet spreading rate, attachment to the lower and side wall, and the recirculation bubble size will vary to find an optimum combination. Care has to be taken that the minimum pressure in the throat (-22.6kPa in the current design) does not fall to the vapour pressure value (at typical pool temperatures) as this will imply cavitation. Reduction of the slot will increase the losses through the nozzle and reduce the delivery of the pump, thereby changing the system curve of the nozzle and move the operating point on the pump curve.

2. Investigation show the influence of the inlet bend entrance angle on the effective thrust. This investigation can be linked to the variation to the alignment of the jet above.

3. Improvement to the shape of the inlet bend will reduce the losses in the bend. The external flow conditions can also be optimised by design and a higher capacity pump can be used.

The device according to a preferred embodiment of the invention is shown in figure 4, with the nozzle shown in figures 1 to 3 attached. The device comprises a buoyant body 10 which has a seat 11 and with stern 12 and bow 13 mimics a small boat. The body is moulded in polystyrene in this example, but can be made of an inflatable sheet material. The body is shown floating in water 14 and the nozzle 1 is submerged underneath the body. The nozzle is attached by means of a shaft 15 passing through a tube 16 which is moulded in the body. Handle bars 17 at the top of the shaft 15 allow steering the nozzle to endow the body with steer able mobility. A swivel connector 18 connects a hose 19 to the connection 6 and the hose leads to the return orifice 20 at the pool edge. The return orifice is for the return of water to the pool from the pump and filter system of the pool.

Water is pumped out of the orifice 20 and via the hose 19 to the nozzle 1 providing a jet exiting from the nozzle as indicated by arrow 21.