WO1986004942A1

WO1986004942A1 - Arrangement in boom structure

Info

Publication number: WO1986004942A1
Application number: PCT/NO1986/000018
Authority: WO
Inventors: Jan Monrad Tangen; Per Hartwig; Ole Fritjof Nyhammer; Svein Tore Rabben
Original assignee: Bennex Services A/S
Priority date: 1985-02-22
Filing date: 1986-02-20
Publication date: 1986-08-28
Also published as: NO156297B; NO156297C; NO850738L; EP0213167A1

Abstract

A boom structure comprises a skirt (1) of impervious fabric, elongated floating means (2) in the form of pipes, and spacers (3) which are attached to the floating means and to the upper and lower edges (6, 8) of the skirt for keeping the skirt extended. The floating means (2) are constituted by two adjacent plastic pipes held together by lashings (5). The spacers are constituted by short pieces of pipe (3), also of plastic material, with the axial direction transversely of the longitudinal direction of the boom. The spacers are attached to the floating means (2) by means of the same lashings (5), which may be constituted by belts provided with buckles. The supporting structure of the boom consisting of the lashed pipes (2) and pieces of pipe (3) give the boom good sideways stability and also sufficient flexibility in the vertical plane.

Description

Arrangement in boom structure

The present invention relates to an arrangement in a boom structure, comprising a skirt of impervious fabric, elongated floating means in the form of at least one flexible pipe having relatively high stiffness in the axial direction, spacer means attached to the floating means and to the upper and lower edges of the skirt in order to hold the latter extended, and possibly ballasting means attached to the lower edge of the skirt in order to hold the latter generally vertically in the sea.

Boom structures of this type are often used to limit oil spill from a potential source of pollution, for instance a loading and unloading terminal for tankers. The boom is held in standby condition in that it is lying submerged on the bottom in a ring around the potential source of pollution. Should for instance an oil spill occur, the boom is raised to the surface by filling the floating means with air.

In order for the boom to stay in place both in standby condition on the bottom and in floating position during use without the necessity of too many mooring points, the floating means may advantageously have a certain stiffness, at least in the axial direction. Thus, it has been found expedient to use floating means in the form of a long plastic pipe. It has the desired stiffness, but is concurrently sufficiently flexible in the vertical plane to be able to follow the wave move¬ ments most likely to occur.

The spacer means holding the skirt of the boom extended in the vertical direction and providing attach¬ ment for the floating means, usually have consisted of stiff stays of metal or glass fiber reinforced plastic. Such stays have the disadvantage that they are prone to getting hooked into mooring ropes and the stabilizing net usually provided at the lower edge of the boom. This problem is often largest when the boom lies in standby condition on the bottom, where current and waves may cause movements in the boom. The stiffness of the stays may also contribute to damage to the boom fabric due to wave movements. If waves move in the longitudinal direction of the boom, the floating means will usually be able to follow these, the boom thus assuming a generally sinusoidal form in the vertical . plane. In the wave troughs, where the top of the boom will be upwardly concave, slack occurs in the boom fabric and top rope. On the wave crests, however, the boom will assume a convex form, but since the floating means, due to their axial stiffness, will tend to maintain their length, the upper edge of the boom may be stretched beyond its nominal length. During such circumstances one has found both that the boom fabric has been torn and that the stays have been broken or bent.

Further deficiencies in previously known booms of this type are that they have been cumbersome to assemble and have shown low stability during sideways influence from wind and current.

The object of the present invention is to provide an improved boom structure of the type mentioned in the introductory paragraph.

According to the invention this is obtained in that the floating means are constituted by at least two pipes arranged alongside each other, and in that the spacer means are each constituted by two pipe pieces, preferably of plastic material, which are attached to the floating means on opposite sides of these, the central axes of the pipe pieces extending transversely of the longitudinal direction of the floating means.

Thus, one has avoided spacers in the form of stays which can get hooked into the stabilizing net and mooring lines, so that the boom can stand movements while lying standby on the bottom. Spacers in the form of pipe pieces of plastic material facilitates a certain mov- ability of the attachment points for the boom fabric in the longitudinal direction of the boom, so that the slack occuring in a wave through may be transferred to the con- c vex portion on the adjacent wave crest. Therefore, one has to a substantial degree reduced the danger of over¬ loading and damage to the boom fabric and spacers. The pipe pieces constituting the spacers may be cut from commercially available pipe material, which contributes

I_Q to making the entire boom structure simple and inexpen¬ sive.

According to an advantageous feature of the inven¬ tion, the pieces of pipe are attached to the floating means by means of a lashing which has been run around the

_|c floating means and through the pipe pieces. This contri¬ butes to the flexibility of the pipe pieces in the longi¬ tudinal direction of the boom, so that this may more easily adapt to wave movements without overloading. The lashings also constitute a very simple means for holding n the two pipes constituting the floating means in place but, nevertheless, permit a certain relative axial move¬ ment between the pipes if these, due to production tole¬ rances in the material properties or for other reasons, should change differently when they are subjected to

25 environmental effects.

The lashing may advantageously consist of a belt having a buckle, both preferably made from synthetic material. Thus, the lashing may very quickly be brought in place and tightened to the desired degree, so that

30 assembling the boom may take place in a simple manner at the place of use, which is often necessary due to the relatively great length of the pipes constituting the floating means.

