The present invention concerns a winch and a method for lowering or launching lifeboats with a redundant breaking system. Winces for launching life boats must satisfy rigorous regulations to ensure proper operation in all conditions including emergencies.

A recent change in the regulations for lifting appliances brought forward new challenges related in winch design. The name of the regulation is Norsok R-002. According to this standard, fail-safe or redundant components must be used, dependent on the result of a risk assessment. The standard does however not specify how such failsafe or redundant components can or shall be used.

The main purpose of a life boat winch is to hold the life boat in a davit during storage and boarding, and to launch the life boat at a controlled rate of decent from the davit to the sea surface.

Accordingly, such a winch has at least one brake for holding the boat in position, and a brake or constant speed holder for maintaining a substantially uniform and controlled winch speed during launching. This is normally achieved without any form of power supply, and this contributes to the reliability of the winch.

Such winches do however usually include a motor for driving the winch and to enable the winch to lift the life boat. The ability to lift the life boat is important in connection with installation of the boat and for repositioning the boat after training/emergency exercises etc. The requirement for allowing lifting operations are however less critical as these operations normally not are performed during emergencies.

The holding brake is traditionally a disk or drum brake that is released mechanically or by hydraulic pressure. Springs normally bias brake shoes or brake pads toward the drum or disk to hold the winch drum in position. A brake of a multiple disk design is commonly used. The brake or constant speed holder is often a centrifugal brake or a hydraulic motor / pump with a constant flow valve at the outlet to limit the flow through the motor / pump to a predetermined flow and thus to allow the motor to rotate at a given speed.

The hydraulic motor is connected to the winch drum through a winch gear to reduce the required holding moment of the motor, and thus the motor size.

The winch gear may also be used in connection with lifting operations, as an electric motor may drive the winch drum through the same winch gear.

Failure of the holding brake, the hydraulic motor / pump, the constant flow valve or the winch gear could have a potentially catastrophic effect that the holding brake could release the boat, thereby launching the boat at more or less at free fall.

A different scenario is that the boat not is allowed to be launched, also with a potentially catastrophic effect.

To reduce the likelihood of system failure, it is proposed a solution with a redundant system.

Accordingly, the present invention presents a solution in terms of how a redundant system can be implemented.

The present invention concerns a winch for lowering lifeboats with a redundant breaking system. The winch includes a double winch drum for simultaneous accommodation of two winch wires. A primary winch gear is mechanically connected to the winch drum. A primary brake pump with an inlet and an outlet is mechanically connected to the primary winch gear through a shaft. An electric motor for driving the winch is located on the side of the winch. A transmission between the electric motor and the primary winch gear connects the motor and the primary winch gear. Furthermore the winch includes a normally applied, primary brake connected to the transmission. A primary throttle valve allows a first flow rate f1 through the primary brake pump connected to the outlet of the primary brake pump. A tank for hydraulic fluid is connected with the inlet of the primary brake pump. A base provides a means for attachment of the winch to a foundation. The winch comprises further:

a secondary brake pump with an inlet and an outlet mechanically connected to a secondary winch gear, a normally applied, secondary brake connected to the secondary winch gear, and a secondary throttle valve for allowing a second flow rate f2 through said secondary brake pump. The secondary throttle valve is connected to the outlet of the secondary brake pump.

The secondary brake pump, secondary winch gear, secondary brake and secondary throttle valve, are redundant components that will ensure proper operation / braking in the event of failure of the primary system

The primary brake may be a hydraulic pressure releasable brake.

The primary brake may be connected to a primary hydraulic accumulator and to a secondary hydraulic accumulator through a primary brake release valve and a secondary brake release valve. The primary brake release valve is then a valve that remains in an open position after a release of an actuation input (pull and go) and the secondary brake release valve is a valve that returns to a closed position after a release of an actuation input (stop and go). Any of the brake release valves will open both brakes with pressure from any of the accumulators.

The secondary brake may be a hydraulic pressure releasable brake.

The secondary brake may be connected to a primary hydraulic accumulator and a secondary hydraulic accumulator through a primary brake release valve and a secondary brake release valve, wherein the primary brake release valve is a valve that remains in an open position after a release of an actuation input (pull and go) and the secondary brake release valve is a valve that returns to a closed position after a release of an actuation input (stop and go). Any of the brake release valves will release both the brakes with pressure from any of the accumulators, thus providing a redundant system. Both of the brakes must be released to allow rotation of the winch drum.

