Patent Description:
In the oil and gas and marine industries, helicopter access is accommodated on drilling rigs, ships and other offshore structures by a helideck for helicopter take-off and landing. Helidecks are also used onshore on buildings and like elevated structures where helideck safety nets, or perimeter nets, contribute to the safety of helicopter operations due to their capability to arrest and restrain a person or item falling off an edge of the helideck, without causing injury or damage.

<CIT> describes a helideck safety net formed of lines connected at their crossing points, the net being secured to a perimeter frame by, among others, ropes wound around opposite frame bars passing through the openings at the edges of the net.

Beyond the fundamental requirement for providing an energy absorbent structure able to safely withstand the required loads in a cost-effective manner, the harsh environment in which it is used means that the netting system must have an operational life, after which it should be replaced. However, many prior art solutions have features that make installation and uninstallation of perimeter nets relatively problematic. For instance, the net fastening may require multiple tools or multiple fasteners that are time-consuming to install and present a drop hazard, or produce localised weaknesses from stress concentration, and it is particularly advantageous to avoid welding that may also present a fire danger.

It is an object of the present invention to overcome or substantially ameliorate the above disadvantages or, more generally, to provide an improved helideck safety net.

According to one aspect of the present invention there is provided a helideck safety net including:.

Not only is this helideck safety net more readily installed and uninstalled, it has been found that under drop testing, providing a spreader bar according to the invention has provided a significant increase in the load at which the net first starts to fail, compared to nets secured by the edge line alone and it is believed that this is achieved by better distribution of loads away from highly loaded lengths.

While the line forming the lengths may comprise a rope or tape of natural and/or synthetic fibres, this line is preferably formed of wire, or like resilient material to provide bending resilience. Otherwise, for instance, a rope or tape of natural and/or synthetic fibres may be reinforced by a wire to provide a line with bending resilience. The bending resilience is advantageous in a net of this construction, as it tends to naturally collapse to close the cells as the lengths return to their original, generally straight, form. Advantageously, with the lengths adjacent one another, the collapsed net forms a bundle that is elongate and compact in the transverse direction and so can be wound on a narrow coil, avoiding the need for folding the net for transport, or winding the net onto a coil that is the full width of the net.

Preferably the at least one end edge comprises a pair of end edges that are longitudinally opposing, each end edge comprising a respective end row of cells, and the at least one spreader bar comprises a pair of spreader bars that are each adapted to pass through the cells of one of the end rows.

The net may be formed to suit the perimeter frame, and in particular may be sized so that when installed and properly tensioned, the edges of the net are spaced inward from the perimeter members of the perimeter frame. Typically the net will have straight longituduinal edges that are parallel, which is advantageous for simple net construction, but not essential, and all the edges may be curved.

Preferably the wire is a multi-strand wire, such as a twisted wire i.e. a twisted wire cable or rope.

Preferably the fastening means comprise crimps, ferrules, welds, or the like, that permanently fasten the lengths.

Preferably the line forming the lengths and the edge line are of the same construction.

Preferably the spreader bars are tubular. The smooth external shape of the spreader bars is believed to contribute to their performance. In this regard, rectangular or triangular hollow sections have a sufficiently smooth external shape owing to their rounded corners, and may perform satisfactorily. Alternatively, the spreader bars may be of solid material.

Preferably the net, edge line and spreader bars are constructed of the same material, particularly from inherently corrosion resistant steel.

Preferably the openings of the array of openings extend transversely through the spreader bar, and are axially spaced apart.

Preferably the openings are disposed in coaxial pairs in diametrically opposing wall parts of the spreader bar.

Preferably central axes of the openings generally lie in longitudinal plane that bisects the spreader bar.

Preferably a notch is formed in each of the longitudinally opposing ends of the spreader bar, the notches adapted to receive parts on transversely opposing edges of the net to spread the net transversely.

Preferably the notch comprises notch parts in diametrically opposed sections of the respective end of the spreader bar, an axis of the notch being aligned generally orthogonal to the central axes of the openings.

Preferably the helideck safety net further comprises the perimeter of frame, which may comprise parallel outer and inner longitudinal members joined by shorter transversely extending inclined members.

In another aspect, the invention provides a method for installing a helideck safety net, the method including:.

Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein:.

