GB2041024A

GB2041024A - A Modular Net Component for Use in Towing Icebergs

Info

Publication number: GB2041024A
Application number: GB7902599A
Authority: GB
Original assignee: Iceberg Transport International ITI Ltd
Current assignee: Iceberg Transport International ITI Ltd
Priority date: 1979-01-25
Filing date: 1979-01-25
Publication date: 1980-09-03

Abstract

A pair of short vertical posts (12) are interconnected by a plurality of long horizontal straps (14). Cross- straps (16) hold the horizontal straps apart at regular intervals. The posts have end fastening means (26,27) for connection to other net components one above the other and lateral drawplates (24,25) for connection to other net components or to a cable for towing the net as a whole. <IMAGE>

Description

SPECIFICATION A Modular Net Component The present invention relates to a modular net component particularly, but not exclusively, for use in offshore applications.

Three main off-shore applications are envisaged: 1. A net for towing small Northern icebergs out of the way of oil rigs, e.g. off the coast of Alaska.

In such an application, the net holds the iceberg while a tug or tugs tow on cables which are connected to the ends of the net.

2. A sea anchor from which large objects, such as icebergs and oil rigs, can be towed by winching.

3. A protective flexible sheet to mitigate the effect of wave action on the flanks of a tabular iceberg.

The common feature of these listed applications is the need for a very large net or sheet which is capable of wthstanding heavy mechanical loading. Clearly there are other applications which could also benefit from a net suitable for use in any or some of the listed applications and the invention is not limited to any particular application.

The present invention provides a modular net component, the component comprising a pair of short posts interconnected by a plurality of long, parallel straps, each post being provided with end fastening means at each end for fastening to the end of a post of another, like modular component in an axial relationship, and being further provided with lateral fastening means for fastening to the lateral fastening means of a post of another, like modular component in a parallel relationship.

Such a component is intended for assembly with other, like components to constitute a net of very large size, although naturally there may be occasions when a single component is sufficient on its own. Thus the component can be of a size which is relatively easy to manipulate, e.g. having posts that are 1.5 metres high and straps that are 100 metres long. Typically the straps of one component are capable of transmitting a force of about 90 tonnes weight. For greater forces, further components need to be disposed in parallel. For the same force spread over a greater extent, components can be connected end-to-end by the lateral fastening means of their posts.

Two main strap configurations are envisaged: in the first, the straps are spaced apart leaving substantially strap-sized gaps between adjacent straps. This configuration is the more obviously net-like configuration. In the second configuration, the straps are laid substantially side by side forming a nearly continuous sheet. In both configurations the straps are held at the desired spacing by cross-straps spaced out evenly along their length.

The first or more net-like configuration is primarily intended for an application such as holding small Northern iceberg for towing out of harm's way.

The second, or more sheet-like configuration is primarily intended as a deliberately permeable protective barrier for mitigating the effect of wave action on the flanks of a tabular (Southern) iceberg.

Both configurations can be used to constitute sea anchors from which large objects can be towed by winching. This is perhaps a little unexpected of the first configuration, but its dynamic resistance to moving through water is high at moderately low speeds, even though its static resistance is less than that of the second configuration.

Two modular net components embodying the invention and arranged in several different ways are described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side view of one end of a first modular net component; Figure 2 is a plan view of the component shown in Figure 1; Figure 3 is a side view of the ends of four assembled components; Figure 4 is a side view showing the ends of two components arranged for towing; Figure 5 is a section along the line V-V of figure 2; Figure 6 shows portions of figure 5 to a larger scale; and Figures 7 and 8 are similar to figures 5 and 6 but show a second modular net component.

In figure 1 and 2 it can be seen that an end of a modular net component (10) comprises a short vertical post (12) connected to eight horizontal straps (14). Each strap (14) comprises a flattened loop of nylon braid with an eye (40) at each end.

The eyes (40) are threaded by a strap-retaining pin (20) which also threads eight pairs of lugs (22) projecting from the post (12); each pair of lugs (22) corresponding to a respective one of the straps (14). A short cross-strap (16) passes between the two arms of each of the horizontal straps (14) and each cross-point is stitched. The horizontal straps (14) are about 100 metres long and the post is about 1.5 metres high. Crossstraps (16) are evenly spaced at intervals (of about 5 metres) along the span of the horizontal straps (14).

The post (12) has two drawplates (24) and -(25) These plates constitute lateral fastening means for the post and they are capable of transmitting the load bourn by the straps. The post (12) is made of steel tube, and the lugs (22) as well as the drawplates (24) and (25) are welded thereto. It also has end fixing means in the form of supporting plates (26) and (27).

