MARINE VESSEL

Field of the Invention

The present invention relates to a method and apparatus for controlling the motion of a marine vessel. In various configurations the method and apparatus may provide control whether the vessel is at anchor, underway or sailing.

Background of the Invention

It is known to use gyroscopic stabilisers (gyro stabilisers) for the purposes of stabilising marine craft and in particular minimizing the effects of roll created by wave action while the vessel is underway.

A gyroscopic stabiliser may be operated in two ways in order to apply a torque to reduce a vessel's roll. The most power efficient method is as a passive gyroscope, where rolling motion of the vessel generated by wave action generates a precession moment in the gyroscope which in turn generates a torque opposing the motion induced by the waves. However the most effective method on the basis of size of the gyroscope is to operate the stabiliser in an active mode where precession of the gyroscope is controlled by an external device such as a motor or a brake governed by a sensor.

Summary of the Invention

According to a first aspect of the present invention there is provided a method of controlling motion of a vessel normally at anchor comprising: installing a gyroscope in the vessel, the gyroscope having a fly wheel that spins about a spin axis and

mounted on a trunnion axis lying in a plane perpendicular to a plane containing the spin axis, the plane of the trunnion axis further aligned with a plane containing motion of the vessel created by wave action on the vessel; spinning the fly wheel; and, wherein the fly wheel precesses about the trunnion axis in response to wave created motion of the vessel to produce a reactive torque that resists the wave created vessel motion.

Preferably the method comprises spinning the fly wheel at a speed greater than 4000rpm and more preferably spinning the fly wheel at a speed of greater than 6000rpm.

Preferably the method comprises spinning the fly wheel at a speed of greater than SOOOrpm.

Preferably the method further comprises mounting the fly wheel on the trunnion axis in a manner to allow precession of the fly wheel about the trunnion axis of at least between plus or minus 40°, and more preferably of at least plus or minus 60°, and, most preferably up to plus or minus 80°.

Preferably the method further comprises coupling the fly wheel to a drive motor through a clutch and selectively disengaging the clutch when the fly wheel speed exceeds a first speed.

Preferably the method further comprises engaging the clutch when the fly wheel speed is less than a second speed where the second speed is slower than the first speed.

Preferably the method further comprises coupling an energy conversion machine to the gyroscope in a manner whereby

precession of the gyroscope is converted into energy by the machine.

Preferably the method further comprises operating the energy converting machine as a brake to thereby brake precession of the gyroscope about the trunnion axis.

Preferably the method further comprises operating the energy conversion device as a non-linear brake.

Preferably the method further comprises operating the energy conversion device as a non-linear brake where a braking effect of the machine increases non-linearly with increasing degree of precession about the trunnion axis.

Preferably the method further comprises constructing the gyroscope including the drive motor and energy conversion device to have a mass of approximately 0.5% of the mass of the vessel.

Preferably the method further comprises enclosing the fly wheel in a sealed atmosphere of a gas having a density less than air.

Preferably the gas comprises helium.

Preferably the method further comprises biasing the fly wheel about the trunnion axis in a manner to urge the spin axis to lie in a vertical plane.

In one embodiment the fly wheel is a hollow fly wheel. The hollow fly wheel may comprise first and second shells that are joined together. The shells may be of substantially identical shape and configuration. Most conveniently, the shells join along a plane perpendicular to the spin axis of the fly wheel.

Each shell may comprise a mount aligned with the spin axis of the fly wheel, whereby the fly wheel is supported by the mounts along the spin axis. Each mount may be formed integrally with its corresponding shell. Moreover the mount may be formed to extend from an outer surface of the fly wheel in a direction of the spin axis.

The shells may be formed with a thickness that is different at at least two different locations . Moreover each shell may have a thickness measured in a direction perpendicular to the spin axis that changes in the direction of the spin axis. The thickness in the direction perpendicular to the spin axis is at a maximum at a location along the spin axis distant the mount. This location coincides with the plane containing the join between the first and second shelves.

The hollow fly wheel may be formed with an outer radius that varies in the direction of the spin axis . The outer radius is at a maximum at a location coincident with the plane containing the join between the first and second shells. These also coincide with the location of the maximum thickness of each shell.

