Monohull having stern stabilizers for a high speed ship

The technical field of the invention is that of ship building, more particularly making ship hulls. A monohull with stern stabilizers, also known as a pseudo-trimaran, for constituting a very high-speed ship comprises a central float (1) and two shorter side floats (2) situated towards the stern of the central float (1) and connected thereto by faired link arms (5); according to the invention, the underwater portions of the three floats (1, 2) are always immersed at least in part and regardless of speed, with the side floats (2) having tiltable underwater foils (3) and with the fineness coefficients of the three floats lying in the range 0.25 to 0.35, with ratios of length over beam lying in the range 12 to 20, and with the ratio of the length of the central float over the length of the side floats lying in the range 2.5 to 4.5.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to monohulls with stern stabilizers for
 high-speed ships.
 The technical field of the invention is that of ship building, and more
 particularly manufacturing ship hulls.
 2. Description of the Related Art
 The main application of the invention is building high-speed ships, i.e.
 capable of more than 38 knots or as much as 54 knots or even more, of mean
 length greater than 50 meters (m), and capable of carrying in particular
 passengers and vehicles both for civilian and for naval uses.
 Over thousands of years, boat building has made considerable progress in
 ship propulsion for increasing speed and endurance: starting from muscle
 power in the time of the ancient Egyptians to wind power, and then to
 steam and oil and recently atomic energy. However during this revolution
 in terms of drive, hulls have hardly changed at all: monohulls have always
 been favored because of simplicity, light weight, and buoyancy, both
 static and dynamic, even though stability, at least in terms of comfort,
 is not perfect.
 However, over the last few years, numerous novel designs have been studied
 and developed to take the place of the monohull with the purpose of
 achieving greater speed and better stability, with this being at the
 request both of navies and of shipping companies; shipping companies would
 like to become much more competitive than airlines by seeking to reduce
 the time required to cross an ocean to half or less while being capable of
 carrying many more passengers than can be carried by a large airliner.
 Nevertheless, it is clear that many very large vessels are probably going
 to remain monohulls for a long time yet, particularly in circumstances
 where neither stability nor high speed are considered as being major
 advantages, such as in transporting oil, for example.
 To achieve high speeds, i.e. speeds greater than 30 knots, various types of
 hull have been developed, some making use solely of hydrostatic support
 like monohulls but by increasing the number of hulls, as with catamarans
 and trimarans in particular; hydrodynamic support has also been used by
 means of underwater "wings" which serve to lift the load-carrying hull out
 of the water above a certain speed; other principles have been developed,
 in particular those using aerostatic support, such as air cushion
 vehicles.
 The present invention makes use of all of those support principles on the
 basis of a trimaran type design; until now, development and
 implementations of three-hulled ships have been associated essentially
 with recreational boating and in particular with sailing, specifically for
 the purpose of beating speed records: however, in that type of use, the
 float situated upwind from the central hull is functionally practically
 unused, the boat then being supported by the central float and by the side
 float on the downwind side. Various trimaran hull designs have also been
 developed to beat mechanical propulsion speed records, but without seeking
 to carry goods or passengers, for example the ship described in Australian
 patent application AU 521518: that relates to a kind of trimaran having
 three hydroskis enabling it to travel on three support surfaces disposed
 in a triangular configuration, one at the bow and the other two at the
 stern, and enabling the hull to be lifted completely out of the water, but
 that cannot be extrapolated to a heavy transport ship for carrying
 passengers or vehicles.
 In the field of commercial transport, rather few projects have been
 developed. French published patent applications FR 2671775 and FR 2675460,
 corresponding to U.S. Pat. No. 5,529,009, describe multi-hull ships, none
 of which have been built at this time, doubtless because of problems
 relating essentially to stability and cost. These publications relate to
 hulls in which the superstructures and the central float are rather
 conventional, even though the side floats are quite fine, but incapable of
 achieving maximum speeds in excess of 40 knots. In addition, the hulls are
 rather heavy and the usable portions of their superstructures and their
 overall centers of gravity are placed very high above the water.