Referring to <FIG>, helideck safety nets or net assemblies <NUM> are shown installed alongside one edge of a helideck <NUM> and fixed inside a perimeter frame <NUM>. On the octagonal helideck <NUM> that is shown, the perimeter frame <NUM> may extend around all eight sides for holding safety nets <NUM> around the entire perimeter, with the frame <NUM> being fixed to underlying or adjacent structure (that is not shown in the drawing). The safety net assemblies <NUM> may be adapted to suit the perimeter frame <NUM>, and may include trapezium-shaped nets <NUM> (two of which are shown in <FIG>).

The perimeter of frame <NUM> may comprise like elongate members <NUM>, <NUM>, as with inner member <NUM> disposed alongside an edge of the helideck <NUM> and outer member <NUM> offset outward and generally parallel. Cross members <NUM>-<NUM> are relatively shorter and extend between the inner and outer members <NUM> and <NUM> to which they may be welded at their respective ends. The assembly of the members <NUM>-<NUM> may be considered as a sub-frame <NUM> in which component members <NUM>-<NUM> are generally coplanar, and either horizontal or inclined with the inner and outer members <NUM> and <NUM> horizontal, but with the outer member <NUM> relatively higher. The cross members <NUM>-<NUM> may be transverse (in the case of cross members <NUM>-<NUM>), or inclined (as in the case of cross members <NUM> and <NUM>). The complete frame <NUM> for the octagonal helideck <NUM> shown may be effectively an assembly of eight sub frames <NUM> joined at their ends (where they share the inclined cross members <NUM>, <NUM>). It will be understood that this is an example, and the perimeter frame <NUM> need not take this shape, and need not have straight edges, and may have more or less than the number of members shown here.

The safety net assembly <NUM> shown in <FIG> includes the two nets <NUM> that together close the perimeter frame <NUM>, and both include a net <NUM> elongated in a longitudinal direction that is trapezium shaped. An end row <NUM> of cells is formed at both longitudinally opposing transverse edges of each net <NUM> and two spreader bars <NUM> are used, each passing through the cells of a respective one of the end rows <NUM>, as in a woven manner.

Securing the spreader bars <NUM> and the transverse edges of the nets <NUM> is an edge line <NUM> that is wound generally helically in loops, each loop going through a cell <NUM> of the end rows <NUM> and simultaneously inside the spreader bars <NUM> and around adjacent ones of the cross members <NUM>, <NUM> and <NUM>.

This same edge line <NUM> may extend in loops around the longitudinal members <NUM>, <NUM> and through cells at the longitudinal edges of the nets <NUM>, for the purpose of fixing the nets <NUM> to the frame <NUM>.

<FIG> show a preferred construction of the nets <NUM> which are made of line, preferably in the form of twisted strand wire lengths <NUM>, <NUM>, <NUM> etc arrayed in the longitudinal direction alongside one another. Nodes of the net <NUM> are formed by crimps <NUM> that provide fastening means and are plastically deformed to join adjacent lengths <NUM>, <NUM>, <NUM> pairwise at intervals to form cells <NUM> of the net <NUM>.

The bending resilience of the wire lengths <NUM>, <NUM>, <NUM> means that a load must be applied to stretch the net <NUM> and spread the lengths to the position shown where they take up the sinusoidal wave-like form illustrated. In a relaxed state, the lengths <NUM>, <NUM>, <NUM> tend to be approximately straight, thus the net <NUM> has an inherent tendency to collapse transversely. A cell <NUM> at a longitudinal edge of the net may be formed by turning back one length on itself, so that a pair of adjacent lengths are integral. For instance, the lengths <NUM> and <NUM> are shown to be integral.

<FIG> shows one configuration of the net <NUM> to provide the trapezium shape of <FIG>, where the inclined edge is formed with the edge row <NUM> of loops or cells <NUM> inclined to the longitudinal edge row <NUM>, and formed by turning back one length <NUM>, <NUM>, <NUM> on itself. The other, approximately orthogonal, edge row <NUM> shown in <FIG>, comprises cells <NUM> that are not formed by turning back the length by are instead closed by crimps <NUM> that lie along the edge.

Correspondingly, the inclined edge row <NUM> need not comprise loops formed by turning back the length but may be formed instead by joining separate lengths at this transverse edge by crimps <NUM>, as shown in <FIG>.

