GB1559845A - Floating breakwaters - Google Patents

Description

(54) FLOATING BREAKWATERS (71) We, FLOATING BREAKWATERS LIMITED, a British Company, of 1, Little London, Chichester, Sussex, PO19 1PP, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to floating breakwaters. Examples of floating breakwaters are disclosed in British Patent Specification No. 1,293,521.

According to the present invention, there is provided a floating breakwater comprising a plurality of strakes each extending from the front to the rear of the breakwater, one end of each strake being joined to an adjacent end of one of its two neighbouring strakes while the other end of the said strake is joined to the neighbouring strake on the other side the connection between the adjacent strakes being capable of transmitting torsional loads about axes parallel to the general length direction of the breakwater. Particularly where the breakwater is of some length, it will be provided with mooring means for holding it in position relative to the bed of the sea or other body of water in which it is used.

The strakes may be formed individually, for example, by timber baulks or hollow reinforced concrete beams or two or more of the strakes may be formed integrally, for example of reinforced concrete or fabricated from steel plates or tubing.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a plan view of a portion of a floating breakwater in accordance with the invention, Fioure 2 is a vertical sectional view along the line Il-II of Figure 1, on an enlarged scale, Figure 3 is a plan view showing a mooring arrangement for the breakwater shown in Figures 1 and 2, Figure 4 is a vertical section on the lines IV-IV of Figure 3, Figure 5 is a view similar to Fig. 3 of a second embodiment of the invention, Figure 6 show some of the strakes of Fig. 5 on an enlarged scale, Figure 7 shows a vertical section through one of the strakes of Fig. 6 on the line VII-VII of Fig. 6, on an enlarged scale, Figure 8 is a view similar to Fig. 1 of a third embodiment, Figure 9 is a vertical elevation on the line IX-IX of Fig. 8, Figure 10 is a plan view of a fourth embodiment incorporating standard dredging pipe, Figure 11 shows a portion of Fig. 10 at the junction of two adjacent strakes on an enlarged scale, Figure 12 is an end elevational view in the direction of the arrows XII-XII of Fig.

11, Figure 13 shows a vertical section on an enlarged scale through a joint between two strake sections of the embodiment shown in Fig. 10, Figure 14 is a plan view of a fifth embodiment formed of rectangular section steel tubular construction, Figure 15 is vertical section on the line XV-XV of Fig. 14, Figure 16 is a plan view of a sixth embodiment made of reinforced concrete in continuous lengths, Figure 17 shows a portion of Fig. 16 at the junction of two adjacent strakes on an enlarged scale, Figure 18 is an end elevation view in the direction of the arrows XVIII-XVIII of Fig. 17, and Figure 19 is a vertical elevational view of part of a strake in the direction of the arrow XIX in Figure 17.

The floating breakwater shown in Figures 1 to 4 is assembled from a large number of identical hollow reinforced concrete strakes 1.

Each strake 1 is of hollow rectangular cross-section as shown in Figure 2 and its interior is divided into chambers 2 by a central vertical partition 3 and transverse vertical partions 4 (Fig. 1). Each chamber 2 is filled with synthetic plastics foam of the closed cell type which acts as shuttering for the formation of the chamber 2 while the strake is being constructed and resists impregnation by water in the event of damage to the strake in operation. The concrete walls of the strake are reinforced by longitudinal and circumferential reinforcement rods such as those indicated at 5 in Fig. 2, thereby enabling the strake to withstand substantial bending moments.

Each strake 1 has an angled face 6 at each of its ends, the two faces 6 being on opposite sides of the strake. During assembly of the breakwater, the faces 6- of adjacent strakes 1 are bolted securely together by spaced tie-bolts 7 of high tensile steel, thereby enabling torsional loads about an axis normal to the faces 6 and thus parallel to the general length direction of the breakwater formed Iby the strakes to be transmitted from one strake to the next.

As shown in Figs. 3 and 4, the assembled breakwater is securely moored to the seabed 8 by mooring ropes 9 which are several times longer than the strakes 1 to allow the breakwater to rise and fall with the tide. The mooring ropes 9 are secured to suitable anchors 10 on the seabed, for example, in the form of heavy blocks.

As indicated in Fig. 2, the buoyancy of the strakes is preferably selected so that the assembled breakwater floats with its upper surface just awash. The energy in an approaching wave-front 11 is in the form of orbital motion in a vertical plane.

As the wave-front 11 attempts to pass through the breakwater, it is progressively intercepted by the top surfaces of the strakes. The angular momentum associated with the orbital motion of the wave is correspondingly progressively given up by the wave and converted into moments tending to tilt the strakes about horizontal axes extending in the general length direction of the breakwater. Typically, one part of the strake will be subjected to an upwards force while another part is sub acted to a downwards force. The reinforcement system 5 withstands the bending moments thus generated, and the resultant torsional load is transmitted to neighbouring strakes by the junctions between the faces 6. Variations in the tensions in the mooring ropes 9 due to the wave action itself are very slight.The main purpose of the mooring ropes is to secure the ;breakwater against drift due to current or wind.

