GB2230745A - Vehicle ferry having floodwater dumping means - Google Patents

Abstract

To prevent floodwaters taken on board RO-RO ferries through bow and stern doors respectively and trapped on the vehicle decks in quantities resulting in capsize a RO-RO ferry is provided with intelligent washports 6 which, being located just above the vehicle deck level, are power-operated; watertight, and failsafe. The controls are intelligent inasmuch as the presence of floodwater on the vehicle deck is sensed by water pressure sensors 29 and waterflow sensors 30 and the washports power automatically activated to open and dump the floodwaters overside. When the deck is cleared of floodwater the washport control is de-activated and the washports close and lock shut watertight by the combined action of spring force and gravity. Safety features are included in the control circuitry to prevent any inflooding through the washport apertures. <IMAGE>

Description

A VEHICLE CARRYING FERRY VESSEL HAVING FLOODWATER DUMPING MEANS TO ENHANCE ACCIDENT SURVIVABILITY.

This invention relates to ferry type vessels, especially to Roll-On/Roll-Off passenger and/or freight ferries.

It is known to provide vehicle carrying ferries with scupper pipes capable of draining small quantities of water from the enclosed Main vehicle deck to the ship's bilges. Also it is known to provide vessels with washports, or freeing ports, in their bulwarks at weather deck level to allow gravity dumping overside of any solid water or spray accumulation taken on board in heavy weather which would otherwise remain trapped on deck to the detriment of the vessel's stability.

Washports are positioned low down in the bulwarks close to deck level and at intervals along the shipsides, being of increased dimensions and/or frequency adjacent any interruptions in the weather deck level where water can accumulate.

Normally the washports are open apertures in the bulwarks, but may have the apertures filled with top-hinged plates so arranged as to open outwards by water pressure on the inboard side. Such top-hinged washports are characterised by the absence of any active opening or closing mechanism, with the possible exception of passive counterbalancing, and the washport perimeters are not fitted with seals of rubber type material.

The present invention seeks to provide large and small RO RO ferry vessels with means to prevent the accumulation of water in the enclosed vehicle deck space between Main and Upper decks as may occur following collision or the breaching of bow; side; or stern door, and which water accumulation at a rate far in excess of the capacity of the scupper pipes to drain to bilges eventually generates a "free-surface" moment which can destroy the vessels stability and lead to capsize conditions.

Accordingly, the present invention provides a RO-RO ferry vessel with washports at the enclosed vehicle deck level which washports, being intelligent to sense the presence of floodwater on the Main deck, automatically open to dump the accumulated water overboard.

A ferry vessel of the invention is provided with a series of intelligent washports located Port and Starboard in the shipsides just above Main vehicle deck level. It is of course inappropriate for the washports to be closed simply by passive top-hinged non-watertight plates as on weather deck locations.

The washports envisaged would be in effect small power-operated watertight doors arranged failsafe so that they close and remain closed secure and watertight by the combined action of gravity on the washport panel, and by the thrust of the internal spring in the full-bore of the actuating cylinder which moves the actuating linkage into an 'over-centre' locked position.

The intelligent washports have their lower edges close to Main vehicle deck level and are located at intervals in way of the low part of the deck sheerline which normally extends over approximately half of the ship's length amidships.

Some scalloping of the top of the shipside fendering may be necessary in way of the washports.

The intelligent washports are preferably grouped for control purposes, there being a forward group and an after group on each side of the vessel, and each group having water pressure sensors inside and outside the hull in circuit with a water flow sensor. Actuation of a group of washports in an emergency may be by pneumatic or hydraulic pressure acting on the annulus ends of the cylinders to move the actuating linkages from locked 'over-centre' positions and compressing the internal springs in the full bore ends of the cylinders as the washports open.

Without manual intervention, apart from ensuring that the pneumatic or hydraulic source is continuously operational, the washports will respond automatically to dump floodwaters rapidly from the Main deck area in an emergency and before such floodwaters accumulate to diminish/destroy the ferry's transverse stability. In an emergency and with the vessel upright or near upright, the presence of water on the Main vehicle deck is sensed by a watertight pressure switch located as close as practible to deck level and at or near the midlength of the group of washports it controls. The pressure switch signal activates a relay which in turn opens a solenoid valve to pressurise the annulus ends of the washport actuating cylinders thereby opening the washports.When cleared overside to minimal level the water pressure drops and the pressure switch disengages releasing pressure from the annulus ends of the actuating cylinders whereupon spring force in the cylinder full bore ends together with gravity quickly closes the washports.

The external pressure sensing switch in each control circuit is a safety feature to ensure that water pressure sensed on the outside hull irdexcess of the pressure sensed internally, as would occur in a heavily listing or heeled vessel, de-activates the relay and solenoid valve thereby releasing pressure from the annulus ends of the actuating cylinders to close the washports.

