GB2075451A

GB2075451A - Steering Gear

Info

Publication number: GB2075451A
Application number: GB8110806A
Authority: GB
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1980-04-17
Filing date: 1981-04-07
Publication date: 1981-11-18

Abstract

A two pump (10, 11), four ram (6, 7, 8, 9) steering gear assembly for ships has two hydraulic fluid tanks (12, 13), two leak sensing elements in each tank indicating a low (20A, 21A) and a low low (20B, 21B) fluid level, alarm systems actuated by the sensing elements and associated pipework and valves so that (a) when a low level is indicated in either tank, both tanks and pumps are brought into operation, and (b) when a low low level is indicated in either tank, the system having the depleted tank is isolated and the other tank and pump is brought into or kept in operation. <IMAGE>

Description

SPECIFICATION Steering Gear for Ships This invention relates to steering gear for ships, particularly tankers, which increase safety and which, in particular, meet the proposed l.M.C.O.

regulations.

One current form of steering gear for ships, particularly large tankers, utilises four rams and two pumps for moving the tiller and rudder stock.

The rams are positioned two on either side of the -rudder stock near the ends and the rams are actuated by hydraulic cylinders which are supplied wifh hydraulic fluid by pumps. Normally each pump supplies two cylinders and only one pump is in operation. The other pump, supplying the other two cylinders, is available for standby or both pumps and all four rams cab be used for manoeuvring in confined waters.

There is, however, normally only a single hydraulic fluid tank and a single hydraulic system.

Circumstances can arise, therefore, when tankers can lose all steering capability. Such circumstances have arisen in recent years and have contributed to oil pollution (e.g. the grounding of the Amoco Cadiz on the Brittany coast). Because of this a Tanker Safety and Pollution Prevention Conference was convened by I.M.C.O. in 1 978 and a Protocol was established to require improved emergency steering standards for tankers. Subsequent rulings have indicated a move towards a requirement for the automatic division of the hydraulic circuit of a steering gear into two independent systems following a failure of one side.

The present invention is concerned with a steering gear assembly which provides such automatic division of the hydraulic system into two independent systems, but which is, nevertheless, relatively simple. The invention can be used not only on new tankers but can also be used to modify, relatively easily, steering gear assemblies of existing tankers.

According to the present invention a two pump, four ram steering gear assembly for ships includes also two hydraulic fluid tanks, one for each pump, two leak sensing elements for each tank indicating a low or a low fluid level, alarm systems actuated by the sensing elements and associated pipework and valves so that: (a) when a low level is indicated in either tank, both tanks and pumps are brought into operation, and (b) when a low low level is indicated in either tank, the system having the depleted tank is isolated and the other tank and pump is brought into or kept in operation.

The invention is, therefore, suitable for use with the conventional two pump, four ram assembly in which one pump is normally in operation with the other on standby or available for additional power for manoeuvring in confined waters. By having separate hydraulic fluid tanks for eack pump and a low level sensing arrangement for each tank an early warning of fluid loss is given and the second pump brought into operation to work in tandem with the leaking system. This provides the opportunity for an early check and quick correction if the leak is small. If the leak continues the low low level sensing element gives a further warning and isolates that side of the system so that a more detailed investigation of the leak can be made. Throughout the operation at least one pump is in operation so that steering capability is maintained.

The assembly could not cope with the simultaneous heavy loss of fluid from both tanks but no dual system could cope with this unlikely eventuality. However, since the present assembly has the ability to operate both tanks and pumps in tandem even when there is some fluid loss from either or both sides, steering capability can be maintained even in the event of some damage to both sides of the system.

The associated pipework and valves to allow the assembly to operate will include pipework connecting each of the pumps to each of the four cylinders of the rams and isolating valves in that pipework so that the pumps can be isolated from each other and supply only two of the cylinders. In addition there will be two lengths of pipe connecting the two cylinders on the same side of the rudder stock and a valve in each length so that the cylinders can be isolated or connected.

The invention is illustrated with reference to Figures 1 to 4 accompanying this specification which show diagrammatically the method of operation for normal running (Figure 1), low level leak on one side (Figure 2), low low level leak on one side (Figure 3), low low level leak on one side and low level leak on the other (Figure 4).

