NZ576786A - Scallop dredge with tow point release to surface - Google Patents

Abstract

A scallop dredge is provided with top and bottom tow connections 55 and 53 to the main tow line 57. When both tow connections are connected to the main line the hydrofoil 15 of the dredge forces the dredge toward the bottom so as to dredge the scallops when the dredge is towed along the bottom 121 in a first direction. At the end of the scallop dredging tow the tow line 57 is allowed to go slack which has the effect of releasing the top tow connection 55 from the tow line 57 by tripping of the release mechanism 23 whilst the bottom tow connection 19 remains connected to the main tow line. When again the dredge is towed in the first direction the angle of attack of the hydrofoil 15 forces the dredge to the surface at which point a float 91 can be run down the main tow line toward the dredge to keep the dredge on the surface for collection.

Description

Patents Form # 5 NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION AFTER PROVISIONAL NO.: 576786 PRIORITY DATE : 07 May 2009 TITLE : Improvements relating to Dredges and Dredging I, MAIR, Peter Lawrence Address: 99 Brookby Road, Manurewa, Auckland, New Zealand, 2576 Nationality: A citizen of New Zealand do hereby declare the invention for which I pray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement: 204539NZ_Cap_20100728_1618_PBA.doc FEE CODE 1050 FIELD OF THE INVENTION This invention relates to a dredge, and in particular, but not exclusively to a dredge and related equipment, and a method of dredging, for gathering shellfish or molluscs such as 5 scallops.

BACKGROUND Shellfish or molluscs, and in particular scallops, are typically gathered using a dredge which is towed along the seabed and which gathers the shellfish from the seabed and collects them in a net or bag attached to the dredge. The dredge will typically include 10 tines which can penetrate a little into the seabed to help in dislodging and collecting the shellfish.

At the end of a dredging run, it is then necessary to raise the dredge to the surface of the water to retrieve the shellfish. This can be difficult due to the weight of the dredge and of the shellfish collected by it.

To work effectively, the dredge should penetrate consistently into the surface of the sea bed and not tend to ride over the humps and hollows that are typically found on a sea bed. If the dredge merely rides over the surface, many scallops, particularly the larger scallops which tend to lie in the hollows, can be missed.

In addition, scallop dredging is often carried out by people in relatively small pleasure 20 craft. A scallop dredge typically has a size in the region of 1.0 metre by 0.5 metres by 0.4 metres and includes tines which project from the dredge. Such an article is difficult to stow in a small boat and it can cause injury if a person bumps against it.

The task of deploying a scallop dredge, and of retrieving it after a dredging run can at times be difficult. The weight of the dredge when it is full can make it difficult to lift 25 back to the surface of the water. Dredges which can be towed to the surface can be more convenient to use, however some require complex manoeuvres of the boat before the dredge can be towed to the surface. 204539NZ_CAPSpec_Ji.il 10.doc/PA In this specification unless the contrary is expressly stated, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge; 5 or known to be relevant to an attempt to solve any problem with which this specification is concerned.

OBJECT It is therefore an object of the present invention to provide a dredge, or a method of dredging, which will at least go some way towards overcoming the above mentioned 10 problems, or at least provide the public with a useful choice.

STATEMENTS OF THE INVENTION Accordingly, in a first aspect, the invention may broadly be said to consist in a towable dredge having a hydrofoil, at least one upper tow connection point and at least one lower tow connection point, the dredge being configured such that when in use and being towed 15 from both the upper and the lower tow connection points the dredge can be orientated such that the hydrofoil has a negative, or downwards, angle of attack, and when the dredge is towed from only the lower tow connection point the dredge will be orientated such that the hydrofoil has a positive, or upwards, angle of attack.

Preferably the hydrofoil is a substantially flat plate.

Preferably the hydrofoil forms at least a part of a top of the dredge.

Preferably the hydrofoil produces a downwards force when the dredge is being towed through the water by the upper and lower connection points.

Preferably the hydrofoil produces an upwards force when the dredge is being towed through the water by the at least one lower connection point Preferably the dredge includes two lower tow connection points.

Preferably the dredge is adapted for collecting molluscs, and in particular, scallops. 204539NZ_CAPSpec_Jull0.doc/PA Prcfcrably a bottom part of the dredge is formed of an open construction through which water can pass with minimal resistance, for example a construction comprising a matrix of spaced apart wires or bars.