In figure 1 a second post (12') of a second net component (10') is shown in a chain dotted outline. The posts (12) and (12') are identical except that they are opposite ways up. The drawplate (24) is further from its end of the post (12) than is the drawplate (25) from its end, and the corresponding drawplates (24') and (25') are likewise displaced. The posts (12) and (12') are connected to each other at their drawplates and in each case a plate (24) or (24') is adjacent a plate (25') or (25). This asymetric offsetting of the drawplates makes it possible to join net components end-to-end without changing the level of the straps from one component to the next. The preferred method of ensuring that the plate off-sets are complementary, is to have the posts at each end of a single net component oppositely oriented with respect to each other.An alternative solution would be to deploy some net components upside down relative to the others.

The net configuration shown in figure 1 is an open configuration with a substantially strapwidth space extending between adjacent straps.

Such an arrangement could typically withstand 6 tonnes weight per strap giving a total load of 48 tonnes weight on the posts to be transmitted through the drawplates. However, it is also possible to have a denssr or slit-sheet configuration with adjacent straps touching or nearly touching (in such a configuration the lugs (22) should be evenly spaced out along the post (12)). In such a case the total load would be 90 tonnes weight (1 5 straps) and so for the most modular arrangement all posts (12) should be capable of transmitting 90 tonnes weight via the drawplates and should have regularly spaced lugs (22).

Figure 3 shows the use of the supporting plates for connection, via links (28) to net components above or below each other. The links do not need to transmit the principal loads (which in å typical case may approach 100 tonnes, see above) but they must be strong enough to hold an assembly of net components together.

A similar arrangement is shown in figure 4, which further shows a buoy (30) supporting the top of a vertical connection of posts (12), and towing arrangements attached to the drawplates of each post (12). The towing arrangement comprises two bridle arms (31,32) connected together and to a towing cable (34) by a ring (36) and connected to respective drawplates by shackles (38). It is also possible to connect two posts (12) together by their drawplates (as shown in figures 1 and 3) and then connect towing arrangements there as well. This is useful in the sea anchor application.

Figures 5 and 6 are sections through the configuration of net shown in figures 1 to 4 while figures 7 and 8 are sections through the slit-sheet configuration. In all four of these figures the vertical member is a cross-strap (16) while each of the horizontal straps (14) passes on both sides of the cross-strap (16).

Figures 6 and 8 show a ballasting arrangement for ensuring that the net components are properly oriented in water. Between the two parts of the uppermost horizontal straps (14) there is a layer of low-density float material (42) while between the two parts of the lowermost horizontal straps there are several runs of steel cable (44) acting as ballast. The net result is a tendency for the net components to occupy a vertical plane when in water. The posts (12) should be closed or filled with low-density material so that the components have a substantially neutral buoyancy.

List of Reference Numerals 10,10' modular net component 12,12' short post 14 horizontal straps 1 6 cross-strap 18 20 strap-retaining pin 22 lugs 24,25 drawplates 26,27 supporting plates 28 links 30 buoy 31,32 bridle arms 34 cable 36 ring 38 shackles 40 eye at end of strap 14 42 float material 44 steel cable

Claims

1. A modular net component, the component comprising a pair of short posts interconnected by a plurality of long, parallel straps, each post being provided with end fastening means at each end for fastening to the end of a post of another, like modular component in an axial relationship, and being further provided with lateral fastening means for fastening to the lateral fastening means of another, like modular component in a parallel relationship.

2. A net component according to claim 1, wherein the straps are at least twenty times as long as the posts.

3. A net component according to claim 1 or 2, wherein the straps occupy about half of the area between the posts, leaving open spaces between adjacent straps of substantially the same widths as the straps.

4. A net component according to claim 1 or2, wherein the straps occupy nearly all of the area between the posts leaving little open space between adjacent straps.

5. A net component according to any preceding claim, and including short straps parallel to the posts and fastened to the long straps.

6. A net component according to claim 5, wherein the short straps are at intervals of about 5 metres.

7. A net component according to any preceding claim, wherein the straps are made of nylon.

8. A net component according to any preceding claim, wherein each strap comprises a flattened loop with an eye at each end for fastening to a respective one of the posts and having two lengths extending between the posts.

9. A net component according to claim 8, of approximately neutral overall buoyancy, and having an elongated float inserted between the two lengths of an upper one of the straps and elongated ballast inserted between the two lengths of a lower one of the straps, whereby the component has a tendency to adopt a vertical position when in water.

10. A net component according to any preceding claim, wherein the posts are made of steel tube.

11. A net component according to any preceding claim, wherein the posts at each end of the net component are identical in structure, with the lateral fastening means being suitable for fastening to identical fastening means of another, like net component.

12. A net component according to claim 11, wherein the lateral fastening means are asymmetrically disposed along the length of each post and the posts at opposite ends of a single net component are oriented in opposite directions.

1 3. A net component according to any preceding claim, wherein the lateral fastening means are strong enough to transmit loads at least as great as those which can be transmitted by the set of straps in their axial direction.

14. A modular net component substantially as herein described with reference to, or as illustrated in figures 1 to 6, or figures 1 to 6 as modified by figures 7 and 8 of the accompanying drawings.