GB2167714A - Emergency gangway - Google Patents

Abstract

An emergency gangway capable of being deployed from an emergency support vessel and being landed safely on an offshore platform in gale force conditions, despite movements of the vessel relative to the platform comprises: (a) a first section 2 pivotally and rotatably mounted on a support vessel, (b) a second section 3 telescoping within the first, (c) a servo-mechanism for controlling the extension of the second section of the gangway, (d) a servo-mechanism for controlling the elevation of the gangway, (e) a servo-mechanism for controlling the slew of the gangway and (f) stabilising means for stabilising the end of the gangway in space. <IMAGE>

Description

SPECIFICATION Emergency gangway This invention relates to an emergency escape gangway suitable for installation on an emergency support vessel.

In recent years the number of offshore oil production platforms has grown considerably, particularly in waters which are exposed to severe climatic conditions such as the North Sea where gale force winds and temperatures below freezing are not infrequent. Provision must always be made for emergencies which require the rapid evacution of these platforms.

In extreme conditions, traditional means of escape such as lifeboats or escape chutes are occasionally inoperative, often hazardous and sometimes leave victims immersed in the sea or under exposed conditions for undesirably long periods of time, with possibly fatal results.

For this reason an emergency support vessel (ESV) has been built and is permanently on-station in the North Sea in the vicinity of a group of production platforms. This vessel has both emergency and support roles. One of its emergency roles is to provide a rescue and lifesaving facility to a stricken offshore installation by enabling direct evacuation of personnel by means of a gangway.

The vessel is designed to keep station both in the vicinity of a platform or close to it, linked by the gangway, in poor weather conditions without recourse to mooring. This is achieved by a dynamic positioning system.

Under poor weather conditions, with the ESV subject to pitch, roll, yaw, heave, sway and surge, the deployment of a conventional gangway and its positioning on the platform is a difficult and sometime impossible undertaking. Movement of the ESV due to rolling is magnified at the end of the gangway and the possibility of the gangway making a violent impact with the platform and damaging itself and possibly the platform is a very real one.

We have now devised an emergency gangway capable of being deployed from an ESV and being landed safely on an offshore platform in gale force conditions, despite movements of the vessel relative to the platform.

Thus according to the present invention there is provided a telescopically extendable gangway comprising: (a) a first section pivotally and rotatably mounted on a support vessel, (b) a second section telescoping within the first, (c) a servo-mechanism for controlling the elevation the extension of the second section of the gangway, (d) a servo-mechanism for controlling the elevation of the gangway, (e) a servo-mechanism for controlling the slew of the gangway and (f) stabilising means for stabilising the end of the gangway in space.

The gangway may additionally comprise (g) a relatively short third section connected to the remote end of the second section in such manner that in use the third section slopes downwardly from the second section.

The connection between the second and third sections may be rigid, in which case the second and third sections are permanently offset, or pivoted, in which case they may be aligned for better storage, or when not in use, and more flexibly deployed when in use.

The third section reduces the magnitude of the impact load during deployment since its mass is small.

The angle between the second and third sections in use is governed by the maximum safe slope for carrying stretcher-borne casualties. A typical value lies between 25" and 30".

Landing can be on an area of the platform which is above the level of the base of the gangway. It is preferred, however, to employ the gangway in an approximately horizontal position from the ESV to a specially designed and positioned landing area on the platform.

Accelerometer based sensors and compensators provide suitable stabilising means. The sensors continuously monitor deviations from the last known position and the compensators take restorative action.

The landing tip of the gangway preferably comprises landing wheels which on contact actuate the servo mechanism controlling the telescoping of the gangway so that it may compensate for changes in distance between the base of the gangway and the landing area on the platform caused by relative motion between the ESV and the platform.

It is envisaged that the operation of the gangway will be implemented manually by one operator with stabilising assistance provided by the gangway control system. This allows maximum flexibility of operation to cater for unforeseen circumstances whilst also being well within the limitations of one man's capabilities.

The elevation and slew servos are capable of operating in the following modes: (a) Unstabilised (b) Space stabilised (c) Idle.

The unstabilised mode has two functions. Firstly, when moving the gangway from the stowed position on the ESV, the gangway should be driven relative to deck. This will avoid any possible collisions due to deck motions if the gangway were stabilised in space. When the gangway is safely outboard of the vessel structure, the stabilised mode can be selected.

The principle of the space stabilised scheme means that over a sensible limited period of time, the elevation and slew motions of the gangway will be space stabilised. The extension motion of the gangway during deployment remains a manual operation, since expected short-term excursions in this direction are within t 1 metre.

The extension system is therefore capable of operating only in two modes, namely: (a) manual (b) automatic.

In "manual", the extension of the gangway is manually controlled by the operator at the gangway control console. In the "automatic" mode, the gangway extension is controlled automatically once successfully deployed on the platform.

When the elevation and slew servos are in the "idle" mode, a preset pressure will be maintained across the elevation rams or motors thus countering any net out of balance whilst also ensuring the hydraulics are free to move in sympathy with the gangway.

During gangway deployment, the operator will position the gangway in elevation and slew so that the gangway is pointing at the platform. He will then leave this motion alone while the gangway control system maintains the end point approximately stable in space.

During this period, the operator is then free to concentrate on manually extending the gangway to the required position before lowering the tip and finally locking it in the drooped position.

Once the gangway tip is lowered and locked in position, the operator may switch the elevation and slew systems to "idle" and the extension system to "auto".

