Patent Description:
Hydraulically powered down-the-hole hammers generally include three principal components - an impact piston to impart percussion energy to a drill bit or tool located at a forward end of the hammer; a shuttle or control valve to control the flow of hydraulic fluid in the hammer, to apply pressure to faces of the impact piston, thereby creating cyclical forces that cause reciprocal motion of the piston; and one or more accumulators to take in, store and deliver back pressurised hydraulic fluid to accommodate the varying instantaneous flow requirements created by the reciprocation of the piston.

A conventional hydraulic down-the-hole hammer <NUM> is shown in <FIG>. In such conventional hammers, the piston <NUM> is typically solid and reciprocates within an outer cylinder to impact a bit <NUM> at a forward end of the hammer. The piston drive chambers <NUM>, <NUM> are arranged between the piston and an outer cylinder <NUM>, and the control valve <NUM> and accumulators <NUM> are positioned at a rear end <NUM> of the piston. Working fluid is provided to the hammer via pressure line P and returned via return line T. A separate flow of flushing fluid <NUM> is provided to flush cuttings from the hole. Because of the position of the control valve, the distance dvalve between the control valve and the drive chambers is relatively large. The accumulators <NUM> are typically upstream of the valve <NUM> and so the distance daccu between the accumulators and the drive chambers is even greater. The long flow channels between the piston and the valve and accumulators can generate pressure waves that can be harmful to the hammer components. The long flow channels also result in pressure losses. The accumulators do not operate efficiently, since the communication delay between the piston and the accumulators is substantial, due to the distance between them.

In a typical water-powered hydraulic hammer, the set-up is similar to that outlined above and shown in <FIG>. However, in the water-powered hammer <NUM> shown in <FIG>, there is no return line T. Instead, the drive fluid is used for flushing flow <NUM>. Furthermore, the piston <NUM> is fully submerged in water and only a small portion of the cross-sectional area of the piston is used to drive the piston. The rest of the cross-sectional area is idling, as it is exposed to water at ambient pressure. This means that the non-driving area of the piston needs to displace a large amount of water during operation of the hammer. This is achieved by having a central bore <NUM> through the piston so that the forward <NUM> and rear <NUM> ends of the piston are in fluid communication with one another. The bore must be sufficiently large to avoid a significant pressure loss, which would negatively affect hammer performance. Pressure losses can also be reduced by minimising the size of the non-driving areas of the piston. Increasing the size of the central bore and decreasing the size of the non-driving areas of the piston results in a piston with a very small cross-sectional area, which tends to be too lightweight for effective drilling. This is addressed by increasing the length of the piston in order to provide sufficient weight. However, this in turn leads to a hammer that is impractical due to its length, an issue which is exacerbated by the position of the valve to the rear of the piston. Existing water hammers are also complex in design and therefore expensive to produce.

It would be desirable to provide a hydraulic down-the-hole hammer that addresses some of the disadvantages associated with existing arrangements.

Subsea piles may be used to anchor structures used to moor offshore structures such as wind turbines to the seabed. The upper layers of the seabed are often composed of soil or silt and may be weak or unstable. A pile is a load-bearing element that extends through these upper layers to lower, more stable layers of compacted soil and rock, thereby transferring the load from the anchored structure to these lower layers of the seabed.

Existing terrestrial pile installation involves drilling a hole using a hammer, with a casing being pulled down the hole by the hammer as the hole is drilled. Once the hole has reached a target depth, the hammer is removed from the hole, leaving the casing in place. A reinforcing steel bar is dropped down the centre of the casing and the hole is then filled with grout. The casing may be removed before the grout is cured, in which case the grout bonds the reinforcing steel bar to the material of the surrounding terrain.

However, subsea pile installation presents a number of difficulties which mean that such terrestrial installation methods are unsuitable. One common method of fixing subsea anchors to the seabed is using driven piles, where the pile is driven into the seabed by a large underwater hydraulic hammer. Alternatively, a suction pile installation method may be used where a hollow pile is dropped onto the seabed, creating a seal between the bottom of pile and the seabed. Water is then pumped out from the hollow centre of the pile to create a suction effect which pulls the pile further down into the seabed.

Subsea piles as described above may be used to fix a subsea anchor to the seabed. Such subsea anchors may comprise a frame or template which is fixed to the seabed using one or more piles. A wind turbine or other offshore structure can then be moored or otherwise fixed to the subsea anchor.

