The present invention relates to a landing craft and particularly but not exclusively relates to a military landing craft for landing military personnel and equipment on a beach or river bank or the like.
Landing craft are well known and typically comprise a generally flat transport deck mounted on a hull. The underside of such craft is typically formed from a planar bow ramp inclined to the transport deck, and a flat bottomed hull extending from the inclined bow to the stern of the craft. The hull of the craft thus provides stability to the craft when the hull contacts the beach or river bank such that the bow ramp can be lowered to enable personnel and/or equipment to be off loaded from the transport deck. This arrangement is commonplace and has been used without significant modification for decades.
A problem with such an arrangement is that the flat bottomed hull restricts the craft to a relatively slow speed, particularly in waves. This is aggravated by the necessity for a relatively wide, flat bow ramp that is hinged near the waterline of the craft.
The current invention stems from some work to try to provide a faster, more efficient craft that retains the ease of off-loadifig provided by a relatively wide, flat bow ramp.
International patent application
According to a first aspect of the invention there is provided a landing craft for landing personnel and/or equipment on a beach or river bank or the like, the craft comprising a hull on which a transport deck is provided, a ramp being provided at the bow of the craft and arranged to be movable from a closed position in which the ramp closes the transport deck to a lowered position in which the ramp opens the transport deck, the hull comprising three sub-hulls that are relatively transversely spaced apart across the landing craft, at least the two outermost sub-hulls having substantially the same draught such that the outermost hulls provide stability to the craft when in contact with a beach or river bank or the like, characterised in that the intermediate sub-hull extends only partially along the length of the craft such that the craft has three sub-hulls for only part of its length, and wherein the bow portion of the intermediate sub-hull terminates behind the bow portions of the two outermost sub-hulls, when viewed from the side, to define an intermediate recessed region at the bow, in which the ramp is hinged, and wherein the ramp, when in the lowered position, is located between the two transversely outermost sub-hulls.
The longitudinal axes of the outermost sub-hulls may be substantially parallel.
Preferably the hinge axis of the bow ramp is spaced above the waterline of the craft.
Preferably the bow ramp is a bi-fold ramp comprising two ramp sections hinged together by an intermediate hinge part way along the length of the ramp.
Preferably the craft comprises a propulsion system which may comprise a water jet propulsion system.
Preferably the water jet propulsion system comprises a water jet in each sub-hull.
Preferably the propulsion system comprises a main propulsion motor in each sub-hull.
Preferably the top of each main propulsion motor is located below the plane of the transport deck.
Other aspects of the present invention may include any combination of the features or limitations referred to herein.
The present invention may be carried into practice in various ways, but embodiments will now be described by way of example only with reference to the accompanying drawings in which:
Referring to the Figures, a landing craft 1 comprises a hull 3 on which is mounted a superstructure 5 which includes a substantially flat transport deck 7 suitable for carrying a load such as personnel, equipment and/or vehicles for example.
The superstructure 5 also includes a suitable deckhouse and ancillary structures as are well known.
The hull 3 comprises three sub-hulls 9, 11 that are transversely spaced across the width of the hull 3 such that the hull 3 comprises a trimaran at the bow. The two outermost sub-hulls 9 each extend along the length of the craft 1 from the bow to the stern, have substantially parallel longitudinal axes, are symmetrical about the longitudinal axis of the craft 1, and are of identical draught. The lowermost part of each sub-hull 9 comprises a substantially flat surface 10 although differently shaped profiles are envisaged - for example each sub-hull 9 may comprise a V-shaped profile. The two outermost sub-hulls 9 and the underside 13 of the top of the hull 3 define between them a flow channel 15 .
The sub-hull 11 comprises an intermediate sub-hull positioned between the two outermost sub-hulls 9 to bisect the flow channel 15 to define two adjacent sub-flow channels 15A, 15B. The intermediate sub-hull 11 may be of the same or lesser draught than the outermost sub-hulls 9, and the lowermost part of the intermediate sub-hull 11 may be substantially flat or profiled as required.
The intermediate sub-hull 11 comprises a tapered bow portion 11A that widens into a substantially cuboidal mid-portion 11B that extends to the stern of the craft 1. The hull 3 is shaped, when viewed from the side, such that underside 13 at the bow of the craft is above the waterline 24, but drops below the waterline aft of the bow of the craft 1 such that the hull 3 at the stern of the craft 1 comprises a mono-hull
The tapered bow portion 11A of the intermediate sub-hull 11 is spaced behind the bow of the craft 1 as defined by the bow portions 9A of the outermost sub-hulls 11, when the craft 1 is viewed from the side. The bow 11A of the intermediate sub-hull 11 thus terminates before the bow of the craft 1 such that a hull free recessed area 17 is defined at the bow of the craft 1 transversely between the bow portions 9A of the outermost sub-hulls 9.
