WO2008104712A1 - Semi permanent/permanent anchoring device for mooring floating bodies - Google Patents

Abstract

The invention relates to an anchoring device (1) that comprises a rod (2) extending along a longitudinal axis X, said rod (2) including: at least one helical surface or helical blade (3), wherein the blade is to be screwed in the sea bed and comprises an upper end (3a) and a lower end (3b) extending radially relative to said rod; fixation means (4) such as an eyelet, a ring or a loop provided at one of the ends of the rod (2) and protruding outside the sea bed, wherein said fixation means is to be connected to the ground tackle of the anchoring device (10); characterised in that said at least one blade (3) has an evolutive pitch in the screwing direction along the X direction.

Description

 SEMI PERMANENT / PERMANENT ANCHORING DEVICE FOR MOUNTING FLOATING BODIES

The present invention relates to an anchoring device intended to moor or support floating bodies, such as ships, and in particular an anchoring device, which is non-destructive of the seabed, especially those composed of posidonia meadow, and removable from said seabed, also non-destructively.

Anchoring devices can be used to moor beacons, such as shoreline beacons, harbor beacons, safety beacons, chests, for example for naval vessels, navigation channel buoys , fires, floating anchor docks for ships, work barges, for example for fish farms, floating pontoons, or drilling rigs. In known manner, there are two categories of anchorages: temporary anchorages (anchorage) and permanent / semi-permanent anchorages. Permanent or semi-permanent anchoring can not be moved easily. It most often corresponds to a very heavy body placed or buried on the seabed. A provisional anchor is usually an anchor stored on a ship that can be thrown at sea and reboarded depending on the desired navigation. This system works by penetration and hooking of the anchor in the seabed.

However, the seabed, especially the Mediterranean Sea, are made up of many varieties of plants, such as the posidonia meadow (Zostera marina). This flowering plant, which only exists in the Mediterranean, represents not only a habitat, a food source and a breeding area for many species, but also a significant source of oxygen for the ecosystem. In addition, it helps to stabilize the seabed and reduce beach erosion. This is why this species is protected. However, this plant, which grows slowly (1 cm / year), is very fragile and is threatened by the anchoring of ships or floating bodies, whether temporary or permanent. Indeed, an anchor works by opposing the force exerted by the floating body attached to it, such as a ship. Forces which are exerted on the anchorage are thus due to the waves, the currents, but especially to the wind which is exerted on the structure of said ship. Therefore, under the combined force of waves, wind and current, the ship can rotate a few degrees at 180 ° (reverse currents) around its anchorage point and thus sweep and thus sterilize, over an area, said circle of evasion, the seabed.

Anchoring will thus have the direct consequence of tearing off the roots and stems of aquatic plants, particularly those of the Posidonia meadow, and as a consequential consequence of having an adverse impact on the fauna and flora. However, the regeneration of the herbarium is too slow to compensate for these uprooting.

In addition, there exists in the seabed of the Mediterranean, a green alga of tropical origin, accidentally introduced by humans in the region: the Caulerpa taxifolia. This alga, known as the "killer alga", has become an invasive species because of its toxicity to the fauna due to the presence on the seaweed of several terpenes intended to protect it from herbivores, its negative impact on biodiversity, and its worrying speed of development. Indeed, because of its highly invasive appearance, Caulerpa taxifolia may eliminate other species of marine flora. It threatens in particular posidonia meadows. In addition, the disappearance of the flora would also cause the movement of wildlife to uncontaminated areas.

Thus, an anchor thrown in an area invaded by Caulerpa taxifolia would increase the risk of recovery (for example, by dispersing a dozen cuttings) and banalization of the seabed by this invasive algae.

