A remotely operated underwater vehicle

Abstract

A remotely operated underwater vehicle (ROV) for close range visual inspection of a surface by means of a camera array (14). The ROV comprising a number of buoyancy elements (50, 52) and a number of components including a number of at least six propulsion devices (12) for maneuvering the remotely operated underwater vehicle in a three-dimensional space. The number of propulsion devices may be arranged for generating thrust when maneuvering the remotely operated underwater vehicle in a substantially pure translational motion or a substantially pure rotational motion.

Description

[0001] A remotely operated underwater vehicle

[0002] DESCRIPTION

[0003] The present disclosure is directed to a remotely operated underwater vehicle (ROV), specifically to a survey or inspection ROV capable of close-range visual inspection of a surface such as a port wall, harbor structure, or any other water-based port infrastructure or offshore infrastructure or a ship hull and hull and niche areas such as propellers or anchor. By inspecting the surface, issues such as corrosion, fouling, or damage may be detected.

[0004] The ROV uses thrusters / propulsive devices such as waterjets or propellers controlled by a controller for maneuvering the ROV. However, the propulsive devices generate jets of water, which may stir up sediment causing a disturbance of the inspection. The jets of water may also cross each other which may increase the sediment stirring - it will also make controlling the ROV harder, as turbulence and other non-linearities will be created.

[0005] Conventionally, underwater visual inspection is done with diverse or remotely operated underwater vehicles. Navigation underwater is particularly difficult due to the lack of GPS and limited visibility due to sediment, particles, bubbles, and marine life.

[0006] Sonars or sound-based navigation systems can be deployed, but due to the complex geometries in harbors and near underwater structures, and the resulting complex echoes created, it can be very hard to get a good quality localization out of these technologies in all conditions.

[0007] So, the very nature of the visual inspections in the bad visibility conditions requires the robot to get very close to the object being inspected.

[0008] Underwater vehicles / submersible vehicles are generally equipped with thrusters / propel- lers, which provide means of moving the vehicle by creating jets of water and using the reaction force of Newton’s laws to provide an equal and opposite force on the vehicle. Water is pushed in one direction; the vehicle is pushed in the other direction. For closerange visual inspection, this can be problematic, as the water jets might disturb sediments on the surface that is being inspected, which will reduce visibility in the water, and therefore limit the quality of the inspection. In some environments, this can get to the point where there is no longer any visibility in the water.

[0009] Some underwater vehicles are designed with a clear direction of “up” and “down”. This is the case for most manned underwater vehicles (submarines), one obvious reason relates to the comfort of the crew. But for ROVs and other unmanned underwater vehicles, it can be advantageous if they can freely move in all six degrees of freedom (3 rotation and 3 translation directions), to better get through environmental obstacles, or inspect hard-to-get-to surfaces or points.

[0010] It is advantageous for underwater vehicles to minimize the power of water jets, and at the same time have full six degrees of freedom movement capabilities. This disclosure describes a way of achieving this, by using a carefully designed thruster layout, combined with a robot where the center of gravity is close to the center of buoyancy.

[0011] By using more than the minimally required number of thrusters for the vehicle (more than six), a thruster configuration can be designed so that all thrusters are always active for realizing the desired motion of the vehicle. This has the added effect that the total thrust is always distributed among all thrusters, which limits the power of individual water jets. This again reduces the disturbance of sediments on the inspected surface, which again leads to less visibility deterioration and therefore improved visual inspection results.

[0012] A first aspect of the present disclosure is:

[0013] A remotely operated underwater vehicle for close range visual inspection of a (underwater) surface, said remotely operated underwater vehicle comprising:

[0014] - a camera array including a pair of cameras facing said surface for capturing images of said surface,

[0015] - a plurality of propulsion devices for maneuvering said remotely operated underwater vehicle in a three-dimensional space, and

[0016] - a controller for controlling said plurality of propulsion devices. The controller and the plurality of propulsion devices may be arranged for generating thrust from a number of at least four propulsion devices for maneuvering said remotely operated underwater vehicle in a substantially pure translational motion substantially parallel to said surface for reducing sediment stirring during said close range visual inspection.

