GB2178132A - Shock absorber for apparatus deployed under liquid - Google Patents

Abstract

A shock absorber 10 (Fig. 1) for use submerged in a liquid environment comprises a piston 11, 15 slidable in a cylinder 12 to define an enclosure 18, and aperture means communicating between the enclosure and the liquid environment and providing a passage for environmental liquid. The aperture means may take the form of an orifice 20 in the piston head 15 and a tapered spigot 27 defining the orifice area as a function of piston position. An external compressive load force is resisted by pressurisation of the environmental liquid in the enclosure and the rate at which it can be expelled by the orifice defined by the piston position and the aperture (orifice) area variation with piston position may be chosen to give a desired deceleration characteristics to a load lowered onto the device. The use of environmental liquid means that a reservoir for the liquid is not required and the aperture means which replaces conventional valves results in a simpler and cheaper arrangement which also is not restricted in scale. The aperture means may be formed instead by an apertured cylinder wall the effective cross-sectional area of which aperture also may vary with piston position. <IMAGE>

Description

SPECIFICATION Shock absorber for apparatus deployed under liquid This invention relates to shock absorbers and particularly to a shock absorber for use with apparatus deployed under liquid.

It is intended that the shock absorber itself is deployed and operated submerged in the liquid and for convenience in this specification and appended claims the term "submerged shock absorber" is used.

Shock absorber or motion damping arrangements are known in many forms and in many fields of mechanical engineering, usually in gaseous atmospheres, and frequently take the form of a compression spring operably connected to a reciprocable piston and cylinder arrangement, the cylinder being a sealed enclosure containing hydraulic fluid (possibly viscous) through which the piston is forced with, or by spring motion, resistance to motion being effected by limiting the flow of fluid past the piston to a rate determined by the dimension of orifices or valve openings in the piston.

A not inconsiderable part of the cost of such shock absorber constructions is in the provision of a fluid container, and in the prevention of fluid leakage, relating to the choice of fluid properties and external seal materials, dimensional tolerances of relatively movable parts and surface finish where movement relative to a seal is involved.

It is an object of the present invention to provide for use in a liquid environment a submerged shock absorber of simple construction and easier manufacture than heretofore known and a submerged object support arrangement including such a shock absorber.

According to a first aspect of the present invention a submerged shock absorber comprises a cylinder member, closed at one end thereof and a piston member, including a piston head, contained within the cylinder to define an enclosure between the piston head and said closed end of the cylinder and slidable therein to vary the volume of the enclosure as a function of the relative positions of piston and cylinder, and aperture means providing a passage for environmental liquid between the enclosure and liquid environment, a change in the enclosure volume due to relative displacement of the piston and cylinder members by an externally applied force being resisted by a pressure difference developed between the liquid in the enclosure and the environmental liquid by said force and permitted at a rate determined by the rate of flow of liquid through the aperture means.

According to a second aspect of the present invention a submerged object support arrangement includes hoisting means operable to lower an object in a liquid environment, a support bed in the environment to receive and support the lowered object, a submerged shock absorber as defined in the preceding paragraph attached to either one of the object or the support bed, with the axis of the relative displacement of piston and cylinder members thereof extending in the object lowering direction, and adapted to buffer against the other one as the object is lowered, and means to secure the object to the support bed with the submerged shock absorber intermediate the supported object and the support bed.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectional elevation through a shock absorber according to the present invention in an extended or unstressed, state with a first form of aperture means, Figure 2 is a sectional elevation through the shock absorber of Figure 1 but in an orthogonal direction and showing the shock absorber in a shortened compresssed state, Figure 3 is a side view of a submerged object positioning and support arrangement and showing an object, to which the shock absorber of Figures 1 and 2 is attached, being lowered to a support bed, Figure 4 is a side view of the arrangement of Figure 3 showing the object secured to the support bed with the shock absorber located between them, Figure 5 is a partly cut-away perspective view of the piston and cylinder members of a shock absorber arranged according to the present invention illustrating an alternative form of aperture means comprising a plurality of discrete through-apertures, and Figure 6 is a partly cut-away perspective view of the piston and cylinder members similar to Figure 5 but showing an alternative form of aperture means in the form of a slot.