In order to protect coastal and island sites, particularly in the Mediterranean, protective measures have been taken. Decree 91-1110 of October 22, 1991 specifies, in particular in its article 13, that "the equipment and installations established by the holder of the authorization on the mooring area and the light equipment or used for its exploitation must be demolished at the end of the authorization and the places returned in the state ". According to the prior art, various types of permanent or semi-permanent anchors exist in order to maintain a floating body, such as a ship. The anchor must besides not only keep the ship in all circumstances including during storms, but also be easily detachable, for example to tow in a port a beacon for maintenance or to defuse a ship. Permanent anchoring can be carried out in known manner by means of a dead body. The latter usually consists of a concrete slab or a heavy object, placed at the bottom of the water and connected by a rope or a chain to a buoy so that the boats can moor there. This technique has the disadvantage of being difficult to remove, to be polluting and to damage the seabed.

The document FR 2 444 755 describes an anchoring device in a sea floor comprising a tube, subjected to an axial force and provided with one or more helically shaped portions arranged discontinuously on said tube, each of the forms being not constant and extending approximately one turn. Injection ports of a curable liquid soil reinforcement are provided on said tube and arranged in the direction of the axial force, traction or compression, applied to said tube. However, this anchoring system does not prevent the removal of said device upward, that is to say, it does not have sufficient resistance to tearing. Thus, this type of system may damage the flora and may not comply with the regulations in force. In addition, a cylindrical rod provided with a helical ramp, capable of being anchored in a seabed by screwing and further comprising on its upper part a ring for anchoring and transmission of screwing forces and unscrewing, is known according to document FR 2 503 657. Such an anchoring system proves to be destructive for the plant species present on the sea floor. Indeed, sediments are inserted between the helical turns, harden and subsequently form a core with said anchoring device which will also be removed during removal of the anchor. Thus, when the mooring area is removed, as provided by the decree, the installation area can not be restored. EP 0 947 420 describes an anchoring device and a method of anchoring underwater in a posidonia meadow.

The anchor as described in this document consists of a helical winding of a height of a few meters, consisting of a rigid wire (such as a spring).

However, as indicated in application EP 0 947 420, the posidonia meadow does not constitute loose soil. In fact, the Posidonia meadow corresponds to "a dense network of rhizosomes and roots over a thickness of several meters", which prevents "access to the underlying soil". However, with the anchoring system as defined in document EP 0 947 420, the dense network of rhizosomes and roots surrounds and invades, as and when it develops, the helical winding of the anchor, forming there too a carrot. Thus, such an anchoring device does not allow during its uninstallation, to make the natural environment intact, without locally tearing the herbarium.

US2006 / 0051183 relates to an anchor comprising a portion intended to be engaged in the ground, said portion itself comprising an elongated member (rod) and a spiral extending around at least a portion of the rod. The spiral according to Figure 6 of this document, which may have a variable pitch (number of revolutions per unit length), is separated from the rod by a gap, the spiral being connected to the rod by bridges. This gap increases the actual area covered by the rod and spiral to improve the anchorage against the movement of the anchor in a direction parallel to the rod.

GB2 290 093 discloses a screw anchor intended in particular to support the electricity pylons. This screw anchor preferably comprises two blades of substantially square shape (FIG 1). The surplus of material due to this square shape compared to the circular anchors, increases the anchoring force of said anchor. These blades each have a rounded entry portion of a first radius R1 and a second radius R2 curvature, to promote the screwing of the anchor in the ground. In addition, as shown in Figures 3 and 4, the pitch of the blade from the upper edge is not zero or substantially zero. The pitch of the blade according to this document is not indicated. It seems to be equal to a nominal value. JP 2006-312879 describes with reference to Figures 1-2, a device having two rods extending along a longitudinal axis. The first rod carries at least one helically shaped surface (helical blade), each having an upper end and a lower end extending radially relative to said rod. The second rod carries a fastening means intended to protrude from the ground and to be connected to a branch for example. In addition, the pitch of each blade appears nominal and the unit length of each blade is the same (Figures 1 and 2). The present invention aims to propose a new anchoring device that avoids all or part of the aforementioned drawbacks.