A further optional safety feature, to guard against a faulty pressure switch situation where the washports are open to dump floodwaters overside but the flooding vessel slowly heels to an angle which submerges the washports and brings waterlevels outside and inside the vessel to the same level at which there is no significant pressure differential and which would normally result in the equal pressures de-activating the cylinders, is the introduction of a water flow sensing switch in way of one of the washports. The switch, which may be activated by a paddle arm or by propeller, would sense inflow of water through the washport and would after a short time delay override the faulty pressure switch(es) and de-activate the relay and solenoid to close the washports.The short time delay is to prevent the washports actuating system becoming hyper-active in response to every slight inflow reversal as may occur in wave conditions.

Viz-a-viz prior-art ferries, a RO-RO ferry vessel of the invention is not at risk of capsize from floodwaters as would accumulate on the Main vehicle deck in the event of breaching of bow or stern donors, or from collision breaching of the shipside above Main deck level in rough sea conditions.

The improved survivability of a ferry vessel equipped with the invention is achieved at reasonable cost and with but small reduction in the ferry's deadweight carrying capacity.

The invention is suitable for retrofitting to existing RO-RO passenger and freight ferries, and there may be prospect of reduction in hull insurance premiums for vessels so equipped.

A preferred embodiment of the invention will now be described, though by way of illustration only, with reference to the accompanying drawings in which Figure 1 is a longitudinal outboard profile of a passenger and vehicle ferry equipped with intelligent washports.

Figure 2 is an inboard profile of an intelligent washport, looking outboard.

Figure 3 is a transverse section of the centre hinge and actuating mechanism of an intelligent washport in closed, secure, and watertight position.

Figure 4 is an inboard profile of the centre hinge and actuating mechanism, looking outboard.

Figure 5 is a transverse section of the centre hinge and actuating mechanism of the washport in the open position for dumping of floodwater overside.

Figure 6 is a transverse section though a partially flooded ferry in which the intelligent washports have automatically opened to dump floodwaters overside to Port and to Starboard.

Figure 7 is a transverse section through a partially flooded ferry which has heeled under the asymetrical weight of floodwater taken on board as a consequence of collision damage or breaching of a bow or stern door, and in which the washports have automatically opened on the 'downside' to shed the floodwater overside.

Figure 8 is a transverse section through a partially flooded ferry which has listed severely to an angle of loll under the asymetrical weight of floodwater and/or from the asymetrical loss of buoyancy in a damaged hull compartment, at which angle the water level outside the hull is above the level of floodwater inside and in which the intelligent washports have automatically closed.

A ferry vessel of the invention floats normally at waterline 1, and has a Main vehicle deck 2; an Upper deck 3; Bow and Stern doors respectively 4 and 5, and intelligent washports 6 control-led by waterpressure sensors inside and outside the hull, and waterflow sensors 3O.

Each washport 6 comprises a shipside panel 7 hinged at 8 on three hinge arms of which the centre hinge armgis extended for connection of the operating links 10 and the outer hinge arms 11 are without extensions. All three pairs of hinge mountings 8 are of split construction to permit mounting/dismounting as an assembly of the panel 7, hinge arms 9 and 11, and the connecting torsion tube 12. Optionally, a stiffener 13 may be welded to panel 7 for increased rigidity of the assembly. Shipside frames supporting the shipside plating normally run as shown at 14, but the frames 15 in way of the washport require to be cropped and 'bridged' to frames 14 by stiffeners 16 to preserve structural continuity.A steel frame 31 is welded into a prepared aperture cut in the shipside plating and houses a "D" section neoprene type rubber seal 32 against which the washport panel 7 seals watertight when closed. The seal 32 may conveniently be glued to frame 31. The operating links 10 connect at their top ends to crank 17 which is free to rotate through approximately 90 degrees about hinge pin 18 secured to hinge blades 19.

Crank 17 is connected to the rod end of actuating cylinder 20 at clevis hinge pin 21, the cylinder heel mounting 22 being hinge pin 23 connected to hinge blades 19. The operating links 10 which transmit the forces for opening and closing of the washport panel 7 are hinge pin connected 24 at their lower ends to hinge arm 9, and hinge pin connected 25 at their top ends to crank 17. Either or both of the hinge pins 24 and 25 may have eccentric offset (not shown) for fine adjustment of the overcentre locking action during installation. In the fully closed position crank 17 is arrested by buffer block 26 to give a small positive over-centre locking angle 27, simultaneously lugs 28 on the washport panel7 arrest against frame 31 giving a predetermined compression to the watertight seals 32.The extended hinge blades 19 in way of the centre hinge arm 9 additionally support the cylinder heel pin 23 and pin 18 about which crnak 17 rotates. The outer hinge arms 11 have hinge mountings 8 on short hinge blades 33, and a horizontal stiffener 34 connects all of the hinge blades 19 and 33 to shipside structure 16.