Referring to Figure 1 a shock absorber 10 comprises two coaxial hollow tubular members 11, 12 the tubular member 11 being slidable axially within the tubular member 12.

The outer tubular member 12 is closed at one end thereof by a closure member 13 and comprises a cylinder member. The inner tubular member 11 is open to the environment by apertures 14 therein and comprises a piston member, carrying at the end thereof nearest to the closure member a piston head 15. The piston head is dimensioned to form a sliding fit within the cylinder member 12, which fit is made substantially liquid tight by a seal 16 located in a recess 17 of the piston head.

The outer tubular member 12, closure member 13 and piston 15 define an enclosure 18 which enclosure is pierced by aperture means providing a passage for liquid between the enclose and the environment. The aperture means comprises an orifice 20 in the piston between the enclosure and the inside of the inner tubular member 11, that is, communicating with the environment. A bleed aperture 19 through the closure member provides some communication between the enclosure as will be described later, but has little effect of liquid flow in operation of the aperture means.

The enclosure 18 contains a compression spring 21 coaxial with the tubular members and extending between the piston and closure member so as to exert a bias force between the piston head and the closure member. The extent of axial displacement of the tubular members by this bias is limited by guide means 22. The guide means comprises a base member 23 which is secured to the end of the inner tubular member remote from the piston 15 and supports guide rods 24 extending therefrom parallel to the longitudinal axis of the tubular members. The outer tubular member is provided with apertured flanges 25 which extend from the member wall, the guide rods 24 extending through the apertures such that the outer tubular member is slidable thereon to and from the base member and, therefore, relative to the inner tubular member 11.

The upper part of each guide rod carries a stop 26, such as provided by locked nuts on a threaded portion of the rod, to limit separation of the flange member from the base member by the spring 21, the displacement being such that the piston 15 remains within the outer tubular member.

The closure member 13 also carries a spigot 27 which extends into the enclosure along the longitudinal axis of the tubular members and coaxial within the piston orifice 20, the spigot 27 having a substantially parallel sided shank portion 28 and a tapered end portion 29.

The dimensions of the spigot are such that with the shock absorber fully extended by the spring 21 as shown in Figure 1 the narrowest part of the spigot, the tip 29', is contained in the orifice 20.

The orifice is in operation reduced in its effective cross sectional area in accordance with the thickness, that is, diameter, of the portion of the spigot contained in the orifice and varies from a maximum with the tip of the spigot, when the shock absorber is fully extended, to a minimum when the shank portion 28 almost fills the orifice.

The closure member 13 carries attachment means 30 by which the shock absorber is attached to the bottom of an object to be lowered from a surface vessel to a support structure on the sea bed (shown in Figures 3 and 4) and the base member 23 is adapted to provide a buffer surface for the shock absorber and load upon landing.

Operation of the shock absorber is best described in relation to a situation wherein it is employed as part of a submerged object support arrangement intended primarily for positioning a load object onto the sea bed from a floating vessel which is subject to positional variations with respect to the sea bed, that is, due to wave motion, and the greatest component of such motion is heave.

Such an object is shown in Figure 3 generally at 31. A floating vessel 32 is stationed above a position on the sea bed 33 at which is located (by lowering or under-water erection) a support-bed 34 for an object 35 which may be delicate sub-sea control equipment for an oil well or the like. The support bed 34 has a pair of location posts 36 from which guide wires 37 are extended to the vessel and kept taut by constant tension winches 38.

The load object 35 is provided with guidance channels 39 through which the guide wires pass and is suspended from, and lowered by, hoisting means 40.

The arrangement so far described permits the load object to be positionally guided as it is lowered and automatically located in the desired position with the location posts 36 extending into guide channels, after which the object may be secured to the support bed and the guide wires 37 and hoisting means 40 removed.

The arrangement as described cannot however accommodate vertical displacements of the vessel, hoisting means and suspended load other than compensatory operation of the hoisting means which involves both prediction of the displacement motion and limitation to operation with a small amplitude of such motion.

In accordance with the second aspect of the present invention the shock absorber 10 is secured to the bottom of the object 35 by way of the attachment means 30 whilst the object is on vessel 32 prior to hoisting.

As the object is lowered into the sea the shock absorber is in the "extended" state shown in Figure 1 that is, with the spring 21 extended, and with the enclosure filled with atmospheric air.

