AU2012241102B2

AU2012241102B2 - Installing an Anchor

Info

Publication number: AU2012241102B2
Application number: AU2012241102A
Authority: AU
Inventors: Michael Arthur Keith Baker
Original assignee: New Zealand Trustee Services Ltd
Current assignee: New Zealand Trustee Services Ltd
Priority date: 2012-10-15
Filing date: 2012-10-15
Publication date: 2018-02-22
Anticipated expiration: 2032-10-15
Also published as: AU2012241102A1

Abstract

Apparatus suitable for use in installing an anchor in an underwater environment, comprising support means suitable for use at a water craft, at least two weights, 5 weight support lines, a driver and a driver support line where the support means has motion compensation means. The apparatus is formed such that when it is in use the support means can be positioned on a watercraft at the surface of a body of water and used to lower the weights to the waterbed by way of the weight support lines so that the weights provide spaced fixed work points at the waterbed. 10 The driver is adapted to enable it to be lowered to the waterbed by way of the driver support line while using the weight support lines, under tension, to guide the driver to a desired waterbed position between the weights so that the driver can, when desired, drive an anchor into the waterbed. The motion compensation means is adapted to take up pressure in the weight support lines due to movement 15 of the boat so as to prevent the weights from being moved off or across the waterbed due to movement of the boat. Figure 1 5 6b 8 9b 11b 7a3 4

Description

TITLE

Installing an anchor.

Field of Invention

This invention relates to the installation of an anchor, for example a screw pile, in an underwater environment.

BACKGROUND

In many situations it is important to install an anchor such as a screw anchor in a seabed, lakebed or riverbed. It is normal to use a boat as a working platform above the site of installation, but this can present problems in that waves and water currents can cause the boat to move away from an optimal installation position. It is accordingly an object of a preferred form of the invention to go at least some way towards addressing this problem, or to at least provide the public with a useful choice.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided apparatus suitable for use in installing an anchor in an underwater environment, comprising support means suitable for use at a water craft, at least two weights, weight support lines, a driver and a driver support line; the support means having motion compensation means; the apparatus formed such that when it is in use the support means can be positioned on a watercraft at the surface of a body of water and used to lower the weights to the waterbed by way of the weight support lines so that the weights provide spaced fixed work points at the waterbed, the driver adapted to enable it to be lowered to the waterbed by way of the driver support line while using the weight support lines, under tension, to guide the driver to a desired waterbed position between the weights so that the driver can, when desired, drive an anchor into the waterbed, the motion compensation means adapted to take up pressure in the weight support lines due to movement of the boat so as to prevent the weights from being moved off or across the waterbed due to movement of the boat.

Optionally the motion compensation means has a gas accumulator arranged to take up pressure in the weight support lines due to movement of the boat.

Optionally the accumulator is connected by a hydraulic fluid containing line to a cylinder, and a piston is adapted to operate in the cylinder so that an outwards pulling force on the piston causes the hydraulic fluid to impart force against a gas bladder within the accumulator to compress gas within the bladder.

Optionally the driver has a pair of spaced guide arms, each guide arm arranged to engage and run along a respective one of the weight support lines to enable the driver to be directed to a desired position when lowered to the waterbed.

Optionally each guide arm has a sleeve through which the respective weight support line is able to pass when the apparatus is in use.

Optionally the guide arms are arranged to stabilise the driver against twisting when the driver is in use.

Optionally the support means comprises a gantry.

Optionally the gantry is associated with a winch for driving the driver support line to raise and lower the driver as desired.

Optionally the gantry is associated with at least one winch for driving the weight support lines to raise and lower the weights as desired.

Optionally the apparatus has GPS means to enable the weights and/or the driver to be accurately positioned at the waterbed.

According to a further aspect of the invention there is provided a method of installing an anchor comprising the steps of: (a) obtaining apparatus as set out above so that the apparatus is at a watercraft above a waterbed installation site; (b) using the support means and the weight support lines to lower the weights to the waterbed; (c) lowering the driver, fitted with an anchor to be installed, towards the waterbed between the weights while the weight support lines are under tension so that the driver engages the weight support lines and is guided by these towards the installation site; (d) activating the driver so that it causes the anchor to be installed in the waterbed at the installation site; and (e) withdrawing the driver, leaving the anchor behind; the motion compensation means being in operation during at least some of the above steps to compensate for upwards movement or sideways drift by the watercraft to maintain the driver at or near to the installation site.

Optionally the anchor is a screw anchor and the driver causes this to be screw driven into the waterbed.

