FIELD OF THE INVENTION

The present invention relates to an off-shore mooring for a vessel and a method of installing the same.

BACKGROUND OF THE INVENTION

Two main types of moorings are commonly used for mooring vessels in coastal waters. "Cyclone" moorings are installed by blasting three radially arranged holes, and inserting anchor weights into the holes. These anchor weights are connected by lengths of heavy chain to a central ring on a swivel, then via another chain to a surface buoy. "Swing" moorings, the more common type, usually consist of a single heavy anchor (often an engine block or block of concrete) , connected to a surface buoy by a very long length of heavy chain. It has been discovered that, due to natural water movement, the chains constantly roll over the sea bed causing severe scouring and loss of vegetation. Measurements taken by the Environmental Protection Authority of Western Australia, indicate that the area of scouring due to a single mooring ranges from approximately 3 square meters to 300 square meters depending on the type of mooring and the length of chain used.

The loss of vegetation has detrimental physical and biological effects on the immediate environment. Sea bed vegetation, including sea grasses, slow the rate of water flow over the sea bed and this enhances the rate of sediment deposition as suspended particles fall from the water when velocities decrease. These sediments are then bound by a network of growing rhizomes which stabilise an otherwise unstable environment. Sea grasses therefore allow the establishment and maintenance of sediment communities and aI.so help to prevent the erosion of these sediments. Furthermore, sea grasses form an integral part of the food chain and their destruction can have devastating ecological effects. ("Effect of Boat Moorings on Sea Grass Beds in a

Perth Metropolitan Region" - environmental protection authority, Perth, Western Australia, Technical Series No. 21, December 1987)

In addition, as swing and cyclone moorings rely solely on gravity for their operation they are prone to drag in adverse weather conditions. This can result in substantial damage to sea grass areas and to damage to or loss of a moored vessel.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a mooring which attempts to alleviate at least one of the above-described disadvantages in the prior art. It is a further object of the invention to provide a method of installing such a mooring. According to one aspect of the present invention there is provided an off-shore mooring for a vessel comprising: an elongate element for location in a hole formed in a submerged ground surface; a settable material surrounding said elongate element when located in said hole; and, a tether connected at one end to an end of said elongate element near said ground surface when the elongate element is in said hole and connected at an opposite end to a first float.

Preferably said mooring further comprises a second float connected to said tether at a point intermediate said elongate element and said first float, the length of said tether and location of said intermediate point being arranged so, that in use said tether remains substantially elevated above the submerged ground surface.

In one embodiment said elongate member comprises a plurality of parallel rods arranged about and connected to one or more spacers, said spacers disposed at locations spaced in the direction of the length of said rods whereby, in use, said rods are embedded in said settable material.

In an alternate embodiment said elongate element comprises a pipe. Preferably the pipe is provided with at least one protrusion extending from an outer surface of said pipe for embedding in said settable material. Advantageously said protrusion comprises a flange or lug extending radially of said pipe.

Preferably said hold comprises an upper length which opens at one end onto said submerged ground surface and a lower length extending contiguously from an opposite end of said_upper length in to said ground the maximum width of said lower length being greater than that of said upper length, whereby, in use, the mass of settable material in said lower length can be formed with a maximum width greater than the maximum width of the upper length. Preferably, said settable material is a cementitious material.

According to another aspect of the present invention there is provided a method of installing an off¬ shore mooring for a vessel comprising the steps of: forming a substantially vertical hole in a submerged ground surface; inserting an elongate element into said hole; filling said hole with a settable material; connecting one end of a tether to an end of said elongate element near said submerged ground surface; and, connecting a first float to an opposite end of said tether.

Preferably, said method further includes the step of connecting a second float to said tether at a point intermediate said elongate element and said first float, the length of said tether and the location of said intermediate point being arranged so that in use the tether remains substantially elevated above the ground surface.. Preferably, said method further comprises the initial step of driving a hollow pipe substantially

vertically into said ground and evacuating said hollow pipe to thereby form said hole.

Preferably, said hole forming step comprises forming said hole with an upper length which opens onto said ground and a lower length contiguous with an opposite end of upper length, the maximum width of said lower length being greater than that of said upper length whereby, in use, the mass of settable material in said lower length can be formed with a maximum width greater than the maximum width of said upper length.

Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a first embodiment of the off-shore mooring in-situ;

Figure 2 illustrates a second embodiment of the off-shore mooring in-situ; and,

Figure 3 illustrates an alternative arrangement of an elongate element used in the off-shore mooring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in Figure 1, an off-shore mooring 2 for a vessel (not shown) comprises an elongate element in the form of a pipe or rod 4 located in a hole 6 formed in a submerged ground surface 8 such as, for example, a sea bed. In this embodiment the sea bed comprises sand, mud or silt. A settable material which is preferably in the form of a cementitious material such as for example grout or cement 10 surrounds the pipe 4 when located in the hole 6. One end of a tether 12 in the form of a chain is connected to an end of the rod 4 near the sea bed 8 by a U-shaped coupling member 14. An opposite end of the chain 12 is connected to a first float 16 which floats at the surface 18 of a body of water 20 overlying the sea bed 8. A second float 22 is connected to

the chain 12 at a point 24 intermediate the pipe 4 and the first float 16. The length of the chain 12 and location of the intermediate point 24 are arranged so that the chain 12 remains substantially elevated from the sea bed 8. The location of the intermediate point 24 is largely dependent upon tide conditions.