In fact all the lengths <NUM>, <NUM>, <NUM> comprising the net <NUM> may be integral, i.e. the net may be formed using a single line laid out in a boustrophedonic pattern, as shown in <FIG>. This drawing also shows how the loops, or turned back sections, may be provided at both ends of each length. Of course, while making the net using a single line for form the lengths may offer advantages it is not essential to the invention.

Two different examples of a spreader bar <NUM> are shown in <FIG>, and both are preferably tubular for a smooth external shape.

Openings <NUM> for receiving the edge line <NUM> are disposed in row and axially spaced apart. Each opening <NUM> may be circular, and extend transversely through the spreader bar <NUM> with the openings <NUM> disposed in coaxial pairs in diametrically opposing wall parts. Central axes of the openings <NUM> generally lie in a common longitudinal plane that equally bisects the spreader bar. The openings may be equally longitudinally spaced. The openings <NUM> may be arrayed in two sets, one set adjacent each longitudinal end (as per <FIG>), or in a single set, as near the middle of the spreader bar <NUM> (as per <FIG>).

A notch <NUM> is formed in each of the longitudinally opposing ends of the spreader bar <NUM>, the notches adapted to receive parts on transversely opposing edges of the net <NUM> to spread the net <NUM> transversely. The notch <NUM> comprises notch parts in diametrically opposed sections of the respective end of the spreader bar, and an axis of the notch <NUM> lies generally orthogonal to the axes of the openings <NUM> that lie in the common longitudinal plane that equally bisects the spreader bar. This arrangement provides that the axis of the notches <NUM> lie approximately in the plane of the installed net, with the axes of the openings <NUM> substantially perpendicular to the plane of the installed net <NUM>.

In use, the nets <NUM> are transported to the installation site, in a collapsed state, where their compact size and low weight is helpful. To install a net <NUM>, a spreader bar <NUM> may be first installed along each transverse edge or end row <NUM> of cells <NUM>, where it passes through each cell <NUM> in the row <NUM>. By then inserting each longitudinal edge of the net <NUM> in a respective one of the notches <NUM>, the resilience of the net <NUM> and its tendency to collapse transversely, ensures that the spreader bars <NUM> are firmly connected to the net <NUM>. Optionally, prior to moving to the perimeter frame <NUM>, one end of the edge line <NUM> may also be fixed to one of the spreader bars <NUM>.

<FIG> illustrates the fastening of the edge line <NUM> to the spreader bars <NUM>, in which the edge line <NUM> is inserted back and forth through the openings <NUM>, thereby providing a high degree of friction that prevents unwanted release of the line <NUM>. The line <NUM> extends through the bar <NUM> and the openings <NUM> of one pair before a tight loop <NUM> reverses its direction, to extend through the next opening <NUM>, which may be immediately adjacent. These steps are then repeated, as to form four, five or more loops <NUM>. The end <NUM> of the edge line <NUM> may be directed vertically downward to prevent water ingress. When using a polymer coated <NUM> to <NUM> diameter wire edge line <NUM>, a satisfactory fixing can be achieved by hand using this method i.e. without the need for tools.

Generally, the installation is then completed by placing the spreader bar <NUM> adjacent a transverse one of the members of the perimeter frame, for instance transverse member <NUM>. Loop type fasteners <NUM>, such as cable ties may be used to temporarily secure edges of the net <NUM> to the perimeter frame <NUM>. The edge line <NUM> is then helically wrapped in loops about the transverse member, passing it through each cell <NUM> through which the spreader bar <NUM> itself extends, and inside the spreader bar <NUM>, securing it firmly to the inside of the member <NUM>. A like method is used to secure one longitudinal edges of the net <NUM>, looping the edge line <NUM> through the cells <NUM> on the longitudinal edges.

If a single edge line <NUM> extends around the entire perimeter of a net, the sections of this line <NUM> securing the opposing end rows <NUM> may be fixed to the respective spreader bar <NUM>, as described above, by looping the line <NUM> through the openings <NUM>. In this manner, each section is made independent, in that a break in one section, that extends between two sets of openings <NUM>, does not affect the integrity of any other section so, for instance, a single break in the line <NUM> cannot allow the entire edge line <NUM> to be unwound. To divide the line <NUM> into further independent sections, the sections of the line <NUM> wound around the longitudinal members <NUM> and <NUM> can be separately fixed to these longitudinal members <NUM> and <NUM>, as by a fastening loop <NUM> that is fixed to the edge line <NUM> by a crimped sleeve <NUM> or the like, as shown in <FIG> (where the net <NUM> is omitted for clarity).