In a further embodiment, the method may further comprise mounting the gyroscope in a manner whereby the gyroscope can move linearly athwart the vessel. Moreover the method comprises sensing motion of the vessel arising from a gust of wind and moving the gyroscope toward a windward side of the vessel in response to the motion arising from the gust of wind. The moving of the gyroscope may typically be under computer control, the computer receiving input in relation to wind direction and velocity as well as gyroscope position and precession characteristics; and on the basis of these inputs controlling an actuator to move the gyroscope to a position to where torque applied by the

gyroscope in precession is directed to counter movement of the vessel arising from the gust of wind.

A further aspect of the present invention provides a gyroscope comprising a hollow fly wheel.

A further aspect of the present invention provides a method for controlling motion of a vessel subjected to heeling motion arising from a gust of wind, the method comprising mounting a gyroscope in the vessel in a manner to allow motion of the gyroscope athwart the vessel; sensing motion of the vessel arising from a gust of wind; and, moving the gyroscope athwart the vessel to a position when torque applied by the gyroscope in procession acts in a direction to counter the heeling motion of the vessel.

Brief Description of the Drawings

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of a method of controlling motion of the vessel in accordance with the present invention;

Figure 2 is a schematic representation of a gyroscope for applying the present method;

Figure 3 is a schematic representation of a bar system incorporated in the gyroscope shown in Figure 2;

Figure 4 is a schematic representation of a second bar system incorporated in the gyroscope shown in Figure 2; Figure 5 is a cross section view of a hollow fly wheel in accordance with an embodiment of the present invention;

Figure 6 is a schematic representation of a shell portion of the fly wheel;

Figures 7A, 7B and 7C are schematic representations making a comparison between a convention fly wheel and a hollow fly wheel in accordance with the present invention; and,

Figure 8 is a schematic representation of a further embodiment of the invention that may be used to counter healing motion of the vessel.

Detailed Description of Preferred Embodiments

Figure 1 represents a vessel 10 to which an embodiment of the present method is applied to control motion of the vessel particularly though not exclusively when at anchor. Installed in the vessel 10 is a gyroscope 12 having a fly wheel 14 mounted for rotation about a spin axis 16. The gyroscope 12 is mounted in a gimble (not shown) having a trunnion axis 18 that is mounted athwart the vessel 10. In a steady state condition where the vessel 10 is not subject to any external forces the spin axis is in a vertical plane, and the fly wheel 12 is in a horizontal plane. Further, the trunnion axis 18 is aligned in a plane containing motion of the vessel 10 created by a wave of motion that is designed to be controlled. In this instance, the motion created by the vessel that is desired to be controlled is roll motion. The roll is about a roll axis 20 that extends fore and aft the vessel 10 and is perpendicular to both the trunnion axis 18 and spin axis 16. The direction of roll is further indicated by curve 22 in Figure 1.

A significant departure in the method of operating the gyroscope 12 from the prior art is pivotally mounting the gyroscope (ie fly wheel 14) to enable precession about the trunnion axis of more than plus or minus 40° and more preferably at least plus or minus 60° and most preferably

up to plus or minus 80°. In the prior art, precession is limited to approximately plus or minus 35°. In addition the fly wheel is spun at a rate substantially greater than the prior art which typically sets spins rates in the order of lOOOrpm to 3500rpm. It is envisaged in the present method that the fly wheel will spin at the rate of at least 4000rpm and more preferably at greater than 6000rpm.

As explained further below, the benefit of the increased precession range is the ability to use the precession of the gyroscope to generate energy. Also, by providing much greater spin rates enables higher gyro-coupling torque compared with the gyro inertia. This produces much quicker anti-rolling torque and reduces the phase angle between the torque applied to the gyroscope by the wave motion and the reactive torque. This enables the construction of a much smaller gyroscope to produce the same torque that can counter react to a higher frequency of excitation (ie wave motion) while also allowing the gyroscope to be substantially lighter and occupy less space in the vessel.

It is envisaged that by operating the gyroscope at the spin rates mentioned above enables the entire gyroscope to be constructed of a mass no more than 0.5% of the mass of the vessel. In comparison, earlier models of brute gyroscopes typically had a mass of between 1% to 2% of the mass of the vessel and operated at low spin rates. Present embodiments enable vessel stabilization, for example of a vessel at anchor subject to relatively high frequency waves generated by the wake of a passing vessel.

Figure 2 depicts the fly wheel 14 encased in a casing 24 which is pivotally supported on the trunnion axis 18. A drive motor 26 is mounted to the casing 24 and drives the fly wheel 14 to its required speed.