As the shock absorber and the object to which it is attached are lowered into the sea, the enclosure 18 fills with sea water by way of the orifice 20 expelling all air therefrom by way of the bleed aperture 19 in the closure member which forms at this time an upper wall of the enclosure.

The shock absorber maintains this extended state as the object load is lowered. When the buffer surface provided by the base member 23 engages the support bed and is brought to rest an axially compressive force acts between the base member and closure member along the axis of the tubular members tending to slide the member 12 relative to the member 11.

The resultant shortening of the enclosure is resisted in part by the spring 27 but mainly by the liquid in the enclosure which is thereby placed under pressure and is permitted only at the rate at which the liquid is forced from the enclosure by way of the orifice 20 and to a much lesser extent by way of bleed aperture 19.

It will be appreciated that the deceleration force imposed upon the load object is provided by the thrust of the enclosure liquid on the piston head and is directly proportional to the pressure difference between the liquid in the enclosure and the environmental pressure.

This pressure and the effective area of the orifice determines the rate at which the pressurised liquid leaves the enclosure and thus the rate at which the piston can move in relation to the cylinder under the action of the applied force. In particular it is known that the rate of flow of liquid through the orifice is directly proportional to the effective area of the orifice and to the square root of the pressure difference across the orifice.

Equations of motion are commonly known relating deceleration, velocity and distance travelled of a body and it will be seen that in respect of a predetermined deceleration distance and deceleration value (which may be constant or variable) the velocity is defined for any position. In respect of the shock absorber 10 this velocity is that of the piston relative to the cylinder as a function of distance from the tip of the spigot portion in the orifice.

As an example, for a constant level of deceleration the square of this velocity is proportional to the displacement of the orifice from the spigot tip.

Relating these quantities it will be seen that for such a constant deceleration, for which the aforementioned enclosure pressure should remain constant, then for any changes in apparatus dimensions the orifice flow rate should remain proportional to the effective orifice area. However to give such constant deceleration the square of the piston velocity, and therefore the square of the flow rate, is required to vary with piston displacement so that the cross-sectional dimensions of the spigot are required to vary along its length such that the effective orifice area, that is, the annular space between the spigot and the orifice wall in the piston head, decreases as the square root of distance from the tip to a value approaching zero at a piston displacement where the deceleration reduces the load object to rest.

The relationship between the component parts of the shock absorber in this compressed state is shown in sectional elevation in Figure 2.

It will be appreciated that such constant deceleration characteristics represent only one possibility amongst many which may be defined for the arrangement and for which variations in the effective aperture area with piston displacement are suitably effected by variations in spigot taper.

It will be appreciated that the deceleration force developed by the pressure of liquid in the enclosure acting between the piston and cylinder members may be greater than the applied force in order to bring it to rest in a short distance but when the load has been brought to rest the pressure of the enclosure liquid will act on the load forcing it away, effectively acting as a liquid spring. One way of avoiding such a situation is to limit the pressure permitted to develop in the enclosure to a value which is no greater than any residual load force acting on the shock absorber, for example, the weight of the load but such an arrangement may require an unacceptable length of piston travel.

One way of reducing the travel length of the shock absorber for any desired deceleration characteristic is to vary both the effective orifice area and enclosure pressure as a function of piston/cylinder displacement such that the liquid flow rate through the orifice satisfies the desired deceleration characteristics whilst the enclosure pressure is reduced, at least towards the end of the motion, by correspondingly reducing the rate of decrease of the orifice area to maintain the deceleration rate.

Such an alternative configuration may be considered for the situation of a lowered object load as described wherein the load, and particularly the attached shock absorber, impact a support bed and the shock absorber is required to bring the load substantially to rest and support it, temporarily whilst it is secured to the support bed.

In this respect the enclosure pressure required to produce a load supporting thrust equal to its static weight, if such pressure is to be maintained constant, would require an excessive piston stroke in view of the compressive force, at least initially, in excess of this due to impact loading. Thus it will be appreciated that in order to have a practicably short working piston stroke it is necessary to vary the enclosure pressure during at least a part of the motion by suitably varying the effective orifice area.

It will also be appreciated that in order to mitigate any impact effects on the load by sudden initial pressurisation of the enclosure liquid the initial flow rate may be chosen larger than required and reduced, by variation of effective orifice such that the pressure is increased over a finite part of the piston/cylinder displacement.