A method for installation of such subsea pile anchors is disclosed in United States Patent Application Publication No. <CIT>. The method involves placing a frame on the seabed, arranging a seabed drill on the frame and using the drill to drive a pile anchor into the seabed. Grout is then pumped around the pile anchor to bond the pile to the ground. This process may be repeated for several pile anchors to fix the frame to the seabed. A mooring connection on the frame may then be used to moor an offshore structure to the anchor.

There are a number of disadvantages associated with these installation methods. Both driven piles and suction piles are relatively slow to install. For driven piles, the underwater hammer is large, complex and expensive and requires a large support vessel. The suction method is only suitable where the seabed is soft and sandy, and cannot be used where there are boulders or obstacles.

It would be desirable to provide a method and system for installing a pile or load-bearing element in a seabed, for example, for anchoring a structure such as a wind turbine, which overcomes some of the disadvantages associated with existing methods.

<CIT> relates to an in-hole rock drilling machine. <CIT> relates to an axial return hammer.

According to an aspect of the present invention, there is provided a hydraulic down-the-hole hammer comprising:.

The term "forward" is used herein to indicate an end of the hammer towards the percussion bit, that is, the drilling end of the hammer. The term "rear" is used herein to indicate an end of the hammer, away from the percussion bit, that is, an end of the hammer that is uppermost during drilling.

There are several advantages associated with this arrangement. Because the valve is arranged within the piston, the distance travelled by the fluid between the valve and the drive chambers is minimised, thereby eliminating harmful pressure waves. Pressure losses are also very low. Because the drive chambers are inside the piston, rather than between the piston and an outer sleeve, the sealing diameters are reduced as compared with a conventional hammer. This reduces leakage which is particularly important for water-powered hammers due to the low viscosity of the working fluid. The hammer is also less expensive to produce due to its simple design.

Preferably, the control valve is arranged internally of the shaft.

In preferred embodiments, the piston has a monolithic or unitary construction, that is, it is formed as a single piece. Because the annular shoulder on the piston dividing the forward and rear chambers is provided on the inside of the piston bore, it is possible to manufacture and assemble the piston into the hammer in a single piece.

Ideally, the piston is arranged to impact an annular shoulder at a rear end of the percussion or drill bit. The annular shoulder may be provided on the skirt of the drill bit. An advantage of this arrangement is that the impact force is transmitted directly to the gauge of the drill bit at the point where the highest impact energy is required for drilling.

In certain embodiments, the hammer may comprise at least one accumulator arranged at a rear end of the piston. Because the valve is arranged within the piston, the accumulator or accumulators may be positioned much closer to the piston than in conventional arrangements, thereby reducing daccu and consequently improving efficiency.

In an embodiment of the hammer, the working fluid is water. In this embodiment, the rear chamber may be connected to a pressure fluid channel and the control valve may be arranged to connect the forward chamber to the rear chamber while the piston is moving in a rearward direction and arranged to connect the forward chamber to a flushing fluid channel through the shaft and the percussion bit when the piston is moving in a forward direction. Because the rear chamber is connected to a pressure fluid channel throughout the piston cycle, there is a constant pressure in the rear chamber and an alternating pressure in the forward chamber.

In some embodiments, the hammer may further comprise an outer wear sleeve, such that the piston is housed within the wear sleeve. As in conventional hammers, the outer wear sleeve protects the piston from wear during drilling. The percussion bit may be arranged at a forward end of the wear sleeve. In an embodiment, the hammer is a closed-loop hammer and a flushing fluid channel may be provided between the piston and the wear sleeve and through the percussion bit. This means that the full outer surface of the piston may be exposed to flushing flow, thereby providing very efficient cooling for the piston.

In another embodiment, a working fluid of the hammer is water and a flow annulus is provided between the piston and the outer wear sleeve to provide fluid communication between forward and rear ends of the piston. A flushing fluid channel is provided through the shaft and the percussion bit. Because the drive chambers of the hammer are provided inside the piston bore, the flow communication between forward and rear ends of the piston may be provided by the flow annulus on the outside of the piston, rather than via the piston bore as in conventional water hammers. Such a flow annulus has inherently large flow area even with a small radial clearance between the piston and wear sleeve. This means that the cross-sectional area of the piston may be increased as compared with conventional water hammers, thereby allowing sufficient piston weight to be achieved with a short piston. The placement of the valve within the piston further decreases the length of the hammer.

According to an aspect of the present invention, the piston is the outermost component of the hammer. That is, the hammer does not include an outer wear sleeve to house the piston. By omitting the conventional outer wear sleeve from the hammer, the cost of the hammer is reduced, allowing it to be used as a single-use, sacrificial or disposable hammer. Because the piston is the outermost component of the hammer, it will be exposed to wear from cuttings. However, since the hammer is disposable, the piston need only last long enough to drill a single hole. For example, the hammer may be left in the hole when the hole has been drilled.