[0017] The surface to be inspected is not necessarily planar, e.g. it may comprise harbor poles or holes. Thus, with parallel is meant that the ROV tries to maintain an average distance to the surface as it moves along the surface, despite any protrusions and indentions and other irregularities the surface might have - like a satellite in a fixed orbit. It could be contemplated that a plane is defined, and this plane is located at an average distance with respect to protrusions and indentations or other irregularities and the ROV maintains a fixed distance to that plane.

[0018] The ROV may also comprise one or two cameras for navigation.

[0019] The number of propulsion device may be at least 5, or 6 or 7 or 8 propulsion devices.

[0020] The pair of cameras may have a substantially fixed distance to said surface during said substantially pure translational motion.

[0021] Each active propulsion device is arranged for generating a jet of water in a direction not crossing a direction of a jet of water generated by another active propulsion device.

[0022] It is desired that the ROV is maintained at a substantially fixed distance to the surface to be inspected. This distance may be in the range 0.1 m to 1.5 m such as 0.2 m - depending on the visibility under water and how easy it is to maneuver the ROV in the sea. The distance may off course vary due to for example currents. It may vary with up to 50 % of the desired fixed distance.

[0023] In the following, specific examples according to aspects of the present disclosure will be explained in more detail with reference to the accompanying drawings. The present disclosure may, however, be embodied in different forms than depicted below, and should not be construed as limited to any examples set forth herein. Rather, any examples are provided so that the disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements throughout. Like elements will, thus, not be described in detail with respect to the description of each figure.

[0024] Fig. 1 illustrates a perspective view of a remotely operated underwater vehicle (ROV).

[0025] The ROV is illustrated in an upright position, e.g. it has a longitudinal extent in a vertical direction during intended operational use - the extent of the ROV in a vertical direction is greater than its extent in a horizontal plane.

[0026] Other geometries may be contemplated - for example that the longitudinal extent of the ROV is in a horizontal plane, or that the ROV defines a cube, e.g. all sides of the ROV having equal length.

[0027] The ROV has a handle 52 at the top.

[0028] It is advantageous if the longitudinal extent is in a plane parallel to the surface 10 during inspection (surface shown in fig. 3), because a separation of the cameras may be achieved, e.g. two front facing cameras may have a distance to each other of at least 25 % such as 50 % of the longitudinal extent of the ROV.

[0029] Specifically, the height / longitudinal extent may be 985 mm. The length / depth may be 227 mm, and the width may be 375 mm.

[0030] The ROV illustrated in fig. 1 comprises 8 cameras including a first camera 14 for capturing images of the surface (not shown).

[0031] Six of the cameras are part of a camera array arranged at the front of the ROV, e.g. the side of the ROV facing the surface during inspection. The array comprises a pair of cameras at the center of the ROV (such as a stereo camera), a camera at the top / prox- imal end of the ROV, a camera between the top camera and the pair of cameras, a camera at the bottom / distal end (opposite the top), and a camera between the bottom camera and the pair of cameras.

[0032] The top camera and bottom camera may be inclined, e.g. facing upwards at an angle (for the top camera) and facing downwards at an angle (for the bottom camera). The top of the ROV is the part that is closest to the water surface - if the ROV is used in an upright position.

[0033] The two remaining cameras are arranged facing to the left and right of the ROV respectively for using these cameras for navigation - they may also capture images of the surface in some situations.

[0034] The ROV may comprise 8 propulsive devices / thrusters including a first thruster 12 for maneuvering the ROV, and a controller 18 for controlling the ROV as well as one or more battery packs including a first battery pack 20 for providing power to the ROV.

[0035] Each thruster may be static, e.g. it is stationary at a fixed position and does not rotate.

