GB2034641A - A method of arranging a protective skirt for towing and deploying around an iceberg - Google Patents

Abstract

The skirt comprises a string of floating posts (20, 22) interconnected by panels (12) of flexible sheet material which are suspended in a vertical plane between each pair of adjacent posts. The posts comprise an underwater buoyancy chamber (24) of large diameter and a small diameter pole (26) projecting up out of the water therefrom. The skirt is folded in a zig-zag manner between a leading group I of hinge posts A, C, E and a trailing group II of posts B, D, F. The posts of the two groups are fastened together as are pairs of corresponding intermediate posts (22) of the innermost pair of stretches of skirt between the two groups. The length of the folded skirt may be in the order of several hundred meters, whereby a length of skirt sufficient to protect a tabular iceberg can be handled as a single unit during towing from its assembly point in sheltered waters to an iceberg and during deployment around the iceberg. <IMAGE>

Description

SPECIFICATION A method of preparing a protective skirt for towing and deploying around an iceberg The present invention relates to preparing a protective skirt for a tabular iceberg for transport of the skirt from a location where the skirt is prepared to a site where it is deployed around an iceberg. The invention also relates to the deployment of the skirt around the iceberg.

There have been several proposals for towing tabular icebergs, such as are calved from Antarctic ice shelves, to coastal regions that require fresh water. Recent proposals have mostly envisaged regions such as the Arabian peninsular, Australia and California. Because of their regular shape, tabular icebergs from Antarctic are essential for this purpose (even for Northern Hemisphere destinations). Other icebergs, and especially Arctic icebergs, are irregular and are therefore prone to capsizing as their flanks are eaten away by melting and the mechanical action of the waves. Nonetheless, to avoid excessive loss, even from a tabular iceberg, it is necessary to provide some form of thermal and mechanical protection around the iceberg during towing. Such protection is provided by a barrier referred to herein as a "skirt".In outline, such a skirt comprises three main components: floats; an upper portion which is supported by the floats and which provides mechanical protection against waves and swell in addition to the thermal protection it provides by trapping a zone of cold water around the iceberg; and a lower portion which provides thermal protection around that part of the iceberg which remains submerged even in the heaviest seas expected.

These components are described in greater detail elsewhere and for an understanding of the present invention it is sufficient to understand that our preferred floats are generally stable vertically in spite of waves e.g. by virtue of their principal buoyancy chamber being located deep below the surface of the sea and their portion which projects above the surface being of relatively small cross section. This portion which projects above the surface may be in the form of a pole or a hollow tower according to the design used and the term "post" is used herein as being generic of such portions regardless of their relative outside dimensions.The preferred upper portion of the skirt comprises at least one layer of matted nylon braid slung in vertical panels between the posts of two adjacent floats, while the preferred lower portion comprises panels of plastics material which, when in position, are suspended from cables joining the lowest points of adjacent floating posts. The lower portion is released for deployment of the manner of a Venetian blind only after the remainder of the skirt has been installed around an iceberg and it is therefore not of direct bearing on the present invention.

The problem of protecting a tabular iceberg, and in particular of deploying a protective skirt around a tabular iceberg, is principally a question of scale. A typical tabular iceberg is 200m to 250m thick and its width must be sufficient to keep it from capsizing, even after suffering some loss from melting and wave attack - say 400m to 500m. Its length may be of the order of 1 km to 2 km or even more. This results in a total perimeter in the order of a few km. Some previous propoals for transport and deployment of protective skirts for icebergs have contemplated the use of a skirt made up of sections which are assembled together in situ around the iceberg they are to protect. In view of the hazardous conditions under which such work will have to be performed, there is a need for reducing such assembly operations as much as possible.The present invention provides a step in that direction in the form of a method enabling protective skirts to be assembled into lengths of up to at least a few km in protected waters and then to be handled as a single unit during towing to an iceberg and during deployment around the iceberg.

The present invention provides: A method of preparing a protective skirt for towing at sea for subsequent deployment around an iceberg, the protective skirt comprising a string of floating posts interconnected by panels of flexible sheet material which are suspended in a vertical plane between each pair of adjacent posts, the method comprising dividing the skirt into a plurality of portions of substantially equal length, the portions being interconnected by posts designated as hinge posts, and then folding the skirt so that the hinge posts and the end posts are collected in two end groups of alternate posts with the said plurality of skirt portions extending in parallel between the said two end groups, and inter-connecting the hinge posts and the end posts in each of the said end groups, whereby the entire skirt may be towed from one of said end groups acting as a leading end group with the other end group forming a trailing end group.