Advantageously, the motor 26 is coupled to the fly wheel 14 via a clutch (not shown) so they can be selectively engaged and disengaged. Further, a sensor (not shown) is provided to sense the rotational speed of the fly wheel 14 and provides an output used to selectively engage and disengage the clutch. More particularly, the gyroscope is operated so that the clutch is disengaged to decouple the fly wheel 14 from the motor 26 when the speed of the fly wheel is sensed as exceeding a first speed, for example 7000rpm. Thereafter, the clutch may be engaged automatically when the sensor senses that the speed of the fly wheel 14 drops below a second speed for example 5000rpπι. In addition to the operation of the clutch, the output of the sensor may also be used to selectively connect and disconnect the motor 26 from a power source simultaneously with engaging and disengaging the clutch. In this way the motor 26 does not consume energy when it is not required to impart drive or torque to the fly wheel 14. In addition this also ensures that the motor 26 does not apply drag to the fly wheel 14.

The gyroscope 14 is arranged so that it can precess about the trunnion axis through an angle of plus or minus θ from a vertical axis 28 where θ may be up to 80°. This provides a total arc 30 of precession of up to 160°.

It should be noted that the gyroscope 14 is able to precess through its precession arc in the same time as prior art gyroscopes. Accordingly, as the arc length of the precession is much longer, the precession rate is also higher. Typically the gyroscope 14 will precess at about lOrpm.

Due to the rate of precession and the extent of the precession arc 30, an energy conversion device 32 such as an electric generator or hydraulic motor can be coupled to

the gyroscope 14 for the purposes of converting the precession of the gyroscope 14 into energy. This energy can be stored, for example in batteries for use on the vessel 10 including for the purposes of powering the drive motor 26. In this particular embodiment, respective pulley wheels 34 and 36 are coupled to the gyroscope 14 and machine 32 to provide a mechanical advantage whereby the precession rate of the gyroscope results in a ten fold increase in rotational speed of the pulley wheel 36. In addition, the incorporation of a gear box may provide further increase in rotational speed of the machine 36 so that for example, the precession rate of lOrpm in the gyroscope provides a rotational speed of 400rpm in the machine 32.

It should be appreciated that the machine 32 also acts as a brake to the precession of the gyroscope. Depending on the structure of the machine 32 the braking effect may be subject to control for example by a computer. This further enables the braking effect to be non-linear so that a greater braking effect is applied toward the outer limits of the precession arc. For example this may be achieved where the machine 32 is a hydraulic pump by computer control of one or more valves restricting flow of fluid at greater angles of precession away from the axis

28. The use of non-linear braking over the precession has several benefits including minimising the phase difference between the gyroscope's precession and the roll motion and enabling a greater usage of the gyroscopic coupling in non-regulated wave patterns.

In order to reduce energy requirements and consumption, the casing 24 may be formed as a sealed casing containing a gas of a density less than air, such as for example helium. Further, the atmosphere may be at a pressure less than atmospheric pressure. It is believed that the combination of these effects will assist in reducing drag

on the fly wheel 14 as it rotates thereby reducing energy loss. Similar effects may also be achieved by evacuating the casing 24 so as to produce a relative vacuum.

Typically in the prior art, the gyroscope is self- centralised by virtue of mass. That is, the mass of the gyroscope including attached drive motors in used to centralise the gyroscope in a gimble so that the spin axis is urged toward the vertical. However, the present invention also envisages the provision of mechanical springs for biasing the gyroscope towards a centralised position where the spin axis 16 lies in a vertical plane. This has the benefit of enabling a reduction in weight thereby reducing the inertia of the gyroscope about the precession trunnion making it more responsive to higher frequencies and reducing phase lag between wave action causing motion of the vessel 10 and the gyroscopes reaction.

Figures 3 and 4 schematically depict two different methods of applying spring bias to centralise the gyroscope. In Figure 3, two helical springs 38 which act with identical moment arms about the trunnion axis 18 for restoring the fly wheel 14 to the horizontal plane and the spin axis 16 to the vertical plane.

In Figure 4, the helical springs 38 have been replaced with a spiral spring having a central axis coincident with the trunnion axis 18 acting to bias the fly wheel 14 to the horizontal plane and the spin'axis 16 to the vertical plane.