A flushing port may be provided in the shaft extending from the central bore of the shaft to an outer surface of the shaft at a forward end of the piston. This allows a portion of the flushing water to exit between strike faces of the piston and the bit, thereby flushing cuttings away from the strike faces to avoid damage thereto.

In various embodiments of the hammer according to the present invention, the shaft may comprise a coupling element at forward end thereof, wherein the coupling element couples the percussion bit to the hammer and transmits rotational drive thereto.

Engagement means may be formed on the coupling element engageable with complementary engagement means formed internally of the bit whereby rotational drive from the shaft may be transmitted to the bit. In an embodiment, the coupling element is formed with a central bore and the flushing port is provided in the coupling element, extending from the central bore thereof to an outer surface of the coupling element at a forward end of the piston. The engagement means may comprise a plurality of axially extending splines formed externally of the coupling element and the complementary engagement means may comprise a corresponding plurality of axially extending splines formed internally of the bit. In other embodiments, the engagement means may comprise a portion of the coupling element with a hexagonal or square cross-section, and the complementary engagement means may comprise an internal portion of the bit formed with a correspondingly-shaped inner wall.

The hammer may further comprise bit retaining means on the coupling element adapted for engagement with complementary retaining means on the bit to retain the bit in the hammer. The bit retaining means may comprise a first screw thread formed externally of the coupling element at a forward end thereof, and the complementary engagement means may comprise a second screw thread formed internally of the bit. The hammer bit may be assembled to the hammer by threading the bit onto the coupling element such that the first screw thread is located forward of the second screw thread. This arrangement retains the bit in the hammer and allows limited longitudinal movement of the bit.

In another embodiment, the bit retaining means comprises a bit retaining ring, comprising a plurality of part-annular sectors, and the complementary engagement means comprises a shoulder formed internally of the bit. In this embodiment, the coupling element may comprise a chuck.

A hydraulic down-the-hole hammer <NUM> according to an embodiment of the present invention is illustrated in <FIG>. The hammer comprises an elongate shaft <NUM> formed with a central bore <NUM>. A piston <NUM> also has a central bore <NUM> therethrough. The shaft is received within the piston bore such that the piston is slidably mounted for reciprocal movement on the shaft <NUM> and arranged to impact an annular shoulder <NUM> at a rear end <NUM> of a percussion bit <NUM>. The piston <NUM> is housed within an outer wear sleeve <NUM>, and the percussion bit <NUM> is arranged at a forward end <NUM> of the wear sleeve.

Forward <NUM> and rear <NUM> drive chambers for the piston are disposed between the piston <NUM> and the shaft <NUM>. An annular shoulder <NUM> on the piston formed internally of the piston bore <NUM> separates the forward chamber <NUM> from the rear chamber <NUM>. An internal diameter of the piston <NUM> to the rear of the shoulder <NUM> is greater than the internal diameter of the piston forward of the shoulder, such that the rear chamber has a larger driving area than the forward chamber. The hammer also comprises a control valve <NUM> arranged within the central bore <NUM> of the shaft to control reciprocation of the piston. In other embodiments, the valve <NUM> may be arranged within the central bore <NUM> of the piston, between the piston and the shaft.

The hammer <NUM> is a closed-loop hammer in which working fluid is provided to the hammer via pressure line P and returned via return line T. A flushing fluid channel <NUM> is provided between the piston <NUM> and the wear sleeve <NUM> and through the percussion bit <NUM>, such that the flushing fluid exits the channel at the bit face <NUM>.

The hammer <NUM> further comprises pressure and return fluid accumulators <NUM> arranged at a rear end <NUM> of the piston. The accumulators are arranged a distance daccu from the rear drive chamber <NUM> of the piston.

A hydraulic down-the-hole hammer <NUM> according to another embodiment of the invention is illustrated in <FIG>. As in the embodiment of <FIG>, the hammer comprises an elongate shaft <NUM> formed with a central bore <NUM>. A piston <NUM> also has a central bore <NUM> therethrough. The shaft is received within the piston bore such that the piston is slidably mounted for reciprocal movement on the shaft <NUM> and arranged to impact an annular shoulder <NUM> at a rear end <NUM> of a percussion bit <NUM>. The piston <NUM> is housed within an outer wear sleeve <NUM>, and the percussion bit <NUM> is arranged at a forward end <NUM> of the wear sleeve.

