Subsea device with vertical axis for removal of sediment, comprising a pump unit which supplies pressurized water to a nozzle assembly and nozzle assembly comprising a central nozzle. The nozzle assembly furthermore comprises at least two additional nozzles directed with an inclination in relation to the central nozzle and arranged angularly symmetric in relation to the vertical axis of the device.

BACKGROUND 
       [0001]    The disclosure relates to subsea devices, and particularly to a subsea device for removal of sediment. 
         [0002]    There is often a need for excavating masses at a seafloor, for example to level areas before installations of structures, trenching of ditches before deployment of pipes, uncovering of deployed pipes. The masses to be moved can vary from clay and silt to rocks. 
         [0003]    A number of devices for trenching sediment at the seafloor are known in the art, hereunder devices which make use of conventional centrifugal pumps as well as ejectors for establishing suction power. Known technology also encompass blowers which direct a powerful water-jet towards the seafloor in order to disintegrate sediment and blow them away. An example of the known technology in this field is WO 2008/065360 (Rotech Holdings Ltd.). 
         [0004]    The disadvantage with the prior art technology is that the masses are blown into a cloud that rapidly envelopes the blower, takes away all visibility and renders visually controlled work impossible. Furthermore it is a challenge that trenched masses fall back into the ditch/ hole and form layers of unstable sediment. 
       SUMMARY 
       [0005]    The disclosed embodiments allow masses to be blown farther away and out of for example a ditch line. The remaining seafloor remains as intact as possible and it is an object to maintain visibility so that the trenching can be handled in a controlled manner adjacent to vulnerable objects. The blower is smaller, lighter and more effective than blowers of prior art technology and manufactured largely from standard components. 
         [0006]    The disclosed embodiments render it possible to blow sediment away from the seafloor. The device renders it possible to move sediment farther away compared to what is possible with conventional blowers; the sediment can be removed in chosen and desired direction and with larger capacity than what has earlier been possible. At the same time the device allows visibility to a much larger extent than with conventional blowers. The disclosed device includes a housing comprising a pump device arranged to blow water in a mainly downwards direction, water inlet to allow water to enter the pump device, a nozzle assembly to discharge water directionally controlled out from the housing as well as a particular device for holding the device in a certain desired orientation during work operations. The device may also be denoted a “blower”. 
         [0007]    The device includes a unique nozzle assembly which has proved to place the device in a pocket empty of sand and sediment even under challenging work operations. Furthermore it is of importance that the device can be maintained in desired position at any time and independent of varying inflicted loads. By “angularly symmetric” about an axis is understood that the respective nozzles are arranged with constant angular distance so that the sum of the horizontal forces from the nozzles are zero. If there are only two inclined nozzles, they are arranged with a mutual angular distance of 180 degrees. If there are more than two nozzles, they can be arranged in pair, still with 180 degrees between each nozzle in each pair. Other configurations are also contemplated when more than two nozzles are employed, but balanced such that the force components in horizontal direction sum up to zero. 
         [0008]    With regard to the pump unit, it can be of any per se known type. 
         [0009]    The arrangement for holding the device in a certain, desired position can typically comprise two opposite thrusters that maintain the orientation of the blower. This is preferably achieved automatically based on signals from an integrated gyro unit. The arrangement for holding the device in a certain desired position can also be an eccentric anchoring or suspension that prevents the device from rotating. Alternatively adjustable flaps or rudders may be used on the water jets from the main nozzles. In the case that the blower has just one single nozzle, the directionally controlling unit may typically be a wire suspended from a boat, barge, or other stationary or movable object. 
         [0010]    The pump device suitable for creating the downward oriented water jet that can erode the sediment may typically comprise one or more thrusters (propels) that create a water jet downwards and out from the nozzles. 
         [0011]    The nozzle assembly comprises two or more nozzles that are arranged with a downward inclination and in the case where there is no external bottom anchoring, to opposite sides. 
         [0012]    Typically one nozzle will point downwards and two nozzles will be downward inclined, but it is also contemplated that a number of nozzles can be arranged with varying orientations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1A  is a side sectional view of a blower according to an embodiment of the disclosed subsea device. 