 In any event, at present and without profligate use of power for propulsion
 purposes which then makes the ship uncomfortable because of vibration and
 which is not economically feasible, no high-speed ship can travel faster
 than 35 knots under normal circumstances because the ship is limited by
 hydrodynamic resistance to forward travel which increases with the cube of
 speed, specifically for high speeds in excess of 30 to 35 knots.
 The problem posed is thus to be able to make ships capable of transporting
 passengers and/or freight, such as vehicles for the most part, that is at
 least 50 m long, that is suitable for traveling at high speed in excess of
 40 knots and even of 50 to 60 knots, whatever the weather conditions,
 while maintaining acceptable stability in terms of rolling and pitching,
 firstly to make it comfortable to travel in, in particular for passengers,
 and secondly to avoid overstressing the structures of the hulls which must
 be simple to manufacture, rigid, and strong.
 SUMMARY OF THE INVENTION
 A solution to the problem posed is a ship hull comprising a central main
 float and two side floats of shorter length, situated towards the stern of
 the central float, connected thereto by link arms, and having underwater
 foils. The underwater portions of all three floats are always immersed at
 least in part and should therefore always be considered as forming a
 moving hull regardless of speed and of weather conditions. The fmeness or
 block coefficients of the three floats lies in the range 0.25 to 0.35 with
 ratios of length over beam lying in the range 12 to 20, and with a ratio
 of the length of the central hull over the length of the lateral hulls
 lying in the range 2.5 to 4.5.
 This basic design using a very long central hull, as described in greater
 detail below, provides very low resistance to forward motion and efficient
 behavior in short swells of the kind found in closed or semiclosed seas
 such as the Mediterranean or the Channel. Transverse stability is provided
 by the stern floats which might cause the hull of the invention to be
 referred to as a "trimaran" even though it is more of a "pseudo-trimaran";
 such stern floats, as defined by their characteristics as specified below,
 give the ship remarkable behavior which is unlike that of a catamaran
 because of the long period roll to which they give rise; roll is also
 controlled by the effectiveness of the stabilizer foils which are
 preferably movable and tiltable in alternating operation so as to be
 always of positive incidence, i.e. providing lift that is always directed
 upwards. Such underwater stabilizers or foils also provide a hydrodynamic
 support effect contributing to reducing the displacement of the stern
 portion of the central hull above a certain speed.
 Furthermore, to provide good transverse stability for a moderate overall
 width of the hull, while maintaining minimum drag and a one-piece
 structure for said pseudo-trimaran assembly, these small stern floats that
 are lightly immersed have a rather large stem slenderness ratio with a
 V-shape giving very fine penetration into the water, and lightly immersed
 towards the stern, giving movement that is very gentle and practically
 self-stable at speed.
 Pitching is minimized by a shape that is likewise a narrow V-shape for the
 stem of the central float, giving it fine penetration into the water and
 little rake, thus enabling the hull to be referred to as a "wave-cutter";
 the stern position of the floats also tends to interrupt quickly any
 pitching that might begin in a swell.
 To assist in this basic design which is described in the description of the
 figures below, and to respond to the problem posed, the link arms of the
 invention are faired to have airplane wing shapes, thereby creating two
 ground effect nozzles between inner abovewater side surfaces of the
 central float and the side floats, and the liquid surface over which the
 trimaran hull is moving. These link arm wings are of relatively small span
 but of large chord, traveling at a height lying between one-half and
 one-fourth of the mean chord above the water. Aerodynamic support is thus
 obtained due to the dynamic pressure obtained by air being accelerated as
 it passes through these kinds of nozzles constituted by the undersides of
 the link arm wings connecting the floats to the central hull, and the
 surface of the water. This dynamic pressure increases with speed;
 calculated estimates have made it possible to assess that for a lift area
 of each link arm Ad abut 220 m.sup.2, and at a speed of 40 to 50 knots,
 this ground effect produces lift of the order of 50 to 60 metric to for
 these wing-shaped arms a curved profile of the type known as the Gottingen
 type, for example the type referred to as G652 (arched). The combination
 of this "hyperlift" with that obtained by the underwater stabilizers, also
 known in the present technical field as "foils", and which are secured to
 the side floats, which foils form respective surface areas of about 6
 m.sup.2 each, and for a speed lying in the range 40 knots to 50 knots,
 also give lift of the order of 60 tons, makes it possible for the total
 lightening that is obtained to be of the order of 20% of the mass of a
 ship that displaces 550 tons, corresponding to the areas mentioned above,
 i.e. a length of about 100 m and the ship considered when half laden.