The preferred arrangement for such folding is for the centermost hinge post to form the leading post of the leading group for towing and for the end posts to form the outermost posts of the trailing group. Such an arrangement facilitates deployment around the iceberg since the skirt can then be unfolded by two tugs towing the end posts in opposite directions around the iceberg. Indeed the preferred method of deploying the skirt is to tow it so that it lies generally perpendicular to the windward side of the iceberg with its leading group at the windward end (away from the iceberg) and its training group closer to the iceberg. The leading group can then be released and two tugs can each take one of the end posts in tow and then steam in opposite directions around the iceberg.The wind will tend to push the central portion of the skirt against the iceberg while the work of towing the end portions upwind towards the end of the deployment operation (the tugs should steer wide of the iceberg to ensure proper unfolding of the skirt) is little hindered by the wind since this part of the tow takes place in the wind shadow of the iceberg.

Preferred methods of preparing a protective skirt for towing at sea and of subsequently deploying the skirt around an iceberg are described by way of example with reference to the accompanying drawings, in which: Figure lisa plan view of a folded skirt ready for towing; Figure 2 is a plan view on a larger scale of the ends of the skirt shown in Figure 1; Figure 3 to 6 are successive plan views of a skirt during deployment around and iceberg; and Figure 7 is an elevation showing a detail of the skirt when in position against an iceberg.

The nature of the protective skirt is best seen in Figure 7 which shows the skirt in its operative position. The top of a tabular iceberg (10) can be seen projecting above panels (12) of the protective skirt. The panels (12) are slung in a vertical plane parallel to the flank of the iceberg (10) between adjacent pairs of floating posts e.g. a winch post (20) and an intermediate post (22). The surface of the sea is indicated at (14) and since about 7/8ths of an iceberg is below the surface it will be appreciated that the bottom of the iceberg (10) is well below the bottom edge of the drawings.

Both of the floating posts (20) and (22) comprise a deeply submerged buoyancy chamber (24) in the form of a large diameter horizontal disc or wheel supporting an upwardly extending pole (26) of much smaller diameter. The floating poles are ballasted so that they remain upright and their vertical displacement in a swell is considerably less than that of the surrounding water surface. The winch post (20) constitutes a hinge post of the folded skirt. It is distinguished from an intermediate floating post (22) by including a helicopter deck (28) and two vertically extending furling drums (30) for winching in (furling) the panels of skirt to which the winch post (20) is attached. The furling drums (30) are hydraulically driven by a diesel-powered hydraulic system, not shown.The intermediate floating post (22) is terminated by a cap (32) and is connected to the panels (12) by pins (34) which are not equipped to be rotated.

The panels of protective skirt are constituted by a large number of horizontal tapes of nylon braid which are placed substantially edge to edge with each other. At intervals these tapes are fastened to vertical tapes (16) (e.g. by stitching) to provide a partially permeable trellis-like or hurdle-like matted barrier to the sea. The panels are reinforced longitudinally on either side thereof by horizontal straps (18).

The lower portion of the protective skirt for thermal protection of the flanks of the iceberg (10) below the matted panels (12) is not shown. It consists of a concertina-like or Venetian-blind-like arrangement suspended on cables connecting together the buoyancy chambers (24) of adjacent floating posts. The lower portion is not deployed downwards from its supporting cables until after the upper portion of the skirt has been put in position around the iceberg (10) and it is therefore not a feature of the present invention.

On referring to Figure 1 and 2 it can be seen that the floating posts (20) or (22) are represented by large circles (the buoyancy chambers 24) with smaller concentric circles (the poles 26). The panels (12) are shown as lines joining the poles (26), and the winch posts are lettered A to F and include helicopter decks (28) which can be seen to be octagonal in plan.

The skirt is folded from a centermost winch post (20) labelled A and extends in two parallel portions or stretches for about 500m to two further winch posts labelled b and F. Pairs of intermediate posts (22), one from each stretch of the skirt, are fastened together by lashing indicated by chain-dotted lines, and are held apart by fenders (36) inserted between their buoyancy chambers (24). Two further stretches extend from the posts B and F back to the vicinity of the post A. These further stretches are on the outside of the first pair and they terminate in winch posts C and E. The procedure is repeated one more time to an end winch post D and an end intermediate post a. On each side of the train thus constituted the outer stretches of skirt are held apart by the innermost pair whose intermediate posts are lashed and fendered.The posts at the folds in the skirt i.e. the winch posts A, B, C, E, and F constitute hinge posts of the folding arrangement. The hinge posts and the two end posts D and a are fastened together in a leading group I and a trailing group II. The posts in each of these groups are protected from each other by fenders (36). The entire folded skirt can be towed from the post A as indicated by an arrow.

Although the spacing between intermediate posts (22) is even, the spacing between winch posts and their adjacent intermediate posts is adjusted differently in order to interspace the intermediate posts along the stretches between the leading and the training groups I and II. This adjustment may be conveniently performed by using the furling drums (30).

The folding operation has been described from the middle outwards as this the preferred order in order to facilitate fastening of the corresponding pairs of the intermediate posts (22) of the middle stretches.

Naturally it.would also be possible to start from one end and work towards the other.