Forward <NUM> and rear <NUM> drive chambers for the piston are disposed between the piston <NUM> and the shaft <NUM>. An annular shoulder <NUM> on the piston formed internally of the piston bore <NUM> separates the forward chamber <NUM> from the rear chamber <NUM>. An internal diameter of the piston <NUM> to the rear of the shoulder <NUM> is greater than the internal diameter of the piston forward of the shoulder, such that the rear chamber has a larger driving area than the forward chamber. The hammer also comprises a control valve <NUM> arranged within the central bore <NUM> of the shaft to control reciprocation of the piston.

The hammer <NUM> shown in <FIG> is an open-loop hammer in which a working fluid such as water is provided to the hammer via pressure line P. However, unlike the hammer of <FIG>, the hammer <NUM> does not have a return line. Instead, the drive fluid is used for flushing flow <NUM> through the central bore <NUM> of the shaft and the percussion bit <NUM> to exit at the bit face <NUM>. Unlike prior art hammers, the outer surface of the piston is not a sealing surface and so a flow annulus <NUM> to allow fluid communication between the forward and rear ends of the piston is provided between the piston and the wear sleeve, rather than via the piston bore as in the conventional water hammer shown in <FIG>. This allows the cross-sectional area of the piston to be increased as compared with such conventional water hammers, thereby allowing sufficient piston weight to be achieved with a short piston. The placement of the valve <NUM> within the piston allows the distance daccu to be reduced and further decreases the length of the hammer.

A low-cost disposable or single-use hydraulic down-the-hole hammer <NUM> according to an embodiment of the invention is illustrated in <FIG>. As in the embodiment of <FIG>, the hammer comprises an elongate shaft <NUM> formed with a central bore <NUM>. A piston <NUM> also has a central bore <NUM> therethrough. The shaft is received within the piston bore such that the piston is slidably mounted for reciprocal movement on the shaft <NUM> and arranged to impact an annular shoulder <NUM> at a rear end <NUM> of a percussion bit <NUM>. Forward <NUM> and rear <NUM> drive chambers for the piston are disposed between the piston <NUM> and the shaft <NUM>. An annular shoulder <NUM> on the piston formed internally of the piston bore <NUM> separates the forward chamber <NUM> from the rear chamber <NUM>. In this embodiment, an internal diameter of the piston <NUM> to the rear of the shoulder <NUM> is smaller than the internal diameter of the piston forward of the shoulder, such that the forward chamber has a larger driving area than the rear chamber. The hammer also comprises a control valve <NUM> arranged within the central bore <NUM> of the shaft to control reciprocation of the piston.

Like the hammer of <FIG>, the hammer <NUM> shown in <FIG> is an open-loop hammer in which a working fluid such as water is provided to the hammer via pressure line P. However, unlike the hammer of <FIG>, the hammer <NUM> does not include an outer sleeve, so that the piston <NUM> is the outermost component of the hammer. This reduces the cost of the hammer so that it can be used as a disposable or sacrificial hammer that is used to drill a single hole only.

In this embodiment, the rear chamber <NUM> is connected to a pressure fluid channel P so that there is a constant pressure in the rear chamber. The control valve <NUM> is arranged to connect the forward chamber <NUM> to the rear chamber <NUM> while the piston is moving in a rearward direction and to connect the forward chamber <NUM> to a flushing fluid channel <NUM> through the central bore of the shaft and the percussion bit when the piston is moving in a forward direction, so that there is an alternating pressure in the forward chamber <NUM>.

Because the hammer <NUM> does not include an outer wear sleeve or cylinder, the piston itself will be exposed to wear from drill cuttings. However, since the hammer is disposable, the piston need only last long enough to drill a single hole. In addition, radial flushing ports <NUM> extend from the central bore <NUM> of the shaft to an outer surface of the shaft, allowing part of the exhaust fluid to exit between a forward end <NUM> of the piston <NUM> and the strike face <NUM> of the bit. This keeps drill cuttings away from the strike faces of the bit and the piston and prevents premature damage to the strike faces.

<FIG>, <FIG> illustrate a coupling arrangement for coupling a percussion bit to a hammer according to the present invention. Hammer <NUM> shown in <FIG>, <FIG> is similar in several respects to disposable hammer <NUM> shown in <FIG> but the coupling arrangement shown may also be applied to hammers <NUM>, <NUM> shown in <FIG>, as well as other hammers in accordance with the invention.