Thus, as outlined above the enclosure pressure may advantageously be not maintained constant but varied also as a function of piston displacement in the cylinder between initially low, high and then low values by variation of the orifice area, by means of the spigot taper profile,. as a function of position along it length, to provide with the instantaneous enclosure pressure and piston velocity at that point in accordance with any chosen deceleration characteristic.

The techniques involved in relating flow rates, aperture sizes and displacement distances for particular loads and deceleration characteristics are well known in the art of dampers and shock absorbers and need not be given here in detail.

Whilst it is theoretically desirable to determine the motion such that the load is brought to rest at the end of the shock absorber compression, it will be appreciated that to bring the load completely to rest would require an accurate sealing between the spigot and orifice to stop liquid flow and maintain the load supporting pressure. Apart from any practical difficulties such an arrangement would depart from the spirit of the invention in terms of manufacturing accuracy. However it can be shown that the combination of a small aperture and a relatively low terminal enclosure pressure results in only a small flow rate which is manifested as a correspondingly slow residual compression of the shock absorber.

The compressed state at which the load is brought substantially to rest, or retains only residual motion as referred to above, is arranged to be reached prior to complete compression of the spring 21 so that there is no shock loading between closure member 30 and base member 23 (buffer) by the binding of spring coils.

It will be appreciated that if the load supporting characteristics are such that the load is essentially supported by the compressed liquid in the enclosure when brought substantially to rest then some form of mechanical support is necessary as the liquid pressure in the enclosure will eventually equalise with that of the environmental liquid either by way of a residual effective orifice or by way of the bleed aperture.

Such mechanical support may be provided by the spring on which the device may be permitted to settle or, by employing a suitably high spring rate in relation to the object weight, the spring after compressing under the impact loading of the object upon landing, being able to iift the static load of the object and return to the extended state.

Whether or not the spring 21 is load bearing it provides a bias force exerted between the piston and closure member tending to separate them, that is, maximise enclosure volume such that whenever a load is raised from the submerged shock absorber it becomes primed with the enclosure extended and filled with environmental liquid.

However it will be seen that upon removal of a compressive force, whether by removal of the loading or resilience of the spring 21 overcoming it, the rate at which the enclosure can extend is limited by the rate at which the environmental liquid. can be drawn into it. Initially, with the orifice 20 having a minimum effective area because of the spigot shank portion, this rate, and the initial rate of extension, is limited in relation to the rate of compression first encountered upon impact.

When the load object 35 is deployed on the support bed 34 with the aid of the shock absorber device, that is, when equilibrium of the shock absorber motion is achieved, and with the shock absorber then located intermediate the object and the support bed, the object is secured to the support bed. The shock absorber may be removed or may be retained in position, attached to the object as lowered, and the object and/or shock absorber secured to the support bed 34 as shown in Figure 4.

This enables the object to be lifted and redeployed, with or without removing it from the sea.

In such operating circumstances it may be preferred to use a relatively weak spring so that the shock absorber assumes a compact compressed configuration but which automatically returns to the extended state when the load to which it is attached is lifted.

Where it is desired to secure the shoc' absorber also to the support bed the buffer surface, that is, base member 23, may be provided with further attachment means, such as the apertures shown at 41 in Figures 2 and 4.

Preferably, when the shock absorber is to be maintained in postion in a compressed state the apertured flanges 25 of the outer tubular member 12 are formed with additional apertures 42 aligned with apertures 41 through both of which apertures bolts 43 attach both tubular members to the support bed and maintain the shock absorber compressed until they are removed. The views of the shock absorber in Figures 2 and 4 are in a direction orthogonal to that of Figure 1 and do not show the guide means 22.

The above description has related to the shock absorber being attached to a load object 35 that is lowered to a support. bed 34.

It will be appreciated that the shock absorber may be attached to the support bed and the load lowered by the hoisting means onto a buffer surface of the device.

Such an arrangement may use the configuration in the orientation substantially as shown in Figures 1 and 2, with the attachment means being formed at base member 23 and the buffer surface at the closure member 13.

Alternatively the arrangement shown in Figures 1 and 2 may be inverted, whether attached to a load object or a support bed.