 In addition, other characteristics of the invention combine with those
 described above to respond to the problem posed and to provide additional
 advantages, in particular:
 to obtain sufficient thrust to enable such speeds of at least 40 to 50
 knots to be obtained, propulsion is provided by at least one waterjet and
 preferably by two, exiting from the stern portion of the central float,
 preferably associated with one other waterjet thruster or "hydrojet"
 situated at the stern of each of the side floats, thus preferably giving a
 total of four waterjets; the ejection nozzles for these waterjets are
 preferably steerable upwards and downwards through about 12.degree.
 relative to the horizontal, adding to the above-described effects of the
 underwater foils, of the hull shapes, and of the link arm shapes, for the
 purpose of reducing pitching and rolling motion: the movements of said
 nozzles and of said foils are, for this purpose, servo-controlled from an
 inertial unit;
 to provide and maintain such high speeds, given the large amount of drag
 developed by the portions in air at such speeds in excess of 40 knots, the
 portions in air i.e. the superstructures or deadwork of the hull are
 optimally aerodynamic, with the front ends of the corresponding hull
 portions being rounded in shape, like an airplane fuselage; the deadwork
 does not have any projections, nor does it have any sharp edges so as to
 obtain a minimum drag coefficient relative to wind. In addition, the
 central float has a vertical tail fin at its stern which is provided with
 a movable control surface, thus constituting a natural stabilizer and
 delivering a small amount of thrust from the side opposite to the apparent
 wind; a balance is also established between the lift obtained by this rear
 air-foil which can be controlled using its control surface for steering
 purposes, and the front deadwork area of the central float; and
 in order to give the ship at a speed in excess of 45 knots a horizontal
 trim and a maximum waterline length so as to minimize energy consumption,
 the ship hull of the invention, at rest, has slightly negative trim
 corresponding to its stem pitching down slightly. It will be observed that
 conventional ships in motion always move down towards the stern when it is
 desired to exceed a speed of 45 knots: thus by rearing up, they cannot, in
 fact, exceed this speed of 45 knots. In the present invention, the
 combination of the support provided by the stern side floats, the immersed
 foils, and the lift-providing wings of the support arms prevent this
 downward deflection of the stern or rearing up of the stem, and even leads
 to the stern being raised, consequently keeping the ship horizontal on
 these lines even at 45 knots, thereby enabling it to exceed this speed.
 The result is a novel design of monohull having stern stabilizers, also
 referred to as a "pseudo-trimaran" hull, for a high speed ship capable of
 satisfying the problem posed with the various advantages mentioned above.
 The solution described in the present invention for achieving the speeds
 indicated and for exceeding the 30 to 35 knots of present ships under
 normal propulsion, is to reduce a portion of the hydrodynamic drag,
 thereby making it possible to achieve speeds of about 50 to 60 knots (100
 to 115 km/h) with power levels that are still reasonable (35,000
 horsepower for a ship having the dimensions given above). From speeds of
 about 35 knots and because of the special configuration of the hull of the
 invention, selfstabilizing occurs automatically to some extent, making it
 possible to increase speed by about 15 to 25 knots while requiring only
 relatively little additional power; in any event, the drag of the hull of
 the invention does not increase with the cube of speed for speeds in
 excess of 30 to 35 knots.
 In addition, the pseudo-trimaran hull of the present invention makes it
 possible to have rather low total height on the water while retaining
 large capacity (as can be seen from the accompanying figures), when
 compared with presently-known trimaran hulls: for a central hull having a
 length of 100 m or more, the overall height above the water is no more
 than 10 m, with the link arm being at a height of 3 m to 6 m above the
 water and with the vessel having an overall width of 30 m to 35 m, for
 example.