Preferably the dredge includes skids or skis adapted for travel across a sea or lake bed.

Preferably the dredge includes tines adapted to rake a sea or lake bed to dislodge molluscs and to direct the molluscs into the dredge.

Preferably the dredge includes a net adapted to contain molluscs that are collected by the dredge.

Preferably the dredge has a substantially rectangular profile including the hydrofoil 10 forming at least a part of the top, two sides and a bottom, each being pivotally connected to the other allowing the dredge to be folded down to reduce the overall volume of the dredge for storage purposes.

In a second aspect, the invention may broadly be said to consist in a release mechanism for connecting a first connecting line or fitting to a tow line and releasably connecting a 15 second connecting line or fitting to the tow line, the release mechanism having a keeper member which can move between a first position in which it is able to hold the second connecting line or fitting connected to the mechanism and a second position in which the second connecting line or fitting can be released from the release mechanism, the keeper member being biased towards the second position by a first biasing means, and the keeper 20 member can be selectively held in the first position by a latching means, the latching means being configured to release the keeper member if held in the first position in response to a change in the tension in the tow line.

Preferably the first connecting line or fitting and the second connecting line or fitting are lines or fittings of a dredge.

Preferably the release mechanism is configured such that tension in the tow line is able to hold the keeper in the first position. 204539NZ_CAPSpec_Jull0.doc/PA Preferably the latching means is configured to release the keeper member if held in the first position when the tension in the tow line exceeds the force being exerted by the first biasing means.

Preferably the second connecting line or fitting is only released from the release 5 mechanism after the tension in the tow line has first increased and then decreased.

Preferably the first biasing means is configured such that the keeper member will not move to the second position while the dredge is being towed.

Preferably the latching means is biased toward a latch released position by a second biasing means.

Preferably the latching means engages with the keeper when holding the keeper in the first position.

While the first and/or the second biasing means can include an elasticised member or a chamber adapted to hold a gas in compression, preferably the first and/or the second biasing means include a spring.

In a third aspect, the invention may broadly be said to consist in a dredging assembly incorporating a towable dredge substantially as specified herein and incorporating at least one release mechanism substantially as specified herein.

Preferably the dredging assembly further includes at least one floatation device which is connectable to a tow line suitable for towing the dredging assembly.

Preferably the floatation device is connectable to the tow line using a shackle which is adapted to slide in one direction only along the tow line.

Preferably the floatation device is collapsible for storage purposes.

In a fourth aspect, the invention may broadly be said to consist in a method of dredging including the steps of; ® attaching a first connecting line or fitting of a dredge substantially as described herein to a release mechanism substantially as described herein, 204539NZ_CAPSpec_Jull0.doc/PA • attaching a second connecting line or fitting line of the dredge to a releasable connection on the release mechanism, • placing the dredge into a body of water and towing the dredge using a tow line connecting the release mechanism to a powered water craft, ® finishing the tow and allowing the tow line to become slack allowing the release mechanism to release the second connecting line or fitting. • towing the dredge a second time to raise the dredge to the waters surface.

Preferably the method further includes a step of slidably attaching a flotation device to the tow line prior to beginning the second tow and raising the dredge to the waters surface.

Preferably the slidable attachment of the flotation device to the tow line allows the flotation device to slide along the tow line in one direction only, toward the release mechanism.

In a fifth aspect, the invention may broadly be said to consist in a method of dredging including the steps of; • Using a release mechanism to connect a dredge to a tow line, the release mechanism having a non-releasable connection point and a releasable connection point, and the release mechanism being configured to release a line or fitting from the releasable connection point when a reduction in tension in the tow line is detected by the release mechanism, ® attaching a first connecting line or fitting of the dredge to the non- releasable connection point of the release mechanism, ® attaching a second connecting line or fitting line of the dredge to the releasable connection point of the release mechanism, ® placing the dredge into a body of water and towing the dredge using the tow line, 204539NZ_CAPSpec_Jul 10.doc/PA • finishing the tow and allowing the tension in the tow line to reduce and become slack allowing the release mechanism to release the second connecting line or fitting. • towing the dredge a second time by the first connecting line only to raise 5 the dredge to the waters surface.

Preferably the method further includes a step of slidably attaching a flotation device to the tow line prior to beginning the second tow and raising the dredge to the waters surface.

