Device for positioning of a buoy body

Abstract: Device for positioning of a buoy body (22), comprising a ballast weight (2) in use positioned under said buoy body and being provided with anchoring means (10), and coupling means (20, 24) connecting said ballast weight to said buoy body. The mean horizontal cross sectional dimension of the buoy is smaller than the height of the buoy.

Description: The invention relates to a device according to the preamble of claim 1. Such a device is known from GB-A-2,015,455 of applicant, wherein a buoy body is described having a substantial flat shape. This means that its mean horizontal cross sectional dimension is larger than the height of the buoy. All other buoys used in the prior art for this kind of devices are embodided in substantially the same way. However, during use it became clear that this buoy has the drawback that the large surface area near the water line of the buoy body is a disadvantageous attacking point for waves and ice. Forces of waves are sent through the coupling means to the ballast weight and from the ballast weight via the anchor lines to the sea bed. Because of the relatively large influence of waves on the buoy body the anchor lines are subjected to considerable peak loadings during high sea. Of course it is important for the buoy body to have sufficient floating capacity. The invention aims to obviate these drawbacks. According to the invention this is realized by the features of the characterising part of claim 1. By having the buoy long and slender the surface area subjected to the influence of the forces occurring at the water line is considerably decreased whilst the buoyancy is maintained. This means that high waves do not give such an extreme peak force on the anchor lines as with the prior art buoy body. Furthermore the decreased surface area gives a smaller surface on which floes can hit. Because of the cooperative action of the buoy body, ballast weight and anchor line a considerable displacement of an anchored vessel can be realized before the connection from the vessel to the sea bottom is in a straight line. Through the use of several anchor lines connected to the ballast weight a considerable momentum against tilting of the ballast weight is provided by the weight of the anchor lines. Because of this the resistance against movement of the buoy body will increase during its displacement not only because of increased buoyancy at submerging of the buoy body, but also because of the tilting action of the ballast weight. It is remarked that from FR-A-2,290,345 an elongated buoy body is known. However, this buoy body is connected to the vessel through an arm having at its other extremity a float 23. In this structure no ballast weight is provided and only a single chain is connected to a pipe connected to the buoy body. Displacement of the vessel is counter acted by the weight of the float. Because of the considerable surface area of the float the object aimed with the subject invention i.e. to protect the mooring device against the influence of waves and ice, cannot be realized with such a device. According to a preferred embodiment of the invention the coupling means comprise at least one articulated connection to one of said buoy body, and said ballast weight. By having at least one articulation point bending moments in the tubular member can be reduced. However, this embodiment has as drawback that it is relatively complicated and that the buoy body size has to be increased to compensate for the extra weight of the articulation points. Such a structure will preferably be used in deep water where the forces acting on the several components will be increased considerably. Even if the articulation joint is between the connecting means and the ballast weight the tilting momentum described above of the ballast weight is realized because of the tensile force tending to place the ballast weight under an angle relative to the sea bottom. According to a further embodiment of the invention this disadvantage is obviated in that said tubular member is embodied such that a substantial rigid connection between the buoy body and the ballast weight is obtained. The device according to the invention acts as a tumbler such that when a vessel exerts a traction force to the buoy body it will not longer remain in the same horizontal position with regard to the water surface as with the prior art but tilted. Because of this an extra restoring moment in the system is generated by the buoyancy of the device, which is at a distance from either an articulation point or from the weight which acts as an articulation point around the anchor lines, the traction force from the vessel will lift the anchor lines, this increases the weight suspended from the buoy body which consequently will submerge the buoy body and thus decrease the peak forces even further. By not having a pivot connection at the buoy body it is possible to embody this buoy body much smaller such that its resistance to the waves will decrease. This also has a beneficial effect if ice is present in waters wherein the device according to the invention has to be used. Flow lines from the ballast weight can be routed through the tubular member, such that a much better protection is obtained against exterior influences than with the device according to the prior art in which the flow lines were outside of the link member. According to the invention a swivel body is provided at the buoy body. This swivel preferably comprises at least two spaced bearings rotatably mounted relative to said tubular member. Because of this an increased distance between the bearings is possible resulting in an structural improved embodiment. According to a further embodiment the buoy body is provided with an end cap at its end remote from the ballast weight and at least one opening for the flow line(s) in the swivel is located below water level. By having the openings for the flow lines below water level they are not exposed to such a heavy environment as in the prior art wherein these openings are above water level and wherein the flow lines are subjected to the motion of the waves and to ice. The invention will be further elucidated with reference to the drawing wherein: Fig. 1. schematically shows a first embodiment according to the invention having a rigid connection between the buoy body and the ballast weight and Fig. 2 schematically shows a further embodiment having coupling means being articulated connected to the buoy body and ballast weight. In Fig. 1 the device according to the invention is generally indicated with 1 and comprises a ballast weight 2, a riser 3 and buoy body 4. The device 1 is designed to anchor a vessel 5 of which only a part is shown. Flow lines 7,8,9 connect the sea bed 6 with the vessel 5. Ballast weight 2 is connected with anchor and anchor lines 10 to sea bed 6. Vessel 5 is connected to buoy body 4 with mooring line 11. Between riser 3 and buoy body 4 bearings 13,14 are provided such that buoy body 4 acts like a swivel relative to riser 3. The end of flow line 8 is connected to conduit 15 by means (not shown) to enable a rotation of buoy body 4 relative to riser 3. The conduit 15 opens near 16 e.g. below water level from buoy body. Riser 3 is fixed to ballast weight 2 and rotatably connected to buoy body 4. This means that if a traction force is exerted on mooring line 11 both buoy body 4 and ballast weight 2 will tilt giving a larger restoring moment compared with devices described in the prior art. Because of the fixed connection between riser 3 and ballast weight 2 it is relatively simple to introduce flow line 7 in riser 3 (flow line 8) where it is protected against exterior influences. By having flow line 9 below sea level as much as possible also this flow line is protected against the influences of waves, ice etc. After vessel 5 has been disconnected from buoy body anchor line 11 and flow line 9 will be in the position indicated with chain lines respectively 19 and 17 because of the presence of floating body 18. Also in this condition these lines are protected against influences acting near sea level. In Fig. 2 a further embodiment of the invention is show. In this embodiment ballast weight 2 is provided with an articulating joint 20 to a riser 21. Buoy body 22 is provided with swivel 23 having an articulating joint 24 being connected to riser 21. In this embodiment the flow line is indicated with 25, 26, 27, 28. Because of the articulation joints 20, 24 it is not preferable to have the flow line inside riser 21, 29 indicates the bearing of the swivel 23 buoy body 22. The embodiment according to Fig. 2 is particular useful if large bending moments are to be expected. An articulated connection can avoid larger bending moments than the rigid connection shown in Fig. 1. Although the embodiment shown is a preferred embodiment at the time being it has to be realized that it is possible to introduce many variations being obvious for the person skilled in the art, for example the introduction of the swivel arrangement of 1 into figure 2.