The first and the secondary brakes may be released by pneumatics. In this case, the hydraulic accumulators may be substituted with air pressure tanks supplied with pressurized air from some source. Clearly also the hydraulic circuit for charging the accumulators may be omitted.

The primary throttle valve may be set to allow the first flow rate f1 , and the a secondary throttle valve may be set to allow a second flow rate f2 such that the second flow rate f2 is greater than the first flow rate f1 .

The transmission between the electric motor and the primary winch gear may comprise a planetary hoisting gear with an input shaft connected to an output shaft of the electric motor, a driven sprocket on the shaft mechanically connecting the primary winch gear and the primary brake pump, a driving sprocket connected to the a primary brake and the hoisting gear, and a chain between the driven sprocket and the driving sprocket. Other types of hosting gears may be used.

The primary and the secondary brake pumps may be gear pumps.

The primary and the secondary brakes may be unidirectional, to allow rotation of the brakes in one direction when the brakes are applied, to allow hoisting even if the brakes are applied.

The primary throttle valve and secondary throttle valve may each be bypassed by a conduit with a check valve for allowing flow past the throttle valves and for allowing unrestricted flow and hence rotation of the primary brake pump and the secondary brake pump in one direction. The hoisting process may however be so slow, that these check valves are unnecessary due to the low flow rate at hoisting speed. The winch may further include a second, primary throttle valve at the outlet of the primary brake pump, allowing a third flow rate f3 through the second, primary throttle valve. A shut off maintenance valve selectively allows flow through the second primary throttle valve for selectively decreasing or increasing the flow rate through the primary brake pump and for decreasing or increasing the winch launching speed.

The first and the second primary throttle valves may be connected to a common connecting block at the outlet of the primary brake pump.

The flow through the primary brake pump is then selectively f1 + f3 or only f1 . Under normal operation / emergencies the flow rate is f1 + f3. During training and maintenance, the shut off maintenance valve is closed, the flow rate is f1 , and the winch speed is lower. In the case of failure of any of the parts on the primary braking side of the winch, the winch speed in increased, limited by the flow rate f2 through the secondary braking side of the winch.

During normal operation then f1 + f 3 < f2, thus preventing the secondary braking side of the winch from braking unless the primary braking side of the winch fails.

The default, standby position is the position that should be used such that flow is allowed through both the first and the second primary throttle valves, thus allowing a flow rate that can be expressed as f1 +f3.

The winch may further include a sensor for monitoring a mode of operation, and display on a control panel in proximity of the winch, displaying the mode of operation and a display inside the boat displaying the mode of operation. The control panel or control panels may receive signals from a pressure transmitter in connection with the accumulators, and a level transmitter, monitoring the level of the tank/reservoir for the hydraulic fluid.

The sensor may be an inductive transducer on the maintenance valve. The maintenance valve may be a ball valve. The winch has two primary modes of operation during launching that are the training mode and the standby mode as explained above.

There is also a hoisting mode as will be explained below.

The hoisting can be represented by the following sequence:

The power must be switched ON to the winch starter cabinet, which is fitted with a remote operators control box.

The primary brake is closed by spring tension.

The electric motor is started from either the main or remote control.

As the motor turns the planetary gear rotates and drives the chain, which in turn drives the primary winch gear. The winch drum is connected to the primary winch gear and therefore the winch drum turns, reeling in the wires and hoisting the lifeboat. The secondary winch gear is also connected to the winch drum, thereby turning the secondary winch gear.

The secondary brake which is on the same shaft as the secondary winch gear, turns as the hoisting commences. The brake remains ON due to the spring tension, but lifting is possible due to an integrated free-wheel/ non return lock design.

Lifting of the lifeboat may continue until limit switches cut off power supply to the electric motor. Hoisting of the lifeboat shall however ideally be stopped before the limit switches are reached, and the life boat shall be hand cranked to its final position as explained below. The primary purpose of the limit switches is as fail safe switches to prevent excessive stresses on the lifeboat, davit or winch.

When the electric motor stops the load hangs on non-return locks integrated into the motor, the primary brake and the secondary brake. If the lifting is inadvertently continued, then a second limit switch cuts the power to the motor.

