The invention relates to a transponder support.

Transponders which are placed on or near the sea bed, for example to serve as position reference for the dynamic positioning of vessels, are subjected to impact from fishing implements and other equipment which is being moved along the sea bed. For example, a loading hose which partly extends along the sea bed between an oil installation and a vessel loading hydrocarbons, may sweep away or damage transponders, which are used to make it possible for the vessel to maintain its loading position.

To avoid fishing implements, or a loading hose as mentioned, damaging or dislodging a transponder, it is known to provide the transponder with a flotation body and anchor the transponder to the sea bed by a line, so that the transponder may float somewhat above the sea bed. If movable equipment such as fishing implements, or a loading hose as mentioned, gets into contact with such a free-hanging transponder, or the line holding

it, the transponder will yield and then revert to a position above the anchoring point in the sea bed, when the movable equipment has passed. A drawback of this known solution is, that the water currents will also carry the transponder away from its ideal position, which is straight above the anchoring point. The position fault thus occurring, is not usually a problem, but as water currents normally vary continuously both in strength and direction, the transponder will be constantly moving, and this interferes with the wireless signalling between the transponder and vessels and possible signalling between transponders.

This drawback of a freely floating, anchored transponder may be avoided by securing the transponder in a support which is stationary on the sea bed. Such a support then must provide sufficient friction against the sea bed, so as not to be carried away, or dislodged, by water currents or equipment being moved along the sea bed. Even if supports of this type may be provided with spikes or other elements engaging the sea bed, they must have a comparatively big mass then, so as not to be dislodged if they are hit by fishing implements, loading hoses or other movable equipment. It is a substantial drawback, that because of their weight, such supports must be brought into position and picked up from the sea bed by a special vessel provided with powerful hoisting equipment. Further, supports which do not yield or do not let themselves be carried away, may easily damage fishing implements, loading hose or other e ^* xpensive equipment.

Supports for transponders may be formed with rounded corners and repelling surfaces which guide fishing implement, loading hose and other movable equipment

over or round the support. Such a repelling support surrounding the transponder, may, for instance, be formed as a frustum, pyramid or as a spherical segment of steel or concrete. Fishing implements or loading hose will then slide upwards along the repelling faces and pass the top of the transponder without getting caught and without dislodging the support. A drawback by such supports is that the repelling faces, such as the surface of a cone, must form a relatively large vertical angle to work as intended. An ordinary transponder may extend two metres upward from the sea bed, and the resulting transverse dimension (the diameter of the cone at its base) will thus be so large, that a special vessel of large deck space will be needed, to carry and put down for example ten transponders complete with supports. To reduce the space requirements during transport, such repelling supports may be made collapsible, for example comprising foldable stays, which form a cone of a large transverse dimension and a large vertical angle in the operative unfolded state. A drawback of such a solution is that it requires a relatively complex and expensive mechanical construction, and the construction will still be so heavy, that it cannot readily be brought into position by a vessel which has a lifting capacity of a few tons.

The object of the invention was to provide a transponder support, in which said drawbacks have been eliminated.

The aim is reached through features as stated in the following description and subsequent claims.

A transponder support according to the invention comprises a holder which extends upward from the sea bed and is kept in an essentially vertical operating position by a biased spring device, which is arranged to let the holder swing sideways about its lower end portion, typically on a pivot at the lower end of the holder, into a mainly horizontal position, whenever the holder, in relation to said pivot, is subjected to a torque exceeding a predetermined value. The smallest torque which may swing the holder aside, is chosen, according to the invention, to be greater than the total torque which may be caused by forces from water currents affecting the holder and transponder.

Equipment moving along the sea bed and getting into contact with the transponder support, or the transponder, by a sufficient force, will apply a torque to the holder, exceeding the predetermined value. Therefore, the holder swings aside and lies down along the sea bed, so that said equipment may pass, whereafter the holder is raised to its vertical working position by means of the force of said spring device. A transponder sitting in the holder is normally provided with a flotating body, which also assists in raising the holder into the vertical working position.

The value of the torque affecting the holder, and possibly exceeding the predetermined value, so that the holder swings aside and lies down, depends on the magnitude of the force affecting the holder, and on the distance from the pivot at the lower end of the holder to the line of action of the force.