It will be appreciated that it is generally desirable for the piston member to be biased with respect to the cylinder member so as to maximise the enclosure volume in the absence of a load, that is, to be self-priming. As an alternative to the spring 21 contained within the enclosure this bias may be provided by equivalent resilient member-separating means the operating orientation of the shock absorber open to choice. However, where the operating orientation is well defined in a verti cal plane with one member of the shock absorber attached to the lowered object and suspended therefrom, gravitational forces acting on the other member may effect the enclosure-forming bias.

The shock absorber may be permanently submerged or transfered between the air and liquid environments, each immersion being accompanied, if necessary, before shock absorbing operation by a delay to permit liquid filling of the enclosure. Also, where such filling of the enclosure is a feature of operation the position of the bleed aperture 19 must be considered to avoid the formation of a compressible air pocket in the enclosure.

Other constructional variations will readily suggest themselves such as a different form of attachment means and guide means. Similarly variations may be made to the manner of defining the variable aperture. The spigot and orifice need not be concentric with the longitudinal axis of the piston and cylinder members such that the piston member can be formed other than as a hollow tube 11. If desired the variable area aperture may be effected by a plurality of such spigot and orifice arrangements.

The aperture means may however take a different form from the spigot and piston orifice described above.

Such an arrangement is illustrated in Figure 5 by a partly cut-away perspective view of piston and cylinder members 50 and 51 respectively. The piston member 51 comprises a piston shaft 52, corresponding to the tubular member 11 of Figure 1, which may be hollow or solid as it does not form a passage for the liquid. The piston member includes a piston head 53 corresponding to that 15 of Figure 1 but without a fluid orifice. The piston member is slidable along the longitudinal axes of cylinder member 51 defining an enclosure 54 between the piston head and the closed end of the cylinder (which may be formed by a separate closure member 55). The aperture means is provided by an elongate throughaperture or slot 56 in the tubular wall of the cylinder member.The slot 56 may be parallel sided causing the effective cross-sectional area to decrease linearly with piston displacement although in general the slot may be caused to taper in accordance with the relationships relating fluid flow and any desired enclosure pressure to desired load deceleration characteristics.

Aperture means formed by such a slot 56, although simple to design and manufacture may cause a weakness of the cylinder wall which has to be compensated for in terms of material or dimensions and which may offset advantages of simplicity.

An alternative arrangement of aperture means is shown in a corresponding cut-away perspective view of Figure 6. In this arrangement the aperture means comprises a series of discrete through-apertures 57 in the tubular cylinder wall extending in the direction of relative longitudinal movement between the piston and cylinder members. The through-apertures may be disposed such that their longitudinal separation increases and/or individual crosssectional areas decrease towards the closed end of the cylinder and the strength of the cylinder may be maintained by having the through-apertures for the various longitudinal positions disposed circumferentially around the wall of the cylinder, and possibly effected by more than one through-aperture at each longitudinal position.

In all constructional forms described above it will be appreciated that the efficiency of seal 16 and between the spigot shank and orifice to the leakage of fluid from the enclosure is not crucial to the operation of the device, offering at worst a slightly greater rate of bleeding, and is of no relevance at all in respect of the loss of damping fluid per se.

Because the device is not limited in performance by fluid capacity or manufacturing tolerances there is no limit on the scale of the device.

Also, it will be appreciated that although the description has related to the use of the shock absorber at sea with vertical motions and sea-water as the envirorimental liquid the same principles may be employed with any liquid environment and offer resistance to impacts between bodies moving in any direction provided the forces associated with the motion, or at least a component of the motion, act in the direction of permitted relative movement of the piston and cylinder members.

The shock absorber embodiments described have all been in respect of devices undergoing compression by external forces to cause a shortening of the enclosure. It will be appreciated that the enclosure may be defined between the piston head and a closed cylinder end through which passes the piston stem such that a force tending to extend the device, rather than comprises it, is resisted.

Claims (6)

1. A submerged shock absorber comprising a cylinder member, closed at one end thereof and a piston member, including a piston head, contained within the cylinder to define an enclosure between the piston head and said closed end of the cylinder and slidable therein to vary the volume of the enclosure as a function of the relative positions of piston and cylinder, and aperture means providing a passage for environmental liquid between the enclosure and liquid environment, a change in the enclosure volume due to relative displacement of the piston and cylinder members by an externally applied force being resisted by a pressure difference developed between the liquid in the enclosure and the environmental liquid by said force and permitted at a rate determined by the rate of flow of liquid through the aperture means.