[0036] The ROV may also have a fewer number of thrusters such as 6 or 7 thrusters or a larger number of thrusters such as 9 or 10 thrusters.

[0037] The controller may be a PIC microcontroller for example. Each thruster comprises a driver motor (not shown) for driving each propulsive device, e.g. typically the driving motor is connected to a propeller via a shaft for converting rotation into thrust. Each driver motor being controlled by the controller.

[0038] The ROV comprises a plurality of lights including a first light 16 for illuminating the surface.

[0039] Fig. 2 shows a front view of the ROV with only the thrusters being visible.

[0040] The thrusters are arranged such that the ROV has six degrees of freedom including three translational degrees of freedom and three rotational degrees of freedom. Each degree of freedom is used to define the position of the ROV, e.g. where it is and what angle it has.

[0041] In an (rectangular) xyz coordinate system, the six degrees of freedom may be represented by the unit vectors x,y, z, rx,fy,fzwhere the last three refers to rotation / angle around the three axes (xyz), e.g. three translational unit vectors and three rotational unit vectors. The six unit vectors are orthogonal to each other, e.g. having no projection on / component of another unit vector. Any displacement d of a point of the ROV may be written as a weighted sum of these unit vectors: d = d x + d2y + d3z + dyrx+

[0042] The z axis is parallel to the longitudinal axis of the ROV during intended use. However, the ROV may also be configured such that the y axis is parallel to the longitudinal axis of the ROV during use.

[0043] For the ROV, the x axis may be parallel to the normal of the surface to be inspected - assuming the surface is vertical plane. The z axis is vertical, and the y axis is orthogonal to the x and z axis.

[0044] These six degrees of freedom are typically called walking or surging, strafing or swaying, elevating or heaving, roll rotation, pitch rotation, and yaw rotation.

[0045] Thus, the ROV can be displaced in six independent ways, e.g. the weights dtmay be zero for all degrees of freedom except one, e.g. the ROV may experience a displacement defined by a displacement vector comprising a single unit vector, such as mov- ing / surging towards the surface to be inspected without having any swaying, heaving, roll, pitch or yaw.

[0046] Thus, each thruster has a configuration (unit) vector (defined by the orientation and location of the thruster) and each thruster is controlled such that a rotational motion may be generated for each rotational degree of freedom without generating a translational motion during the rotational motion (or without generating any other rotational motion). Or vice versa, a translational motion may be generated for each translational degree of freedom without generating a rotational motion during the translational motion (or without generating any other translational motion).

[0047] A displacement defined by a rotation only comprising a rotational unit vector and not any translational unit vector is said to be a pure rotational motion. For such a motion all points at the same radius from the center of rotation have the same velocity during the motion.

[0048] A displacement defined by a translational motion only comprising translational unit vectors and not any rotational unit vector is said to be a pure translational motion. For such a motion, every point in the ROV experiences the same velocity during the motion. In praxis, it may be difficult to achieve either of such pure motions. It could be that the same velocity cannot be achieved, but that there is a difference in velocity for two points in the ROV - this difference not being greater than 10 %, e.g. there may be a minor translational motion during a rotation or a minor rotation during a translational motion.

[0049] The control signal q for each thruster may be defined by a linear mapping f of the desired displacement d. The linear mapping is defined by the configuration matrix comprising the configuration vector for each thruster, e.g. the inverse of the configuration matrix multiplied with the displacement vector. Below is an example of the equation and a specific configuration vector:

[0050] -1

[0051] -0.13-0.22 0.22 0.13 0.13 0.22 -0.22-0.13- rx- -0.15 0.24 -0.24 0.15 0.15 -0.24 0.24 -0.15ry 0.05 -0.05-0.05 0.05 0.05 -0.05-0.05 0.05rz 0.71 -0.71 0.71 -0.71 0.71 -0.71 0.71 -0.71 X

[0052] -0.68-0.68 0.68 0.68 -0.68-0.68 0.68 0.68 y —0.17—0.17—0.17—0.17 0.17 0.17 0.17 0.17 - -z -

[0053] It is desirable that the thrusters are arranged and controlled (by the controller) in order to distribute the thrust over as many thrusters as possible - for displacing as much water as possible with as little thrust as possible in order to reduce sediment stirring. Turning on a single thruster would mean that the thruster would have to output more power, and the jet of water generated by that thruster would be more powerful than if several thrusters were used for the same motion.