The shaft <NUM> of hammer <NUM> comprises a coupling element <NUM> at forward end <NUM> thereof. As shown in <FIG>, an outer diameter of the coupling element is greater than an outer diameter of a main body <NUM> of the shaft, so that the forward chamber is sealed by the coupling element and the piston. A portion <NUM> of the coupling element is formed with a square cross-section and a corresponding internal portion <NUM> of the bit <NUM> is formed with a square-shaped inner wall, such that, when the bit is assembled to the coupling element of the shaft, the portion <NUM> of the coupling element is received within the portion <NUM> of the bit, to allow rotational drive to be transmitted from the shaft to the bit. In other embodiments, the portion <NUM> of the coupling element may be formed with a hexagonal or octagonal cross-section and the internal portion of the bit may be correspondingly shaped. In further embodiments, axially-extending splines may be provided externally of the coupling element, engageable with corresponding splines provided internally of the bit, for transmission of rotational drive.

The coupling element <NUM> further comprises bit retaining means engageable with complementary bit retaining means on the bit <NUM> for longitudinal coupling of the bit to the hammer. In the embodiment shown in <FIG>, <FIG>, the bit retaining means comprises a first screw thread <NUM> formed externally of the coupling element <NUM> at a forward end <NUM> thereof. The complementary engagement means comprises a second screw thread <NUM> formed internally of the bit.

The bit is coupled to the hammer by threading the second screw thread <NUM> bit through the first screw thread <NUM> such that the first screw thread is forward of the second screw thread. This couples the bit to the coupling element in a longitudinal direction and retains the bit in the hammer, while allowing limited longitudinal movement of the bit. Next, the bit is rotated to line up the portion <NUM> of the bit with the square-shaped portion <NUM> of the coupling element, such that the portion <NUM> of the coupling element is received within portion <NUM> of the bit to engage the rotational coupling. The coupling element <NUM> is coupled to the main body <NUM> of the shaft by way of a screw-threaded connection.

A control valve <NUM> suitable for use in a hammer <NUM> according to the present invention is illustrated in <FIG>. The valve is particularly suitable for a disposable hammer according to the present invention, such as that shown in <FIG>. The valve <NUM> comprises a top or rear inlet port <NUM> and a top or rear outlet port <NUM>. The valve further comprises a bottom or forward inlet port <NUM> and a bottom or forward outlet port <NUM>. Also shown in <FIG> are the valve chamber <NUM>, the pilot chamber <NUM>, the pilot port <NUM>, the front control edge <NUM>, rear control edge <NUM> and the control valve cap <NUM>.

An example of the hammer cycle for a disposable hammer including the valve of <FIG> is illustrated in <FIG>. In <FIG>, the piston <NUM> is moving in an upward or rearward direction (to the left as shown in the drawings). The rear chamber <NUM> is connected to pressure fluid throughout the hammer cycle. The forward chamber <NUM> is connected to high pressure fluid through the valve chamber <NUM> and the rear chamber <NUM>, as shown by the arrows. The forward chamber has a bigger pressure area than the rear chamber, due to the increased internal diameter of the piston <NUM> so that the piston moves in a rearward direction. The valve pilot chamber <NUM> is pressurised through the front control edge <NUM> which has connected the pilot chamber to the rear chamber <NUM>. The pilot chamber has a bigger pressure area than the valve chamber. The flow connection between the forward chamber <NUM> and the shaft bore <NUM> is closed and the flow connection between the forward chamber and the valve chamber <NUM> is open. The valve chamber is continuously connected to the rear chamber <NUM> via the rear outlet port <NUM>.

In <FIG>, the piston <NUM> has reached a point where a flow connection has been opened from the pilot chamber <NUM> to the ambient pressure via the rear control edge <NUM>. The pressure in the pilot chamber will drop and there will be a net hydraulic force causing the valve <NUM> to switch.

In <FIG>, the valve <NUM> has switched. The valve has closed the forward inlet port <NUM> and opened the forward outlet port <NUM> so that exhaust water flows into the shaft bore <NUM>, as shown by the arrow. The hydraulic force reverses the direction of the piston <NUM> and drives it towards the drill bit <NUM>. The main portion of the exhaust water will flow through the shaft bore and the bit to exit at the bit face <NUM>, as shown by the arrows, to flush cuttings from the bit face. A small portion of the exhaust water will flow out through the radial holes or ports <NUM> located close to the bit strike face <NUM>, as shown by the arrows, to flush cuttings from the strike faces of the bit and the piston.