From an operational viewpoint, it is preferred that droop snoot can be locked in any position with respect to the gangway. This allows for easier and more flexible operation than if discrete locking positions are used.

In this mode the ESV gangway will automatically extend and shorten, due to ESV motions, to maintain the end point stationary on the platform.

If the operator wishes to modify the position of the end point on the platform, he can switch the extension system to manual, reposition the end point with the joystick and then revert to "auto". The gangway end point will then be maintained at this new position. This adjusting operation can be performed with the slew and elevation systems remaining in "idle".

To return the gangway from the deployed to the stowed position, the elevation and slew servos will be returned to the "stabilised" mode, the extension system returned to manual, and the tip will be lifted off the platform. The operator will then move the gangway towards the stowed position and final stowage will be implemented with the elevation and slew servo in the "unstabilised" mode. The previous operation assumes that, after deployment, the gangway rests on the rig with both elevation and slew servos in the idle mode. This concept results in inertial forces due to the ESV base motion being transmitted to the platform. These forces can be reduced by incorporating a suspension system on the end of the gangway which results in relative motion between the gangway and platform as energy is absorbed.

An alternative configuration is a stabilised gangway wrist with the angled tip being allowed to rest freely on the platform.

This configuration reduces the loads on the landing.

The invention is illustrated with reference to Figures 1-5 of the accompanying drawings wherein Figure 1 is an elevation of the gangway with the telescopic section fully retracted, Figure 2 is an elevation with the telescopic section fully extended, Figure 3 is a plan view with the telescopic section partially extended, Figure 4 is an elevation showing the gangway in two different positions and Figure 5 is a schematic diagram of the control systems.

With reference to Figures 1-4, the gangway is rotatably and pivotably mounted on a slewing base 1.

The gangway comprises an inboard section 2, a telescopic section 3 and a "droop snoot" 4. Operation is controlled from a cabin 5.

Section 3 is extended by means of a drive winch 6 and associated wires and sheaves.

The droop snoot 4 is pivoted to the telescopic section 3 at 7 and hydraulic rams 8 control the desired configuration. A landing wheel assembly 9 is fitted to the tip of the snoot.

The gangway extends from a stowed length of 25 m to a maximum of 43 m and is approximately 0.6 m wide. It is constructed from lightweight hollow steel sections.

Figure 4 shows the gangway at rest in the horizontal position. The Figure also shows the inboard section 2 in the elevated position, the other sections being omitted for reasons of clarity.

A short flight of steps 10 leads down from the gangway to the deck 11 of the ESV.

With reference to Figure 5.

Additionally shown are a slew motor and gearbox assembly f2 for slewing the base 1, and hydraulic cylinders 13 for elevating the gangway.

A position stabilising accelerometer pack 14 is fitted to the inboard section 2 of the gangway.

TV cameras 15 for viewing tip motion are fitted at the end of the droop snoot 4.

A hydraulic powerpack 16 supplies hydraulic fluid to the various units and signals are relayed to a control console 17 containing servo processing and power supplies 18 and video screens 19 as follows: Signal Description Function 21 Gangway Wheel Rig Position Sensor Measures rotation of wheels which indicates the need to telescope and actuate tele scoping servo 22 Systems Landed Interlock Detects gangway landing from axle load on wheels 23 Accelerometer Signals Velocity feedback on elevation 24 DP Transducer Telescopic extension limiting hydraulic pressure feedback signal 25 Servo Valve Spool Position Feedback of telescoping velocity 26 Servo Valve Signal Telescoping control command 27 Blocking Valve Signal Stops gangway telescoping on loss of hydraulic pressure.

Locks hydraulic supply line 28 Tacho Feedback on velocity of telescoping 29 Elevation Inertial Signals Feedback on angle of elevation 30 Tacho Feedback on rate of change of angle of elevation 31 Tacho Feedback on rate of change of angle of slew 32 Blocking Valve Signal Stops gangway slewing on loss of hydraulic pressure. Locks hydraulic supply line hydraulic supply line 33 Servo Valve Signal Slew control command 34 DP Transducer Slew limiting hydraulic pressure feedback signal 35 Servo Valve Spool Position Slew velocity feedback 36 Servo Valve Signal Elevation control command 37 Blocking Valve Signal Stops gangway elevation on loss of hydraulic pressure. Locks hydraulic supply line 38 DP Transducer Elevation limiting hydraulic pressure feedback signal 39 Servo Valve Signal Elevation control command 40 Slew Reference Data Inertial slew reference in space 41 Powerpack Tell backs Warning in case of malfunction 42 Powerpack Control Signals Powerpack control

Claims (6)

1. A telescopically extendable gangway comprising: (a) a first section pivotally and rotatably mounted on a support vessel, (b) a second section telescoping within the first, (c) a servo-mechanism for controlling the elevation of the gangway, (d) a servo-mechanism for controlling the elevation of the gangway, (e) a servo-mechanism for controlling the slew of the gangway and (f) stabilising means for stabilising the end of the gangway in space.

2. A gangway according to claim 1 comprising (g) a relatively short third section connected to the remote end of the second section in such manner that in use the third section slopes downwardly from the second section.

3. A gangway according to claim 2 wherein the second and third section are pivoted.

4. A gangway according to either of claims 2 or 3 wherein the angle between the second and third sections in use is between 25" and 30".

5. A gangway according to any of the preceding claims wherein the stabilising means comprise accelerometer based sensors and compensators.

6. A telescopically extendable gangway as hereinbefore described with reference to Figures 1-5 of the accompanying drawings.