FR2780940A1 - Hull structure for motor catamaran has interior curved step generated along line connecting points of inflexion conforming to flotation line. - Google Patents

Abstract

The hull structure is formed from two hulls connected by a central bridge. It has an interior curved step that projects from the hull and is positioned above the flotation line. The curved step is generated along the length of a line that connects the points of inflexion of the hull, and makes an angle ( alpha ) with respect to the vertical and ends as a tangent to the horizontal. The points of inflexion conform to the flotation line.

Description

HULL STRUCTURE FOR MOTOR CATAMARAN

  The present invention relates to a hull structure for a catamaran

  powered and more particularly intended for pleasure craft.

  The hull structure according to the present invention is more particularly applicable to pleasure motor catamarans which are in the range of boats from 10 to 20 m and intended to sail at speeds of 10 to 20 knots over long distances, the performance having to be at the level of comfort and autonomy more than that of

  traveling speed or acceleration.

  UÀ monocoque generally has a relatively wide hull profile to give it a certain stability to roll so that the hull profiles of monohulls significantly limit the crossing of waves and they tend to go over it and therefore follow the sinusoid

  generated by the phenomena of waves and swells.

  Unlike monohulls, catamarans have narrow hulls and a central deck that connects the two hulls. Indeed, the cabins are generally arranged in the hulls but the place of life, remains the central deck and its cockpit, particularly used in particular during navigation. A particularly sensitive point is the fact of seeing the structure in contact with water from below the central bridge mainly due to direct pitching and / or pitching and rolling combined when the state of the sea is sufficiently degraded to generate swell or waves from a height causing such phenomena. This action of water on the underside

  from the central bridge is known as "slamming".

  Indeed, the contact of this almost flat surface of the underside of the central bridge with the water causes particularly unpleasant shocks for the comfort of the passengers because the pitching movement, during the insertion phase, is suddenly interrupted. In addition, the noise generated by the water shocks on this central bridge propagates and confers when violent feelings of insecurity and at least this noise remains incompatible with

  the desired atmosphere when using such a ship.

  In addition, these shocks can also cause unnecessary fatigue in the elements that make up the shell structure requiring

  generally reinforcements so that the structure resists this type of shock.

  One solution is to provide hulls with a large longitudinal section upwards from the waterline so that when the hull sinks, the buoyancy increases very quickly when sinking each hull, which limits this sinking, more or less gradually but in all cases much more flexible

  than in the case of contact with the central bridge.

  However, the problem is more complex in the sense that the goal is also to have a boat that is not braked more than necessary, for advancement, because even if speed is not a desired parameter, the fineness of the hull is of great importance on the drag in the water and on consumption, therefore on autonomy and consequently on operating costs. This very flared shell structure solution is not satisfactory

  because the cross section in the vertical plane is too large.

  This large cross section also leads the hull to follow the wave profile as closely as possible and thus to create a displacement along a pronounced sinusoid in the vertical plane, which is particularly unpleasant for

  passengers and often a source of seasickness.

  Another solution could consist in having successive lateral strakes but these strakes are generally reserved for pleasure craft of the highly motorized speedboat type. They allow a better resistance to the sea at high speed but have only a weak role to allow to limit the sinking. On the other hand, such strakes increase

  little vertical cross section.

  It is noted in this case that the aesthetic appearance is not satisfactory and above all, the strakes tend to generate very large spray which, by intermediate or even calm navigation conditions but at high speed,

  are detrimental to passenger comfort.

  A too large pitch amplitude also poses problems with regard to propulsion because the propellers, when this transfer mode is used, can come out of the water leading to cavitation detrimental to the quality and

  the propulsion efficiency but also the longevity of the engine.

  In addition, the exaggerated pitching can lead to a feeling of insecurity of the passengers when the bow of the structure bakes and water passes

over the passenger compartment.

  The problem of pitching must also be taken into account in the case of a swell or waves on inland water or at sea of closed type or

  still on the ocean because the frequency and the type of the waves are very different.

  It is therefore necessary to be able to find a compromise so that such a motor catamaran can exhibit suitable behavior in these different situations. It is also useful to deal with the roll problem because in this case, the heeling angle is unimportant since it is a catamaran hull structure but the amplitude must also be limited to the maximum for that the

  passenger comfort is of the best possible quality.

