This invention regards a method of attaching a subsea cutting apparatus. More particularly, it regards a method in which a cutting apparatus designed to cut an object is attached to the seabed. The invention also comprises a device for implementing the method.

Cutting of objects located under water can according to prior art be accomplished by e.g. sawing, grinding, clipping or burning .

The cutting operation is normally performed by placing a cutting apparatus at the cutting site by means of e.g. lifting equipment or a so-called ROV (Remote Operated Vehicle) . Then the cutting apparatus may optionally be connected to the object to be cut. It has proven to be rather difficult to achieve satisfactory attachment of a cutting apparatus by remote control, when using prior art.

For reasons of safety, the actual cutting operation is normally controlled from a location remote from the cutting site, preferably from the surface of the sea.

It is also known to place a cutting apparatus on the seabed during cutting operations. This may prove satisfactory when clipping an object, but as a rule it will not provide sufficient stability when cutting the object by means of sawing or grinding.

The object of the invention is to remedy or reduce at least one of the disadvantages of prior art.

The object is achieved in accordance with the invention, by the characteristics stated in the description below and in the following claims.

A framework structure is placed on or immediately above the seabed by the object to be cut. The framework structure is provided with a cutting head arranged to be displaced (advanced) in the direction of the object to be cut, in a manner that is known per se.

The cutting head may, in dependence of the cutting method em- ployed, comprise e.g. cutting tools that represent prior art per se, such as a diamond wire saw, a saw blade saw, a grinding rig in which is used an abrasive wheel or a fluid to which has been added an abrasive. Alternatively the cutting head may comprise torch equipment based on gas or electric- ity. It may also be appropriate to combine various cutting equipment .

The framework structure is provided with at least one fastener portion arranged to be coupled to an attachment projecting into the seabed.

Most preferably the attachment is brought to the seabed along with the cutting apparatus. When the cutting apparatus is in a planned position the attachment or attachments can be moved into the seabed. When attached to the seabed, the attachments are made to accommodate the forces transferred from the cutting head to the framework structure.

The attachment may be pre-mounted at the mounting site and may in addition to the attachment also comprise a coupling portion for coupling to the framework structure.

Advantageously the attachment is designed as a suction anchor or a ground screw. In special cases other solutions such as a pile or hooks may be appropriate.

The following describes a non-limiting example of a preferred method and embodiment illustrated in the accompanying drawings, in which:

Figure 1 is a plan view of a cutting apparatus placed in po- sition about an object to be cut;

Figure 2 is a side view la-la of figure 1;

Figure 3 is a side view Ib-Ib of figure 1;

Figure 4 shows the same as figure 1, but here the object has been partially cut;

Figure 5 shows a cutting apparatus equipped with ground screws ; and

Figure 6 shows a cutting apparatus equipped with piles.

In the drawings, reference number 1 denotes a cutting appara- tus comprising a framework structure 2 and a cutting head 4 displaceably coupled to the framework structure.

The framework structure 2 comprises two parallel spaced-apart frame members 6. The frame members 6 are assembled by means of a cross member 8 extending between the frame members 6 near one end of the frame members 6. The cross member 8 and the frame members 6 together form an open U-shape . Thus the framework structure 2 can be moved in across an object 10 to be cut, so that the object 10 will be between the frame members 6, see figure 1.

The frame members 6 each have a rail 12, which rails are mutually parallel. The rails 12 are a complementary fit to drive and running wheels (not shown) provided in the wheel- houses 16 of the cutting head 4.

The wheelhouses 16 are rigidly interconnected by a profile 18. The wheelhouses 16 also form the supports for the driving disk 20 and reversing disk 22, respectively, of the cutting head.

The driving disk 20 is connected to a driving motor 24. A sawing wire 26 preferably provided with diamond cutting means runs endlessly around the disks 20, 22.

The outside of the framework structure 2 has a number of fastener portions 28, here three, for coupling to respective attachments 30.

In this preferred embodiment the attachments 30 are suction anchors 32.

The required control and power connections to the cutting apparatus 1 are of a type that is known per se, and are not shown.

When an object 10 is to be cut the cutting apparatus 1 is placed on the seabed about the object 10. The suction anchors 30 are moved into the seabed 34 in a manner that is known per se, by removing the water present inside the suction anchor 30. This results in a negative pressure in the suction anchor 30, causing the suction anchor 30 to move into the seabed 34.

After the cutting apparatus 1 has been tied in to the seabed the driving motor 24 is started, thus causing the sawing wire 26 to rotate about the disks 20, 22. Then the cutting head 4 is advanced towards the object 10, whereby the sawing wire 26 cuts into the body of the object 10, see figure 4.

When the cutting has been completed the sawed-off part of the object 10 may be removed, whereupon the cutting apparatus 1 can be released from the seabed 34.

In an alternative embodiment, see figure 5, the cutting apparatus 1 is provided with ground screws 36. The ground screws are designed with a screw thread 38 and are arranged to be screwed into the seabed 34 by turning the ground screw 36

about its own longitudinal axis. The ground screw 36 extends rotatably through a through opening 40 in the fastener part 28.

In another embodiment the cutting apparatus 1 is provided with piles 42 extending through respective openings 40 and into the seabed 34, see figure 6.