In the above described embodiments, it is assumed that the fly wheel 14 is a conventional fly wheel in a form of a solid disc made of steel or other metal. However Figures 5 and 6 depict an alternate form of the gyroscope comprising a hollow fly wheel 14A. The fly wheel 14A

comprises first and second shells 5OA and 50B (hereinafter referred to in general as "shells 50") . The shells 50 are, in this embodiment, made of identical configuration and join in a plane 52 that extends perpendicular to the spin axis 16. The shells are of a generally U shaped or bowl shaped configuration. Each shell 50 is provided with a mount 52 that extends from an outside surface of the fly ^¬ wheel 14A in a direction of the spin axis 16. The mount 53 is typically in a form of a boss that forms a bearing seat to enable to fly wheel 14A to be supported along the spin axis 16.

A bulk of the mass of the fly wheel 14A is concentrated about an outer circumferential band 54. More particularly, it will be seen that the thickness of each shell 50 varies in the circumferential band 54 in a direction along the spin axis 16. The thickness is at a maximum thickness Tl at a location adjacent the joint plain 52. Moving in a direction along the spin axis 16 toward the mount 53 the thickness at location T2 is decreased. The variation in thickness can be manifested by having an outer radius of the fly wheel that also varies in a direction along the spin axis 16 as depicted in Figure 5. For example the radius Rl at a location near the joint plain 52 is greater than the radius R2 at a location along the spin axis 16 closer to the mount 53. This results in the fly wheel 14A having a generally convex shaped central circumferential band 54 viewed from outside the fly wheel. However in an alternate embodiment the variation in thickness, if required, can be manifested by having an inner radius of each shell 50 that varies in the direction of the spin axis 16.

Providing the convexly curved circumferential band 54 optimises the maximum outer radius of the fly wheel 14a as well as its volume. Further, the load provided by the fly wheel is transferred to the mounts 53 where bearings are

located to minimise vibration. Further, as the fly wheel 14a does not have a central shaft weight savings are made.

Figures 7A - 7B depict schematically a comparison between a conventional fly wheel 14 and a fly wheel 14a in accordance with the present embodiment. In Figure 7A, the fly wheels 14 and 14a have the same radius/volume but fly wheel 14a has a lower mass or weight. In Figure 7B, the conventional fly wheel 14 and fly wheel 14a have the same inertia and mass but the fly wheel 14a has less radius/volume. Figure 7C depicts an arrangement where the conventional fly wheel 14 and the present fly wheel 14a have the same weight and same radius/volume but the fly wheel 14a has a greater inertia,

Figure 8 depicts a further embodiment of the present invention where the gyroscope 12 is used to control or compensate for heeling of the vessel 10 in response to the action of a gust of wind applied to the vessel 10 in a direction D. Here, the gyroscope 12 is mounted for movement athwart the vessel 10. This may be achieved by mounting the gyroscope 12 on a track or rail system 60 that traverse the vessel 10. Typically, gusts of wind are difficult to compensate for. The gusts often last for only 3 - 5 seconds.

While it is known to use ballast and more particularly moveable ballast to react to gusts of wind, the motion of the ballast is often too slow to provide effective compensation to the heeling motion generated by the gust.

By mounting the gyroscope on the rail system 60 the gyroscope may be moved to the windward side in order to provide a torque that is directed in a manner to counter the heeling motion generated by the gust of wind. The gyroscope 12 is mounted with its spin axis 16 in a vertical plane and pivotally mounted on its trunnion axis

18 aligned athwart the vessel 10. A controller such as a computer (not shown) is provided to received data inputs relating to wind speed and direction as well as the position of the gyroscope 12, speed of rotation of which the fly wheel 14/14A and the precession characteristics of the gyroscope 12. Data relating to vessel motion and orientation may also be provided as computer inputs. It will be appreciated that the gyroscope will start to precess when the vessel commences to heel. An actuator (not shown) such as a hydraulic ram, electric screw jacks, or a chain system driven by an electric motor is controlled by the computer to move the gyroscope 12 in an outboard direction along the track or rail system 60 so that its reactive torque acts in the direction to counter the heeling of the vessel 10. The precession of the gyroscope may be controlled actively or passively and the fly wheel may be in the form of a conventional fly wheel or a hollow fly wheel as described herein and above.

However when the gyroscope is used to control heeling motion it is considered beneficial that it have a mass of up to approximately 5% - 10% of the vessel. Further, the gyroscope 10 for the purposes of controlling heeling motion should be located near the middle of the vessel 10.

The vessel 10 may be provided with a single gyroscope to control roll and heeling motion or one or more gyroscopes to control the rolling motion, and one or more gyroscopes to control the heeling motion.

Modifications and variations of the above embodiment as would be apparent to a person of ordinary skill in the art are deemed to be within the scope of the present invention the nature of which is to be determined from the above description.