2. A submerged shock absorber as claimed in claim 1 in which the aperture means has an effective cross-sectional area which varies as a function of piston member position relative to the cylinder member.

3. A submerged shock absorber as claimed in claim 2 in which the effective cross-sectional area of the aperture means varies with relative piston member and cylinder member displacement to provide a resistance force to piston motion caused by the applied force effecting constant deceleration of the piston member relative to the cylinder member.

4. A submerged shock absorber as claimed in any one of claims 1 to 3 in which the aperture means comprises at least one through-aperture in the wall of the cylinder member communicating directly between the enclosure and the environment.

5. A submerged shock absorber as claimed in claim 4 in which the aperture means comprises a plurality of discrete apertures disposed in the direction of relative movement of the piston, the effective aperture area for any position of the piston member relative to the cylinder member being the total cross-sectional area of the through apertures between the piston head and closed end of the cylinder member.

6. A submerged object support arrangement substantially as herein described with reference to, and as shown in, Figure 3 or Figure 4 of the accompanying drawings.

6. A submerged shock absorber as claimed in claim 5 when dependent on claim 3 in which the cross-sectional area and/or spacing of the individual through apertures varies as a function of piston member displacement from the closed end of the cylinder.

7. A submerged shock absorber as claimed in any one of claims 1 to 3 in which the aperture means comprises an orifice in the piston head and a spigot carried in fixed relationship with the cylinder member, extending in the direction of relative movement between the piston and cylinder members and into said aperture such that relative motion between the piston and cylinder members causes the spigot to vary the effective cross-sectional area of the aperture.

8. A submerged shock absorber as claimed in claim 7 when dependent on claim 2 or claim 3 in which the spigot is tapered such that the effective cross-sectional area of the orifice is varied as a function of the relative positions of the piston and cylinder members.

9. A submerged shock absorber as claimed 8 when dependent on claim 3 in which the spigot taper is arranged to provide an effective orifice cross-sectional area which varies as the square root of distance along the spigot from the tip.

10. A submerged shock absorber as claimed in any one of the preceding claims operable in response to a force exerted between piston and cylinder members to reduce the volume of the enclosure and in which the piston member is arranged to be biased out of the cylinder member to maximise enclosure volume in the absence of a force acting between them.

11. A submerged shock absorber as claimed in claim 10 including a compression spring contained within the enclosure and exerting a bias force between the piston head and the closed end of the cylinder.

12. A submerged shock absorber as claimed in any one of the preceding claims including a liquid bleed aperture between the enclosure and environment located such that upon immersion of the shock absorber into the liquid atmospheric air therein is replaced by the environmental liquid.

13. A submerged shock absorber as claimed in any one of the preceding claims including attachment means carried by one of said piston or cylinder members and a buffer surface carried by the other member.

14. A shock absorber as claimed in any one of the preceding claims in which the buffer surface includes further attachment means operable to enable the shock absorber to be attached as an intermediate body between an object to which attached and a further object against which engagement shock constituting said force exerted between piston and cylinder members is absorbed.

15. A submerged shock absorber as claimed in claim 13 or claim 14 in which the cylinder member comprises a tubular member closed at said one end by a separate closure member and in which the attachment means is carried by the closure member.

16. A submerged shock absorber as claimed in claim 15 in which the attachment means is adapted to attach the shock absorber to the bottom of an object to be lowered under gravity with, and onto, the shock absorber.

17. A submerged shock absorber as claimed in claim 16 when dependent on claim 12 in which the bleed aperture is in the closure member.