Claims: Mooring device comprising in the position of use an upper buoy body (4, 22) comprising a swivel, having two parts being rotatable with regard to each other, one of said pants having mooring line connecting means for a vessel and the other part being connected to an elongate tubular member (3, 21), said tubular member extending downwards and being connected at its lower end to a lower ballast weight (2), said ballast weight being provided with anchoring line means to connect said ballast weight to the sea bottom, said anchoring line means extending in different directions, wherein fluid conduit means are provided extending from said upper buoy, via said tubular member to said lower ballast weight for connection to a vessel and the seabed respectively, characterized in that the mean horizontal cross-sectional dimension of the buoy body is smaller than the height of the buoy body, such that in use the mooring device becomes submerged when subject to waves at least in a high sea and/or when a traction force on the mooring device from a vessel moored thereto causes the mooring device to incline significantly away from its vertical position, wherein the connection between the upper buoy body and the ballast weight by means of the elongate tubular member is such that as the mooring device inclines away from its vertical position a restoring moment acts via the tubular member. Device according to claim 1 wherein said elongate tubular member (3,21) comprises at least one articulated connection (20,24). Device according to claim 1 wherein said elongate tubular member (3,21) is embodied such that a substantial rigid connection between the buoy body (4,22) and the ballast weight (2) is obtained. Device according to any of the previous claims wherein the swivel comprises at least two spaced bearings (29) rotatably mounted relative to said said elongate tubular member. Device according to one of the preceding claims wherein the buoy body (4) is provided with an end cap at its end remote from ballast weight (2) and wherein at least one opening for the conduits (15) in the buoy body (4) is located below water level. Device according to one of the preceding claims wherein the buoy body (4,27) comprises foam material.

Inventors: DE BOOM WILLEM CORNELIS, POLDERVAART LEENDERT, DE BOOM, WILLEM CORNELIS, POLDERVAART, LEENDERT
Applicants: SINGLE BUOY MOORINGS, SINGLE BUOY MOORINGS INC.
Application year: 1989
Main classification: B63B21
IPC codes: B63B22