Optionally the driver comprises a pair of spaced guide arms which engage the weight support lines and run along such lines when the driver and anchor are lowered towards the installation site.

Optionally the guide arms are used to stabilise the driver against undesired twist while it drives the anchor into the waterbed.

BRIEF DESCRIPTION OF THE DRAWINGS

Some preferred forms of the invention will now be described by way of example and with reference to the accompanying images, of which:

Figure 1 is an end elevation illustrating the installation of a screw pile in an area of seabed;

Figure 2 is a side elevation of a gantry used for the installation; and Figure 3 is a schematic illustration of a pressure compensating mechanism used in the installation.

DETAILED DESCRIPTION

Referring to figure 1, a boat 1 is positioned at the waterline 2 above an area of seabed 3 into which a screw anchor 4 is to be installed. The boat has a gantry 5 which can be tilted sternwards when in use to overhang the stern of the boat. The gantry has extendable cantilevered arms 6a, 6b so that it can assume a disposition wider than the boat. Each arm 6a, 6b provides a crane-like support for a clump weight 7a, 7b to be lowered to the seabed by way of a cable 8. The clump weights provide fixed points for work at the seabed.

With further reference to figure 1, when the clump weights 7a, 7b are in place on the seabed the associated clump weight cable is in each case tensioned and a hydraulic drill 9, loaded with the screw anchor 4, is lowered to the seabed by way of a drill cable 10. The tensioned clump weight cables 8 provide positioning guides for the drill 9 and screw anchor 4 as they descend. More specifically, the drill 9 has a pair of outwardly extending arms 9a, 9b, the extremities of which have a sleeve 11a, 11b respectively. The clump weight cables 8 proceed through the sleeves 11a, 11b to keep the drill 9 and screw pile 4 centred. When the screw anchor 4 is positioned at the seabed the drill 9 is activated from the boat to cause the screw anchor to rotate and bore into the seabed, until it is fully installed. At that point the drill 9 is disconnected from the screw anchor 4 and is pulled back to the boat, leaving the screw anchor behind. The clump weights are then also retrieved to the boat.

In a preferred embodiment of the invention the gantry 5 incorporates a motion compensation mechanism to assist in stabilising the position of the drill 9 after the clump weights have been installed. This is important because frequently the boat may have to operate in conditions where waves or currents cause it to move up and down or sideways. But for the compensation mechanism, such movement may cause the clump weights to be pulled from the seabed or from the desired location for them generally with the result that the drill 9 and screw anchor 4 are forced out of position.

Figure 2 shows detail for the motion compensation mechanism incorporated into the gantry. Figure 3 illustrates, schematically, a hydraulic system forming part of the motion compensation mechanism. The hydraulic system relates to the right hand side extendable arm 6b, and the other arm 6a (not shown in figure 3) is associated with a similar mechanism so that both function in substantially the same way. As shown, the cable 8 of the right hand side clump weight 7b extends upwards to and around a grooved wheel 12 at the outer end of a ram 21 associated with arm 6b. The cable then proceeds to a cable winch 13 (shown in figure 2). It is the winch 13 that is used to lower and raise the clump weight 7b. The other end of the ram is in the form of a piston 14 within a cylinder 15. The cylinder contains hydraulic oil to the right of the piston head. When the cable 8 is tensioned due to wave action lifting the boat, the ram 21 comes under a rightwards directed pulling force. This causes the hydraulic oil to come under pressure and such pressure transfers through the oil, via a hydraulic pipeline 16, to a gas pressure accumulator 17.

The accumulator 17 contains and internal flexible/expandable rubber bladder 18 filled with a suitable gas, nitrogen in this instance. The pressure from the oil crushes against the bladder to cause the gas therein to compress and take up the load which would otherwise cause undesired movement of the clump weight 7b. When tension on the cable 8 abates, for example when the boat is in a trough between waves, the pressure in the oil reduces and the gas expands to enable the bladder to assume its original state. In this way the pressure caused by up and down movements of the boat, or indeed sideways movements, is taken up by the motion compensation mechanism to allow the clump weights, the drill 9 and the screw anchor 4 to remain in the desired seabed position.

With further reference to figure 3, the cylinder 15 has an air line 19 to the left of the piston head. This enables the motion compensation mechanism to breath, avoiding undesirable vacuum pressure to the left of piston head. The outlet end 20 of the air line preferably opens into air space above the surface of oil in an oil tank 23.