In the embodiment shown in- Figs. 5 to 7, the individual strakes 21 are secured at right angles to their neighbours. As can be seen most clearly in Fig. 6, each strake 21 has one end 22 bolted to the end portion of a side 23 of an adjacent strake. With this arrangement, a bending moment apply to one strake is transmitted as a torque or torsional load to its neighbour. As shown in Fig. 7, the strakes 21 may be of increased width (as compared with Figs. 1 to 4) in relation to their depth and have several, for example three, longitudinal internal partitions 24.

In either embodiment, the reinforcing rods 5 may be pre- or post-tensioned.

If desired, tension members such as chains may be used to interconnect the two ends of each pair of adjacent strakes opposite to the ends which are bolted together.

Suitable positions for such optional chains are indicated at 12 in Fig. 1.

The floating breakwater shown in Figs.

8 and 9 is similar to that shown in Figs. 1 to 3 but differs from it in that the strakes 1' taper as seen in plan (Fig. 8) so as to be wider at their leading ends 31 facing the oncoming waves 11 than at their trailing ends 32. Further, the leading ends 31 are chamfered to form a sloping leading edge 33. Either or both of these modifications may be applied to the embodiments shown in Figs. 1 to 7.

Particularly in the embodiments shown in Figs. 1 to 4 and Figs. 8 and 9, the connections between adjacent strakes may be hinge connections having horizontal hinge axes perpendicular to the length direction of the breakwater, these hinge connections being effectively rigid for transmission of torque about axes in other directions.

The embodiments of the invention shown in Figures 10 to 19 differ from those shown in Figures 1 to 9 in that the strakes are parallel. Each end of a strake is joined to a neighbour by a spacing connection which is designed to give the required flexibility or rigidity.

Thus, the floating breakwater shown in Figures 10 to 13 comprises parallel strakes 31 each composed of three lengths 32 of a standard pipe bolted together end-to-end by bolts 33 (Fig. 13) passed through the mating flanges 34 on the pipe lengths 32.

In this embodiment, each pipe length 32 has a nominal diameter of 0.8 meters and a length of 4 meters. Such standard pipe lengths are frequently employed on the sites where floating breakwaters are required for example to protect construction work.

Each end of each strake 31 (except of course the two end-most strakes) is joined to one neighbour, respectively on one side and the other, by a spacing joint connection 35 shown in more detail in Figs. 11 and 12.

Each joint 35 consists of a pair of spaced pipe lengths 36 which may be cut from the ends of a standard pipe length 32 and each of which has a flange 37 to mate with the flanges 34 of the pair of strakes 31. The two pipe lengths 36 are held at their required spacing by means of a box-section spacing arrangement fabricated from 12 mm. steel plate comprising an end plate 38 having upper and lower edges and convex semi-circular ends, a vertical stiffening plate 39 having upper and lower parallel edges and two concave semi-circular ends and a lower stiffening plate 40 and an upper stiffening plate 41, each tangential to the pipe lengths 36.

In order to prevent the spacing between two adjacent spacing connections 35 from varying, and thus permitting the leading or trailing edge of the breakwater from departing from a straight line as seen in plan, a flexible linking strip 42 is clamped to the top plate 41 of each joint 35. For this purpose, a strip 43 is welded to each plate 41 and carries a pair of studs 44, one on each side of the strip 42. A clamping plate 45 having apertures to receive the studs 44 is then bolted down on top of the strip 42, thereby clamping it against the strip 43.

It will be appreciated that the flexibility of the strip 42 prevents it from interfering with the normal intended relative vertical motion between adjacent connections 35.

Anchorage points for mooring the floating breakwater may also be welded to appropriate strips 43. Also, as shown in Fig. 11, each end of each flexible linking strip 42 may be formed with a suitable mooring eye 48.

It can be seen in Fig. 13 that each pipe section 32 is made independently buoyant by welding a circular diaphragm 49 into each end of each pipe lengtn 32, the diaphragms 49 being inset by about 25 mm.

from the face of the flange 34 to accommodate the welds 50 and also the head of a plug 51. The plug 51 is screwed into a nut or threaded bush 52 which is welded to one of the diaphragms 49 at a height corresponding to the water level 53 required within the drain pipe to obtain a desired buoyancy for the floating breakwater, typically with 7% of the height of the breakwater above the water level. A suitable sealing washer 54 is placed under the head of the plug 51. With the bush 52 in its lowermost position, with the pipe 32 horizontal the plug 51 is removed and the interior of the pipe section 32 is filled with water up to the level of the bore through the bush 52, the plug 51 is then screwed home into the bush thereby ensuring that the pipe section will float with the desired buoyancy and ballast.

