GB2096563A - Sea swell and shock load compensator - Google Patents

Abstract

A hoist or crane incorporating such a compensator is used in transferring or supporting a load either between two stations at least one of which is floating in water subject to a sea swell or between a single station which is either floating in the water, or fixed, and the water itself, and is installed at either of the two stations or at a single station. The compensator 17 is hydraulically operated to heave in hoisting rope when subjected to less than a given load and to pay out hoisting rope when that load is exceeded. The hydraulic system is pressurised by gas loaded accumulators 8, 9 and includes a selector 16 for achieving either bi-directional flow of the hydraulic fluid between the accumulators and the compensator to compensate for load position movements, or a uni-directional flow permitting heaving in but preventing subsequent paying out, whereby the load is removed from the sea at the wave crest level. <IMAGE>

Description

SPECIFICATION Sea swell compensation (hoists) This invention relates to a sea swell and shock load compensator and to a hoist or crane incorporating such a compensator for use in transferring or supporting a load either between two stations at least one of which is floating in water subject to a sea swell or between a single station which is either floating in the water, or fixed, and the water itself, and for installation at either of the two stations or at a single station. An example of the application of the invention is a crane for use on offshore oil or gas rigs and platforms or for use on a barge or ship lifting loads out of the water or from the deck of another barge or ship, or into the water or on to the deck of another barge or ship.

There have been numerous accidents involving cranes working offshore due to shock loading caused by sea swell due to the load descending on the sea swell when its weight is suddenly transferred to the crane.

According to one aspect of the invention there is provided a sea swell and shock load compensator comprising a hydraulically-operated means for heaving in and paying out a hoist rope, a low pressure hydraulic system for supplying hydraulic fluid to the means so as to enable the means to heave in the hoist rope under a given small load and to pay out hoist rope when such given small load is exceeded, the hydraulically-operated means being pressurised by gas loaded accumulators and a means for selecting bi-directional flow of hydraulic fluid between the accumulators and the means so as to compensate for sea swell or selecting unidirectional flow from the accumulators to the hydraulically operated means so that hoist rope will be wound in by the means on an ascending swell under a small tension but hoist rope will be prevented from being paid out by the means when the crest of the swell has been reached thereby transferring the load being lifted from the sea swell or ship to the crane at the crest of the sea swell.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows diagrammatically for incorporation in a hoist or crane, part of a sea swell and shock load compensator controlled by a hydraulic circuit having a pre-loaded low pressure hydraulic system.

Figure 2 shows, diagrammatically, an electronic or electric logic circuit used with the hydraulic circuit of Figure 1.

Figure 3 shows diagrammatically means to operate the hoist winch of the hoist or crane when the ram of the compensator is nearer the limits of the its travel during compensation so that the ram will automatically be centered within the extent of its travel and should the sea swell be greater than the ram is able to allow for itself then the ram will be augmented by movements of the hoist winch at the top and bottom of the swell.

Figures 4A, 4B, 4C and 4D shows various versions of a sea swell and shock load compensator including a ram or rams.

Figures 5shows a modification of the hydraulic circuit of Figure 1 applicable to the use of sea swell and shock load compensator including instead of ram or rams, a hydraulic pump-motor capable of acting as a pump driven by a winch when hoist rope is being paid out or of acting as a motor driving the winch when hoist rope is being hove in.

In Figure 1 hydraulic pump 3 draws hydraulic fluid from reservoir 1 along line 2 which is used to pre-charge gas loaded hydraulic accumulator 8 through line 4. In line 4there is a shut-off valve 5 to isolate the pump 3 from the hydraulic circuit after pre-charging has been completed. Thereafter pump 3 is only used to make up hydraulic losses in the system. Line 4 is joined by line 6 which includes shut-off valve 7 for lowering the hydraulic pressure in the circuit by leading fluid back to reservoir 1. Also a pressure gauge may be attached to line 4.

Pneumatic pump 12 is connected by line 10 to the gas bladder of accumulator 8 and to back-up gas bottles 9 and includes shut off valve 11. Pump 12 is similarly used only to precharge gas to accumulators 8 and gas bottles 9 and thereafter is shut off from the circuit and thereafter is only used to make up gas losses in the circuit.

Hydraulic fluid is connected by lines 4 and 13 to the hydraulic means 17 for paying out and winding in hoist rope. Line 13 includes a shut off valve 14, flow directional sensor 15 and 2/2 directional control valve 16 controlled by a solenoid operated hydraulic pilot valve (pilot lines not shown) with a return spring biassing the valve 16 to a unidirectional position. The activation of the solenoid of valve 16 allows bi-directional flow between accumulator 8 and the hydraulic means 17.

Between valve 16 and the hydraulic means 17 line 13 is joined to line 18 which leads back to line 13 and includes a sequence valve 22 which is set to pass fluid back to line 13 should the pressure in line 18 indicate that the crane or hoist is being subjected to a load more than its safe working load. Line 18 also includes a pressure switch 19 which prevents the activation of the solenoid of valve 16 if there is a load on the hoist or crane causing pressure greater than compensating pressure in the ram 17 and line 18.