18. A submerged shock absorber comprising two coaxial hollow tubular member slidable axially one within the other, the outer tubular member being closed at one end thereof by a closure member to comprise a cylinder member and the inner tubular member being open to the environment, and comprising a piston member carrying at one inner end thereof nearest to the closure member a piston head adapted to make a sliding substantially liquid tight seal with respect to the inner wall of the cylinder member and defining an enclosure between the piston head and the closure member, an orifice in the piston head between the enclosure and the inside of the inner tubular member, said enclosure containing a spigot carried by the closure member, protruding into the enclosure along an axis parallel to the longitudinal axis of the enclosure, the spigot having a tapered portion arranged to pass into the orifice in the piston head and define the effective cross-sectional area of the orifice as a function of the piston position within the cylinder, attachment means operable to attach one of the tubular members to an object and a buffer surface carried by the other tubular member, operable immersion of said shock absorber in the liquid environment with the piston member spaced from the closure member causing the enclosure to be filled with the liquid by way of the piston orifice and axial force, acting between the attachment means and buffer surface, causing the liquid to be expelled under pressure from the shortening enclosure, by way of the piston orifice and inner tubular member, to the environment.

19. A submerged shock absorber substantially as herein described with reference to, and as shown in, Figures 1 and 2 or in Figure 5 or Figure 6 of the accompanying drawings.

20. A support arrangement for an object submerged in a liquid environment comprising an object support bed and a shock absorber as claimed in any one of claims 1 to 19 disposed intermediate the object and the support bed.

21. A submerged object support arrangement including hoisting means operable to lower an object in a liquid environment, a support bed in the environment to receive and support the lowered object, a submerged shock absorber as claimed in any of claims 1 to 19 attached to either one of the object or the support bed with the axis of the relative displacement of piston and cylinder members thereof extending in the object lowering direction and adapted to buffer against the other one as the object is lowered, and means to secure the object to the support bed with the submerged shock absorber intermediate the supported object and the support bed.

22. An arrangement as claimed in claim 21 in which the shock absorber includes attachment means carried by one of said piston or cylinder members and a buffer surface, carried by the other member, including further attachment means, the attachment means and further attachment means being operably secured one each to the object and support bed.

23. An arrangement as claimed in claim 22 in which the shock absorber includes a compression spring contained within the enclosure exerting a bias force between the piston head and closed end of the cylinder and rated to be substantially compressed by the static immersed weight of the object and in which the shock absorber is located intermediate the supported object and the support bed in its compressed state.

24. A submerged object support arrangement substantially as herein described with reference to, and as shown in, Figure 3 or Figure 4 of the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 to 24 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:

1. A submerged object support arrangement including hoisting means operable to lower an object in a liquid environment, a support bed in the environment to receive and support the lowered object, a submerged shock absorber, comprising a cylinder member, closed at one end thereof and a piston member, including a piston head, contained within the cylinder to define an enclosure between the piston head and said closed end of the cylinder and slidable therein to vary the volume of the enclosure as a function of the relative positions of piston and cylinder, and aperture means providing a passage for environmental liquid between the enclosure and liquid environment such that a change in the enclosure volume due to relative displacement of the piston and cylinder members by an externally applied force is resisted by a pressure difference developed between the liquid in the enclosure and the environmental liquid by said force and permitted at a rate determined by the rate of flow of liquid through the aperture means, said shock absorber being attached to either one of the object or the support bed with the axis of the relative displacement of piston and cylinder members thereof extending in the object lowering direction and adapted to buffer against the other one as the object is lowered, and means to secure the object to the support bed with the submerged shock absorber intermediate the supported object and the support bed.

2. An arrangement as claimed in claim 1 in which the shock absorber includes attachment means carried by one of said piston or cylinder members and a buffer surface, carried by the other member, including further attachment means, the attachment means and further attachment means being operably secured one each to the object and support bed.

3. An arrangement as claimed in claim 2 in which the shock absorber includes a compression spring contained within the enclosure exerting a bias force between the piston head and closed end of the cylinder and rated to be substantially compressed by the static immersed weight of the object.

4. An arrangement as claimed in any one of claims 1 to 3 in which the shock absorber aperture means comprises a through-aperture or a series of through-apertures in the wall of the cylinder member communicating directly between the enclosure and the environment, said aperture or series being extensive in the direction of relative movement of the piston, the effective aperture area for any position of the piston member relative to the cylinder member being the total cross-sectional area of the through-aperture or apertures between the piston head and closed end of the cylinder member.

5. An arrangement as claimed in claim 4 in which the aperture means comprises a series of discrete through-apertures and the crosssectional area and/or spacing of the individual through-apertures varies as a function of piston member displacement from the closed end of the cylinder.