When the frame <NUM> is made of dissimilar material to the (stainless steel of the) nets <NUM> and edge line23, to mitigate the potential for galvanic corrosion, polymer strips (not shown) may be provided at the interface between the frame <NUM> and the nets <NUM>, as where the nets overly the intermediate members <NUM>, <NUM> and <NUM>, to prevent contact between the frame <NUM> and the nets <NUM>. Likewise, the nets <NUM> may be fixed inside the inner edges of the frame, as by about <NUM>, to avoid them making contact with the frame <NUM>.

Multiple variations of the fastening steps of this method are possible, and it is of course unnecessary for a single edge line to be secured around the entire perimeter of the frame <NUM>, with both line ends fixed to the same spreader bar <NUM>. Advantageously, using two edges lines <NUM> allows the two spreader bars <NUM> and respective ends of the net to be first fixed to the perimeter frame <NUM>, with the terminal ends of each of these two lines fixed, in the manner described above, to a respective one of the two spreader bars <NUM>. Likewise, a single helical section of the edge line <NUM> around a single transverse member may simultaneously secure two spreader bars <NUM> on opposite sides, as in the member <NUM> in <FIG>.

<FIG> and <FIG> illustrate another manner in which one or more spreader bars <NUM> may be used to fasten transverse edges of a net, in which the spreader bar <NUM> is used to connect two transverse edges together, as to join transverse edges of two nets. In this different application, the use of the spreader bars <NUM> also offers similar advantages in terms of ease of installation and strength for improved ratings. In both <FIG> and <FIG>, adjacent ones of the lengths forming the nets 10a, 10b are joined by crimps <NUM>, thereby forming the cells of the end rows <NUM> that defines these transverse edges.

<FIG> shows the use of a single spreader bar <NUM> to connect two transverse edges together, so as to join two nets 10a, 10b end-to-end. The spreader bar <NUM> passes through the cells the end rows <NUM> of net 10a, in a woven manner, and at the same time passes through the cells the end rows <NUM> of net 10b, in a woven manner. The spreader bar <NUM> may be secured in place by effectively connecting the two ends of the spreader bar <NUM> to the frame <NUM> using an edge line 23a that also serves to secures the longitudinal edges of the net 10a to adjacent members <NUM>. This may be done by passing the edge line 23a sequentially through four adjacent ones of the openings <NUM> near the ends of the spreader bar <NUM>, and passing the edge line 23b sequentially through adjacent ones of another set of the openings <NUM> near the ends of the spreader bar <NUM>, thus providing the added security of fixing each end of the spreader bar <NUM> with two separate lines 23a, 23b.

An alternative arrangement, shown in <FIG>, employs a pair of spreader bars 22a, 22b, each passing through the cells of the end rows <NUM> of a respective one of two nets 10a, 10b, in a woven manner. The edge line <NUM> is then used to connect the pair of spreader bars <NUM> together, by winding the edge line <NUM> in a helical manner around the outsides of both spreader bars <NUM>. Opposite ends of the edge line <NUM> may be fixed to the spreader bars <NUM>, in the manner described above, by passing it consecutively through the openings <NUM>, as shown. A particular advantage of this arrangement is that varying the spacing between the spreader bars <NUM> provides a method for varying the length of the net.

Claim 1:
A helideck safety net (<NUM>) including:
a net (<NUM>) elongated in a longitudinal direction, the net formed of lengths of line (<NUM>, <NUM>, <NUM>) arrayed in the longitudinal direction alongside one another, and fastening means (<NUM>) that join adjacent lengths at intervals to form cells (<NUM>) of the net, wherein a longitudinal row of cells is formed on longitudinal edges of the net and the longitudinal edges are joined by at least one end edge, wherein an end row (<NUM>) of cells is formed along the at least one end edge,
at least one spreader bar (<NUM>) adapted to pass through the cells of one of the end rows, and
an edge line (<NUM>) adapted to secure the net inside a perimeter frame (<NUM>) by being wound generally helically in loops around the perimeter frame, each loop passing through a cell of the longitudinal rows, and through a cell of the end rows and simultaneously inside the at least one spreader bar to secure the spreader bar to the perimeter frame, wherein the at least one spreader bar includes an array of openings (<NUM>) through which the edge line can be threaded to fix the ends of the edge line.