Each davit is equipped with a movable electric motor that can be used if the permanent electric motor fails, and which can be mounted on the winch to hoist the lifeboat back to stowed position, though in reduced speed.

Hoisting mode, hand crank:

The final lifting is done using a hand crank or air ratchet when recovering the lifeboat back to the stowed position in normal operation.

The hand crank is inserted into the adapter slot at the end of the motor.

When inserted, the crank handle activates an automatic shut-OFF for the electric motor, ensuring safe operation for the crank user.

The lifeboat can then be cranked to its final position.

The lifeboat can be cranked manually or with an air ratchet in this manner from any position should the electric motor/power supply fail

Crank out mode, unloaded wire:

There is a crank handle adapter slot at the end of the primary brake, to enable unloaded wire to be cranked out. (without any lifeboat attached/ suspended).

When the crank handle is inserted, the electric motor is automatically shut OFF.

One of the brake release valves from the accumulators to the primary and secondary brake must be opened to provide pressure to- and release the brakes.

Once the brakes are released the wire can be cranked out.

The three throttle valves are adjustable so to enable initial set up of the system.

After the initial set-up, there should be no requirements to change the flow rates. Evacuation mode:

Before commencing the evacuation or lowering operation, the operators are required to check that the pressures in the accumulators are correct. This can be seen locally on gauges at the winch on the davit or on the starter cabinet (pressure transmitters send signals to the starter cabinet). If the pressure levels are too low, a warning light or signal will provide a warning, indicating insufficient pressure. The same relates to the level of the hydraulic fluid in the tank. (A level transmitter in the tank provides a signal) If the pressure is low, the winch accumulators will require topping up. A hand pump is provided for this purpose.

Once all personnel have boarded the lifeboat and the life boat is ready for launch, the coxswain will pull down a green control wire for standby mode from his position in the driver's seat of the lifeboat. During evacuation, the system is configured for PULL AND GO, and the coxswain must pull the green control wire to start the descent. He can then release the green control wire and the lifeboat will continue to the water. The green control wire is attached to a green brake release valve on the winch, previously referred to as the primary brake release valve.

A red control wire for training and maintenance mode is attached to a red brake release valve on the winch, earlier referred to as the secondary brake release valve. To lower the lifeboat in the training and maintenance mode, the coxswain must pull the red control wire and keep the wire in tension until the lifeboat is seaborne. The lowering motion will stop if the control wire is released.

The pressures from the accumulators overcome the brake spring pressure, allowing the planetary gear, chain-wheel and chain to rotate. As a result, gravity and the load of the lifeboat acts on the fall wires and the winch drum rotates, beginning the descent of the lifeboat.

On the same shaft line as the winch drum, the primary and secondary constant speed holders (brake pumps) rotate. As the lifeboat descends, the primary brake pump begins to deliver oil from the hydraulic tank to the hydraulic system, including the accumulators through pipes connected to outlet on the pressure side of the primary brake pump.

The flow rate of the primary brake pump determines the lowering speed of the lifeboat and this is set by two adjustable flow control valves and an isolating valve. When the isolating valve is in a closed position, the pump flow is restricted through a first/ primary flow control valve which is set to control the lowering speed at approximately 30m/min.

When the valve is open, the second primary flow control valve set for a higher flow rate allows a higher flow rate through the pump. The increased flow rate results in less resistance across the pump and therefore produces less braking power, thus increasing the lowering speed to 60 m/min.

This isolation valve should be in a normally open position, ready for evacuation.

If the coxswain is required to stop the lifeboat at any point during the descent, (during training exercises) the control wire for training and maintenance mode can be released, and the red control valve returns to the stopped position, shutting off the hydraulic pressure to the primary and secondary brake. The brakes are thereby activated and the lifeboat stops at its present position.

The electric motor is not utilized during lowering.