Preferably the slidable attachment of the flotation device to the tow line allows the flotation device to slide along the tow line in one direction only, toward the release 10 mechanism.

The invention may also broadly be said to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of the parts, elements or features, and where specific integers are mentioned herein which have known equivalents, such 15 equivalents are incorporated herein as if they were individually set forth.

DESCRIPTION Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which: FIGURE 1 is a perspective view of a towable dredge, FIGURE 2 is a cross sectional view of a release mechanism for use with the dredge, FIGURE 3 is a front elevation view of a shackle for use with the dredge, FIGURE 3 A is a cross sectional view AA of the shackle in figure 3, FIGURE 4 is a first diagram showing the dredge in use and being initially deployed, 204539NZ_CAPSpecJul 10.doc/PA FIGURE 5 is a second diagram showing the dredge in use and being towed along the sea bed, and FIGURE 6 is a third diagram showing the dredge in use and being retrieved after a dredging operation.

With reference to figure 1, a main frame (11) of a towable dredge (13) is shown having a hydrofoil (15), an upper tow connection point (17) and two lower tow connection points (19). A net or bag (21) as shown in figures 4 to 6 can be attached to the rear of the main frame (11) to complete the dredge (13) and to collect items that are gathered by the frame (11). The dredge (13) shown is configured for collecting molluscs, in particular scallops, 10 from the sea bed.

The hydrofoil (15) is a substantially flat or slightly curved plate which in this example forms the top of the dredge (13). The hydrofoil (15) produces a downwards force when the dredge (13) is being towed through the water by the upper and lower connection points (17 and (19), and it produces an upwards force when the dredge (13) is being 15 towed through the water by only the lower connection points (19).

The dredge (13) is configured such that when it is in use and it is being towed from both the upper and the lower tow connection points, (17) and (19), the dredge (13) can be orientated such that the hydrofoil (15) has a negative, or downwards, angle of attack. And when the dredge (13) is towed from only the lower tow connection points (19) the 20 dredge is orientated such that the hydrofoil (15) has a positive, or upwards, angle of attack.

The negative, or downwards angle of attack is helpful in driving the dredge (13) toward the sea bed as it is being towed, and in keeping a downwards pressure on it while dredging along the sea bed.

The positive, or upwards, angle of attack is helpful when the dredging operation has been completed as it allows the dredge (13) be towed back up to the surface of the water. The change over from being towed from both the upper and the lower tow connection points, (17) and (19), with a downwards angle of attack, to being towed from only the lower tow 204539NZ_CAPSpec_Jul 10.doc/PA connection points (19), with an upwards angle of attack, is accomplished using a release mechanism (23) which is explained with reference to figure 2 below.

In the example shown, the dredge (13) includes two lower tow connection points (19). While it could have only one, two are considered advantageous as such a configuration 5 helps to keep the dredge (13) stable when being towed.

The bottom part (25) of the dredge (25) is formed of an open construction through which water can pass with minimal resistance. In this example the bottom part (25) is constructed as a matrix of spaced apart wires or bars (27). Each second bar (27) extends forward and is bent downwards to form tines (29). The spacing of the wires or bars (27) 10 is close enough to prevent scallops falling through it. Earlier attempts to produce a suitable dredge used a perforated plate to construct the bottom part (25) but it was found that this worked like a second hydrofoil which tended to produce lifting forces which were not desirable when deploying the dredge and when towing along the sea bed.

The dredge (13) also includes skids or skis (31) which are adapted to help the dredge (13) 15 to travel across the undulations of a sea or lake bed.

The tines (29) are adapted to rake the sea or lake bed to dislodge scallops and to direct them into the mouth (33) of the dredge (13). The mouth (33) is the opening between the forward end of the hydrofoil (15) and of the bottom part (25), and between the forward end of two side panels (35). The side panels (35) have a peripheral frame and wire mesh 20 panels. The skids (31) are attached to the bottom edge of the side panels (35).

The dredge (13) has a substantially rectangular profile when viewed from the front. The top comprises the flat panel of the hydrofoil (15), and there are two sides (35) and the bottom part (25). Each is pivotally connected to the other, allowing the dredge (13) to be folded down to reduce the overall volume of the dredge for storage purposes. The 25 hydrofoil or top (15) is held in place by two pins (37) which pass through two tabs (39), one of which is connected to the top of each side panel (35). The hydrofoil or top (15) has slots (40) through which the tabs (39) pass.