The present invention also aims to provide a new anchoring device adapted to be installed and fixed in a non-stable soil, such as mud. For this purpose, the subject of the invention is an anchoring device comprising a rod extending along a longitudinal axis X, said rod carrying:

at least one surface of helical shape, called a helical blade, said blade being intended to be screwed into a seabed, and having an upper end and a lower end extending radially with respect to said rod, said at least one blade having a nominal pitch substantially constant in the direction of the screwing in the X direction,

an attachment means, such as an eye, a ring or a loop, disposed at one of the ends of said rod and intended to protrude outside the seabed, characterized in that said blade has, in the direction of screwing in the X direction, at least one pitch variation sector (C), having a decrease of said pitch (C1) relative to the nominal pitch followed by an increase (C2) to return to the nominal pitch, so as to create on the surface of the blade a concave sector

Such an anchoring device has the advantage of remedying the problem of anchoring small and large floating structures, while preserving the seabed either during installation or uninstallation. Advantageously, said blade has a nominal pitch substantially constant with the exception of a first sector extending from the upper edge and having a substantially zero pitch.

According to a first characteristic, the first sector extends over at least 60 °.

According to a second characteristic, the pitch variation sector extends over substantially 90 ° and is positioned substantially between the radii located 180 ° and 270 ° from the upper end of said blade.

Advantageously, the radius of the blade is substantially constant.

According to one embodiment, the blade is produced by deformation of a plane metal plate in the form of a split disc along one of its spokes.

Preferably, the pitch of the blade is in the order of magnitude of the radius of said blade and the pitch on the pitch variation sector passes through a minimum of 0 and a maximum equal to twice the nominal pitch.

Advantageously, said anchoring device comprises several helical blades arranged along said rod in a discontinuous manner, so as to form a discontinuous helical spiral.

Preferably, said anchoring device comprises an anchor blade, called a primer blade, of radius less than or equal to that of the other blades and arranged at the lower part of the rod so as to ensure piercing said seabed, and to facilitate the depression of said anchoring device at the desired level.

According to an alternative embodiment, said system comprises a bar, arranged transversely to said rod and fixed thereto at its upper end, said bar being intended for hooking and lining a rope. The anchor according to this embodiment has the advantage of being easily screwed into a sea floor by a single plunger through the crossbar which facilitates screwing. In addition, this bar also makes it possible to be able to entangle a rope around said bar, which can be unlaced once the anchor is fixed in the ground, so as to give one or more divers the possibility of stabilizing with the aid of this rope during the phases of bearings or during any underwater exercise. The invention will be better understood, and other objects, details, features and advantages thereof will appear more clearly in the following description of several particular embodiments of the invention, given solely for illustrative and non-limiting purposes. with reference to the accompanying drawings. In these drawings: FIG. 1 represents a general view of the anchoring device according to the present invention; FIG. 2 represents a perspective view of an embodiment of a blade of said anchoring device according to the present invention; Figure 3 shows a developed edge of the blade as shown in Figure 2; FIG. 4 represents the figure of a disc before deformation by press, in particular showing cutting along a radius; FIG. 5 represents said anchoring system according to the present invention within a wetting device, and FIG. 6 shows an alternative embodiment of the anchoring device according to the present invention.

In Figure 1, an anchoring device 1 according to the present invention for a wetting line 20 (Figure 5) permanent and / or semi-permanent is illustrated. This figure is a general view and does not represent all the distinctive features of the anchoring device 1 according to the present invention. However, as illustrated in this figure, the anchoring device 1 according to the present invention comprises a rod 2 extending along a longitudinal axis X, on which are fixed several helical portions 3, hereinafter called "blades" and a fastening means 4. Said rod 2 is straight and has two ends: an upper end 2a and a lower end 2b, the upper end 2a being close to the fastening means 4. This rod 2 has at its end upper 2a a straight section, so as to form a flat surface, while the lower end 2b is cut at an angle of 45 °. This last characteristic makes it easier to penetrate into a seabed 21 (FIG. 5) while cutting right of the upper end makes it easier to weld rings or other means of attachment. Said rod 2 can be made of rolled or drawn steel made of carbon or stainless steel. It can have a diameter ranging from about ten millimeters to several hundred millimeters and a length of the order of 1 meter to about 2.5 meters depending on the type of anchoring desired.