Short description of the enclosed figures:

Fig. 1 is a front view, partly in cross section, of a winch according to the invention; Fig. 2 is side view of the winch on fig. 1 ;

Fig. 3 is top view of the winch on fig. 1 ;

Fig. 4 is a top view, partly in cross section, of a detail of the winch on fig. 1 ;

Fig. 5 is a perspective view of a davit with a winch according to the invention; and Fig. 6 is a schematic representation of a hydraulic circuit of a winch according to the invention. Detailed description of an embodiment of the invention with reference to the drawings:

Figure 1 shows a winch with double breaking systems for life boats according to the invention. The winch 1 includes a winch drum 22 with a first wire 23 and a second wire 24 for attachment to a life boat. The primary purpose of the winch is to provide a controlled descent of the life boat from for instance an offshore platform or a vessel to the water / sea level. The winch 1 includes a redundant or secondary braking system for additional safety in the event of failure of a primary braking system. The primary braking system includes a primary brake 9 intended for holding the life boat during storage and boarding until intentional launching of the life boat. The brake 9 is only intended to hold the winch in a static, fixed position, and is not used for braking during the launching operation. The primary brake is a hydraulic release, Stormag multi-disc, multi-spring brake which is on the same transmission line as the electric motor for the winch (not shown on fig. 1 ). The primary brake 9 is released by hydraulic pressure from a primary accumulator 13 or a secondary accumulator 14. The accumulators 13 and 14 are connected to the primary brake 9 through a hydraulic line. A primary brake release valve (not shown) is connected to the brake release line for operating the primary brake 9. The primary brake 9 is designed for one direction only and therefore allows a recovery / hoisting operation when the electric motor is hoisting the life boat and the winch drum rotates in a direction opposite the direction when launching. The primary brake may be designed for a maximum moment of 442 Nm and a lowering speed of approximately 2750 RPM. The primary brake is located at the opposite end of the electric motor shaft, next to the chain wheel or driven sprocket for hoisting, (not shown) driving the duplex chain 17. Accordingly, the brake is released by hydraulic pressure during launch, and the brake is applied all the time during recovery, as the brake only acts in one rotational direction. The brake includes multiple springs which apply a braking force to hold the brake in a braking position at all times until the hydraulic pressure releases the brake. Failure of one of the springs in the brake should have little effect on the braking force that is applied when the system is at rest. A secondary brake 10 may be of the same design as the primary brake 9, but may be of a different brand. The secondary brake 10 is, similarly with the primary brake, also a friction brake that is closed or applied by spring tension and released by hydraulic pressure. The secondary brake 10 is released by hydraulic pressure from any of the brake release valves. Both of the brake release valves are connected to both of the secondary accumulators 14 for redundancy. Both the primary and the secondary brakes must be released simultaneously to lower / launch the life boat.

The winch drum 22 is mechanically connected to a primary brake pump 2 through a primary winch gear 20. The primary brake pump 2 acts as a primary constant speed holder, and may be a 160 cm ³ /rev gear pump. The primary brake pump is driven by the winch gear 20 as it rotates and lowers the life boat. During normal operation, the primary break pump 2 delivers oil from a hydraulic tank 4 to the accumulators 13, 14 and to the brakes 9, 10 through non return valves, thus ensuring the continued release of the brakes and refilling of the accumulators 13, 14 during launch of the life boat. The accumulators 13, 14 may be interconnected with a slide valve. The slide valve is then connected to the two, three-way braking valves. The primary brake pump 2 maintains the pressure within the accumulators 13, 14. The flow rate through the primary brake pump and the displacement of the pump determines the lowering speed of the life boat. The flow rate through the primary brake pump is set by first and second adjustable flow control valves or throttle valves. The first throttle valve 5 for the primary brake pump limits the flow through the primary brake pump. The second throttle valve 5a is also referred to as a maintenance/training valve. As the life boat is launched, the life boat descends driving the winch due to gravity as the winch wires pulls the winch drum in rotation and drives the primary brake pump 2 through the primary winch gear 20. The primary brake pump 2 delivers oil from the hydraulic tank 4 to the hydraulic system. The primary brake pump 2 is fed with oil from the hydraulic tank 4 which is located directly above the primary brake pump 2 to provide a positive pressure head and reduce the risk of air entering the primary brake pump. The primary brake pump 2 discharges the hydraulic fluid back to the hydraulic tank 4, through the primary throttle valve 5 or through both the primary throttle valve 5 and the additional/second primary throttle valve 5a depending on the position of the maintenance valve 6. When the maintenance valve 6 is closed, the launching speed is reduced.

The outlets from the tank 4 to the primary brake pump 2 and the secondary brake pump 3 are positioned slightly above the tank bottom, to restrict the intake of debris, sludge or water that may collect at the bottom of the tank 4. The brake pumps 2, 3 discharge hydraulic fluid back to the hydraulic tank 4 through three small bore pipes, fitted to the two flow control valves 5, 8 and to the maintenance valve 6 respectively.