In <FIG>, the piston <NUM> is travelling towards the bit <NUM> (to the right as shown in the drawings). Just before the impact, the piston <NUM> will connect the pilot chamber <NUM> to the rear chamber <NUM> via the front control edge <NUM>. This causes the valve to switch just after the piston has impacted the drill bit. The cycle begins again as shown in <FIG>.

A hydraulic down-the-hole hammer <NUM> according to another embodiment of the invention is illustrated in <FIG> and <FIG>. The hammer shown is a low-cost disposable or single-use hammer. However, various aspects of this embodiment may also be applied to multiple-use hammers. As in the embodiments described above, the hammer comprises an elongate shaft <NUM> formed with a central bore <NUM>. A piston <NUM> also has a central bore <NUM> therethrough. The shaft is received within the piston bore such that the piston is slidably mounted for reciprocal movement on the shaft <NUM> and arranged to impact an annular shoulder <NUM> at a rear end <NUM> of a percussion bit <NUM>. Forward <NUM> and rear <NUM> drive chambers for the piston are disposed between the piston <NUM> and the shaft <NUM>. An annular shoulder <NUM> on the piston formed internally of the piston bore <NUM> separates the forward chamber <NUM> from the rear chamber <NUM>. In this embodiment, an internal diameter of the piston <NUM> to the rear of the shoulder <NUM> is smaller than the internal diameter of the piston forward of the shoulder, such that the forward chamber has a larger driving area than the rear chamber. The hammer also comprises a control valve <NUM> arranged within the central bore <NUM> of the shaft to control reciprocation of the piston.

The control valve <NUM> is illustrated in more detail in <FIG>. The valve <NUM> comprises a top or rear inlet port <NUM> and a top or rear outlet port <NUM>. The valve further comprises a bottom or forward inlet port <NUM> and a bottom or forward outlet port <NUM>. Also shown in <FIG> are the valve undercut <NUM>, the pilot chamber <NUM>, the pilot port <NUM>, the valve shoulder <NUM> and the valve high pressure chamber <NUM>.

An example of the hammer cycle for a disposable hammer including the valve of <FIG> and <FIG> is illustrated in <FIG>. In <FIG>, the piston <NUM> is moving in an upward or rearward direction (to the left as shown in the drawings). The rear chamber <NUM> is connected to pressure fluid throughout the hammer cycle. The forward chamber <NUM> is connected to high pressure fluid through the rear outlet port <NUM>, the pilot chamber <NUM>, the valve undercut <NUM> and the forward inlet port <NUM>, as shown by the arrows. The forward chamber has a bigger pressure area than the rear chamber, due to the increased internal diameter of the piston <NUM> so that the piston moves in a rearward direction. The valve pilot chamber <NUM> is pressurised through the pilot port <NUM> and/or the rear outlet port <NUM>. The pilot chamber <NUM> has a bigger pressure area than the valve high pressure chamber <NUM>, which is continuously connected to high pressure fluid. The flow connection between the forward chamber <NUM> and the shaft bore <NUM> is closed.

In <FIG>, the piston <NUM> has reached a point where the piston disconnects the rear outlet port <NUM> from the rear chamber <NUM>. The forward chamber <NUM> does not receive pressure fluid from the rear chamber and the piston will continue to move upwards due to its inertia. The pressure in the forward chamber and in the pilot chamber <NUM> will collapse and there will be a net hydraulic force causing the valve <NUM> to switch.

In <FIG>, the valve <NUM> has switched. The valve has closed the flow connection between the rear chamber <NUM> and the forward chamber <NUM> and opened the forward outlet port <NUM> so that exhaust water flows into the shaft bore <NUM>, as shown by the arrow. The hydraulic force reverses the direction of the piston <NUM> and drives it towards the drill bit <NUM>. The exhaust water will flow through the shaft bore and the bit to exit at the bit face <NUM>, as shown by the arrows, to flush cuttings from the bit face. Although not shown, radial flushing ports may also extend from the central bore of the shaft to an outer surface of the shaft, allowing part of the exhaust fluid to exit between a forward end of the piston and the strike face of the bit, as described above.

In <FIG>, the piston <NUM> is travelling towards the bit <NUM> (to the right as shown in the drawings). Just before the impact, the piston <NUM> will connect the pilot chamber <NUM> to the rear chamber <NUM> via the pilot port <NUM>. This causes the valve to switch just after the piston has impacted the drill bit. The cycle begins again as shown in <FIG>.

<FIG>, <FIG> and <FIG> illustrate a coupling arrangement for coupling a percussion bit to a hammer according to the present invention. Hammer <NUM> shown in <FIG>, <FIG> and <FIG> is similar in several respects to disposable hammer <NUM> shown in <FIG> and <FIG> but the coupling arrangement shown may also be applied to other hammers in accordance with the invention.