Said attachment means 4 has the function of attaching said anchoring device 1 to one of the elements of the wetting line 20, such as a chain or a cable, itself connected to a semi-emergent floating object, such as a buoy. Thus, this attachment means 4 is arranged to protrude on the seabed to hook said mooring line. This attachment means 4 may be for example an eye, a ring, a loop or a U-shaped bar or any equivalent means. As shown in Figure 1, the rod 2 also carries three blades 3. These blades 3 are intended to be screwed into a seabed 21. They generally extend either on less than one turn, or preferably on approximately at least one turn of said rod 2, the pitch of the blade 3 being of the order of magnitude of the radius of said blade 3. For example, for a pitch between 100 and 200 mm, such as of the order of 160 mm, has one for a radius of 200 mm.

It is also possible, as illustrated in Figure 1, that said anchoring device according to the present invention comprises several helical blades 3 arranged along said rod discontinuously. This feature avoids much of the coring phenomenon.

Advantageously, the distance between two consecutive blades 3 is between 300 mm and 800 mm.

Each of the blades 3 of substantially helical shape has an upper end 3a and a lower end 3b, these ends 3a, 3b extending radially relative to said rod 2.

The characteristics of said blades 3 according to the present invention will be represented in detail below with reference to FIGS. 2 and 3. FIG. 2 illustrates a perspective view of a blade 3 of the anchoring device 1 intended for a line of mooring 20 according to a mode of realization. As is illustrated in this figure, the blade 3, although of helical shape, has an evolutionary helical pitch along the X axis and in the direction of screwing of said anchoring device in the seabed 21. In fact, each said blades 3 according to the present invention has various sectors of different helical pitch, more exactly 4, which we will name later: sectors A, B, C and D.

First, the sector A extends from the upper end 3a of the blade 3 and is characterized by a substantially zero pitch over at least 50 ° to 60 ° of said blade. As shown in FIG. 3, the zero helical pitch can extend up to 90 °. Thus, the blade according to the present invention has a first sector A perpendicular to any traction that may be exerted on said anchoring device. This feature has the advantage of providing a so-called "stop" effect and therefore to ensure a good tear resistance of said device facing traction.

Sector B also extends over 90 °. It presents a constant step, which we will call "nominal" in the rest of the description. This nominal pitch corresponds to a "classic" type propeller, that is to say to a propeller having a constant pitch. The pitch of the blade at sector B thus merges with that of a conventional propeller, represented by dashed lines in FIG.

The sector C which extends about 90 ° and is positioned substantially between the radii located 180 ° and 270 ° of the upper end 3a, is divided into two subparts, named C1 and C2. These two sub-parts are separated by a change of the value of the helical pitch, which we will call "break".

The subpart C1 which follows the sector B in the direction of screwing the blade into the seabed as shown in Figure 4, is characterized by a decrease of the helical pitch extending over about 40 ° (Figure 3) .

Subpart C2 following subpart C1 at the break, corresponds to an increase in helical pitch extending over about 50 °. This second sector C2 associated with the sector C1 creates on the surface of the blade a concave surface. This concavity has the advantage of ensuring a so-called effect of

"Sucker" and provide, coupled with the effect of sector A, a good resistance to pulling in muddy soil. This can be explained by the suction effect that can occur when said anchoring device is pulled upwards, that is to say during traction exerted for example by the load moored to the mooring line. As shown in Figure 3, the sector D which follows the subpart C2 in the screwing direction of said device also extends over substantially 90 °, between the radii located at about 270 ° and 360 °. This sector D is characterized by a nominal helical pitch. As is illustrated in FIG. 3, the pitch of the blade according to the present invention merges with that of a conventional propeller at sector D. Consequently, the shape of the sector D has the advantage of making it easier to penetrate the anchoring device 1 in said seabed 21.