When the maintenance/training valve 6 is in the CLOSED position the pump flow is restricted through the first flow control valve 5 only and therefore the lowering speed is decreased to max 30 m/min due to the reduced flow rate and increased resistance across the pump element.

When the maintenance/training valve 6 is open, the flow allowed through the primary braking pump 2 is increased as flow is allowed through both the first primary braking valve 5 and the second primary braking valve 5a. This creates less resistance across the pump element and thus less braking power, and the launch speed is increased to 60m/min. This maintenance/training valve 6 should normally be in the OPEN position, ready for evacuation.

A check-valve is connected to the primary brake pump outlet for charging the primary accumulator 13 and secondary accumulator 14.

The winch 1 is intended to be attached to a davit through a base 26.

The brake 9 and the electric motor are connected to the primary winch gear 20 through the duplex chain 17 driving the driven sprocket 18 for hoisting and braking. The duplex chain 17 also connects the primary winch gear 20 with a hand crank 25 inserted into a crank handle adapter slot 25a at the end of the primary brake 9 to enable cranking out wire when the wire is unloaded (no life boat is attached or the winch for some other reason is unloaded). In figure 1 , the hand crank 25 is shown on the left side of the winch inserted into the brake shaft.

Insertion of the crank handle 25 into the crank handle slot 25a ensures that the electric motor is deactivated. When the brake release valves are open to allow pressure from the primary and secondary accumulators 13, 14 to open the primary brake 9 and secondary brake 10, the hand crank 25 may be used to crank out wire.

A secondary or redundant winch gear 21 is connected to a secondary or redundant brake pump 3 through the secondary or redundant brake 10. The secondary brake pump 3 corresponds to the primary brake pump 2, and is hydraulically connected to the hydraulic tank 4 through an inlet and an outlet. A secondary throttle valve 8 for the secondary brake pump 3 is connected between the secondary brake pump 3 and the hydraulic tank 4. The secondary brake pump 3 also acts as a secondary constant speed holder as the flow through the secondary brake pump 3 is controlled by the secondary throttle valve 8 for the secondary brake pump. The secondary throttle valve 8 for the secondary brake pump 3 is set to allow a slightly higher flow rate compared to the combined flow rate through the first and the second primary throttle valves 5, 5a restricting the flow through the primary brake pump 2.

In the event of a failure of the primary brake pump 2, the first primary throttle valve 5 or the second primary throttle valve 5a for the primary brake pump 2, or any other of the components of the primary constant speed holder, the secondary or redundant constant speed holder, will take over, and thus allow a slightly increased speed of the descent of the life boat, as the flow rate allowed through the secondary throttle valve 8 for the secondary brake pump 3 is somewhat higher than the combined flow rate through the first and the second primary throttle valves 5, 5a. During normal operation will however the primary brake pump 2 be governing the speed as the flow rate allowed through the primary throttle valves 5, 5a is lower than the flow rate allowed through the secondary throttle valve 8.

Figure 2 shows the same winch as figure 1 , but is a view from the side of the winch where the primary brake pump 2 is shown. The primary brake pump 2 is supplied with hydraulic fluid through a supply conduit 27 from the hydraulic tank 4. The hydraulic fluid is returned to the hydraulic tank 4 through the primary throttle valve 5. The hydraulic fluid may also return to the hydraulic tank 4 through the additional or second primary throttle valve 5a. The additional or second primary throttle valve 5a may be used by opening the shut off maintenance valve 6 for allowing fluid flow through both throttle valve 5a and the primary throttle valve 5 thus allowing a higher flow rate through the primary brake pump, and a faster launch of the life boat. The maintenance valve is open in a stand-by mode. A primary brake release valve 1 1 allows transfer of hydraulic pressure from the accumulators to the mechanical brakes, and thus release of the brake drum.

Figure 2 also shows the base 26 of the winch and the primary brake 9. Figure 2 also shows a hand crank attachment point 28 that may be used for connecting a hand crank for lowering out wire when the winch is unloaded.

The winch speed with the shut of maintenance valve 6 open may still be lower than the winch speed allowed by the secondary brake pump 3 and the throttle valve 8.