Line 18 may also include a gas loaded snubber 19A which acts as a spring when the load is transferred from the sea swell to the hoist or crane at the top of the swell. Between lines 18 and 13, line 2C includes manually operated 2/2 directional control valve which may be used by the operator to abort a lift at any stage allowing the ram to lower the load to the foot of the swell passing hydraulic fluid back to the accumulator 8 through lines 18,20 and 13.

Information as to the direction of flow of hydraulic fluid in line 13 is passed to logic circuit 41 along electric line 41 A. Electric switch 40 has two positions 'C' to select the compensate mode and 'S' to stop compensating when the operator wishes to lift the load. Signals from the 'C' and 'S' terminals of switch 40 are fed to logic circuit 41.

The hoist winch 31 is driven by bi-directional motor 30 from pump 26 which draws hydraulic fluid from reservoir 1. Line 27 connects pump 26 to motor 30 and line 29 leads fluid from motor 30 back to reservoir 1. In lines 27 and 29 there is a three position control valve which is solenoid operated. The solenoids of valve 28 are normally operated by manual control lever 33 being placed in the 'L' lower or 'H' heave positions and in the 'N' neutral position valve 28 is normally closed. When switch 40 is in the 'S' (stop compensation) position line 38 activates switch 34to isolate control lever 33 in the 'N' position preventing activation of limit switches 23 and 24 which operate the solenoids of valve 28 to the 'lower' and 'heave' positions respectively only when the following conditions are met: (a) Switch 40 is in the 'C' compensate mode.

(b) Control lever 33 is in the 'N' neutral position.

(c) Switches 24 and 23 have been activated by the ram lowering from its topped out position thus activating switches 24 and 23 through switch 25.

Figure 3 shows a diagrammatic scheme of this system of controiling the crane hoist winch by movements of the ram compensator during compensation for sea swell.

Figure 2 shows diagrammatically an example of logic circuit 41. Upon selection of'S' (stop compensation) at switch 40 a signal is passed along line 42 to temporary memory latch 43. This remembers that'S' has been selected and passes a signal along line 44 to input 2 and gate 45. The second signal to gate 45 is received along line 46 for switch 15 indicating a flow towards the ram 17 (i.e. the load is rising on the swell). In line 46 there is a delay circuit 47 to prevent lift being activated on a false crest. When the two signals required to stop compensating are received by gate 45, a signal is passed along line 48 into an invertor gate 49. Invertor 49 also acts as a buffer/ driver four relay 50 through line 51.As the signal from gate 45 is inverted by gate 49, the relay receives no signal and the relay contacts remain in the open position as shown in Figure 3, so that no power is fed through line 53 to the solenoid of valve 16 and the valve remains in the uni-directional mode.

Upon selection of 'C' at switch 40 a signal is passed along line 54 to input 2 and gate 55. When a second signal from switch 19 (indicating no load on the crane hoist rope) is received along line 56 by the other input of gate 55, a signal is passed through line 57 to the 'reset' input of temporary memory latch 43.

This has the effect of cancelling the previous memory (i.e. that 'S' had been selected at switch 40). Gate 43 output not falls to zero so that gate 45 receives no signal from line 44 and its output falls to zero; therefore the signal to gate 49 along line 48 is zero and the output along line 51 to the relay is an activating signal. This changes relay contact 52 to apply a voltage from supply point 58 along line 53 to the solenoid of valve 16 thus moving the valve to the bi-directional position.

This system is best suited to cranes which are lifting loads from the sea itself or discharging loads to the sea itself. When it is used to lift loads from the deck of a ship it would be possible to lift off from a false ascending crest so that the ship would fall away from the load and then lift it again to the top of the true crest.

The hydraulic means 17 can take various forms such as those described in the Inventor's co-pending British Patent Applications Nos. 44693/77; 45494/77; 46333/77 and 6141178 and which are shown in Figures 4A, 4B and 4C and Figure 5.

Claims (2)

1. A sea swell and shock load compensator comprising a hydraulically-operated means for heaving in and paying out a hoist rope, a low pressure hydraulic system for supplying hydraulic fluid to the means so as to enable the means to heave in the hoist rope under a given small load and to pay out hoist rope when such given small load is exceeded, the hydraulically-operated means being pressurised by gas loaded accumulators and a means for selecting bi-directional flow of hydraulic fluid between the accumulators and the means so as to compensate for sea swell or selecting unidirectional flow from the accumulators to the hydraulically-operated means so that hoist rope will be wound in by the means on an ascending swell under a small tension but hoist rope will be prevented from being paid out by the means when the crest of the swell has been reached thereby transferring the load being lifted from the sea swell or ship to the crane at the crest of the sea swell.

2. A sea swell and shock load compensator substantially as hereinbefore described with reference to the accompanying drawings.