Advantageously, said anchoring device 1 comprises an anchor blade, called a primer blade (not shown), of smaller size than the other blades and arranged at the lower part of the rod so as to pierce said bottom. marine, and facilitate the depression of the anchoring device at the desired level.

When the device comprises a firing blade, the distance between said firing blade and the blade immediately above is between about 50 mm and 150 mm.

In an alternative embodiment of this first embodiment, it is possible that said anchoring device 1 as described above also comprises at least one constant pitch blade. Thus, said anchoring device may comprise in the direction X and in the direction of screwing of said anchoring device in the seabed 21, at least one blade 3 having an evolutionary step as described above, at least one blade constant pitch and possibly a primer blade, preferably at constant pitch, to facilitate the screwing of said device in the seabed 21.

The manufacture of an evolutionary step blade 3 according to the present invention will now be described with reference to FIG. 4.

In order to achieve a blade suitable for the present invention, it is preferable to start from a disk-shaped plate and deform it by cold forging. This disc is preferably metal stainless, such as a rolled or drawn steel made of carbon or stainless steel. The blade can also be carbon steel screened.

Said disk generally has a thickness of the order of 1 mm to 5 mm, the thickness being a function of the type of anchoring desired, the nature of the bottom, the size and the weight of the floating unit.

To facilitate the realization of said blade, it is preferable that said disk has a constant radius R.

The radius R of said disk that is suitable for the present invention may vary between 100 and 500 mm and more particularly, the disk has a radius R ranging between 100 and 300 mm when it comes to producing a primer blade. In general, the size of the disk depends on the type of anchorage desired, the nature of the bottom, the size and the weight of the floating unit. For example, the radius R of the disk may be of the order of 204 mm with a thickness of 4 mm. In order to manufacture a blade, a radial slot 5 is first made to form a central orifice 6. In a first section, the disk is not deformed, so as to obtain a substantially flat surface, perpendicular to the axis X, which will have a helical pitch close to 0 over 90 °. On a second section, the disk is deformed so that it takes a helix shape with a determined pitch (nominal) and substantially constant, also on 90 °. In the vicinity of the middle of the helix, a decrease in pitch is caused over about 40 ° -50 °, followed by an increase over 40 ° -50 °. Finally, a return to the nominal pitch is caused locally on the last quarter turn of the propeller. At the end of this step, a blade with an evolutionary helical pitch is obtained.

The embodiment for deforming such a disc is well known to those skilled in the art. It can be deformed by means of an oil press between two dies or cold forged. These techniques are well known to those skilled in the art and will not, therefore, not more detailed in the present application.

Then, the fixing system of the blade or blades 3 and the attachment means 4 is usually by welding. It can be achieved by basic welding, that is to say by inert gas welding (MIG) or by inert gas tungsten welding (TIG). The installation of said anchoring device 1 and its attachment to a permanent and / or semi-permanent wetting line will now be described with reference to FIG.

The anchoring device 1 is preferably installed at low tide in the seabed 21. In this case, it can be screwed by one or more persons by means of a cross-shaped manual key bearing the footprint of the attachment means 4 or by a simple bar adapted to be inserted into the recess of the attachment means 4.

Said anchoring device 1 can also be installed outside the tidal zones. In this case, said device is installed by one or more divers. The latter can screw said device 1 with a wrench mounted on a pneumatic screwdriver.

In both cases, said device 1 is screwed so that the attachment means 4 protrudes from said seabed. As illustrated in FIG. 5, said wetting device 20 in a seabed 21, also called a wetting line, comprises the anchoring device 1 according to one of the preceding characteristics which is connected, thanks to its fastening means. 4, to a first section 23.