In this example, the dredge (13) is folded down using the following steps; 204539NZ_CAPSpec_Jull0.doc/PA • first releasing the two pins (37) which pass through the two tabs (39), ® pivoting the hydrofoil (15) upwards about an upper cross member (41) which lies along the aft top edge of the main frame (11), • when the top (15) has been pivoted upwards and clear of the tabs (39), the sides 5 (35) can each pivot outwardly about a substantially vertical axis at each aft outboard edge of the main frame (11), « pivoting the sides (35) outward a little releases a spigot (43) attached to each side panel (35) from a connection with each end of a cross tube (45) which extends laterally from one end of the bottom part (25) to the other, • the bottom part (25) is then free to pivot about a lower cross member (47) which lies along the bottom aft edge of the main frame (11), • with the bottom part (25) pivoted out of the way, the side panels (35) can then be pivoted toward each other and until they both lie in the same plane, • the top or hydrofoil (15) can then be pivoted about the upper cross member (41) 15 to lie against the two side panels (25), • then the bottom part (25) can be pivoted about the lower cross member (47) until it lies against the other side of the two side panels (35), and ® the net or bag (21) of the dredge (13) can be folded up and can lie between the two side panels (35) and the bottom part (25).

With reference to figure 2, the release mechanism (23) is now described. Figures 4 to 6 show where the release mechanism (23) is used in a dredging system (51). The dredging system (51) comprises a dredge (13) as described herein, a release mechanism (23) as described herein, a first connecting line or fitting (53), a second connecting line or fitting (55) and a tow line (57). The tow line (57) can be towed from a suitable powered water 25 craft (59). 204539NZ_CAPSpec_Jul 10.doc/PA The release mechanism (23) is for connecting the first connecting line (53) to the tow line (57), and for releasably connecting the second connecting line (55) to the tow line (57). The release mechanism (23) includes a keeper member (61) which can move between a first position (as shown) in which it is able to hold the second connecting line or fitting 5 (55) connected to the release mechanism (23) and a second position in which the second connecting line or fitting (55) can be released from the release mechanism (23).

The keeper member (61) is biased towards the second position by a first spring (63), and the keeper member (61) can be selectively held in the first position by a latching means (65). The latching means (65) in this example comprises a small knob (67) with an 10 internal thread which can be screwed onto the end of a small countersunk head machine screw (69). The latching means (65) is biased toward a latch released position by a second spring (71).

The latching means (65) engages with the keeper (61) when holding the keeper (61) in the first position. In this example, this is achieved by engaging an edge of the countersunk 15 head of the machine screw (69) into a suitably shaped recess (73) in the body of the keeper (61). The recess (73) is shaped to partially capture the countersunk head of the machine screw (69) and to prevent the latching means being moved away under the force of the second spring (71).

When in use, the tow line (57) is connected to an eye end (75) which is connected to the 20 forward end (77) of the keeper (61). The first connecting line (53) is connected to a hoop (79) which extends from an aft end (81) of a body (83) of the release mechanism (23). And the second connecting line (55) can be held captive within a releasable connection on the release mechanism (23). The releasable connection comprises a slot (85) and a pin (87) which extends from, and is a part of, the keeper member (61). The slot (85) is 25 formed within a housing (89) which extends from the body (83). The housing (89) partially houses the pin (87).

The release mechanism (23) can be armed for use by placing an end of the second connecting line (55) within the slot (85) while the keeper member (61) is in its second position, and then moving the keeper member (61) toward its first position (as shown) 30 against the force of the first spring (63). The second position of the keeper member (61) 204539NZ_CAPSpec_Jul 10.doc/PA is a position which is a little aft of the position shown in figure 2, and is when the pin (87) does not extend into the slot (85), that is, the end of the pin (87) is situated within the aft end of the housing (89).

The keeper member (61) can be held in the first position by the latching means (65). This 5 is achieved by pushing down on the knob (67), against the force of the second spring (71), to engage the head of the screw (69) in the recess (73) in the keeper member (61) while the keeper member is being held in the first position. By allowing the keeper member (61) to slide slightly toward the second position under the action of the first spring (63), the head of the screw (69) can be held captive within the recess (73) as shown. This holds 10 the latching means (65) in the latched position.