The shaft <NUM> of hammer <NUM> comprises a coupling assembly <NUM> at forward end <NUM> thereof. The coupling assembly comprises a seal flange <NUM> and a coupling element in the form of a chuck <NUM>. As shown in <FIG> and <FIG>, an outer diameter of the seal flange is greater than an outer diameter of a main body <NUM> of the shaft, so that the forward chamber is sealed by the seal flange and the piston <NUM>. The seal flange <NUM> is formed with connection means comprising an internal screw thread <NUM> at forward end thereof. Complementary connection means comprising an external screw thread <NUM> are provided on a rear portion of the chuck. Engagement means, in the form of axially extending splines <NUM> provided externally of the chuck, are engageable with complementary engagement means, in the form of corresponding splines <NUM> provided internally of the bit <NUM>, whereby rotational drive from the shaft may be transmitted to the bit. In other embodiments, the chuck may be formed with a square, hexagonal or octagonal cross-section and the internal portion of the bit may be correspondingly shaped, as described above.

The hammer <NUM> further comprises bit retaining means on the chuck engageable with complementary retaining means on the bit <NUM> for longitudinal coupling of the bit to the hammer. In the embodiment shown in <FIG>, <FIG> and <FIG>, the bit retaining means comprises a bit retaining ring <NUM>, comprising a plurality of part-annular sectors, and the complementary bit retaining means comprises a shoulder <NUM> formed internally of the bit at a rear end thereof.

The bit is coupled to the hammer by screwing the screw thread <NUM> on the chuck into the screw thread <NUM> on the seal flange <NUM>. The seal flange is also connected to the main body <NUM> of the shaft <NUM> by way of a screw-threaded connection. Sufficient space is left between a forward end <NUM> of the seal flange and an annular shoulder <NUM> on the chuck to allow the sectors of the bit retaining ring <NUM> to be inserted therebetween. The drill bit is then pushed over the chuck so that the splines <NUM> on the chuck engage with the complementary splines <NUM> on the drill bit. The screw-threaded connection between the chuck and the seal flange is then tightened by rotating the drill bit <NUM>. As the connection tightens, the annular shoulder <NUM> on the chuck is pushed towards the forward end <NUM> of the seal flange, thereby forcing the sectors of the bit retaining ring <NUM> outwards, as shown in <FIG>. The drill bit is retained in the hammer by engagement between the shoulder <NUM> and the bit retaining ring <NUM>. An assembly <NUM> for use in a system for installing a load-bearing element such as a subsea pile in a seabed is illustrated in <FIG>. The assembly comprises a disposable or sacrificial hydraulic down-the-hole hammer <NUM>. The hammer <NUM> is a water hammer similar to the hammer <NUM> shown in <FIG> and comprises a piston <NUM>, arranged to strike a bit <NUM>. The piston <NUM> is the outermost component of the hammer and the percussion bit <NUM> has a diameter D larger than that of the piston. The assembly further comprises a drill pipe <NUM> connected between a drill rig <NUM> and the hammer, the drill pipe having a central bore <NUM> therethrough.

The drill rig <NUM> is configured to provide rotation and feed force to the hammer during drilling of the hole. The drill rig is connected to the drill pipe <NUM> and hammer <NUM> and lowered to the seabed <NUM> with the hammer prior to drilling.

As shown in <FIG>, the system also comprises an umbilical <NUM>, wherein the hammer is connectable, via the drill pipe, to a supply of pressurised water and a supply of grout through the umbilical. The supply of water and the supply of grout are provided a sea surface level <NUM>. A water pump and a grout pump on a vessel <NUM> provide the supply of water and the supply of grout, respectively.

In use, the drill rig is coupled to the hammer via the drill pipe <NUM>, and the assembly is lowered to the seabed <NUM>. The hammer <NUM> is operated by supplying water thereto via the umbilical <NUM>, to drill a hole <NUM> in the seabed as shown in <FIG> and <FIG>. Rotation and feed force are provided by the drill rig. The operation of the hammer is as described above with reference to <FIG>. When the hole has reached the desired depth, as shown in <FIG>, the rotation and feed force are stopped and the supply of water to the hammer is stopped, for example, by disconnecting the umbilical from the water pump. As shown in <FIG>, a diameter of the drilled hole <NUM> is greater than a diameter of the piston <NUM> so that there exists an annular cavity <NUM> between the piston and a wall of the drilled hole.

