GB2229969A - A ferry having inflatable reserve buoyancy - Google Patents

Abstract

A RO/RO ferry has deployed on the shipsides self-stowing buoyancy chambers 9, 10 which are inflated following unberthing and prior to proceeding to sea. Throughout the voyage the chambers of cylindrical and/or semi-cylindrical cross- section remain inflated to provide instant reserve buoyancy and righting moment against capsize. Upon entering the arrival port the chambers are deflated and, by vacuum assisted exhaustion are arranged to self-stow neatly against the shipsides prior to berthing. No decision to inflate requires to be made in the heat of a crisis situation by the vessel's personnel, and the triple problems of inflation while submerged, angular velocity of the listing vessel, and icing of airpipes associated with ultrarapid inflation are avoided. <IMAGE>

Description

A FERRY VESSEL HAVING INFLATABLE RESERVE BUOYANCY FOR ENHANCED FLOODING SURVIVAL CAPABILITY.

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

It is known to provide ferry vessels with rigid steelframed sponson additions to Prt and to Starboard which increase the breadths of the vessels at their waterlines thereby enhancing the transverse stabilities of the ferries in their normal operations. Such sponsons impair a vessel's propulsive efficiency and can give rise to serious difficulties in the launch and recovery of the vessel's lifeboats or other lifesaving appliances. Further, the increased breadth of the vessel can cause misalignment of the bow or stern doors with the shore RO/RO linkspan.

To increase the transverse stability and survivability of a vehicle type ferry following internal flooding which may arise, typically from collision or breaching of bow or stern door, it is desirable to equip the vessel with buoyancy along her sides.

It is known, and has been since 1984, that sausage shaped air bags could be deployed on the ship sides of a ferry which, following critical damage and flooding, could be inflated to provide both additional reserve buoyancy and righting moment to counteract vessel capsize moment.

Numerous practical difficulties are inherent in such an arrangement.

To be effective the inflation time must be very rapid, however the release of compressed air or gas from high to low - low pressure causes freezing and icing-up of the gas pipe and nozzle which can significantly slow the inflation time.

Automatic initiation of the inflation at a predetermined angle of heel is scarcely possible since rolling of the vessel in a seaway could cause inflation. If the control angle is set at an angle beyond normal rolling the inflation time would require to be near-instantaneous to be effective, with all of the attendant icing problems.

Manual initiation of inflation is fraught with difficulty aince the the time for decision could be very short. Also, there would be a reluctance on the part of the duty officer to trigger what might subsequently prove to have been unnecessary inflation.

The problems of deflating and re-stowing of the buoyancy chambers would be labour-intensive and time-consuming to a degree that - in the case of an inadvertant or unnecessary inflation the vessel may require to be withdrawn from service.

In a rapid capsize situation the 'downside' buoyancy chambers would almost certainly be under water prior to being fully inflated. This water pressure coupled with the shearing effect upon the bag from the angular velocity of the vessel heeling could further delay inflation.

The present invention seeks to improve the survivability of a flooding ferry by the provision of effective inflatable buoyancy in a practical manner which will provide reserve buoyancy and righting moment to counter capsize whilst avoiding the problems of decision to inflate; the problem of icing due to rapid inflation; the twin problems of inflation whilst submerged and - and angular velocity; and the problem of re-stowing the buoyancy chambers upon deflation.

Accordingly, the invention provides a ferry vessel with inflatable bouyancy which does not require rapid inflation; is self-stowing upon deflation, and does not require near-ins;tant decision in the event of flooding and the onset of a potential capsize situation.

A ferry vessel of the invention is provided on each side with one or more inflatable buoyancy chambers having their lower edges located as close as practicable to the vessel1 load waterline, apd extending fore-and -aft over approximately two-thirds of the vessels length. The inflatable chambers, which may be of cylindrical or semi-cylindrical cross-section or may be sperical, are secured to the shipsides and are connected to an on-board compressed air or other gas piped supply line feeding through pilot-operated non-return valves into individual chambers. The chambers, which may comprise a number of individual assemblies alternatively a long multi-compartment assembly, have arrangements which fold the chambers into regular stowed patterns automatically upon deflation thereby obviating the necessity of manual re-stwoing after use.

In an abandon-ship situation where a ferry is at an angle of loll having survived partial flooding by the twin benefits of reserve buoyancy and righting moment of the intact buoyancy chambers on the 'downside', it would be possible to deflate the 'upside' buoyancy chambers to permit the 'upside' lifeboats to skid down the shipside and accross the deflated chambers during launching.

Viz-a-viz prior-art ferries, a vehicle ferry vessel of the invention has large reserves of outboard buoyancy providing righting moment to counter capsize moment and to maintain a partially flooded vessel at an angle of loll. Such buoyancy, by virtue of self-stowing capability to a collapsed depth within the line of shipside fendering, does not cause misalignment of the vessel's bow or stern doors to shore RO/RO linkspans as would occur with permanent fixed buoyancy sponsons, nor cause problems with berthing. When away from berth a departing ferry has it's buoyancy chambers inflated at a leisurely pace of several minutes t,o minimize icing problems at air inlets, and the buoyancy chambers remain inflated throughout the passage.

Upon approach to destination, typically upon entering harbour, the buoyancy chambers are deflated at a leisurely pace by pilot pressure applied to the non-return valves and self-stow neatly against the shipsides permitting normal berthing. With the reserve buoyancy inflated chambers in situ during passage time - be it 20 minutes or 20 hours - no human nor automatic decision to inflate or not to inflate need be made in the event of a crisis.