A force having a line of action close to the sea bed, and thus close to the pivot at the lower end of the

holder, will effect a small torque. Equipment carried or pulled with great force against the holder, may provide such a small torque that the holder does not yield, resulting in the transponder support being dislodged. Therefore, it is a further feature of the invention that the transponder support comprises fenders, preferably in the form of radial, inclined ribs or stays which guide said movable equipment up from the sea bed, so that the predetermined torque is exceeded even by an applied force which is too small to dislodge the transponder support, if the force acts at the base of the transponder support.

The invention is described in the following by means of two illustrating, but not limiting, examples of embodiments, and reference is made to the accompanying drawings, in which

Fig. 1 is a schematic side view of a transponder support with holder and transponder in a vertical working position;

Fig. 2 shows the same transponder support as in Fig. 1, after the holder and transponder have swung aside and adopted an essentially horizontal position;

Fig. 3 shows the transponder support of Figs. 1 and 2, as seen from above;

Fig. 4 is a side view, partly in section and on a larger scale, of a holder with a transponder;

Fig. 5 is a schematic side view of a second embodiment of a transponder support with holder and transponder in a vertical working position;

Fig. 6 shows the same transponder support as in Fig. 5, after the holder and transponder have swung aside and adopted an essentially horizontal position;

Fig. 7 shows the transponder support of Figs. 5 and 6, as seen from above.

In Fig. 1 reference numeral 1 indicates a transponder support carrying a transponder 2 of known type in a vertical working position, so that the one end of the transponder 2, which is provided with a head 3, which is typically arranged for wireless communication with vessels or other transponders, points upwards. The head of the transponder 2 is typically protected by one or more wire bows 4, as indicated in Fig. 1. The transponder 2 is further provided with at least one flotation body 5 which is capable of leading the transponder to the surface of the water.

The transponder 2 is positioned in a vertical cylindrical holder 6, which rests by its lower end on a base 7, which comprises a number of rails 8, the rails

8 being arranged along radials from an area under the holder 6. The rails 8 may have a T-profile as shown, so that the step rests against and sinks into the sea bed

9 and provides adequate friction. The rails 8 may also have an H-profile and are then arranged lying down with vertical flanges and a horizontal step, so that the side edges of the flanges bear against the sea bed 9 to provide friction. On the rails 8 is placed a base plate 10, on which the holder 6 rests by its lower end face,

and which has a preferably circular external profile. One or more fenders in the form of a set of ribs 11 are resiliently or pivotally attached to the holder 6 somewhat above its lower end, and extend radially, at a downward angle towards the base plate 10, so that the ribs 11 define a frustum surrounding the holder 6. The ribs 11 thus form a kind of conical skirt from which the holder 6 and the transponder 2 project in an upward direction, and the ribs 11 serve as fenders to guide equipment, which is being pulled or lead along the sea bed against the transponder support 1, up from the sea bed, so that said equipment hits the holder 6 at the top of the ribs 11.

The holder 6 rests by its lower end face on the base plate 10 and is kept in upright position by the fact that it is pressed against the base plate 10 by means of at least one but preferably more spring-biased lines 12 attached to the holder 6 and taken through openings or holes 13 in the base plate 10 and attached to the base 7 or the base plate 10. Between the base plate 10 and the holder 6 the lines 12 extend symmetrically about the longitudinal axis 14 of the holder 6. Thereby is achieved, that the lines are at their greatest distance form the base plate 10 when the holder is in its upright position. When the holder swings to the side towards the horizontal position, the longitudinal axis 14 and, thereby, the upper end of the lines 12 will move closer to the base plate 10. The lines 12 may be strong elastic bands of rubber or other suitable material, or the lines 12 may be steel ropes, each having a spring 15 arranged thereto and attached to the base 7. For example, there may be one line 12 and one spring 15 for each rail 8 in the base 7, and the lines 12 may extend below the base plate 10 along one rail 8 each.

Advantageously, springs 15 may then be attached to the rails 8. Springs and spring mountings may best be seen in fig. 4. In the step of a T-profile rail 8 is arranged, in a manner known in itself, a plate 16, which is provided with a through hole for a tightening screw 17 which is attached to one end of the spring 15, while the line 12 which is connected to the other end of the spring 15, is taken by way of a guiding 18 through the base plate 10.