It will be appreciated that the starting gas pressure selected for the bladder will depend on the size of the clump weight that one is working with, the heavier the weights the greater the starting gas pressure needed.

Preferably the boat can be deliberately moved forwards or backwards if desired, while attached to the clump weights at the seabed, and with the clump weight cables under tension, to adjust the angle at which the screw anchor 4 attacks the seabed when the drill 9 is activated.

When the clump weights and the drill are not in use they may be stored on the deck of the boat. The gantry is thus arranged to enable them to be hoisted to and from the deck and manoeuvred sideways .

In preferred embodiments of the invention a GPS device is used to determine the correct position for releasing the clump weights to the seabed. The GPS device may be positioned at the centre of the gantry or drill 9, mid-way between the clump weights. In other embodiments the GPS device may be substituted or supplemented by an alternative navigation aid.

It will be appreciated that the above described preferred form of the invention enables one to install a screw anchor in an underwater environment without undue damage to the waterbed. For example, the clump weights drop directly onto the seabed and they, and the associated cables, do not drag across the seabed causing damage to the environment. In some embodiments of the invention the screw anchor may be in the form of a screw pile, depending on the project at hand.

While some embodiments of the invention have been described by way of example it should be appreciated that modifications and improvements can occur without departing from the scope of the following claims.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS

1. A method of using apparatus to install an anchor in an underwater environment, the apparatus comprising support means, at least two weights, weight support lines, a driver and a driver support line; the support means having motion compensation means; the apparatus arranged such that the support means is positioned on a watercraft at the surface of a body of water and used to lower the weights to the waterbed by way of the weight support lines so that the weights provide spaced fixed work points at the waterbed, the driver is lowered to the waterbed by way of the driver support line while using the weight support lines, under tension, to guide the driver to a desired waterbed position between the weights and the driver, when lowered, drives an anchor into the waterbed, and the motion compensation means takes up pressure in the weight support lines due to movement of the boat so as to prevent the weights from being moved off or across the waterbed due to movement of the boat.
2. A method according to claim 1, wherein the motion compensation means has a gas accumulator arranged to take up pressure in the weight support lines due to movement of the boat.
3. A method according to claim 2, wherein the accumulator is connected by a hydraulic fluid containing line to a cylinder, and a piston is adapted to operate in the cylinder so that an outwards pulling force on the piston causes the hydraulic fluid to impart force against a gas bladder within the accumulator to compress gas within the bladder.
4. A method according to any one of the preceding claims, wherein the driver has a pair of spaced guide arms, each guide arm arranged to engage and run along a respective one of the weight support lines to enable the driver to be directed to a desired position when lowered to the waterbed.
5. A method according to claim 4, wherein each guide arm has a sleeve through which the respective weight support line passes.
6. A method according to claim 4 or 5, wherein the guide arms are arranged to stabilise the driver against twisting.
7. A method according to any one of the preceding claims, wherein the support means comprises a gantry.
8. A method according to claim 7, wherein the gantry is associated with a winch for driving the driver support line to raise and lower the driver as desired.
9. A method according to claim 7 or 8, wherein the gantry is associated with at least one winch for driving the weight support lines to raise and lower the weights as desired.
10. A method according to any one of the preceding claims, the apparatus having GPS means that is used to accurately position the weights and/or the driver at the waterbed.
11. A method according to any one of the preceding claims, wherein the anchor is a screw anchor and the driver causes this to be screw driven into the waterbed.
12. A method according to claim 1, wherein the support means comprises a gantry, the gantry having extendable cantilevered arms able to assume a disposition in which the gantry is wider than and overhangs the boat, each arm providing a crane-like support for one of the weights, the driver comprises a hydraulic drill, the anchor comprises a screw anchor, the drill has a pair of outwardly extending arms the extremities of which have a respective sleeve, the weight support lines pass through the sleeves, respectively, to keep the drill centred, and the drill is disconnected from the screw anchor after such anchor has been rotationally driven into the seabed by the dill.
13. A method according to claim 12, wherein the motion compensation means is incorporated into the gantry and comprises: a) a gas accumulator arranged to take up pressure in the weight support lines due to movement of the boat; b) the accumulator is connected by a hydraulic fluid containing line to a cylinder, and a piston is adapted to operate in the cylinder so that an outwards pulling force on the piston causes the hydraulic fluid to impart force against a gas bladder within the accumulator to compress gas within the bladder; and c) each weight support line extends around a respective grooved wheel at the outer end of a ram associated with a respective one of the gantry arms and to a winch for lowering and raising the weights.