While the keeper member (61) is being held in the first position by the latching means (65), a change in the tension in the tow line (57) can be used to release the latching means (65) from the latched position. When the latching means (65) is released, the keeper member (61) can move toward the second position.

The release mechanism (23) is armed as described above just before dropping the dredging assembly (51) into the water. The release mechanism (23) is configured to release the latching means (65) when the dredge (13) is being towed and the tension in the tow line (57) increases and exceeds the force being exerted by the first spring (63). That is, when there is enough tension in the tow line (57), the keeper member (61) will be 20 pulled a little further toward the forward end (77) and the head of the countersunk screw (69) will be released from the recess (73). The second spring will move the latching means (65) up and away from the recess (73) to an unlatched position.

The keeper member (61) is not able to move to the second position while the tension remains in the tow line (57), that is, while the dredge assembly (51) is still being towed. 25 The tension in the tow line (57) is able to hold the keeper (61) in the first position during the tow against the force of the first spring (63). However, when the tow is completed, and the tension in the tow line (57) decreases or is eliminated, and the force of the first spring (63) causes the keeper member (61) to move to the second position. And then the second connecting line (55) is free to exit the slot (85). The aft face of the slot (85) is 204539NZ_CAPSpecJull0.doc/PA angled back to help to ensure that the second connecting line (55) comes free of the slot (85).

The first spring (63) must be carefully sized or configured so that the keeper member (61) will not move to the second position while the dredge assembly (51) is being towed.

This example of a release mechanism (23) uses two springs (63) and (71), however it is envisaged that in an alternative embodiment other biasing means, for example elasticised members or chambers adapted to hold a gas in compression could be substituted.

The dredging assembly (51) can further include at least one floatation device (91) which is connectable to the tow line (57). The floatation device (91) can be connected to the tow 10 line (57), near its connection to the powered watercraft, using a shackle (93) which is adapted to slide in one direction only along the tow line (57). A suitable shackle (93) for this purpose is described below with reference to figure 3 below.

The floatation device (91) can be connected to the tow line (57) using the shackle (93) at the end of a dredging tow. The floatation device (91) can help with the recovery of the 15 dredge (13) after a dredging tow and when it may be at least partly Ml of scallops. At the end of the tow, as described above, the release mechanism (23) can release the second connecting line (55) which then allows the dredge (13) to be towed using only the first connecting line (53) which is connected to the lower tow connection points (19).

Towing from the lower connection points (19) causes the dredge (13) to be orientated in 20 such a manner that the hydrofoil (15) is at a positive or upwards angle of attack. This means that the hydrofoil (15) now produces lift, as opposed to the downwards forces it produced during the initial tow when it had a downward or negative angle of attack. The lift produced by the hydrofoil (15) can be sufficient to cause the dredge (13) to lift to the surface of the water as it is being towed.

The floatation device (91) can slide aft along the tow line (57) and toward the dredge (13) as it rises up through the water. When the dredge (13) has risen to the surface, the floatation device (91) can hold it near the surface while the water craft or boat is turned around and manoeuvred back toward the dredge (13). 204539NZ_CAPSpec_Jul 10.doc/PA The floatation device (91) can be collapsible for storage purposes, for example being constructed of two ends and having a flexible bellows type construction which can be extended to increase the volume of the floatation device. A one way valve can be used to allow air to enter the flotation device (91) and to hold it inside.

Figure 3 shows a suitable rope clamp or shackle (93) for connecting the floatation device (91) to the tow line (57). The shackle (93) comprises a race track shaped ring (95) having a cross brace (97) spanning across the ring (95) and partly toward a top end (99) of the ring (95).

A gate member (101) is pivotally connected to the shackle (93) about the cross brace (97). 10 The free end of the gate member (101) can be serrated to help it grip a rope between its free end and a bottom end (103) of the shackle (93). The shackle (93) also includes a partial shroud (105) which extends about the bottom end (103) and provides an additional surface against which the shackle (93) can grip a rope.

The shackle (93) is also provided with a sliding gate assembly (107) which can be opened 15 to allow the shackle (93) to be fitted onto the tow line (57). The sliding gate assembly (107) includes a sliding sleeve (109), a spring (111), and a small handle (113). The sleeve (109) can be slid up one of the straight sections of the race track shaped ring (95) against the force of the spring (111) to allow the rope to pass through an opening (115) provided in the race track shaped ring (95). A pin (117) can be used to guide the sleeve (109) and 20 to prevent it rotating, to prevent the handle (113) fouling with the gate member (101).