[0054] For a motion along the surface to be inspected, the above specific configuration results in a thrust from each of the eight thrusters.

[0055] More thrusters could be added to the ROV for distributing the thrust even more, but the ROV then gains weight.

[0056] If there are more than eight thrusters one of the thrusters could be idle, i.e. 8 out of 9 (=89 %) thrusters generates thrust. In general, it is desirable that at least six of the thrusters generate thrust for a maneuver, e.g. thrust that contributes to the motion and not counteracts the motion (thrust that opposes the desired motion), but it depends on how many degrees of freedom are desired and how much thrust each thruster should generate (for avoiding stirring up too much sediment). That is the linear mapping may be a 6x6 matrix.

[0057] The ROV may comprise a memory where this mapping is stored.

[0058] Thus, all elements of the thrust control signal vector C should be none zero when the displacement is a pure translational motion such as d = (0,0, 0,0, 1,0) when the ROV is to move sideways along the surface.

[0059] For a displacement vector comprising both rotational and translational motion, the thrust control signal vector may have elements that are zero.

[0060] As can be seen in fig. 2, the thrusters are arranged in two groups. A first group which may include half of the thrusters are at the top of the ROV, while a second group which may include the remaining thrusters are at the bottom of the ROV.

[0061] The thrusters are arranged in pairs, e.g. each group has a thruster with a unit force vector that is inverse to a unit force vector of a thruster in the other group, e.g. uft= -ufj where i refers to the one group and j refers to the other group.

[0062] The unit force vector refers to the direction of a force / thrust generated by a thruster.

[0063] Thus, the two thrusters of a pair of thrusters are arranged symmetric around the center of gravity (mirror symmetric) - the coordinates of the one are the opposite of the coordinates of the other: = -(x^y^ Zj and facing in opposite directions - where the center of gravity constitutes the origin of the xyz axes.

[0064] As can be seen in fig. 2, the thrusters in the top group are facing upwards (z-component for the unit force vector greater than zero) and the thrusters in the bottom group are facing downwards (z-component for the unit force vector less than zero) - when the ROV is in its intended position. Half of the thrusters may be arranged along a vertical line adjacent the right side of the ROV and the other half of the thrusters may be arranged along a vertical line adjacent the left side of the ROV.

[0065] Fig. 3 shows a side view of the thrusters of the ROV.

[0066] It can be seen that the thrusters are arranged two by two on top of each other, e.g. the thrusters are offset from each other along the longitudinal axis of the ROV. For example, in the bottom group there are two bottom thrusters closer to the bottom of the ROV than the other thrusters in the bottom group. Similarly, in the top group there are two top thrusters closer to the top of the ROV than the other thrusters in the top group.

[0067] The two bottom thrusters have a distance to each other, e.g. each is closer to the side of the ROV than to the center of the ROV. The same goes for the other two thrusters in the bottom group of thrusters.

[0068] Similarly, the two top thrusters have a distance to each other, e.g. each is closer to the side of the ROV than to the center of the ROV. The same goes for the other two thrusters in the top group of thrusters.

[0069] The thrusters at the right-hand side of the ROV has unit force vectors with a component facing to the right of the ROV.

[0070] Similarly, the thrusters at the left-hand side of the ROV has unit force vectors with a component facing to the left of the ROV.

[0071] Fig. 4 shows a top view of the thrusters of the ROV.