The brake release valve 1 1 is shown with a release handle in two positions, where one position (the upper position) represents the closed position when the winch is locked, and the other position (the lower position) represents the open position for releasing the brakes and for lowering the life boat. The brake handle is actuated by wires attached to the handle. There may be two valves, one for emergency, that will release the brakes without any possibility of reapplying the brakes, and one for training purposes for allowing the brakes to be applied or released as needed. Figure 3 shows the winch 1 in figure 1 from the top. Figure 3 shows the hydraulic tank 4, the primary brake pump 2, the secondary brake pump 3, the primary brake 9, secondary brake 10 and the base 26. Additionally, figure 3 shows an electric motor 15 aligned with the primary brake 9. The primary brake pump 2 is supplied with hydraulic fluid from the hydraulic tank 4 through the primary supply conduit 27, and the secondary brake pump 3 is supplied with hydraulic fluid through the secondary supply conduit 27a. Figure 3 also shows the hand crank attachment point 28 at the end of the primary brake 9 for allowing wire to be cranked out when the winch is unloaded.

Figure 4 is a partly cut through detail of figure 3, showing how the electric motor 15 is connected to a driving sprocket 19 for braking and hoisting through a planetary gear 16 for the electric motor 15.

The planetary gear 16 drives the sprocket 19 for driving the duplex train 17 and thus the primary winch gear 20 shown on fig. 1 . The brake 9 for holding the winch and thus the life boat in position is also shown. A hand crank 25b at the end of the electric motor 15 is used when recovering the life boat back to a stored / boarding position, as the final lifting is done with the hand crank 25b. The hand crank is inserted into an adapter slot at the end of the motor. When the hand crank 25b is inserted, it activates an automatic shut off for the electric motor, thereby ensuring safe operation of the crank for the user. As the hand crank is connected to the electric motor, it also is connected to the planetary gear 16. The hand crank 25b for manually lifting the life boat during the final approach to the davit is fitted through the fan cover at the end of the electric motor 15. The hand crank 25b attaches to the shaft of the motor 15, thus enabling the motor shaft to be turned and consequently the hand crank will turn the planetary gear 16 and the driving sprocket 19. A one way adapter between the shaft and the hand crank prevents kick-back from the crank. In the event of loss of power to the electric motor 15, the boat may be hoisted by mounting a secondary electric handheld motor to the winch trough the same adapter as the hand crank 25b. Alternatively may a pneumatic ratchet or other pneumatic hand tools be used. The planetary gear / hoisting gear 16 between the shaft of the electric motor 15 and the driving sprocket 19 are located in a separate housing at the side of the winch.

Figure 4 also shows how the primary brake 9 is located on the same shaft as the driving sprocket 19 driven by the planetary gear 16.

Figure 5 shows a winch 1 on a davit, for attachment to a life boat through a first attachment hook 30 and a second attachment hook 31 attached to wires from the winch 1 . Davit 2 also includes one wire shock reducing damping cylinder 33 for each wire, for reducing shock loads on the winch and on the life boat.

The davit / winch may be equipped with limit switches, shutting off power to the electric motor when the lifeboat reaches its top storage position to ensure that the winch stops in time. There are at least two switches to ensure that the winch stops in time to avoid damages and injuries.

The final lifting process may be performed manually as described above to ensure the correct final positioning of the life boat.

Figure 6 is a schematic representation of the hydraulic circuit of the invention where the redundant brake 10 and redundant constant speed holder 3 are included.

Figure 6 shows how the primary brake pump 2 is supplied with hydraulic fluid from the hydraulic tank 4 through the primary supply conduit 27. The primary brake pump 2 also supplies pressurized hydraulic fluid to the primary accumulator 13 and the secondary accumulator 14 through an accumulator feed line 34. A one way valve is connected in the accumulator feed line to prevent hydraulic fluid from a manual pump 40 from entering the primary brake pump 2. The primary throttle valve 5 may also include a one way valve, though this is not strictly necessary. The same regards the throttle valve 5a for reduced fluid flow used during training or maintenance when the maintenance valve 6 is closed. The outlet lines from the throttle valves 5, 5a, 8 into the tank 4 may be located above the liquid level in the tank 4 to prevent liquid from being sucked into the brake pumps 2, 3 to allow reverse operation without breaking when the winch is driven by the electric motor.