When, for example, a loading hose 19 is led sideways against a transponder support 1, as indicated in dotted lines in fig. 1, the ribs 11 guide the loading hose 19 up from the sea bed 9 and the base plate 10 to bear against the holder 6 at the top of the ribs 11. Lateral force from the loading hose 19 will apply a torque to the holder, seeking to swing the holder 6 sideways about a pivot 20 at the lower end of the holder, more precisely diametrically opposite the holder 6 in relation to the loading hose 19. Simultaneously, forces from the biased lines 12 apply an opposite torque, which seeks to keep the holder 6 in the vertical position. Load from the part of the loading hose 19 resting on the ribs 11, will also, through the ribs 11, apply a torque to the holder, which torque will co- operate with the torque from said lateral force. When the total torque applied to the holder 6, exceeds the torque applied by the lines 12, the holder 6 will swing to the side about its lower end, more specifically about the pivot 20, towards an essentially horizontal position, as shown in fig. 2. Thereby, the loading hose 19 may pass.

In fig. 4 is shown how the transponder 2 is introduced into the mantle-shaped holder 6. The transponder 2 is provided with an upper collar 21 resting on the upper

end of the holder 6 and centring the transponder 2 in the holder 6. Below the upper collar 21 the transponder 2 is provided with a lower collar 22, which contributes to centring the lower end of the transponder 2 in the holder 6.

In a manner known in itself, the transponder 2 is provided, at its lower end, with a releasable gripper 23 which grips a transponder fastener 24 in the form of a bow extending upwards from a fixed wall 25 in the holder 6. On its underside, the wall 25 is provided with a line fastener 26 for the lines 12. The gripper 23 may in a known manner be released by remote control, for example from a vessel, by a signal being transmitted through wireless to the transponder 2. The ends of a line 27 are attached to respectively the transponder 2 and the wall 25, and when the transponder 2 is in its working position, the line is coiled in the holder 6 between the lower end of the transponder 2 and the wall 25. The line 27 is longer than the distance from the wall 25 to the surface of the water. When the gripper 23 is released, the transponder 2 will rise to the surface of the water, where a vessel may pick up the transponder 2 and then raise the transponder support 1 by means of the line 27. Before the transponder 2 is put back down on the sea bed, the line 27 is wound into the holder 6. The transponder 2 is introduced into the holder, and the gripper 23 is activated, so that it grips the transponder fastener 24. The support 1 with the transponder 2 in the holder 6 is then lowered to the sea bed by means of not shown hoisting equipment, available aboard the vessel.

In a second example of an embodiment of the invention, as appears from Fig. 5, Fig. 6 and Fig. 7, the fenders consist of telescopic rods 28 which are pivotally

attached, at the one end, to the exterior of the holder 6, somewhat above the lower end of the holder 6. The rods 28 extend radially, sloping downwards towards the base of the transponder support l, on which the rods 28 are pivotally attached to a ring 29 of substantially larger transverse measurement than the holder 6. The rods 28 thus define a frustum surrounding the holder 6, and the rods 28 will have a repelling effect on fishing implements, loading hoses 19 and other things corresponding to that described for the ribs 11 in the preceding example of an embodiment. The ring 29 rests on the base 7 and it is sufficient to have a smaller base plate 30, which covers only a minor part of the base 7, as opposed to the preceding example of an embodiment, and the transponder support 1 will thus encounter less resistance from currents and be more easily lowered to the sea bed 9. In addition a reduction of weight is achieved.

It is a feature of the invention that the torque of the force from the spring device keeping the holder 6 in the working position, will subside as the holder 6 is being swung aside. In the shown example of an embodiment this is achieved by the lines 12, as mentioned, running symmetrically about the longitudinal axis 14 of the holder 6, so that the lines of force from the lines 12 have an increasingly shorter distance to the pivot 20 as the holder 6 is swung aside, said distance decreasing comparatively more than the line forces are increasing, as a consequence of the spring 15 further being tensioned by the movement of the holder 6. In the shown construction, the torque seeking to keep the holder 6 in its working position, will first increase a little as the holder 6 is forced sideways, whereafter the torque caused by the line forces, will subside.

It will be readily understood that the transponder support 1 may be arranged in several ways, and that it may be operative also if the holder 6 is arranged in a horizontal position.