  The present invention relates to a hull structure which is suitable for a motor catamaran with a length of between 10 and 20 m for engine powers of the order of 2 x 60 CV to 2 x 350 CV, capable of sailing. at a cruising speed of 10 knots and a maximum speed of 20 knots, which can "cross" the waves with the least possible lifting effect to limit the onset of seasickness, while avoiding slamming and leaving the bow out of the water, which prevents formation

  spray on the outer side edges and which limits the roll.

  To this end, the hull structure according to the invention, for a ship of the motor catamaran type, comprising two hulls connected by a central deck, is characterized in that it includes an inner recess, projecting relative to the hull, disposed above the waterline, which originates along a line connecting the inflection points of the hull and which forms an angle oc

  with respect to the vertical and which ends tangent to the horizontal.

  In the selected embodiment, the line connecting the inflection points

  is confused with the waterline.

  According to a preferred embodiment, the redent is extended by a

  curve to the central bridge, forming a vault.

  According to another characteristic of the structure according to the invention, there is provided an external step, projecting from the hull, disposed above the waterline, which originates along a line connecting the points d inflection of the hull and which makes an angle s with respect to the vertical and

  which ends tangent to the horizontal, towards the outside.

  Preferably, the angle g is greater than the angle.

  According to an improved arrangement, the two hulls are symmetrical with respect to the central axis of the central bridge and each hull is asymmetrical

  with an internal offset leading to a pinch effect.

  The invention is now described with reference to the accompanying drawings of a particular embodiment of the hull structure according to the invention, drawings in which the various figures represent: - Figure 1, a side elevation view of the hull structure according to the invention with an example of a passenger compartment, - Figure 2, a top view of the same unit, Figure 3, a front view of the different couples superimposed along the longitudinal axis of the hull, and

  - Figures 4-1 to 4-22, the different dissociated couples.

  In Figure 1, there is shown the hull structure according to the invention with mention of the waterline 100 and a passenger compartment 102 above the hull. The location of the pairs in the following figures is mentioned along the longitudinal axis of the hull structure by the numbers 0 to 22. First of all, a distinction is made between the immersed part 104 of the hull and the

part 106 emerged.

  The submerged part 104 has a profile along the longitudinal axis which is narrow at the bow and wide at the stern as shown in the sections

  Figures 4-1 to 4-22.

  Along the longitudinal axis, the submerged height varies to be maximum substantially at the right of the master couple between sections 9 and 10 and for

  decrease towards the two ends from 9 to 0 and from 10 to 22.

  Figure 1 shows one of the characteristics of the invention, namely the asymmetry of each of the hulls on the front relative to the vertical median axis 106 which passes through the keel line 108. These are more particularly couples 0 to 10. The volume of the hull is offset inwards, while the external lateral surface of the hull has

  simultaneously a gentler slope, the inner surface being more vertical.

  Thus, in relation to the vertical median axis of the boat, the shapes of the

  shells are symmetrical with a pinch effect.

  The other pairs are substantially centered relative to the keel line so that the longitudinal axes of the two hulls are parallel on

the whole rear part.

  FIG. 2 also makes it possible to show the constant of the invention, namely a first redent 110, inside, projecting, formed on the lateral face

of each hull, interior side.

  This redent extends over the entire length of the hull and is maximum in the middle part of the pairs. at. Similarly, following

  The longitudinal axis, the redent follows substantially the profile of the keel line.

  It is noted on the section views that this redent has a pronounced curvature which begins in the lower part with a point 112 of inflection of the hull which is coincident with the waterline, this with a large angle of opening and which opens out at its other end on an angular part 114, the curvature being, there, substantially tangent to the horizontal. Note in Figure 3 that the offset D is important. To give an idea, this leads to a step with a 0.20 m offset for

a unit of about 10 m.

  The part located above this redent is inclined with a curve 116 which provides the connection with the central bridge 118 and of which we will see the advantage

  further when describing the behavior at sea of the structure of

shell according to the present invention.