The manual accumulator feed pump 40 allows manual charging of the hydraulic accumulators 13, 14. The secondary accumulator 14 is connected to the secondary brake release valve 12 allowing fluid pressure to release the primary brake 9 and the secondary brake 10. The primary accumulator 13 is connected to the primary brake release valve 1 1 , also for allowing fluid pressure to the primary brake 9 and the secondary brake 10. A control wire 41 is connected to a leaver on the secondary brake release valve 12, and a green control wire 42 for standby mode is connected to the primary brake release valve 1 1 . The primary brake release valve 1 1 is a "pull and go" release valve, such that when the green control wire 42 for standby mode is pulled, the winch drum will be released even if the green control wire 42 is released. The other control wire 41 however, is connected to a spring return leaver with a spring 44, such that the winch can be stopped by releasing the red control wire 41 . The hydraulic tank 4 is used to store the hydraulic oil and the size of the tank is sufficient to accommodate the demands of the system, and to dissipate heat generated in the system before the fluid is returned to the hydraulic circuits. Figure 6 also shows a non-return valve with spring return the accumulators 13, 14 to ensure that the pressure is maintained within each accumulator 13, 14. The primary brake release valve 1 1 and

secondary brake release valve 12 may be individual three way ball valves. As previously mentioned, the primary brake release valve 1 1 is used in standby mode with a "pull and go" system, and the secondary brake release valve 12 is a spring return valve biased with spring 44 towards a closed position without a "pull and go" system for a training and maintenance mode.

Figure 6 also shows that the hydraulic pressure from the brakes 9, 10 is bled back to the hydraulic tank 4 to allow the spring tension in the brakes to apply the brakes 9, 10. From the figure it is clear how the brakes are released by one of the three way valves 1 1 , 12 supplying hydraulic pressure to the brakes, initially from the stored pressure within one of the accumulators. The primary and secondary brakes will be released when hydraulic pressure is supplied by one of the accumulators, thus creating a redundant system. Accordingly each accumulator 13, 14 is capable of providing sufficient oil pressure and volume to release both brakes as both the brakes must be released to release the winch.

When the maintenance or training valve 6 is closed, the flow from the primary brake pump is restricted to pass through the primary throttle valve 5. The primary throttle valve 5 may for instance be set to limit the speed of descent to 60 m/min if the maintenance/training valve 6 is opened to allow additional fluid to flow through the second primary throttle valve 5a.

The accumulators 13, 14 are connected to shut off valves 37, 38 and pressure gauges 45, 46 on the oil side of the bladder inside the accumulators for monitoring accumulator pressure. The accumulators 13, 14 are also joined with a slide valve 39 to produce a common output to the braking circuit. The pressure of the common output is monitored by an accumulator pressure transmitter 36 connected to the control panels previously mentioned. The slide valve 39 prevents

equalization of the pressure in the accumulators 13, 14.

The brakes 9, 10 can be operated both by the primary brake release valve 1 1 , (pull- and go) and the secondary brake release valve 12 (spring return). These release valves are 3-way ball valves. A slide valve 43 prevents pressure from the accumulators to be bled directly into the tank 4 without operating the brakes when one valve is in a bleed to the tank position, and the other valve is open for supply of pressure to the brakes. Normally, a green wire 42 extends from the lever on the primary brake release valve 1 1 , (pull- and go), and a red wire 41 extends from a lever on the secondary brake release valve 12 (spring return). Both of the wires 41 , 42 extend into the life boat to enable operation of the brakes, and thus the winch, from within the boat. The green wire 42 can then be pulled, and the boat will be launched without being able to stop the launching from the boat. The red wire 41 can be pulled for gradual launch of the boat due to the spring return action of the valve.

The normal working pressure of the accumulators is 200bar and the opening pressure of the multi disk brakes 9, 10 is typically 18bar. Each accumulator has a safety valve on the oil side with a shut of valve integrated in the valve block.

A shut off valve 47 in the line ahead of the secondary brake 9 allows the release of the primary brake 10 without releasing the secondary brake 9.

A level transmitter 35 for monitoring the level of the hydraulic fluid in the tank 4 is connected to the control panel or control panels.

The throttle valves 5, 5a, 8 are adjustable to enable initial set up of the system. After the initial setup no adjustment to the throttle valves 5, 5a, 8 should be needed.