 Such a hull makes it possible to carry passengers in comfort that can be
 considered as being equivalent to that of an airplane, and vehicles and/or
 loaded containers in the hold of the central float alone via stern access
 that is closed by any suitable door of conventional design and that can be
 very simple. It should be observed that only the abovewater volume of the
 central float is fitted for transporting passengers and freight, the
 remaining volumes being constituted by leakproof compartments, most of
 which are filled with closed-cell foam so as to guarantee that the vessel
 is unsinkable.
 In addition, the structure of the central float can be overdimensioned and
 by having a dual-cone shape provides a high level of stiffness to the beam
 of the ship so there are no alternating stresses, thus making it possible
 to expect at least 25 years of service life: the dual-cone shape is
 characterized by a section that is larger in the longitudinal mid-portion
 of the float than at its bow and stern ends; without excessively
 penalizing overall displacement, the thickness of the hull skin can be
 about three times that laid down by classification authorities, which is
 required because of the high speeds reached and which is made possible by
 the special design of the ship of the invention which reduces the surface
 area of the hull skin.
 In spite of its rather unusual and highly innovative appearance, this ship
 can be built in a manner that is very simple and indeed unsophisticated,
 building up a structure of various materials and using skins that are easy
 to shape. When making ships of lengths of the order of 50 m to 115 m, the
 selected material can be aluminum, and for sizes in the 120 m to 150 m
 range, the material can be steel or a combination of materials.
 Other characteristics and advantages of the present invention could be
 described, but those mentioned above suffice already to show the novelty
 and the advantage of the invention.
 The following description and figures relate to an embodiment of the
 invention but have no limiting character: other embodiments are possible
 within the ambit of the scope of the extent of the invention, in
 particular by changing certain details of shape for the superstructures
 and the disposition of the internal arrangements.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
 Together, the figures thus show a pseudo-trimaran hull for a very high
 speed vessel comprising in conventional manner a central float 1 and two
 shorter side floats 2 situated towards the stern of the central float 1
 and connected thereto by link arms 5. The underwater parts of the three
 floats 1 and 2 are always underwater regardless of speed and weather
 conditions and ensure travel in which the passenger transport and/or
 freight decks are maintained quasi-horizontal. For this purpose and
 amongst other things, the underwater parts of the side floats 2 include
 underwater foils 3 that are tiltable from an angle alpha equal to about
 45.degree. in the midposition relative to the vertical midplane YY' of
 each float 2 and extending towards the inside of the hull towards the
 central float 1. The foils 3 are preferably hinged beneath each side float
 2 and capable of tilting at least between 40.degree. and 50.degree.. These
 stabilizing foils can, for example, have a so-called "Vaton" profile,
 being of the type defined by Vaton and as manufactured on the vessel
 Charles Heidsieck IV in 1984/85.
 All three floats 1 and 2 remain continuously underwater, at least in part,
 whatever the forward speed of the ship and because of various means and
 shapes specific to the invention which ensure that travel takes place in a
 plane that remains very close to the horizontal. The central float 1 is
 fitted to receive passengers on passenger decks 13.sub.1 and 13.sub.3 and
 vehicles on other decks 13.sub.2 as shown in FIGS. 4 to 6. Naturally other
 arrangements are possible as a function of the dimensions of the central
 hull and of the use made of such a ship. Various viewing portholes 14 are
 preferably provided, at least on those decks 13 where passengers are
 located. A navigation and control bridge 12 is provided at the tope of the
 hull as a whole and is preferably installed on the central float 12
 slightly ahead of the stems of the side floats 2.
 The central hull 1 can have two side keels 8 fixed to the stern of its
 underwater portion 1.sub.1 and has a stern rudder 9 for steering. Beneath
 the decks 13, the structure of the central hull 1 comprises a double
 bottom 18 and towards the stern it comprises the engine room 17 in which
 the motor thruster units are situated which, as mentioned above, are water
 hydrojets whose nozzles 10 are situated at the stern portion of the hull.
 To provide reserve buoyancy even in the event of the hull being torn,
 causing all of the double bottom 18 and some of the transport volume to be
 invaded by water, the hull as a whole can remain afloat, with all of the
 unused volumes of the hull being suitable for filling with buoyancy foam
 in sufficient quantity to compensate for the entire weight of the ship
 when loaded, such as: the bow volume 19, the stern volume 20, all of the
 volumes 21 available between the decks 13 and the remainder of the hull,
 and also the volumes of the arms 5 linking the side floats 2, as shown
 shaded in FIGS. 7 and 8.