As an alternative to the sliding gate assembly (107), a spring biased gate arrangement can be used to allow the shackle (93) to be fitted onto the tow line (57).

In use the shackle (93) is able to slide along the tow line (57) in the direction (119), but is not able to travel along the tow line (57) in the opposite direction since the gate member 25 (101) will jam the rope between its free end and the bottom end (103) of the race track shaped ring (95) and the shroud (105). This means that as long as the shackle (93) is installed on the tow line correctly, it is able to guide the floatation device (91) along the tow line (57) toward the dredge (13) and the release mechanism (23) while the dredge is being towed to the surface. But the gate member (101) will not allow the tow line (57) to 204539NZ_CAPSpec_Jul 10.doc/PA pull back through the shackle (93) and allow the dredge (13) to sink when the lifting tow has been completed.

Figures 4 to 6 illustrate a sequence of steps in a method of dredging using the dredge (13) and the release mechanism (23) as described herein, which includes the steps of; • attaching a first connecting line or fitting (53) of a dredge (13) substantially as described herein to a release mechanism (23) substantially as described herein, • attaching a second connecting line or fitting line (55) of the dredge (13) to a releasable connection on the release mechanism (23), • placing the dredge (13) into a body of water and towing the dredge (13) using a 10 tow line (57) connecting the release mechanism (23) to the boat or powered water craft (59), • finishing the tow and allowing the tow line (57) to become slack allowing the release mechanism (23) to release the second connecting line or fitting (55). • towing the dredge (13) a second time to raise the dredge (13) to the waters surface.

The method can further include a step of slidably attaching the flotation device (91) to the tow line (57) prior to beginning the second tow and raising the dredge (13) to the surface of the water.

The slidable attachment of the flotation device (91) to the tow line (57) can be an attachment using the shackle (93) as described herein. The shackle (93) allows the 20 flotation device (91) to slide along the tow line (57) in one direction only, toward the release mechanism (23). The flotation device (91) and the shackle (93) prevent the dredge (13) sinking down again after it has been raised.

Figure 4 shows the dredging assembly (51) being initially deployed. The dredge (13) is moving forward and is sinking under its own weight and under the action of the hydrofoil 25 (15) which at this stage has a negative, or downward angle of attack and produces downward forces as it is towed through the water. When the dredge (13) reaches the sea bed it will be dragged along the sea bed and carry out its dredging function while the 204539NZ_CAPSpecJull0.doc/PA hydrofoil (15) continues to produce downward forces helping the dredge (13) to remain positively held against the sea bed.

Figure 5 shows the dredging assembly (51) at the end of the first tow of its dredging operation. The dredge (13) is lying on the sea bed (121). The tow line (57) can now 5 become slack allowing the release mechanism (23) to release the second connecting line (55).

Figure 6 shows the dredging assembly (51) being towed back to the surface of the water. The dredge (13) is being towed from its lower tow connection points (19) only and the dredge (13) has orientated itself such that the hydrofoil (15) now has an upward, or 10 positive, angle of attack. The hydrofoil (15) now produces lift and causes the dredge (13) to glide to the surface of the water as it is towed forward. Before beginning this second tow, the floatation device (91) can be slidably attached to the tow line (57) using the shackle (93). During the second tow, and as the dredge (13) is gliding toward the surface, the floatation device (91) can slide toward the dredge (13) under the action of drag on the 15 floatation device (91) as it is towed through the water.

At the end of this second tow, the floatation device (91) can hold the dredge (13) near the surface of the water as the boat or watercraft (59) is positioned close to it. This reduces the amount of lifting that is required to recover the dredge (13).

VARIATIONS Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.

DEFINITIONS Throughout this specification the word "comprise" and variations of that word, such as 25 "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps. 204539NZ_CAPSpec._Jull0.doc/PA ADVANTAGES Thus it can be seen that at least the preferred form of the invention provides a dredge which utilises a hydrofoil to help maintain downward pressure whilst dredging, and which can use the same hydrofoil to assist in raising the dredge to the surface when the dredging 5 operation is completed. The configuration of the towing points on the dredge, and the release mechanism which can be used to disconnect an upper tow connection line when the dredging operation is completed, allows the dredge to be re-orientated to allow the hydrofoil to produce lifting forces.