The procedure for deploying the skirt around an iceberg is shown in Figures 3 to 6. These figures follow a sequence and are substantially self-explanatory. An iceberg (10) is lying, for example, along a N-S axis with a west wind (38) blowing. The folded skirt is towed into the wind from near the iceberg (10) so that it is substantially perpendicular to the axis of the iceberg (10) with is end posts D and a nearest to the iceberg (10). The posts which are fastened together during towing are separated and two tugs (40) and (42) are connected to the end posts D and a respectively. This is the position shown in Figure 3. The tugs (40) and (42) then steam in opposite directions steering a wide path around the iceberg (10) so that the skirt unfolds and follows the tugs around the iceberg. On the windward side of the iceberg the wind (38) pushes the stretch of skirt from posts B to F towards the iceberg while the remaining portions surround the ends of the iceberg and are then towed along its lee side. The hindrance of the wind (38) is therefore lessened on this side by the wind shadow of the iceberg(10).

The end posts D and a may be interconnected by a panel (12) of matted nylon braid that is transported fully wound on the free one of the furling drums of the winch post D.

Other folding arrangements can be devised, but the one shown appears to be the simplest both for initial folding and for subsequent unfolding during deployment around the iceberg. It is safe to assume on most occasions when deployment is to be done that there will be a wind from some direction. Indeed it may be preferable to wait for a wind if there is a flat calm since the skirt has enormous resistance to broadside movement through the water. The force necessary for pushing it sideways as supplied by the wind is evenly distributed along the skirt whereas any attempt at supplying it all from the ends of the skirt via the tugs would either have little effect or could cause damage to the skirt depending on how large a force was applied.

NOMENCLATURE A - F particular winch posts a a particular intermediate post 10 tabular iceberg 12 panels of protective skirt 14 surface ofthe sea 16 vertical tapes 18 horizontal straps 20 a winch post 22 an intermediate post 24 buoyancy chamber of floating post 26 pole of floating post 28 helicopter deck 30 furling drums 32 cap 34 pins 36 fenders 38 wind 40,42 tugs

Claims (12)

1. A method of preparing a protective skirt for towing at sea for subsequent deployment around an iceberg, the protective skirt comprising a string of floating posts interconnected by panels of flexible sheet material which are suspended in a vertical plane between each pair of adjacent posts, the method comprising dividing the skirt into a plurality of portions of substantially equal length, the portions being interconnected by posts designated as hinge posts, and then folding the skirt so that the hinge posts and the end posts are collected in two end groups of alternate posts with the said plurality of skirt portions extending in parallel between the said two end groups, and interconnecting the hinge posts and the end posts in each of the said end groups, whereby the entire skirt may be towed from one of said end groups acting as a leading end group with the other end group forming a trailing end group.

2. A method according to claim 1, wherein the posts in the two portions of skirt extending from the centermost hinge post are fastened to each other in pairs.

3. A method according to claim 2, wherein the posts are symmetrically disposed about the centermost hinge post and wherein corresponding posts in portions of the skirt other than the portions extending from the centermost hinge post are prevented from colliding with each other by virtue of their resting against the outside of the panels of flexible sheet material which are held apart by said posts fastened in pairs.

4. A method according to claim 1,2, or 3, wherein the posts are equally spaced except for the spacings on either side of at least some of the hinge posts which are sufficiently different from the said even spacing so that the posts of at least some portions are located between the posts of other portions.

5. A method according to claim 4, wherein the hinge posts include winch means for winding-in the panels of flexible sheet material which they suspend, said winch means serving to adjust the said different spacing for towing and also serving, once the skirt is deployed around the iceberg to be protected as means for tightening the skirt around the iceberg.

6. A method according to claim 5, wherein one of the end posts also includes winch means, said winch means carrying a panel of flexible material that is to be used to connect the said end post to the other end post (or to the end post of another skirt) once the skirt is deployed around the iceberg to be protected.

7. A method according to any preceding claim, wherein the posts which are fastened together are lashed together and held apart from each other by interspaced fenders.

8. A method of preparing a protective skirt for towing at sea, substantially as herein described with reference to the accompanying drawings.

9. A method of deploying a protective skirt around an iceberg, the skirt being prepared according to any previous claim, the method comprising towing the folded skirt so that it extends perpendicularly from substantially the centre of one of the sides of the iceberg and then towing its end posts simultaneously in opposite directions around the iceberg.

10. A method according to claim 9, wherein the windward side of the iceberg is chosen as the side from which the folded skirt is to extend perpendicularly whereby the wind assists in directing the mid-portion of the skirt against the iceberg and whereby the work of towing the ends of the skirt upwind against the opposite side of the iceberg is reduced by virtue of the icebergs wind shadow.

11. A method according to claim 9 or 10, wherein the end posts both form part of the trailing group and wherein the trailing group is the nearer of the groups to the iceberg when the folded skirt is extended perpendicularly from one of the sides of the iceberg.

12. A method of deploying a protective skirt around an iceberg substantially as herein described with reference to the accompanying drawings.