The first section 23, which may be a chain or a cable is itself connected at its other end to a submerged float 24, such as a foam buoy. In an alternative embodiment, it is possible for the anchoring device 1 to be connected to several first sections 23 of a wetting line 20 via a connecting bar when said wetting line 20 is composed of several 23. In both cases, it is important that the first section

23 and possibly the connecting bar are permanently tensioned by the submerged float 24.

The submerged float 24 is provided at its other end with a fastening means 24a, such as a loop, a hook or a ring or a shackle, said float having a buoyancy sufficient to prevent any contact of the elements of said first section 23 of the wetting line 20 with said seabed 21.

Said wetting device 20 also comprises a second section 25 which may be a textile chain or rope that connects the submerged float 24 to a floating object 26, such as a beacon, a fire, or as shown on FIG. figure 5, a buoy on This may for example moor a pleasure boat 22. This section 25 has a length and diameter sufficient to reach the surface and dampen the traction.

In known manner, it is desirable that the second section 25 of the wetting line 20 form an angle of between 30 ° and 60 °, and more particularly 45 °, when it is stretched with respect to the X axis of the rod 2 of the anchoring device 1, so as to allow an equal distribution in a horizontal plane and in a vertical plane of the force exerted on said seabed 21. The buoy 26 is of size, shape and color variable in depending on the use of the mooring line 20.

In addition, two cables 27 also of variable length, size and color are attached to the buoy 26 in order to anchor or dock the ship 22. Depending on the final use of the anchor line, the number of cables can vary.

With reference to FIG. 6, a second embodiment of the anchoring device will be exposed. The elements of the anchoring device

100 identical or similar to the first embodiment are designated by the same reference numeral increased by the number 100 and are not described again.

Thus, in this figure is shown an anchoring device as described above, except that it also has a bar

107. This bar 107 is transverse to the rod 102 and is positioned at its end 102a, that is to say also at the attachment means 104.

It is fixed by welding to the rod 102 and possibly also to the fixing means 104.

This anchor according to this embodiment 100 thus makes it possible to fix and embrace a rope (not shown), for example by forming an 8 between the two ends of the bar 107 and the axis formed by the rod 102.

The anchor 100 is arranged so that it can be easily carried and screwed by one person. Thus, it has a smaller size than the anchoring device according to the first embodiment. For example, the anchor may be of a size ranging from

40 cm to 1 meter, more particularly from 50 cm to 70 cm. It preferably has a single blade with variable pitch, radius between 5 cm and 20 cm, more advantageously between 8 cm and 15 cm and even more advantageously around 10 cm.

The installation of this anchor will now be described: The user, who will preferably be a diver, goes during an outing at sea, anchor the anchor 100 on the sea floor. He will then dive to screw the anchor into the ground by leaning on the bar

107. Once the anchor 100 anchored, the rope attached to it will be positioned through a buoy vertical to the seabed. Said anchoring device may be used for example to secure the recovery of amateur divers, who have not much experience or who are in training or divers who have not been diving for some time. Clinging to the rope attached to the anchor will help stabilize them, especially during the mandatory landing stages at 9, 6 and 3 meters. In addition, this device can be used during the passages of levels 1 to 4 of diving according to the

FFESM (French federation of underwater studies and sports), for example to learn to stabilize vertically ...

It is also possible to use said anchoring device, in particular according to the first embodiment, on non-immersed surfaces, for example to maintain poles, pylons, such as electrical pylons ...

We will now expose the result of tests performed under usher control, showing the good behavior of the anchors according to the present invention.

On a sandy bottom, in a delimited perimeter, on either side, by four stakes, four elliptical anchors were placed in just one hour.

The four anchors according to the present invention have the following characteristics: Anchor 1:

Anchor 2:

Ancre 4 :Anchor 3:

Anchor 4:

Each of the four elliptical anchors was towed with a traction system of the "DYNAFLOR" type. The boat carrying the traction system is equipped with a motor of twice three hundred horses.

The first anchor was torn off at 1,050 engine revolutions, a force of 800 kilograms (measured by the bailiff using an electronic dynamometer).