The automatic lifting of the full dredge, combined with a floatation system that can be 10 launched from the towing vessel and which can run down the tow line, means that the dredge can be recovered with relative ease and without having to haul it up a long distance.

In addition, the dredge can be folded down to a convenient size, and without tines sticking out, for more convenient and safer storage inside a boat. 204539NZ_CAPSpecJull0.doc/PA Received at IPONZ on 25 October 2011

Claims (13)

1. A towable dredge having a hydrofoil, at least one upper tow connection point, at least one lower tow connection point and a release mechanism, the release mechanism being configured to allow a connection between a tow line of the towable dredge and the at least one upper tow connection point to be released, and the dredge is configured such that when in use and being towed in a first direction from both the upper and the lower tow connection points the dredge is orientated such that the hydrofoil has a negative, or downwards, angle of attack, and when the release mechanism has released the connection between a tow line of the towable dredge and the at least one upper tow connection point and the dredge is towed in the first direction from only the lower tow connection point or points the dredge is orientated such that the hydrofoil has a positive, or upwards, angle of attack.

2. A towable dredge as claimed in claim 1, wherein the hydrofoil is a substantially flat or slightly curved plate.

3. A towable dredge as claimed in claim 1 or claim 2, wherein the hydrofoil forms at least a part of a top of the dredge.

4. A towable dredge as claimed in any one of the preceding claims, wherein the dredge is adapted for collecting molluscs, and in particular, scallops.

5. A towable dredge as claimed in any one of the preceding claims, wherein a bottom part of the dredge is formed of an open construction through which water can pass with minimal resistance, for example a construction comprising a matrix of spaced apart wires or bars.

6. A towable dredge as claimed in any one of the preceding claims, wherein the dredge includes skids or skis adapted for travel across a sea or lake bed.

7. A towable dredge as claimed in any one of the preceding claims, wherein the dredge has a substantially rectangular profile including the hydrofoil forming at least a part of the top, two sides and a bottom, each being pivotally connected to 204539NZ RvsdClms 0ct2011 formal.doc/PA Received at IPONZ on 25 October 2011 - 19- the other allowing the dredge to be folded down to reduce the overall volume of the dredge for storage purposes.

8. A towable dredge as claimed in any one of the preceding claims, wherein the release mechanism has a keeper member which can move between a first position 5 in which the release mechanism is able to maintain the connection between the tow line and the upper tow connection point and a second position in which the connection between the tow line and the upper tow connection point can be released, the keeper member being biased towards the second position by a first biasing means, and the keeper member can be selectively held in the first position 10 by a latching means, the latching means being configured to release the keeper member if held in the first position in response to a change in the tension in the tow line.

9. A towable dredge substantially as described herein with reference to figures 1 and 4 to 6 of the accompanying drawings. 15 10. A method of dredging including the steps of; • Using a release mechanism to connect a dredge to a tow line, the release mechanism having a non-releasable connection point and a releasable connection point, and the release mechanism being configured to release a line or fitting from the releasable connection 20 point when a reduction in tension in the tow line is detected by the release mechanism, • attaching a first connecting line or fitting of the dredge to the non-releasable connection point of the release mechanism, • attaching a second connecting line or fitting line of the dredge to the 25 releasable connection point of the release mechanism, • placing the dredge into a body of water and towing the dredge in a first direction using the tow line, 204539NZ_RvsdClms_Oct2011_formal.doc/PA Received at IPONZ on 25 October 2011 -20- 5

10 • finishing the tow and allowing the tension in the tow line to reduce and become slack allowing the release mechanism to release the second connecting line or fitting. • towing the dredge in the first direction a second time by the first connecting line only to raise the dredge to the waters surface.

11. A method of dredging as claimed in claim 10, wherein the method further includes a step of slidably attaching a flotation device to the tow line prior to beginning the second tow and raising the dredge to the waters surface.

12. A method of dredging as claimed in claim 11, wherein the slidable attachment of the flotation device to the tow line allows the flotation device to slide along the tow line in one direction only, toward the release mechanism.

13. A method of dredging substantially as described herein with reference to any one of the accompanying drawings 15 PIPERS Attorneys for: MAIR, Peter Lawrence 204539NZ_RvsdClms_Oct20U_formal.doc/PA