A VEHICLE FERRY HAVING ENHANCED FLOODING SURVIVAL CAPABILITY COMBINED WITH UNIMPEDED FLOW OF RO-RO TRAFFIC

Abstract: A ferry vessel has a main vehicle deck space (1) and (8) twin extended longitudinal casings (4) having at their extremities large longitudinally closing watertight doors (10) to divide the main vehicle space athwartships into three watertight compartments thereby limiting possible flooding of the vehicle deck (8) in a side compartment due to damage such as colision, or to the centre compartment (1) upon breaching of bow or stern door. In the event of centre compartment flooding, the intact outboard compartments provide substantial righting moment against listing. To further reduce the likelihood of flooding arising from side damage, the vehicle deck levels (8) outboard of the casings may be raised to increase the vessel's freeboard and the hull subdivision transverse bulkheads carried up such that their tops form a stepped ''V'' athwartships. Still further reduction of floodable areas is achieved by a system of transversely located floodgates.

Description: A VEHICLE FERRY HAVING ENHANCED FLOODING SURVIVAL CAPABILITY COMBINED WITH UNIMPEDED FLOW OF RO-RO TRAFFIC. This invention relates to a vehicle ferry vessel having enhanced flooding survival capability, combined with unimpeded flow of RO-RO traffic. It is known to provide a ferry vessel with a continuous main vehicle deck some distance, referred to as freeboard, above the waterline to which deck all of the transverse watertight subdivision bulkheads in the lower hull extend. To comply with International Maritime Organisation regulations, damage resulting in the flooding of one or more of the compartments between the subdivision bulkheads shall not result in the vessel settling deeper and/or listing to Port or to Starboard beyond seven degrees at which angle the margin line, being a line 75 millimetres below the main deck edge, shall not be immersed. It is an essential feature of efficient RollOn - Roll Off vehicle ferries that stern doors, alternatively stern and bow doors, shall provide ready access to the full lengths of lanes of traffic with the minimum of obstructions. The combination of existing I.M.O. regulations and the provision of unobstructed traffic lanes typically lead to the design of the vehicle deck space being an open space, or through deck, extending from stern door to bow doors. Whilst ferry vessels built to I.M.O. regulations and meeting through traffic flow requirements are satisfactory in an undamaged, or unflooded, vessel there are serious shortcomings when flooding of the main vehicle deck occurs due to side collision, breaching of bow or stern door, or other cause. The presence of seawater, especially large areas of flooding, , creates a "free surface" effect which can rapidly destroy the vessel's transverse stability resulting in a capsize situation. The obvious solution of extending the subdivision transverse watertight bulkheads upwards to the upper deck level to break-up the main vehicle deck area, and the provision of watertight doorways in the bulkheads in line with the lanes of RO-RO traffic, results in time delays during loading and unloading of the vessel together with substantial loss of useable lane lengths due to interruptions of the vehicle flows. Such delays and space loss seriously detract from the economics of RO-RO ferry operations. The present invention seeks to provide a vehicle ferry vessel with enhanced stability against capsize whilst not detracting from the uninterrupted vehicle lane lengths so vital for efficient RO-RO operations. Accordingly^ the invention provides a ferry vessel having in the main vehicle deck space twin side casings extending longitudinally, which casings have at their forward and after extremities large watertight doors co-planar with the casings, and capable of being closed by power operation to seal the gaps between the casing ends and shipside structures adjacent the bow and stern doors. The casings, which are permanent watertight structures, in combination with the longitudinally closing doors, effectively divide the vessel .into three longitudinal watertight compartments with minimal effect upon RO-RO traffic whilst effectively reducing the areas of deck liable to flooding following damage or other cause. An increase in freeboard is achieved by extending upwards the tops of the transverse subdivision bulkheads in the form of a stepped "V", being high outboard and low inboard. The depth of the ■ ■ ■ V" step may be shallow in the order of one metre, or deep in the order of two and a quarter metres. The main vehicle deck extends fore and aft over the tops of the bulkheads giving raised side decks outboard of the casings, and a lower centre deck between the casings. Whilst some loss of vehicle height is unavoidable in the lanes outboard of the casings, displaced cars can be located in the upper superstructure which is not an uncommon practice. The stepped deep "V" fromation provides useable cabin and storeroom spaces below the raised side decks, also the deep stepped "V" formation raises the margin line substantially approximately doubling the angle of heel before immersion of the deckedge and consequent commencement of flooding of the vehicle deck. Additional to use for cabins and staorerooms, the spaces below the raised side decks Port and Starboard provide ideal locations for one, or more, sets of power operated floodgates which would be positioned adjacent transverse subdivision bulkheads. The outboard floodgates in the form of single panels rise vertically to act as waterbarriers thus dividing the outboard longitudinal compartments into two, or more, small areas. The centre floodgate, or floodgates, each comprise single panels moving horizontally inboard from Port and Starboard to engage with a pillar at the centreline which rises vertically from the main deck, thereby dividing up the floodable area of the centre longitudinal compartment. Viz - a - viz prior art vehicle ferries, a ferry vessel of the invention has increased freeboard and raised margin line; has the "free surfaces" of floodwaters much reduced; has large reserves of outboard buoyancy to provide righting moment and to maintain a damaged vessel at an angle of loll; has additional hull structure to reduce the depth of penetration of a side collision; and the effects of transverse slippage of vehicles at large angles of heel are reduced. The foregoing benefits are achieved with only a very small rise, if any, in the vessel's centre of gravity; with minimal effect upon conventional ship structure; and without impediment to existing lifesaving appliances practice. A pre erred 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 transverse section through a prior art vehicle ferry having one centre casing. Figures 2 and 3 are respectively the top plan views atτhe main vehicle deck and upper vehicle deck levels of the ferry shown in Figure 1. Figure 4 is a transverse section through a prior art ferry having twin casings seperated athwartships. Figures 5 and 6 are respectively the top plan views at the main vehicle deck and upper vehicle deck levels of the ferry shown in Figure 4 Figures 7 and 8 are respectively the top plan views at the main vehicle deck and upper vehicle deck levels of the ferry shown in Figures 4,5, and 6, with the caiings extended fore and aft, and with the addition of large watertight doors to divide the vehicle decks into three watertight compartments athwartships. Figure 9 is a transverse section of a vehicle ferry having twin casings and the main vehicle deck levels,forming the tops of the transverse subdivision watertight bulkheads of the lower hull, of stepped shallow "V" formation. Figure 10 is a transverse section of a vehicle ferry having twin casings and the main vehicle deck levels of stepped deep ".V" formation. Figures 11 and 12 are respectively the top plan views at the main vehicle deck and upper vehicle deck levels of the ferry shown in Figure 10. Figure 13 is a diagram showing in perspective the side casing and preferred watertight door arrangement. Figure 14 is the same transverse section as Figure 10 with the addition of floodgates. Figures 15 and 16 are respectively the top plan views at the main vehicle deck and upper vehicle deck levels of the ferry shown in Figure 14, with floodgates and all longitudinal doors closed. Figure 17 is a transverse section of a medium sized vehicle ferry having a single vehicle deck of stepped deep"V" formation. Figure 18 is a transverse section of a small vehicle ferry having a single vehicle deck of stepped deep "V" formation. Vehicle ferries of prior art customarily have in their vehicle deck spaces a longitudinally disposed casing located accross, or close to, the centreline of the vessel which, amongst other functions, serves to house the propulsion engine exhaust pipes to the funnel; encloses access stairways for passengers and crew; and provides support for hoistable car decks. Alternatively it is known to provide twin casings to Port and Starboard instead of a single centreline casing. Prior art ferries having single and twin casings, respectively on Sheets 1/8 and 2/8, together with vehicle ferries of the invention on Sheets 3/8 through 8/8, are shown on the accompanying drawings in which the main vehicle deck 1 extends from the bow doors 2 to the stern door 3- Casings 4 extend upwardly from the main vehicle deck 1 to, and through, the upper vehicle deck 5 which on large vehicle ferries is normally a vehicle deck having at the forward and after ends of the superstructure watertight access doors, respectively 6 and 7. The raised side decks 8 of the main vehicle deck 1 in the preferred embodiment of the invention slope down at their ends in the form of fixed ramps 9 to the* level of the centre main vehicle deck 1. The vessel is provided with large doors 10 arranged to roll or fold substantially longitudinally in the preferred embodiment of the invention, which close watertight to the shipside structure adjacent the bow doors 2 and stern door 3. On large vehicle ferries having upper vehicle decks, similar large watertight doors 11 close watertight to the superstructure adjacent the forward door 6 and the after door 7. To facilitate free traffic flow over the ramps 9 leading to, and from, the raised side decks 8, each ramp is preferably provided with a hinged section shown lowered to working position 12, and stowed 13 clear outboard of doors 10. The spaces 14 below the raised side decks in a ferry vessel having stepped deep "V" formation of the tops of the transverse subdivision bulkheads house one, or more, sets of floodgates. Each set of floodgates comprises vertically rising single panels 15 outboard to divide the floodable area of the outboard vehicle decks 8 into the smaller areas 8a and 8f, and horizontally inward moving panels 16 in conjunction with rising centreline pillar 17 to divide the floodable area of the centre vehicle deck 1 into reduced areas 1a and 1b. The height of the centre floodgates does not interfere with hoistable car deck sections 18.