Furthermore, according to the invention it is

35 suggested to make the largest axial dimension of the pipe pieces somewhat larger than the diameter of the floating means. Thus, the pipe pieces will rest steadily against the two pipes constituting the floating means and form a relatively stable structure, making the lateral stability of the boom very good. In other words, the boom will not have a tendency to lie flat in the sea when subjected to c strong wind or current.

The end surfaces of the pipe pieces may advantageously converge in the direction away from the floating means, e.g. so that the smallest axial dimension of the pipe pieces is about half of the largest axial _Q dimension. This tapering form in the direction away from the floating means contributes to the flexibility of the spacers in the longitudinal direction of the boom, while still leaving them with a relatively wide "foot" for resting against the floating means. One will of course 5 also save material in the pipe pieces.

In order for improved understanding of the inven¬ tion, it shall be explained more closely with reference to the exemplifying embodiment shown in the accompanying drawings, in which _Q Fig. 1 shows a side view of a boom structure according to the invention.

Fig. 2 shows the boom structure in section along the line II - II in Fig. 1,

Fig. 3 shows a partial view at a larger scale, 5 seen in the direction III - III in Fig. 1, and

Fig. 4 shows at a larger scale the partial view IV - IV in Fig. 1.

The boom structure shown in the drawings comprises a skirt 1, floating means 2, spacers 3 and a stabilizing _Q net 4. The skirt may be constituted by an impervious fabric, e.g. PVC-coated polyamid. The floating means 2 are constituted by two adjacent pipes of PEHD. The spacers 3 are constituted by pipe pieces, which are cut from a pipe which may also be made from PEHD. The pipe 5 pieces 3 are lashed in pairs to the floating means 2, one on either side, by means of a lashing 5, which advantageously may be constituted by a belt and buckle of synthetic material. The spacers in the form of pipe pieces 3 have their central axes extending transversely of the longi¬ tudinal direction of the boom. They have their largest 5 axial dimension in the part resting against the floating means 2 and taper off in the direction away therefrom. The pipe pieces 3 show a certain flexibility in the longitudinal direction of the boom, not only due to their own elasticity, but also because they to a limited extent

^•JO may roll along the floating means 2, provided that the belts 5 are not too rigid and tight.

Along the upper edge 6 of the skirt 1 a rope 7 is run through eyelets, the rope also being run through two holes in the top of the pipe pieces 3 in order to attach

15 the skirt thereto. The skirt has about 15% excess length as compared to the distance between two consecutive pipe pieces 3 in order to reduce the possibility of over¬ loading the skirt during wave strains, as it best appears from Fig. 3. The lower edge 8 of the skirt is attached

20 iⁿ a similar manner by means of a rope 9, and here also ballasting means in the form of lead weights 10 are attached in order to contribute to maintaining the verti¬ cal position of the boom in the sea. The stabilizing net 4 is also attached to the rope 9 and contributes to

25 stabilizing the boom in the sea. At the bottom the stabilizing net is provided with a bottom rope 11, which i.a. is used as attachment for the moorings of the boom.

Even though the boom structure according to the invention is described above with respect to a certain

30 exemplifying embodiment, the invention is by no means restricted to this example, but may be varied in a number of ways within the scope of the following claims. Thus, as an example, the ropes 7 and 9 at the edges of the skirt need not be run through holes in the spacers, but

35 may instead be connected to the outside of these by means of a clamp attached by screws. Nor do the ropes have to be run through eyelets in the skirt, but may instead be attached to the skirt by means of lashings or straps, suitably with buckles, so that the skirt may be assembled to the ropes in a simple and quick manner, preferably during launching of the boom at the place of use.

Claims

C l a i m s

1. Arrangement in a boom structure, comprising a skirt (1) of impervious material, elongated floating means (2) in the form of at least two adjacent, bendable pipes having relatively high stiffness in the axial direction, spacer means (3) attached to the floating means and to the upper and lower edges (6, 8) of the skirt in order to hold the skirt extended, and possibly ballasting means (10) attached at the lower edge (8) of the skirt in order to hold it generally vertically in the sea, c h a r a c t e r i z e d in that the spacers are constituted by two pieces of pipe (3), preferably of plastic material, which are attached to the floating means (2) on opposite sides of these, the central axes of the pieces of pipe (3) extending transversely of the longitudinal direction of the floating means (2).

2. Arrangement according to claim 1, c h a r a c t e r i z e d in that the pieces of pipe (3) are attached to the floating means (2) by means of a lashing (5) which is run around the floating means (2) and through the pieces of pipe (3).

3. Arrangement according to claim 2, c h a r a c t e r i z e d in that the lashing (5) con¬ sists of a belt with a buckle.

4. Arrangement according to any one of the preceding claims, c h a r a c t e r i z e d in that the largest axial dimension of the pieces of pipe (3) is larger than the diameter of the floating means (2).

5. Arrangement according to any one of the preceding claims, c h a r a c t e r i s e d in that the end surfaces of the pieces of pipe (3) converge in the direc¬ tion away from the floating means (2).

6. Arrangement according to claim 5, c h a r a c t e r i z e d in that the smallest axial dimension of the pieces of pipe (3) is about half of c their largest axial dimension.

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