In order to increase the binding of the grout 10 to the pipe 4, a plurality of protrusions in the form of lugs 26 are provided projecting from a circumferential surface 28 of the pipe 4.

The holding or anchoring power of the mooring 2 can be increased by forming a volume of the grout 10 in a bulb like mass 30 at an end of the pipe 4 opposite chain 12. This can be achieved by forming the hole 6 with a lower length 15 having a maximum width greater than that of a contagious upper length 17. The bulb-like mass 30 has a maximum width greater than that of the upper length 17 hole 6 to prevent passage therethrough after setting.

The coupling of the pipe 4 to the bulb-like mass 30 is enhanced by the provision of two rods 32 connected to the pipe 4 and extending into the bulb-like mass 30. A plate 34 is connected between the ends of rods 32 opposite the pipe 4 and lies in a plane substantially perpendicular to the length of the rods 32. The embodiment illustrated in Figure 1 is particularly adapted for use in sand, mud or silt sea beds 8. Such sea beds allow for the relatively simple formation of the bulb-like mass 30.

In a second embodiment illustrated in Figure 2, in which like features are denoted by identical reference numbers, the mooring 2 is used in a rock sea bed 8.

The most significant variation between the first and second embodiments is the absence of a bulb-like mass 30 of grout 10 in the mooring 2 of the second embodiment. The inclusion of the mass 30 provides no substantial advantage or benefit when the mooring 2 is installed in a solid rock sea bed. A further variation is the provision of annular flanges

36 extending radially about the circumferential surface 28 of the pipe 4 in place of the lugs 26. The flanges 36 are embedded in the grout 10 and assist in preventing relative movement of the grout 10 and the pipe 4. A further embodiment of the elongate element is shown in Figure 3. In this embodiment the elongate element comprises three parallel rods 42 arranged about and connected to two ring like spacers 44. The spacers are disposed at locations spaced in the direction of the length of the rods 42. A coupling 46 is attached to one end 48 of the elongate element. The coupling includes a length of pipe 50, one end of which resides between and is welded to rods 42. A cap 52 which fits over the opposite end of the pipe 50 and is attached thereto by shear bolts 54 which extend perpendicular to the length of the rods 42. A pad eye 56 is welded to the upper end of cap 52 to allow coupling to a chain (not shown) . The shear bolts 54 allow the cap 52 to be replaced easily when it becomes worn. A holding lug 58 is connected to end 60 of each rod 42 which becomes embedded in the grout to further resist upward movement of the elongate member when in use.

The elongate member can be used as a direct replacement for pipe 4 shown in the embodiment illustrated in Figures 1 and 2. All components of elongate member of Figure 3 are made of stainless steel or mild steel. The rods 42 are solid rods having a 20mm outside diameter. The spacers 44 are made from 25mm lengths of pipe having an outside diameter of 45mm. Pipe 50 also has an outside diameter of 45mm and a total length of 200mm one half of which extends beyond the ends 48 of rods 42. Cap 52 has an inside diameter of 47mm with bolts 54 being 12mm shear bolts. When used in sand, mud or silt ground the rods 42 are about 1.7m in length and when used in rock about 1.3m in length.

A further variation between sand and rock applications is the diameter of hole 6. When used in sand, mud or silt the upper length of hole 6 has a diameter (width)

in the order of 180mm. However when used in rock the hole diameter is reduced to 75mm.

The method of installing the mooring 2 will now be described. When installing the mooring 2 in a sea bed of sand, mud or silt, the hole 6 is formed by air-lifting the sand, mud or silt from the sea bed and simultaneously inserting into the hole 6 a pipe or casing 38 of diameter greater than that of pipe 4. Substantially the whole length of the pipe 38 is air lifted into the sea bed 8. This forms a lining for the hole 6 and stops the hole from collapsing upon itself. Continued air lifting results in the formation of the lower length 15 which takes the form of a bulb-like cavity 40 at the bottom of the pipe 38. The pipe 4 with attached rods 32 and plate 34 are lowered into the hole 6. The rod 4 can be suspended in position by passing that pin (not shown) through the U-shaped coupling member 14. Grout 10 is then pumped into the hole 6 including cavity 40 until filled. Alternately the hole 6 can be first filled with grout then the pipe 4 lowered into the hole. Once the grout 10 is hardened, th^ chain 12 is connected to the pipe 6 via the U- shaped coupling 14 and the floats 16 and 22 attached to the chain 12. The length of the chain 12 and the position of connection of the second float 22 are arranged so that the chain 12 is substantially elevated from the sea bed 8.

In one variation of this method the casing 38 is initially driven into the sea bed and then evacuated to form the hole 6 including the cavity 40.