The second anchor resisted pulls of:

450 Kg, or 800 laps,

- 760 Kg, or 1,000 laps,

- 1,200 Kg, or 1,200 revolutions - and 1,660 Kg, or 1,400 revolutions, the anchor was torn off.

Regarding the third anchor, several attempts were made, unsuccessfully, to pull the anchor (the boat can not go beyond 1800 towers): a) at the first attempt: a . at 650 rpm: traction of 610 Kg, b. at 1000 revolutions: tractions of 810 Kg, c. at 1,200 rpm: traction of 1,260 kg, d. at 1400 rpm: 1,720 kg pull, b) on the second attempt: a. at 650 rpm: traction of 380 Kg, b. at 1,000 revolutions: pulling 1,040 kg, vs. at 1200 rpm: traction of 1 230 Kg, d. at 1,400 revs: 1910 kg pull, c) on the third attempt: a. at 1,000 rpm: traction of 1,450 kg, b. at 1400 rpm; traction of 1,920 kg, c. at 1,800 rpm: 2,200 Kg pull. Similarly, the fourth anchor could not be torn off:

- 800 revolutions: a traction of 430 Kg,

- at 1,000 revolutions, ie a traction of 920 kg, - at 1,200 revolutions, or a pull of 1,200 kg,

and at 1400 revolutions, ie at a pull of 1830 kg. These tests thus confirm that said anchoring device according to the present invention has a very good anchoring resistance while preserving the marine environment. Although the invention has been described in connection with several particular embodiments, it is obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims

Anchoring device (1), comprising a rod (2) extending along a longitudinal axis X, said rod (2) carrying: at least one helically shaped surface, said helical blade (3), said blade (3) being intended to be screwed into a seabed (21), and having an upper end (3a) and a lower end (3b) extending radially relative to said rod (2), said at least one blade ( 3) having a substantially constant nominal pitch in the direction of the screwing in the X direction, - An attachment means (4), such as an eye, a ring or a loop, disposed at one end of said rod (2) and intended to project outside the seabed (21), characterized in that said blade (3) has, in the direction of the screwing in the X direction, at least one pitch variation sector (C), having a decrease of said pitch (Cl) relative to the nominal pitch followed by an increase (C2) to return to the nominal pitch, so as to create on the surface of the blade a concave sector. 2. anchoring device (1) according to claim 1, characterized in that said blade (3) has a nominal pitch substantially constant except for a first sector (A) extending from the upper edge ( 3a) and having a substantially zero pitch. 3. Anchoring device (1) according to claim 2, characterized in that the first sector (A) extends over at least 60 °. 4 Anchoring device (1) according to claim 1, characterized in that the pitch variation sector (C) extends over substantially 90 ° and is positioned substantially between the radii located at 180 and 270 ° from the end upper part of said blade (3a). 5. Anchoring device (1) according to one of the preceding claims, characterized in that the radius of the blade (3) is substantially constant. 6. Anchoring device (1) according to claim 5, characterized in that the blade (3) is formed by deformation of a flat metal plate in the form of split disc according to one of its spokes. Anchoring device (1) according to one of the preceding claims, characterized in that the pitch of the blade (3) lies in the order of magnitude of the radius of said blade (3) and in that the pitch on the pitch variation sector (C) passes through a minimum of 0 and a maximum equal to twice the nominal pitch. 8. Anchoring device (1) according to one of the preceding claims, characterized in that it comprises several helical blades (3) arranged along said rod (2) discontinuously, so as to form a discontinuous helical spiral. 9. Anchoring device (1) according to one of the preceding claims, characterized in that it comprises a primer blade, radius less than or equal to that of the other blades and arranged at the bottom of the rod (2) to ensure to pierce said seabed, and to facilitate the depression of said anchoring device to the desired level. 10. Anchoring device (1) according to one of the preceding claims, characterized in that it comprises a bar, arranged transversely to said rod (2) and fixed thereto at its upper end (3a). , said bar being intended for catching and lining a rope.