Should a ferry vessel have forward trim which can cause yaw or course instability, an uncontrollable ever tightening turn can develop if something causes the vessel to list such as water on the vehicle deck following breaching of bow doors. It is conceivable that immersion of the buoyancy chambers could counter the yawing , and either stop the yaw or at least slow it down.

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

The invention is particularly suitable for retrofitting to existing 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 self-stowing inflatable buoyancy chambers.

Figure 2 is a transverse section through the ferry shown in Figure 1.

Figure 3 is a transverse section through a partially flooded ferry in which the inflatable buoyancy chambers have arrested the capsize at an angle of loll.

Figure 4 is a section through a semi-cylindrical selfstowing buoyancy chamber in inflated mode.

Figure 4a shows the buoyancy chamber deflated and selfstowed.

Figure 5 is a section through a cylindrical self-stowing buoyancy chamber in inflated mode.

Figure 5a shows the buoyancy chamber deflated and selfstowed.

Figure 6 is a section through the ship side mounting of a semi-cylindrical buoyancy chamber.

Figure 7 shows a cylindrical buoyancy chamber mounting.

A ferry vessel of the invention shown in the accompanying drawings floats normally at waterline 1, and has a Main Deck 2; an Upper Deck 3; fendering 4; bow and stern doors respectively 5 and 6,and lifeboats 7 under launching davits 8.

To the shipsides Port and Starboard are securely attached self-stowing inflatable buoyancy chambers of cylindrical section 9 below the fendering 4, and of semi-cylindrical section 10 above the fendering.

The superstructure 11 is set inboard from the shipsides and extends upwards from the Upper Deck level.

Each cylindrical buoyancy chamber 9 has internal closespaced ties 12 of elastic material attached at their ends to semi-flexible rods or cords 13 made fast to the flexible envelope material 14 of the chamber. The ties 12 have defined unstretched lengths to fold the envelope 14 into a predetermined configuration upon deflation. A steel angle bar frame 15 is toe -welded to the shipside 16 to which a substantial net 17 of elasticated material is secured by a continuous rope 18 having it's ends attached to a rigging-screw or other tensioning device (not shown). The combined action of the net and internal ties 12 stow the deflated chamber against the shipside 16 within the perimeter defined by the angle framel5. Inflation compressed air, or other suitable gas, enters the chamber through a pilotoperated non-return valve 19.Following inflation the chambers 9 remain filled with locked-in air and can only be deflated upon pilot pressure signal opening the non-return valve permitting exhaustion of the chamber, there being one valve 19 minimum serving each chamber.

Similarly, the semi-cylindrical buoyancy chamber 10 has close-spaced elastic material ties 20 attached to semi-flexible rods or cords 21 made fast to the envelope 22. By the predetermined unstretched lengths of the ties 20, and by their strategic locations segmentally and circumferentially, the envelope 22 upon deflation is constrained into the stowage pattern shown in Fig. 4a. A steel angle frame 23 is toewelded to the shipside 16 to which is bolted 24 the semicylindrical buoyancy chamber mounting assembly,which comprises of a shallow tray 25 and mating perimeter profile 26 both of metal or fibreglass type material. To further ensure gastight effectiveness of the ridges 27 upon the envelope material 22, metal lugs 28 may be fitted in way of the bolts 24.

Inflation and deflation procedures of each semi-cylindrical chamber 10 are through one or more pilot-operated non-return valves 19 in an identical manner to the procedure described above for cylindrical chambers. A feature of the semi-cylind- rical chambers 10 is moisture drain-off cocks 29.

Optionally and additionally an elasticated net 30,similar in mounting and function to that described above for cylindrical chambers, may be fitted to semi-cylindrical buoyancy chambers.

A partially flooded ferry vessel is depicted in Fig.3 in a stable condition due to the "downside" buoyancy chambers 9 and 10 having arrested a capsize situation. The gravity davits 31 have been lowered to launch positions and the lifeboats 32 are in course of descending on the rope falls 33. Deflation of the"upside" buoyancy chambers 10 and 9 as shown in Fig.4a and in in Fig.5a permits the descending "upside" lifeboat to skid down the shipside. The inflated chambers on the "downside" do not impede the lowering , or the launch, of the "downside" lifeboats.

Claims (5)

1. A vehicle-carrying ferry vessel having bow, and/or side, and/or stern doors, and having deployed along each shipside over approximately two-thirds of the vessel length and located as close as practicable to the vessel's waterline one or more gastight self-stowing inflatable buoyancy chambers of flexible material so arranged as to be kept inflated throughout the vessels passage time, having been inflated after the vessel casts-off from the loading berth and prior to leaving harbour, and subsequentlydeflated to self-stow upon entering the destination harbour and before tying-up alongside the discharging berth.

2. A ferry vessel as in Claim 1 in which the self-stowing buoyancy chambers are of cylindrical and/or semi-cylindrical cross section.

3. A ferry vessel as in Claims 1 and 2 in which the selfstowing buoyancy chambers are, for ease of attachment to the shipsides, affixed to and deflate into shallow trays of fibreglass or like material.

4. A ferry vessel as in Claim 1 in which the deflation time for self-stowing of the buoyancy chambers is shortened by vacuum assisted exhaustion.

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