Small yachts and power boats which have on-board electrical lighting and other electrical services have electrical generators on-board which are driven while the vessel is travelling, to feed the electrical on-board systems and to charge the on-board batteries.

However, when the vessel is moored to a buoy or the dockside or at anchor, the power is usually no longer available to drive the generators and so use of the electrical systems quickly depletes the on-board batteries. It has been proposed to supplement the charging of the batteries from a solar panel generator or a wind generator. The problem is that the vessel is usually moored at night when the solar panel is inactive. As far as the wind generator is concerned, winds tend to be variable and so cannot always be relied upon to produce the power. Also, the amount of power generated is fairly low unless a large wind driven propeller is used and this could be impractical on a small boat.

It is an object of the invention to provide an improved system for generating electricity using wave power.

According to the present invention, there is provided an electricity generating system for generating electricity from wave motion, the system being mountable on a vessel and having an elongate retractable member with a portion being securable to a

structure not subject to the same wave motion as the vessel, the system including a reel around which said elongate member can be wound, means for biasing said reel in a sense to retract said elongate member when slack about said reel, one way clutch means for transmitting rotation of said reel to a main drive shaft when said elongate member is drawn off said reel, means coupling said main drive shaft to a power storage mechanism, said power storage mechanism storing power from said main drive shaft when driven by said reel and releasing power to drive said generator.

Electricity generating systems embodying the present invention, will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a view of a sea-going vessel secured to a dockside; Figure 2 is a front elevation of the system with the front cover removed ; Figure 3 is a side view of the system of Figure 2; Figure 4 is a rear view of the system of Figure 2; Figure 5 is a view to an enlarged scale of the system of Figure 3; Figure 5A is a perspective view of a detail of the system of Figure 5; Figure 6 is a view to an enlarged scale of the system shown in Figure 2; and Figure 7 is a view of a detail of Figure 6.

As shown in Figure 1, a boat 2 is moored to a dockside 4 with the aid of tether 6 in the form of a web or belt. The free end of the belt has a loop, which can be looped over a tethering post 8 on the dock 2. The other end of the belt is wound on retractable reel or

capstan 10 of an electricity generating system 12 secured firmly to the deck of the boat 2.

Due to wave motion, the distance between the capstan 10 and the tether post 8 tends to vary and the system 12 acts to draw the belt 6 around the capstan 10 with the aid of a retractable spring when the belt is slack but to couple the capstan 10 to an electric generator 14 when the belt is under tension so that as the belt unwinds from the capstan 10, the generator is driven. The capstan 10 also drives a power spring mechanism to store power at the same time, which power spring mechanism continues to drive the generator during the periods that the belt is not under tension due to wave power.

The system is more clearly illustrated in Figure 5. As shown, the system comprises a pair of spaced support plates 20 and 22. Each support plate 20 and 22 has a respective foot section 20A and 22A which extends at right angles to the plane of the plates. The foot sections 20A and 22A are anchored to the deck of the vessel 2 by means (not shown).

The plate 20 carries a stub shaft 24 which in turn carries a gear wheel 26. The stub shaft 24 also carries the capstan 10 onto which the belt 6 is wound.

The two plates 20 and 22 rotatably support a transversely extending main shaft 26 which projects from opposite sides of the plates 20 and 22. Mounted on the side of the shaft 26, projecting from the plate 20, is a one way clutch 28 supporting a gear wheel 30.

The clutch operates so that when the gear wheel is driven in one sense, the gear wheel 30 is locked to the shaft so that rotation of the gear wheel in that sense will drive the shaft 26 but

rotation of the gear wheel 28 in the opposite sense will allow the gear wheel 28 to rotate relative to the shaft 26.

The gear wheel 30 meshes with gear wheel 26, the gear ratio being 2: 1.

A U-shaped bracket 32 supports a core 34 extending coaxial with the capstan 10 and located within a central recess thereof. A coil spring (not shown) secured at one end to the spool 34 and at the other end to the capstan 10 lies between the core 34 and capstan 10 to bias the capstan 10 for rotation in one sense to draw in the belt 6 around to the capstan.

Rotation of the capstan 10 in this sense is communicated to the gear wheel 30 via the gear wheel 26 and thus clutch 28 will allow the gear wheel 30 to rotate freely about the shaft 26.