[0072] One of the two top thrusters has a unit force vector with a component facing to the front of the ROV, while the other has a unit force vector with a component facing to the back of the ROV. This is similar for the other two thrusters in the top group, but the direction may be interchanged, e.g. the thruster below the thruster with the front facing unit force vector may have a back facing unit vector.

[0073] Thus, for each group of thrusters, there is a unit force vector towards a corner of a square surrounding the group (may be called diamond pattern arrangement of a group of thrusters), e.g. when projected on a horizontal plane the thrusters of a group has unit force vector in four directions with an angle of about 90 degrees between them.

[0074] In this way, the thrusters are arranged such that the jets of water coming from the thrusters do not cross each other - as may be recalled the thrusters of each group has a positive and negative vertical component, which ensures the jets from two groups also do not cross each other.

[0075] Said in other words, the number of active propulsion devices during a maneuver are arranged (location and direction wise) such that each active propulsion device generates a jet of water in a direction not crossing a direction of a jet of water generated by another propulsion device.

[0076] A thruster is said to be active when it generates thrust - and contributes to the desired maneuver, and not counteracting it.

[0077] As seen in the drawings, each thruster has a unit force vector (the orientation / direction of the thruster) with a non-zero component for each dimension e.g. ux,uy,uz#= 0.

[0078] The unit force vectors for the thrusters may be chosen freely as long as the above conditions are fulfilled, e.g. non zero component for each dimension and for each unit force vector there is an inverse unit force vector and all thrusters are to contribute to the motion. From these conditions, a mapping function may be found for mapping a desired motion to control signals for the thrusters.

[0079] Fig. 5 shows a perspective view of the frame of the ROV.

[0080] The ROV comprises an open frame / chassis, e.g. the frame is open in the sense that water may flow through it. The intention is that the ROV is to have a hydrodynamic that is not limiting to the manoeuvrability, e.g. avoiding large surfaces that may be a disadvantage to good manoeuvrability.

[0081] The frame supports the components of the ROV such as buoyancy components and electric components. For the illustrated ROV, it is contemplated that the frame constitutes a buoyancy component, e.g. the frame may be hollow and filled with air such that the frame is less dense than the water it displaces causing a buoyant force. The frame may be configured such that the center of buoyancy is proximate or coincides with the center of gravity of the ROV - or at least as close as possible. For example, the distance between the center of gravity and the center of buoyancy may be less than 10 % of the longitudinal extent of the ROV.

[0082] The center of gravity is defined by the frame and the components supported by the frame, e.g. the frame provides buoyancy, but it also has a mass acted on by gravity, e.g. the geometry and mass of the frame together with the mass and location of the components define the center of gravity.

[0083] With the two centers coinciding, the ROV is neutrally buoyant in the water.

[0084] The frame comprises three oval shaped loops 50a, 50b, 50c connected to each other at the top and bottom. Two of the loops 50b, 50c are in planes parallel to each other, e.g. have identical cross sections in parallel planes. The third oval shaped loop 50a is in a plane orthogonal to these planes (cross sections orthogonal to the two parallel cross section). The third loop spans a larger area than the other two.

[0085] A handle 52 is provided at the top of the frame. The handle is connected to the frame and may also be made of hollow profiles.

[0086] The frame may be made of a plurality of hollow profiles / tubes made of aluminium for example. Each tube may have a round or rectangular cross section.

[0087] Now follows a set of items, which constitute aspects of the present disclosure which may be considered independently patentable and as such the following sets form basis for possible future sets of claims:

[0088] 1 . A remotely operated underwater vehicle for close range visual inspection of a surface, said remotely operated underwater vehicle comprising:

[0089] - a camera array including a pair of cameras facing said surface for capturing images of said surface, - a plurality of propulsion devices for maneuvering said remotely operated underwater vehicle in a three-dimensional space, and

[0090] - a controller for controlling said plurality of propulsion devices.

