Submerged observation unit for a fish tank

1. An observation system for a fish cage, said observation system comprising a submerged observation unit, a surface cable and a surface buoy comprising a hoist winch, wherein the observation unit is suspended from a node cable from the hoist winch of the surface buoy, wherein

the hoist winch is azimuthally rotatable about a vertical axis and the node cable is torsion-resistant,

the node cable is at its upper end wound on the hoist winch having a horizontal drum axis,

the observation unit is motorized and azimuthally rotatable with the hoist winch about a vertical axis, and

the surface buoy is motorized and movable along a main span of the surface cable, wherein the main span spans across a float ring of the fish cage.

2. An observation system for a fish cage according to claim 1 , wherein hoist winch is motorized and mounted on a bearing with a vertical axis provided in the surface buoy and wherein a housing of the observation unit is tightly sealed at a lower end of the node cable.

3. An observation system for a fish cage according to claim 1 , wherein the hoist winch is immobilized and a housing of the observation unit is mounted on a bearing having a vertical axis at a lower end of the node cable.

4. An observation system for a fish cage according to claim 1 , wherein the main span of the surface cable is stretched between a first and a second point on the float ring by means of

a first, elastic stag line attached to the float ring in the first point and provided with a first shackle at a first end of the main span, and

a second, elastic stag line attached to the float ring in the second point and provided with a second shackle at a second end of the main span.

5. An observation system for a fish cage according to claim 4 , wherein the surface cable in addition to the main span also comprises a continuous extension portion at a surface cable end extending beyond a second end of the main span and the second shackle and back to and into the surface buoy.

6. An observation system for a fish cage according to claim 5 , wherein the continuous extension portion is stretched to a third point on the float ring between the first and the second point such that

a third, elastic stag line is attached to the float ring in the first point and provided with a third shackle at approximately midpoint of the extension portion, such that the entire surface cable comprising the main span and the extension portion is stretched within the fish tank.

7. An observation system for a fish cage according to claim 1 , wherein the surface buoy comprises a set of motorized drive wheels that are engageable with the main span of the surface cable for moving the surface buoy along the main span to a desired position on the main span.

8. An observation system for a fish cage according to claim 7 , wherein at least one of the drive wheels is movable with respect to the other drive wheel and detachable from the main span.

9. An observation system for a fish cage according to claim 7 , wherein the surface buoy is provided with at least one guide track which guides the main span towards the drive wheels to achieve directional stability of the surface buoy with respect to the main span.

10. An observation system for a fish cage according to claim 1 , wherein the observation unit comprises at least one of the following optical units provided in or at the housing:

a camera for recording images of fish,

an ultrasonic probe for recording images of fish or determining position of fish,

a laser for performing at least one of the following:

detecting and determining position of fish, and

detecting and determining position of organisms on fish, and

hydrologically measuring instruments.

11. An observation system for a fish cage according to claim 10 , wherein the at least one optical unit is controllable in the vertical plane and in the horizontal plane.

12. An observation system for a fish cage according to claim 1 , wherein there is a signal swivel or an electrical swivel or a signal and electrical swivel between a second end of the surface cable and an upper end of the node cable for signal transmission or current transmission or signal and current transmission in a signal/electrical swivel in the hoist winch.

13. An observation system for a fish cage according to claim 8 , wherein the surface buoy is provided with at least one guide track which guides the main span towards the drive wheels to achieve directional stability of the surface buoy with respect to the main span.