The rear margin 19 of the recessed area 17 comprises the front margin of the transport deck 7 and is provided with a hinge 21 on which a bow ramp 23 is mounted. The mounting hinge 21 of the ramp 23 is thus spaced considerably above the waterline 24 of the craft 1, the waterline 24 at its highest being flush with the underside 13 of the top of the hull 3. The relatively high hinge axis allows a lower entrance angle at the waterline 24 resulting in a lower calm water resistance. The high hinge axis also reduces slamming and speed loss in waves.
The bow ramp 23 comprises a bi-fold ramp comprising two ramp portions 23A, 23B hinged together by hinge 25, the lower ramp portion 23A being hinged to the transport deck 7.
A suitable ramp drive mechanism is provided to move the ramp portions 23A, 23B between a closed position 26, an intermediate position 27, and a lowered position 29. Such a drive mechanism may comprise an electric motor mechanism or a hydraulic mechanism for example.
When in the closed position 25, the second ramp portion 23B is folded onto the first ramp portion 23A and the ramp 23 is in a raised condition wherein the plane of the ramp 23 is inclined to the plane of the transport deck 7. In this position the ramp 23 effectively closes the transport deck 7.
When in the intermediate position 27, the second ramp portion 23B is unfolded from the first ramp portion 23A such that the ramp portions 23A, 23B are co-planar and substantially horizontal. The first ramp portion 23A is positioned between the two outermost sub-hulls 9 with the second ramp portion 23B projecting beyond the bow of the craft 1.
When in the lowered position, the unfolded ramp portions 23A, 23B are inclined down from the transport deck 7 to the beach or river bank or the like onto which the load is to be off-loaded. Again the first ramp portion 23A is positioned between the two outermost sub-hulls 9.
In the illustrated embodiment, a water jet propulsion system is provided comprising a propulsion means 31 in each sub-hull 9, 11 each propulsion means 31 comprising a motor 33, gearbox 35, drive shaft 37 and impeller/jet assembly 39. The craft 1 thus comprises three motors 33, one in each sub-hull 9, 11. This enables smaller motors 33 to be used such that the tops of the motors 33 are below the plane of the transport deck 7 thus improving the load area, and level, of the deck 7.
The motors 33 may be high speed diesel combustion engines although any desired type of motor could alternatively or additionally be used including gas turbines, petrol combustion, electric, hydrogen or hybrid motors.
The stern end 41 of the transport deck 7 extends beyond the stern of the outermost sub-hulls 9. The water jet outlets are positioned below the extended end 41. The extended end 41 may be provided with a stern ramp 43 that can be moved between closed and lowered positions to enable access to the transport deck 7 from the stern of the craft 1. Again, the hinge axis 45 of the stern ramp 43 is spaced above the waterline of the craft 1.
In use of the craft 1, the flat, lowermost surfaces of the bows 9A, 9B of the outer hulls 9 rest on the beach or river bank or the like when the craft 1 is positioned to be offloaded. The outer hulls 9 thus stabilise the craft 1 during the offloading process, the bow ramp 23 being moved to the lowered position 29 in between the two outer hulls 9. Likewise the stern portions of the two outermost hulls 9 provide stability for the stern of the craft 1 if in contact with the beach or river bank or the like.
The intermediate hull 11 may provide additional stability if also in contact with the beach or river bank or the like.
When moving, the three hulls 9, 11 provide a relatively streamlined, stable hull 3 that enables relatively high craft speeds to be attained whilst still carrying relatively high payloads. The arrangement of the three hulls 9, 11 is such that a large increase in craft speed is still possible, despite the relatively wide bow ramp 23.
It is envisaged that the sub-hulls 9, 11 be formed from an aluminium material although any other suitable material, including for example, a composite material, could alternatively be used.
As non-limiting examples only, it is envisaged that the craft 1 be around thirty metres long with a beam of around eight metres, capable of carrying a payload of around eighty tonnes. The draft of the craft 1 may be around 1.5m. With such approximate dimensions, and three motors 33 each of around six MW, speeds of between twenty and forty knots are envisaged.
The three hulls 9, 11 define flow channels 15A, 15B between them having relatively fine entrance angles which render the hull 3 relatively streamlined.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.