Grout <NUM> is then supplied to the hammer via the umbilical, for example, by connecting the umbilical to the grout pump. The grout flows through the central bore <NUM> of the drill pipe and the hammer <NUM> and into the hole <NUM> through the bit <NUM>. Grout is pumped into the hole until the hole has been at least partially filled, as shown in <FIG>. The drill rig is disconnected from the hammer and returned to the surface. When the grout has cured, the hammer, drill pipe and drill pipe are bonded to the material of the seabed so that the hammer, drill pipe and grout form a subsea pile as shown in <FIG>.

An assembly <NUM> for use in a system for installing a subsea anchor on a seabed is illustrated in <FIG>. The assembly comprises an anchor frame or template <NUM>. In the embodiment shown, the anchor frame is generally triangular in shape, with a plurality of ribs <NUM> to enhance its structural integrity. In other embodiments, the anchor may be rectangular, or any other suitable shape. A mooring connection <NUM> is also provided on the anchor frame, to allow a mooring line to be connected thereto, for mooring of an offshore structure, such as a wind turbine.

The assembly further comprises drill rig <NUM> and three sacrificial down-the-hole hydraulic hammers <NUM> and corresponding drill rods or pipes <NUM>, each of which is connected to the anchor frame <NUM> through a connector <NUM>, in the form of a mounting sleeve or boss, provided on an outer edge of the frame <NUM>. Each hammer <NUM> is a water hammer similar to the hammer <NUM> shown in <FIG>. The drill rig <NUM> comprises three identical feed force and rotation systems <NUM>, so that the drill rig is configured to provide a rotation and feed force to each of the hammer <NUM>. In other embodiments, the system may comprise more or fewer hammers and the drill rig may comprise a corresponding number of feed force and rotation systems. As shown in <FIG>, the drill rig <NUM> is configured such that each of the hammer and drill pipe pairs is arranged at an acute angle to the seabed <NUM>.

Each hammer <NUM> and corresponding drill pipe <NUM> is connectable to a supply of working fluid for drilling a hole <NUM> of a desired depth in the seabed <NUM>, as shown in <FIG>. In the embodiment shown, the holes are drilled at an angle to the vertical to minimise bending or shear forces on the anchor. However, in other embodiments, the holes may be drilled vertically downwards into the seabed, or at an angle between <NUM> and <NUM> degrees to the seabed. The working fluid may be supplied from a rig or vessel at sea surface level as shown in <FIG>. Because the drill rig <NUM> comprises three separate feed force and rotations systems <NUM>, the holes <NUM> may be drilled simultaneously. Alternatively, the holes may be drilled in turn. As the hammers <NUM> are operated, each hammer <NUM> and drill pipe <NUM> passes through the corresponding connector <NUM>. As shown in <FIG> and <FIG>, when the holes have been drilled, an upper portion of each drill pipe <NUM> is retained within the corresponding connector <NUM>, to connect the anchor to the drill pipes. Once the holes have been drilled, each hammer is connected to a supply of grout while located in its respective hole to allow the hammer and the hole to be at least partially filled with grout. The grout may be supplied via the umbilical as shown in <FIG>.

Once the holes <NUM> have been filled with grout, the drill rig <NUM> is disconnected from the hammer <NUM> and returned to the surface, leaving the subsea anchor on the seabed as shown in <FIG> and <FIG>. Once the grout has cured, the subsea anchor including the anchor frame <NUM> is secured to the seabed by the hammers <NUM> and corresponding drill pipes <NUM> connected to the anchor frame via the connectors <NUM>. A nut or other fastener may be connected to the upper end <NUM> of each of the drill pipes to fasten the anchor frame to the subsea piles formed by the hammer and drill pipe pairs. Each of the hammer and drill pipe pairs is grouted in place in a respective hole in the seabed such that each hammer and drill pipe is bonded to the material of the seabed <NUM>, thereby securing the anchor in place.

The words "comprises/comprising" and the words "having/including" when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claim 1:
A hydraulic down-the-hole hammer (<NUM>) comprising:
an elongate shaft (<NUM>);
a piston (<NUM>) having a central bore (<NUM>) therethrough, the piston slidably mounted for reciprocal movement on the shaft and arranged to impact a percussion bit (<NUM>), wherein forward (<NUM>) and rear (<NUM>) drive chambers for the piston are disposed between the piston and the shaft and wherein the forward chamber is separated from the rear chamber by an annular shoulder (<NUM>) formed internally of the piston bore; and
a control valve (<NUM>) to control reciprocation of the piston, wherein the control valve is arranged within the central bore of the piston.