 Vehicle access to the various decks 132 is via stern doors 15 of
 conventional type, and passenger access is via at least one side door 16
 situated on the central float 1.sub.2, preferably forward of the stems of
 the side floats 2.
 Hydrojet propulsion is performed by four thrusters 10 which are situated
 one in each side float 2 and two in the central float 1, with water feed
 inlets 11 situated towards the middles of the underwater portions of the
 corresponding floats so as to avoid excessively disturbing flow towards
 the stern portions of the floats. Thus, such inlets 11 are preferably
 positioned at a distance lying in the range 10% to 15% of the waterline
 length of the float in question, either forward or else aft of the point
 where the laminar boundary layer separates. The length of the inlet must
 be 10% to 15% of the length of the laininar boundary layer.
 In addition, to facilitate maneuvering in ports, the central float 1 can
 include retractable bow thrusters (not shown in the accompanying figures).
 Given the fineness characteristics desired for the floats as a whole and
 given their specific dispositions in accordance with the invention, the
 ratio of the immersed volume of the central float 1.sub.1 to the volume of
 the circumscribing parallelepiped enclosing the underwater portion,
 referred to as the "block coefficient", has a value lying in the range
 0.32 and 0.34. Considering the length L.sub.pp between perpendiculars to
 the fore and aft ends of the float and its width at the greatest beam on
 the waterline, the ratio of the length to the width lies in the range 15
 to 18 for the central float 1 having a waterline length that can lie in
 the range 50 meters (m) to 150 m; thus, for a length between
 perpendiculars L.sub.pp of 100 m, the width of the main beam at the
 waterline can be 6 m.
 For the side floats 2, the block coefficient or fineness coefficient
 preferably lies in the range 0.26 to 0.28 with a ratio of length over
 width, as defined above for the central float, lying in the range 13 to
 17; the ratio of the length of the central float 1 over the length of the
 side floats 2 lies in the range 2.5 to 4.5, and preferably in the range
 2.85 to 4.
 The sterns of the two side floats 2 are situated at a distance d forward of
 the perpendicular to the stern of the central float 1 where d lies in the
 range 5% to 20% of the length L.sub.pp of the underwater portion of the
 central float.
 The longitudinal midplanes YY' of the side floats 2 are situated at a
 distance D on either side of the midplane XX' of the central float 1,
 where D lies in the range 10% to 15% of the length L.sub.pp of the
 underwater part of the central float 1.
 Preferably, d lies in the range 10% to 15% of L.sub.pp and D lies in the
 range 12% to 14%.
 All of the above-specified values or ranges for dimensions are applicable
 for the central float 1 having an overall length L.sub.pp between
 perpendiculars lying in the range 50 m to 150 m.
 Similarly, for these hull dimensions, the area of the tail fin 4 is such
 that its ratio to the lateral surface area of the abovewater portion
 1.sub.2 of the central float 1 lies in the range 0.07 to 0.09, and the
 area of each foil or stabilizer 3 relative to the area of the underwater
 portion of the corresponding float 2 lies in the range 0.025 to 0.030.
 The angles of these foils 3 and of the nozzle outlets 10 are controlled by
 electrical controls for stabilizing the ship and associated with an
 inertial unit, and they are steered, for example, by a hydraulic system
 backed up by an emergency pneumatic system which serves at least to return
 the nozzles 10 to a horizontal position in the event of a problem. This
 dual crossed-stabilization between the foils and the nozzles, associated
 with the inertial unit, makes good comfort possible by controlling
 interfering lateral movements, it being understood that such a system has
 practically no effect in terms of energy consumption.
 To give an order of magnitude for the displacement of ships that can be
 made in application of the present invention, a unit having a unit
 L.sub.pp of 62 m has a light displacement of about 190 metric tonnes, with
 a fully laden displacement of 240 tonnes; for a 100 m unit, the light
 displacement could be 485 tonnes and the fully laden displacement 680
 tonnes; and for a 130 m unit, the light displacement could be about 800
 tonnes for a fully laden displacement of 1200 tonnes.