           [0014]      FIG. 1B  is a top view of the blower shown in  FIG. 1A . 
           [0015]      FIG. 2  is a side sectional view of a blower according to another embodiment of the disclosure. 
           [0016]      FIG. 3  is a schematic depiction of operation of the blower shown in  FIGS. 1A and 1B . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Reference is now made to  FIG. 1A . The disclosed subsea device can generally be seen as divided into three sections or floors where the top section is given reference numeral  20 , middle section  30  and bottom section  40 . 
         [0018]    Top section  20  can be denoted a directionally controlling unit which controls and limits rotation around the vertical axis  11 . This unit typically comprises two thrusters  21 , one at each side, but may also be eccentrically connected by a wire that holds back any rotation. 
         [0019]    The middle section  30  can also be denoted a pump unit and comprises water inlet  31 , at least one thruster or propel  32  (two shown in  FIG. 1A ) powered by a motor  33 . The pump unit  30  is arranged to suck water in through the water inlets  31  and to move it vertically downwards to bottom section which is the nozzle assembly  40  of the blower  10 . 
         [0020]    The bottom section or the nozzle assembly  40  of the blower is shown in  FIG. 1A  comprising a central nozzle  41  arranged to direct water substantially vertically downwards with a force sufficient to disintegrate/erode more or less solid masses at the seafloor. In addition the blower has inclined nozzles  42  arranged symmetrically around the vertical axis  11  through the blower  10 . When only two nozzles  42  are arranged mutually symmetrically around a common vertical axis, it means that their horizontal components are directed oppositely in relation to one another and that their angle in relation to the vertical axis is the same. For instance both nozzles can be arranged with an angle deviating 20 degrees from the axis, 25 degrees from the axis, 30 degrees from the axis, or other chosen, common angle for both the two nozzles. 
         [0021]    These nozzles contributes to blow disintegrated material much farther away from the blower compared to what the central nozzle  41  is capable of alone, and these nozzles  42  also contribute to holding the space around the blower free from sediment, so that the operator has good visibility and so that water sucked into the blower does not become severely contaminated. Since the side nozzles come in pairs, the blower maintains a neutral position in the water, since the horizontal forces are nulled out.  FIG. 1B  shows the blower seen from straight above, where the two horizontal thrusters  21  (one at each side) control or limit the rotation of the blower around its vertical axis, or simultaneously or separately are used to move the blower along a line parallel with the thruster axis. Typically it is desirable at the thrusters ensure that the blower's orientation is held stationary, without rotation. The nozzles  41  and  42  (two), a number of three in total, are shown with dotted lines in  FIG. 1B . 
         [0022]      FIG. 2A  shows a slightly different embodiment from that shown in  FIGS. 1A and 1B . The only difference is that there is an extra set of side nozzles  43  which has a direction a little closer to the horizontal line than the side nozzles  42 . This embodiment thus can create an even larger horizontal movement of sediment, but is otherwise equivalent with the embodiment shown in  FIGS. 1A and 1B . Also other nozzle configurations having a substantially vertical central nozzle and a number of inclined nozzles arranged in pair or rotationally symmetrically around the blower's vertical axis are contemplated. 
         [0023]      FIG. 2B  shows a top view of the blower from  FIG. 2A  in principally the same manner as  FIG. 1B  does for the variant according to  FIG. 1A . The dotted lines show the nozzle assembly comprising the nozzles  41 ,  42  (two) and  43  (two), a total of five nozzles. 
         [0024]      FIG. 3  shows the blower suspended by a wire  51  or the like from a crane  52  arranged on a barge or boat  53 . It should be emphasized, however, that the suspensions, cranes or the like do not form part of the inventive aspect of the subsea device and can have entirely different forms than those shown. In some cases a rigid, jointed suspension may be used, thus eliminating the need for stabilizing thrusters present. The disclosed device can advantageously be provided with sonar, echo- sounder or the like (not shown) to monitor the distance to the seafloor and to subsea installations. 
         [0025]    It can furthermore be provided with gyro (not shown) which in cooperation with the thrusters  21  automatically can control and limit any rotation about the vertical axis.