When installing the mooring 2 in a sea bed of rock for example limestone or sandstone, the hole 6 is formed by drilling in a conventior:ιl manner. After drilling of the hole 6, the pipe 4 is lc sred and suspended in the hole 6. Grout is then poured into the hole 6 until filled. Again the hole 6 can be filled prior to lowering of the pipe 4 if desired. Once the grout 10 is hardened, the chain 12 is attached to the U-shaped coupling 14 and the first and second floats 16 and 22 attached to the chain 12. The length of the

chain 12 and location 24 of coupling of the float 22 to the chain 12 are arranged so that the chain 12 is substantially elevated above the sea bed 8.

The lugs 26 and flanges 36 are embedded in the grout 10 and assist in preventing relative movement of the pipe 4 and the grout 10. If desired, the pipe 4 can also be filled with grout 10.

When the mooring 2 is installed in sand, mud or silt it is advantageous that the casing 38 extend 1500mm into the sea bed 8. Pipe 4 with attached rods 32 and plate 34 extend into cavity 40. However, the extent of casing 38 may vary depending on the type of soil constituting the sea bed 8. In the embodiments shown in Figures 1 and 2, the pipe 4 is a 50mm diameter stainless steel pipe, the rods 32 formed of 19mm stainless steel rod which extend 300mm beyond the pipe 4 and the plate 34 made of 10mm thick stainless steel plate. Both the lugs 26 and the U-shaped coupling member 14 are made from stainless steel. The U-shaped coupling extends 75mm from the end of the pipe 4. The chain 12 is made from 9mm stainless steel chain lengths. Pipe 38 is typically PVC pipe.

Tests conducted on the moorings 2, details of which are provided below, indicate that the holding power of the moorings is far in excess of their weight.

TEST 1

In a first test, a mooring of the type shown in Figure 2 was installed on dry land in a sand-stone ground. The length of the rod 4 used in the test was 1.3 metres. Three days after the installation of the test mooring, two pull tests were conducted by connecting a crane directly to the U-shaped coupling member 14. A first pull of 3 ton

(direct lift) was applied for 4 minutes. A second pull of 6 to 7.5 ton (direct lift) was held for a further 4 minutes.

No movement of the mooring 2 was detected during either the first or second pulls. It is to be noted that the grout used

in the test mooring cures to 65% after 7 days and fully cures only after 28 days.

TEST 2 A test mooring of the type shown in Figure 2 was installed on dry land in a sand-stone ground. The length of the rod 4 was 690mm. The test procedure and direct lift applied was identical to that in Test 1 above. Again no movement of the test mooring 2 or grout was detected during the application of the lifting force.

TEST 3

A test mooring of the type shown in Figure 1 was installed in situ on a sandsea bed. A 44 foot long timber boat having a 10 ton displacement and 145 horse power motor was used for applying force to the test mooring. The test procedure was as follows:-

A heavy line was attached between the U-shaped coupling 14 and to the boat. The boat was put into reverse and taken to full power. A diver observing the mooring 2 detected no movement of the mooring or of the surrounding sea bed. The angle of pull applied to the mooring 2, that is the angle of the line connecting the coupling and boat to the sea bed, was approximately 60°. The test was conducted from several different points along an arc about the mooring 2, with the same results. Several days later, the chain 12 and buoys 16 and

22 were attached to the test mooring 2. Further tests were then carried out on the complete installation as follows:

A short heavy rope was attached between an eye on buoy 16 and to a front bollard on the boat. The buoy 16 was connected as close as possible to the bollard so as to achieve an angle of pull of approximately 80°. The revs of the boat motor were then constantly cycled between 2400rpm and 1900rpm to create a snatching effect on the mooring. Divers monitoring the test detected no movement of the mooring or surrounding ground at any time during the test.

It is estimated that the pulling power of the boat used in the test is in excess of 2 ton.

From the above description it will be apparent that a major advantage of the moorings 2 is that their mooring power is essentially independent of their weight. Accordingly, a mooring in accordance with an embodiment of the present invention, can be effective to moor a wide range of vessels of different displacements. However, in the prior art where the holding power is solely dependent upon the weight of the mooring itself, the range of vessels which can be securely moored is very limited. In order to increase the facility of prior art moorings, additional weight must be attached. In addition, as the chain 12 is substantially elevated above the sea bed 8, no damage, or minimal damage, is done to surrounding sea bed vegetation.

Now that embodiments of the present invention have been described in detail, it will be apparent to those skilled in the relevant arts that numerous modifications and variations may be made without departing from the basic inventive concepts. For example, the elongate element is illustrated as being a hollow pipe 4, however, the elongate element may also take the form of a solid rod. Furthermore, the pipe 4 may be of any convenient cross-section, for example, circular or square. Also, while it is preferred that the rod 4 be made of stainless steel, any other suitable material can be used. In addition, the U-shaped coupling member 14 can be in the form of a cap which can be screwed onto the end of rod 4 and held in place by a pin. Finally, while the tether is illustrated as a chain 12, it can take other forms such as, for example, fibre, synthetic, or metal rope. All such modifications and variations are to be considered within the scope of the present invention, the nature of which is to be determined from the foregoing description.