Upon admission of pressure to the annulus end of operating cylinder 20 the piston rod retracts pulling crank 17 from it's over-centre locked position as shown in Fig.3 and continues to pull the crank through approximately 90 degrees simultaneously storing energy by compressing the internal spring (not shown) in the full bore end of cylinder 20. The operating links 10 transmit angular rotation of crank 17 to angular rotation of the centre hinge arm 9 which, being securely fastened to torsion tube 12, further transmits rotation to the outer hinge arms 11; such rotation continuing until arrested by the hinge arms 9 and 11 coming in contact with the perimeter frame 31 with the washport panel 7 in fully open position as shown in Fig. 5.

Release of pressure from the annulus end of cylinder 20 reverses the foregoing sequence with the weight of the washport panel 7 imparting a rotational motion directly through hinge arm 9 and via the torsion tube 12 from hinge arms 11 to give an upthrust to the lower ends of operating links 12. Simultaneously the stored energy from the internal spring (not shown) in the full bore end of cylinder 20 exerts through the piston rod an upthrust to rotate crank 17 and move operating links 10 to the over-centre locked position in which crank 17 bears against buffer block 26, and lugs 28 on panel7 bear against the perimeter frame 31 and with panel 7 sealed watertight against seal 32.

The intelligent control system preferably comprises an internal pressure sensing switch and an external pressure sensing switch located at 29, and a flow sensing switch located at 30. Normally with just air pressure acting on the internal and external pressure sensor switches the washports remain closed. Transitory wave pressures as may occur in heavy seas on the external pressure switch could give 'close' signals however, with the washports already closed, these signals have no effect. In an emergency situation, such as breaching of bow doors when running at speed and with head trim, floodwater could accumulate on the Main vehicle deck until the internal pressure switches 29 Port and Starboard sensed water pressure to open the washports and dump floodwaters overside as shown in Fig.6.

Fig.7 depicts a situation following collision in moderately heavy seas where breaching of the shipside extends above and below Main deck level towards either end of the vessel and flooding of a lower hull compartment has caused the vessel to list allowing waves to enter the vehicle deck space and the floodwaters to run down the sheer and accumulate.

Internal pressure switches 29 have sensed the presence of floodwater which is being dumped overside.

Fig.8 depicts a situation following severe collision or grounding which has breached two or more compartments below waterline. The vessel has heeled severely from loss of bouyancy and asymetrical flooding to an angle of loll, but upflooding seepage via access hatches etcetera is occurring and water is accumulating on the Main vehicle deck. Clearly opening of the washports in this situation would rapidly lead to capsize of the ferry, however the washports remain closed due to the pressure differential arising from the pressures sensed by the external pressure switches exceeding the pressures sensed by the internal pressure switches. Should any malfunction of the pressure switches occur causing the washports to open, flow sensing switches in the apertures of washports just inboard of shipside would sense water inflow and give signals overriding the pressure switch signals and close the washports.

Whilst sensing of water presence by pressure switches is the preferred method, float switches mounted close to the Main vehicle deck level internally, and mounted externally above the level of the washports, would sense water levels and achieve the same control. Fitting of time delays in the control circuit may be necessary to reduce transient external wave pressure or wave levellsignals and/or transient water inflow signals.

Claims (7)

1. A vehicle carrying ferry vessel having bow,and/or side, and/or stern doors has to Port and to Starboard just above the main vehicle deck level one or more intelligent washports arranged watertight and with failsafe controls which upon sensing the presence of floodwater on deck automatically activate the washports actuating mechanisms to unlock and open the washports thereby dumping floodwaters overside, and upon sensing the floodwaters cleared automatically controls the closing of the washports watertight.

2. A ferry vessel as in Claim 1 in which the close mechanism locks in an over-centre position obviating any requirement for cleats or latches to secure the washport watertight.

3. A ferry vessel as in Claim 1 in which the washports open/ close mechanisms are powered by pneumatic or hydraulic cylinders or by electro-mechanical linear actuators.

4. A ferry vessel as in Claims 1 and 3 in which the actuating cylinder has an internal spring which, upon the cylinder being de-activated, forces the close mechanism linkage 'over-centre' to lock the washport shut watertight.

5. A ferry vessel as in Claim 1 in which the presence of water inside the vessel above vehicle deck level and outside above the level of washport apertures is sensed by pressure switches or float switches to control the opening and closing of the washports.

6. A ferry vessel as in Claim 1 in which the controls include a water flow sensing device inboard of the aperture of a washport which, upon sensing sustained water inflow, automatically overrides any malfunction of the normal controls and closes the washports.

7. A ferry vessel as claimed in Claim 1, and substantially as herein described, with reference to and as illustrated in the accompanying drawings.