In the Figures, a steering gear assembly has a tiller and rudder stock 5, four rams 6, 7, 8 and 9 and four associated hydraulic cylinders 1, 2, 3 and 4. There are two pumps 10, 11 each supplied by a hydraulic fluid tank 12, 13. Pipes 14, 15 supply fluid to opposite cylinders 1 or 4 from either pump 10 or 11 or both pumps depending on whether valve 12 is open or shut. Similarly cylinders 2 or 3 can be supplied with fluid from pump 10 or 11 via pipes 16, 17 and valve 11. Pipe 18 with valve B therein connects cylinders 1 and 2 and pipe 1 9 with valve B2 therein connects cylinders 3 and 4.

Finally, each tank 12, 13 has two level sensing devices (20A, 21A and 20B, 21 B) to indicate a low or a low low fluid level.

Normal running is shown in Figure 1 in which valves Ii and 12 are open and valves B1 and B2 are closed. All four cylinders and rams are in operation and can be supplied with fluid from either pump 10 or pump 11 or both pumps.

In Figure 2, it is assumed that a low level leak has been detected by sensing element 20A in tank 12. An audible and/or visual alarm is actuated on the bridge and/or the engine room. At the same time valves Ii and 12 are shut automatically and pump 11 started up (if it is not already in operation). The two pumps and tanks are them separated with pump 10 and tank 12 supplying cylinders 1 and 2 only and pump 11 and tank 13 supplying cylinders 3 and 4 only.

Valves B, and B2 remain closed.

A similar sequence of automatic operations would occur if the low level sensing element 21 A of tank 13 were to detect a leak.

An investigation into the cause of the leak can be made while the operation of Figure 2 continues. If the cause is simple and the remedial action can be applied quickly (including topping up the tank), the sensing element will cease to register and valves 1, and 12 will be re-opened to return the assembly to the normal running of Figure 1.

Since Figure 2 shows that both pumps and systems continue to operate with low level leaks it will be appreciated that steering capability will be maintained even if leaks develop in both systems to a low level.

If however, for whatever reason, it is not possible to restore the assembly to normal running, and the operation in Figure 2 continues, tank 12 will continue to lose fluid until the low low level sensing element 20B is set off. The response is shown in Figure 3. A further audible and/or visual alarm is actuated on the bridge and/or in the engine room.

Valves Ia and 12 remain closed and pump 11 continues operating. Valve B1 is, however, automatically opened (B2 remaining closed) and pump 10 is shut down automatically. The steering is now effected by pump 11 and cylinders 3 and 4 only. Since valve B, is now open fluid can flow between the inoperative cylinders 1 and 2 and there is no locking.

A similar sequence of automatic operations would occur if the sensing element 21 B of tank 13 were to detect a low low level in that tank. In this case valve B2 would open and pump 11 would shut down, the steering being effected by cylinders 1 and 2 and pump 11.

Figure 4 shows the mode of operation in that eventuality, i.e. the steering being effected by pump 10 and tank 12 and cylinders 1 and 2 only.

What Figure 4 also shows is that the system will continue to operate and some steering capability will be maintained even if a-leak develops in the operating part of the system, i.e. if a leak is detected by the low level sensing element 20A of tank 12.

By means, therefore, of the relatively simple system described above, some steering capability is maintained in all but the most severe and unlikely circumstances of total failure of both systems.

Claims

1. A two pump, four ram steering gear assembly for ships characterised in that it includes also two hydraulic fluid tanks, one for each pump, two leak sensing elements for each tank indicating a low or a low low fluid level, alarm systems actuated by the sensing elements and associated pipework and valves so that: (a) when a low level is indicated in either tank, both tanks and pumps are brought into operation, and ib) when a low low level is indicated in either tank, the system having the depleted tank is isolated and the other tank and pump is brought into or kept in operation.

2. A steering gear assembly as claimed in claim 1 wherein the associated pipework and valves includes pipework connecting each of the pumps to each of the four cylinders of the rams and isolating valves in that pipework so that the pumps can be isolated from each other and supply only two of the cylinders of the rams.

3. A steering gear assembly is claimed in claim 1 or 2 wherein the associated pipework and valves includes two lengths of pipe connecting the two cylinders on the same side of the rudder stock and valve in each length so that the cylinders can be isolated or connected.

4. A steering gear assembly as claimed in claim 1 substantially as described with reference to Figures 1 to 4.