Figures 14 and 15 show a floating breakwater which is generally similar to that shown in Figs. 10 to 13 with the exception that the strakes and end connections are formed from rectangular steel tubing, either of the rolled kind or the kind fabricated from plate depending on the size of strakes required.

The particular floating breakwater sections shown in Figs. 14 and 15 is of the latter kind and comprises a plurality of strakes 61 and alternately disposed junction portions 62 integrally interconnecting a pair of adjacent strake ends. Link straps 63 similar to the link strap 42 in Figs. 10 to 13 extends along each of the leading and trailing edges of the breakwater section and is clamped to each of the junctions 62 at 65.

Mooring Ibollards 66 are welded to the upper face of the floating breakwater section where required, particularly at the ends.

As can be seen from the vertical section shown in Fig. 15, the interior of each fabricated strake 61 is reinforced by internal rectangular diaphragms 67 which divide it into a number of separate chambers which can be used as ballasting chambers formed for example with ballast level control plugs of the kind described above with reference to Fig. 13 placed at a suitable height on an exterior face of the strake.

The embodiment shown in Figs. 16 to 19 is of similar configuration to that just described with reference to Figs. 14 and 15 but is of hollow reinforced concrete construction. Each of the parallel strakes 71 is of rectangular cross-section having bottom, top and side walls of concrete, together with diaphragms 73 spaced at intervals along the length of each strake, thereby dividing the interior of the strake into separate compartments while also increasing the resistance of the strake to collapse.

Each of the side walls 72 of the strakes are pre-stressed by tensioning cables 74 which extend along the whole length of the side walls 72.

The ends of adjacent strakes are interconnected by a connection 75 of hollow rectangular section, the walls of which are of concrete integrally cast with the strakes which it interconnects. In addition to top and bottom walls, the connection 75 has two vertical walls 76 and 77 which are prolonged respectively by the end walls 78 of the two adjacent strakes and thick internal diaphragm 79 in the interior of these two strakes. Hollow tubes 80 and 81, for example of mild steel, are cast into these walls and tensioning tendons in the form of macalloy bars 82 and 83 are introduced into the tubes 80 and 81 and extend for the full length of the walls 78, 76 and 78 and of the walls 79, 77, and 79 respectively.

Thus, when suitably tensioned, the bars 80 and 81 ensure that the concrete in the connector 75 as well as that in the end wall 78 and thick diaphragm 79 is maintained under compression.

In order to provide anchorage points for clamping a flexible linking strip 84, a Ubolt 85 may be cast into a thickened wall portion 86 of one of the side walls 72 adjacent the connector 75. Further anchorages 87 may be included at this point for mounting anchorage bollards.

The floating breakwater section in Figs.

16 to 19 may be conveniently constructed in a dry dock, in which case the number of strakes 71 will be determined by the length of the dry dock. Conventional concrete casting techniques may be used, for example casting three strakes at a time using blocks of foam synthetic plastics material, such as polyurathene, to form the internal chambers C within the strakes and thereby also form internal cores for the external walls and for the diaphragms 73 and 79. The tensioning cables 75 and the tensioning bars 80 and 81 may be installed and tensioned after suitable hardening of the concrete. Meanwhile, further strakes can be cast onto the already cast strakes.

As shown in Fig. 16, the floating breakwater section may be joined onto a similar section by means of a joint formation at the position of the connection 75. For this purpose, the end-most strakes have on their outer surface a half connection formation 91. The two mating half connections 91 of adjacent breakwater sections are brought together in alignment (with a suitable packing member there between if desired), and tension elements, for example in the form of macalloy bars already inserted into one of the half connections 91 are fully installed and tensioned up.

WHAT WE CLAIM IS:- 1. A floating breakwater comprising a plurality of strakes each extending from the front to the rear of the breakwater, one end of each strake being joined to an adjacent end of one of its two neighbouring strakes while the other end of the said strake is joined to the neighbouring strake on the other side, the connection between the adjacent strakes being capable of transmitting torsional loads about axes parallel to the general length direction of the breakwater.

2. A floating breakwater according to claim 1 wherein each strake is joined to each of its neighbours at an angle thereto so that the successive strakes form a zig zag.

3. A floating breakwater according to claim 2, wherein the angle is an acute angle.

4. A floating breakwater according to claim 3, wherein the ends of the strakes taper as seen in plan to have a joining face perpendicular to the length direction of the breakwater.

5. A floating breakwater according to any of the preceding claims wherein the leading ends of the strakes are tapered as seen in elevation to present an upwardly sloping surface to oncoming waves.

6. A floating breakwater according to claim 1 wherein, the strakes are substan tially parallel and are spaced apart by spacing connections.