  Each hull also has a second redent 120, exterior. This redent is designed to be substantially identical to the first redent, but its offset d is less important because the opening angle _ is itself

1 5 less important.

  This second redent 120 also starts at the inflection point 1 22 merged with the water line 100 and is extended upwards by the external lateral face of the hull which is smooth and substantially vertical,

  devoid of any protruding shape capable of lifting spray.

  On the rear part, under the keel line, coming from manufacturing, it is

  provided a propeller wing fin 124 crossed by the shaft line.

  The following proportional parameters give a good indication of the different dimensions of an embodiment according to the invention dimension D: 2 to 3% of the length at the waterline, - width of the hulls at the height of the gradient: between 12 and 16 % of the

waterline length.

  Thus, for a boat of 11 m, the width of the hulls is appreciably

  1.40 m and the redent is 0.22 to 0.33 m.

  The hull structure according to the invention makes it possible to have, in calm weather, a narrow section which limits the drag and thus increases the autonomy, which is particularly appreciable for a unit of

  pleasure craft for long distance cabotage.

  As soon as the sea conditions cause an increase in the swell, the downwinds make it possible to limit in a completely satisfactory way the sinking and especially avoids the sinking of the bow, which is reassuring for the sailors. We can cite a comparative example of two identical shells one equipped with redents and the other without redent. The hull structure according to the invention above all makes it possible to limit the impacts of the central deck on the surface of the water resulting from a pronounced sinking of one or both hulls, according to the direction of navigation relative to the orientation swell. To this end, the pronounced curvature very significantly increases the local horizontal section, which slows down the sinking. In addition, the orientation of the tangent curvature to the horizontal makes it possible to repel the water in this horizontal plane, which further limits this sinking. It is noted that the water flows repelled by each of the hulls inwards are directed towards each other, which tends, by reaction, to keep the hull structure above the surface of the water. As for the spray raised by this action, it poses no problem since it is confined by the central bridge before being evacuated to the rear, without

disrupt passenger comfort.

  The curve 116 forms a vault and also provides braking during penetration therefore ultimate protection of the central bridge during excessive penetration. We note that this curve is located relatively high, in the immediate vicinity of the central bridge so as not to disrupt navigation when conditions are favorable and to play an effective role.

  as a last resort when conditions become very unfavorable.

  As for the second step provided on each hull, on the outside, it plays the same role in a less pronounced way, so as not to raise too much spray. The bridge and the side passageways are protected from some spray raised by the second slopes since the

  shell is relatively high on the outside.

  As described above, the two shells are asymmetrical and have a pinch on the front, which makes it possible to reduce the dimensions of the wave generated between the two shells and to increase the external wave. The hull structure according to the invention is particularly comfortable for the type of navigation mentioned above and leads to significant autonomy.

Claims (7)

  1. Hull structure for a motor catamaran type ship, comprising two hulls connected by a central deck, characterized in that it comprises an inner recess (110), projecting relative to the hull, disposed above the line (100) of waterline, which begins along a line connecting the inflection points (112) of the hull and which forms an angle a by   relative to the vertical and which ends tangent to the horizontal.   2. Hull structure according to claim 1, characterized in that the line connecting the points of inflection (112) is coincident with the line (100) of waterline. 3. Hull structure according to claim 1 or 2, characterized in that the internal redent (110) is extended by a curve (116) up to the deck central, forming a vault.   4. Hull structure according to any one of the claims   above, characterized in that it comprises an external redent (120), projecting relative to the hull, disposed above the line (100) of waterline, which arises along a line connecting the points ( 122) inflection of the hull which makes an angle J with respect to the vertical and which ends tangently   horizontally, outwards.   5. Hull structure according to any one of claims   above, characterized in that the angle a is greater than the angle D.   6. Hull structure according to any one of claims   previous, characterized in that the two hulls are symmetrical with respect to the median axis of the central bridge and in that each hull is asymmetrical with respect to the median axis (106) with an internal offset   leading to a pinch effect.   7. Hull structure according to any one of claims   above, characterized in that the different dimensions are dimension D: 2 to 3% of the length at the waterline, - width of the hulls at the height of the slope: between 12 and 16% of the waterline length.