Rigidly mounted on that end of the shaft 26 which projects from the plate 22 is a spring spool 36. Located in side by side relationship with the spool 36 is an auxiliary spring spool 40. The auxiliary spring spool 40 is mounted for free rotation about a stub shaft 38 which projects from the plate 22 and has an axis which extends parallel to the axis of the shaft 26.

A coil spring 42 has one end rigidly secured to the core of the spool 36 and the other end secured to the core of the auxiliary spool 40. The coil spring 42 is wound in its normally wound sense about the auxiliary spool 40 and connected to be wound in the opposite sense about the spool 36 (see Figure 6).

A worm gear 46 located between the two plates 20 and 22 is rigidly secured to the shaft 26. The worm gear 46 meshes with a worm 44 which is rigid with the rotary shaft 48 of an electric generator 50. The housing of the generator 50 is rigidly secured to the support plates 20 and 22.

The gear rotation between the worm gear and the worm is 25: 1 but may lie in the range of from 20: 1 to 30: 1.

The length of the belt 6 is typically 1 to 2 m so that it can be accommodated fully wound on the capstan 10. It may, however, be extended by attaching to its free end whatever length of rope is required.

In operation, starting from the point at which the belt 6 is at least partially wound around the capstan 10 and the wave motion of the sea is acting to move the boat and therefore the system 12 away from the tethering post 8, the belt 6 will slowly be drawn off the capstan 10 causing the capstan to rotate. The force to which the belt is subject to will depend upon the weight of the boat (which may well be several tons) as well as the frequency and size of the waves and therefore may be quite considerable. As the belt 6 unwinds, the capstan will rotate which in turn will rotate the gear wheels 26 and 30.

The clutch mechanism 28 will lock the gear wheel 30 to the shaft 26. Rotation of the shaft 26 will wind up the coil spring 42 and at the same time drive the worm gear 46.

Rotation of the worm gear 46 will in turn drive the worm 44 and therefore the rotor of the

generator 50. Rotation of the generator rotor will generator an AC electrical current which is fed to a transformer and an AC to DC rectifier circuit (both not shown) for conversion to a charging current to charge the vessel's batteries.

When the tension in the belt 6 ceases and the belt becomes slack, the coil spring about the spool 34 will act to rotate the capstan 10 in the opposite sense and so wind the belt 6 back up onto the capstan. This rotation will not drive the shaft 26 because of the de- coupling action of the clutch 28. In the meantime, the tension previously built up in the spring 42 will now be released and will continue to drive the drive shaft 26 in the same direction so maintaining the drive to the generator during the periods that the belt 6 is not under tension.

The gearing of the system and the power of the spring 42 is so selected that the generator is driven at a speed of around 1500 revolutions per minute. In order to avoid over-tension the spring 42, a spring release mechanism is provided (see Figure 6). As can be seen, a lever 52 is supported by a pivot 60. One end of the lever 52 rests on the coil spring 42 wound on the auxiliary spool 40 and is urged against the spring 42 by a bias spring 54. The other end of the lever 52 engages a pivotal latch 56 which when triggered releases the spring tension. In operation, as the shaft 26 starts to rotate, it draws the spring 42 from the auxiliary spool 40 onto the main spool 36. The lever 52 follows the reduction in the thickness or amount of spring 42 wound on the auxiliary spool 40. When a predetermined thickness has been reached, the latch 50 will lock the spool 40 against further rotation. Instead, the latch may act to de-couple the spring 42 from the shaft 26 with

the aid of a clutch (not shown).

In addition or instead, the clutch 28 may be designed to slip while in engagement when a predetermined tension is reached.

It will be appreciated that the belt may be tethered to a structure other than a dock 2, for example, to the sea bed via a buoy or an anchor provided that there is relative movement between the vessel and the structure. In a modification, the system may be fitted the other way around with the generator secured to the dock 2 and the belt secured to the vessel.

It will be appreciated that while the worm drives the rotating shaft of the generator, it can instead be coupled to a gear mechanism which drives the stator and rotor of the generator in opposite directions at the same or different speeds thereby reducing the absolute speed at which each is driven.

In yet a further modification, the generator may be driven by a turbine (not shown) from compressed air supplied from a reservoir (not shown). The main shaft 26 is then used to drive a compressor which supplies compressed air to the reservoir. In the latter case, the worm gear, the worm and the spring mechanism are omitted.