[0091] 2. The remotely operated underwater vehicle according to any of the preceding items, said controller and said plurality of propulsion devices arranged for generating thrust from a number of at least four propulsion devices for maneuvering said remotely operated underwater vehicle in a substantially pure translational motion substantially parallel to said surface for reducing sediment stirring during said close range visual inspection.

[0092] 3. The remotely operated underwater vehicle according to any of the preceding items, said number comprising at least 5, or 6 or 7 or 8 propulsion devices.

[0093] 4. The remotely operated underwater vehicle according to any of the preceding items, said pair of cameras having a substantially fixed distance to said surface during said substantially pure translational motion.

[0094] 5. The remotely operated underwater vehicle according to any of the preceding items, each active propulsion device arranged for generating a jet of water in a direction not crossing a direction of a jet of water generated by another active propulsion device.

[0095] 6. The remotely operated underwater vehicle according to any of the preceding items, said controller and said plurality of propulsion devices arranged such that said remotely operated underwater vehicle having six degrees of freedom.

[0096] 7. The remotely operated underwater vehicle according to any of the preceding items, said six degrees of freedom including three translational degrees of freedom and three rotational degrees of freedom.

[0097] 8. The remotely operated underwater vehicle according to any of the preceding items, said controller and said plurality of propulsion devices arranged for generating a rotational motion for each rotational degree of freedom without generating a translational motion during said rotational motion or for generating a translational motion for each translational degree of freedom without generating a rotational motion during said translational motion. 9. The remotely operated underwater vehicle according to any of the preceding items, said percentage of said plurality of propulsion devices arranged such that each propulsion device generates a unit force vector having a non-zero projection on all of said three translational degrees of freedom.

[0098] 10. The remotely operated underwater vehicle according to any of the preceding items, said percentage of said plurality of propulsion devices arranged such that each propulsion device generating a unit force vector having a non-zero projection on all of said three rotational degrees of freedom.

[0099] 11 . The remotely operated underwater vehicle according to any of the preceding items, said three-dimensional space being spanned by three perpendicular axes.

[0100] 12. The remotely operated underwater vehicle according to any of the preceding items, every point in said remotely operated underwater vehicle experiencing the same velocity during said pure translational motion.

[0101] 13. The remotely operated underwater vehicle according to any of the preceding items, all points at the same radius from the center of rotation having the same velocity during said pure rotational motion.

[0102] 14. The remotely operated underwater vehicle according to any of the preceding items, the greatest difference in velocity between two points being 10 %.

[0103] 15. The remotely operated underwater vehicle according to any of the preceding items, each translational degree of freedom defined by a unit vector, each unit vector having no projection on another unit vector.

[0104] 16. The remotely operated underwater vehicle according to any of the preceding items, each rotational degree of freedom defined by a unit vector, each unit vector having no projection on another unit vector.

[0105] 17. The remotely operated underwater vehicle according to any of the preceding items, having a proximal end and a distal end opposite said proximal end. 18. The remotely operated underwater vehicle according to any of the preceding items, a first group of said plurality of propulsion devices arranged at said proximal end, said first group preferably including 50 % of said plurality of propulsion devices.

[0106] 19. The remotely operated underwater vehicle according to any of the preceding items, a second group of said plurality of propulsion devices arranged at said distal end, said second group preferably including 50 % of said plurality of propulsion devices.

[0107] 20. The remotely operated underwater vehicle according to any of the preceding items, said first group including a first propulsion device generating a first unit force vector, and said second group including a second propulsion device generating a second unit force vector, the center of gravity constituting a symmetry point such that said first unit force vector and said second unit force vector being substantially mirrored symmetrically with respect to said symmetry point.

[0108] 21. The remotely operated underwater vehicle according to any of the preceding items, each propulsion device generating a unit force vector having no overlapping projection on a unit force vector generated by another propulsion device.