7. A floating breakwater according to claim 6, wherein the strakes are tubular.

8. A floating breakwater according to claim 7, wherein the strakes comprise lengths of piping joined end-to-end.

9. A floating breakwater according to claim 7 or 8, wherein the strakes or piping lengths each form sealed buoyancy cham bers.

10. A floating breakwater according to claim 6, wherein the structure is of welded metal plate construction.

11. A floating breakwater according to any of claims 1 to 7, wherein the strakes are of hollow reinforced concrete.

12. A floating breakwater according to claim 11, wherein chambers within the strakes are defined by rigid foamed synthetic plastics material blocks.

13. A floating breakwater according to any of the preceding claims, wherein a plurality of the strakes and the spacing connections form a unitary fabricated structure.

14. A floating breakwater according to any of the preceding claims and including flexible link means extending along an edge of the breakwater to hold the breakwater straight.

15. A floating breakwater according to claim 14, wherein the link means comprises a flexible strip clamped to each junction of a pair of adjacent strakes.

16. A floating breakwater substantially as hereinbefore described with reference to any of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (1)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   walls and tensioning tendons in the form of macalloy bars 82 and 83 are introduced into the tubes 80 and 81 and extend for the full length of the walls 78, 76 and 78 and of the walls 79, 77, and 79 respectively.

   Thus, when suitably tensioned, the bars 80 and 81 ensure that the concrete in the connector 75 as well as that in the end wall 78 and thick diaphragm 79 is maintained under compression.

   In order to provide anchorage points for clamping a flexible linking strip 84, a Ubolt 85 may be cast into a thickened wall portion 86 of one of the side walls 72 adjacent the connector 75. Further anchorages 87 may be included at this point for mounting anchorage bollards.

   The floating breakwater section in Figs.

   16 to 19 may be conveniently constructed in a dry dock, in which case the number of strakes 71 will be determined by the length of the dry dock. Conventional concrete casting techniques may be used, for example casting three strakes at a time using blocks of foam synthetic plastics material, such as polyurathene, to form the internal chambers C within the strakes and thereby also form internal cores for the external walls and for the diaphragms 73 and 79. The tensioning cables 75 and the tensioning bars 80 and 81 may be installed and tensioned after suitable hardening of the concrete. Meanwhile, further strakes can be cast onto the already cast strakes.

   As shown in Fig. 16, the floating breakwater section may be joined onto a similar section by means of a joint formation at the position of the connection 75. For this purpose, the end-most strakes have on their outer surface a half connection formation 91. The two mating half connections 91 of adjacent breakwater sections are brought together in alignment (with a suitable packing member there between if desired), and tension elements, for example in the form of macalloy bars already inserted into one of the half connections 91 are fully installed and tensioned up.

   WHAT WE CLAIM IS:- 1. A floating breakwater comprising a plurality of strakes each extending from the front to the rear of the breakwater, one end of each strake being joined to an adjacent end of one of its two neighbouring strakes while the other end of the said strake is joined to the neighbouring strake on the other side, the connection between the adjacent strakes being capable of transmitting torsional loads about axes parallel to the general length direction of the breakwater.

   2. A floating breakwater according to claim 1 wherein each strake is joined to each of its neighbours at an angle thereto so that the successive strakes form a zig zag.

   3. A floating breakwater according to claim 2, wherein the angle is an acute angle.

   4. A floating breakwater according to claim 3, wherein the ends of the strakes taper as seen in plan to have a joining face perpendicular to the length direction of the breakwater.

   5. A floating breakwater according to any of the preceding claims wherein the leading ends of the strakes are tapered as seen in elevation to present an upwardly sloping surface to oncoming waves.

   6. A floating breakwater according to claim 1 wherein, the strakes are substan tially parallel and are spaced apart by spacing connections.

   7. A floating breakwater according to claim 6, wherein the strakes are tubular.

   8. A floating breakwater according to claim 7, wherein the strakes comprise lengths of piping joined end-to-end.

   9. A floating breakwater according to claim 7 or 8, wherein the strakes or piping lengths each form sealed buoyancy cham bers.

   10. A floating breakwater according to claim 6, wherein the structure is of welded metal plate construction.

   11. A floating breakwater according to any of claims 1 to 7, wherein the strakes are of hollow reinforced concrete.

   12. A floating breakwater according to claim 11, wherein chambers within the strakes are defined by rigid foamed synthetic plastics material blocks.

   13. A floating breakwater according to any of the preceding claims, wherein a plurality of the strakes and the spacing connections form a unitary fabricated structure.

   14. A floating breakwater according to any of the preceding claims and including flexible link means extending along an edge of the breakwater to hold the breakwater straight.

   15. A floating breakwater according to claim 14, wherein the link means comprises a flexible strip clamped to each junction of a pair of adjacent strakes.

   16. A floating breakwater substantially as hereinbefore described with reference to any of the accompanying drawings.