Claims: — o — CLAIMS 1. A vehicle erry vessel with bow and stern doors and having twin permanent side casings arranged watertight athwartships and located longitudinally to Port and to Starboard of the vessel's centreline, together- with four large rolling/sliding/folding watertight doors of proximately the same height as the casings and each door of sufficient length when closed to bridge the gap between the fore, or aft, extremity of the casing and t e forward, or after, shipside structure adjacent the bow, or stem, door. On a ferry vessel having a stern door and no bow door, or vice-versa , only two large watertight doors would be fitted at the extremities of the side casings adjacent the stern, or bow, door whilst the opposite ends of the side casings would continue forward, or aft, as permanent structures to merge with the shipsides thus obviating any gaps athwartships. 2. A ferry vessel as in Claim 1. in which most of the transverse subdivision watertight bulkheads in the lower hull terminate at their top edges in a stepped substantially "V" formation which may be shallow or deep, and having the high points at the shipsides and the low point at the longitudinal centreline of the vessel. The vehicle deck to which the top edges of the bulkheads connect is stepped athwartships with high level side decks outboard of the twin casings and lower centre deck level between the casings. Optimally the height of the step to permit the outboard spaces to be utilised for cabins and storerooms. 3. A ferry vessel as claimed in the preceeding claims in which the higher side parts of the stepped deep "V" formation enclose at one or more locations along the length of the vessel adjacent one or more transverse hull subdivision bulkheads, a system of inwardly and upwardly closing watertight floodgates arranged to cause minimum obstruction to the loading or unloading of RO-RO traffic. 4. A erry vessel as claimed in Claim 1. and substantially as herein described, with reference to and as illustrated in the accompanying drawings.

Inventors: BROWN JOHN GEORGE, BROWN, JOHN, GEORGE
Applicants: BROWN JOHN GEORGE, BROWN, JOHN, GEORGE
Application year: 1989
Main classification: B63B3
IPC codes: B63B43