[0109] 22. The remotely operated underwater vehicle according to any of the preceding items, each propulsion device of said percentage of said plurality of propulsion devices generating a unit force vector causing a motion for each degree of freedom.

[0110] 23. The remotely operated underwater vehicle according to any of the preceding items, comprising a frame for supporting said components, said frame including hollow profiles such that said frame constituting a buoyancy element.

[0111] 24. The remotely operated underwater vehicle according to any of the preceding items, said frame defining the center of buoyancy.

[0112] 25. The remotely operated underwater vehicle according to any of the preceding items, constituting an open frame remotely operated underwater vehicle.

[0113] 26. The remotely operated underwater vehicle according to any of the preceding items, constituting an unmanned remotely operated underwater vehicle. 27. The remotely operated underwater vehicle according to any of the preceding claims, comprising a number of buoyancy elements, and a number of components including said number of propulsion devices, said buoyancy elements and said components arranged such that said remotely operated underwater vehicle having the center of gravity proximate the center of buoyancy.

[0114] 28. The remotely operated underwater vehicle according to any of the preceding items, having a longitudinal extent in a plane substantially parallel to said surface.

[0115] 29. The remotely operated underwater vehicle according to any of the preceding items, said plane and said surface having an angle with respect to each other of no more than 15 degrees when inspecting said surface.

[0116] 30. The remotely operated underwater vehicle according to any of the preceding items, the center of gravity and the center of buoyancy having a distance to each other of no more than 10 % of said longitudinal extent.

[0117] 31. A method for close range visual inspection of an underwater surface by means of a remotely operated underwater vehicle, said method comprising:

[0118] - providing the remotely operated underwater vehicle according to any of the preceding claims for said close range visual inspection,

[0119] - controlling said plurality of propulsion devices by means of said controller for maneuvering said remotely operated underwater vehicle,

[0120] - capturing images of said surface by means of said camera array while said remotely operated underwater vehicle manoeuvring.

Claims

CLAIMS1. A remotely operated underwater vehicle for close range visual inspection of a surface, said remotely operated underwater vehicle comprising:- an open frame,- a camera array including a pair of cameras facing said surface for capturing images of said surface,- a plurality of propulsion devices for maneuvering said remotely operated underwater vehicle in a three-dimensional space, and- a controller for controlling said plurality of propulsion devices, said controller and said plurality of propulsion devices arranged for generating thrust from a number of at least four propulsion devices for maneuvering said remotely operated underwater vehicle in a substantially pure translational motion substantially parallel to said surface for reducing sediment stirring during said close range visual inspection.

2. The remotely operated underwater vehicle according to any of the preceding claims, said number comprising at least 5 or 6 or 7 or 8 propulsion devices.

3. The remotely operated underwater vehicle according to any of the preceding claims, said pair of cameras having a substantially fixed distance to said surface during said substantially pure translational motion.

4. The remotely operated underwater vehicle according to any of the preceding claims, each active propulsion device arranged for generating a jet of water in a direction not crossing a direction of a jet of water generated by another active propulsion device.

5. The remotely operated underwater vehicle according to any of the preceding claims, comprising a number of buoyancy elements, and a number of components including said number of propulsion devices, said buoyancy elements and said components arranged such that said remotely operated underwater vehicle having the center of gravity proximate the center of buoyancy.

6. The remotely operated underwater vehicle according to any of the preceding claims, constituting an unmanned remotely operated underwater vehicle.

7. The remotely operated underwater vehicle according to any of the preceding claims, said frame including hollow profiles such that said frame constituting a buoyancy element.

8. The remotely operated underwater vehicle according to any of the preceding claims, said frame defining the center of buoyancy.

9. The remotely operated underwater vehicle according to any of the preceding claims, every point in said remotely operated underwater vehicle experiencing the same velocity during said substantially pure translational motion.

10. The remotely operated underwater vehicle according to any of the preceding claims, the greatest difference in velocity between two points out of said every point being 10 %.

Images