WO1990015531A1

WO1990015531A1 - A float, especially for fish-trawling nets, and a method of manufacturing same

Info

Publication number: WO1990015531A1
Application number: PCT/DK1990/000146
Authority: WO
Inventors: Hilmar Í. LÁGABØ
Original assignee: Lagaboe Hilmar I
Priority date: 1989-06-15
Filing date: 1990-06-12
Publication date: 1990-12-27
Also published as: DK296689A; AU5955290A; DK296689D0

Abstract

In the float (11) (shown before being finally assembled) of the kind consisting of two half-spheres (12, 13) with half-tubes (14, 15) formed integral with each half-sphere, the latter in the finished state (not shown) being welded together to form a liquid-tight hollow body with a through-going duct in a 'center tube' (14, 15), the novel feature is that the center tube (14, 15) is reinforced with at least one sleeve (16, 17) of e.g. steel. In this manner, the ability of the float to withstand great loads, in prior-art floats having caused breakage of the center tube (14, 15), is increased.

Description

A FLOAT, ESPECIALLY FOR FISH-TRAWLING NETS, AND A METHOD OF MANUFACTURING SAME.

TECHNICAL FIELD

The present invention relates to a float of the kind set forth in the preamble of claim 1.

BACKGROUND ART

Practical experience has shown that with floats of this kind, the through-going tube, in the trade referred to as the "center tube", is the first part of the float to fail under great loads. For this reason, floats of this kind are not well suited for use in deep-sea trawling, where the loads may be extremely great.

DISCLOSURE OF THE INVENTION

The disadvantage referred to above is remedied with a float, according to the present invention additionally exhibiting the feature set forth in the characterizing clause of claim 1. This feature causes a strengthening of the center tube, in practice having proved sufficient to reduce or eliminate the risk of breakage of the center tube, even at exceedingly high loads.

The present invention also relates to a method of manufacturing a float according to the present invention. This method is of the kind set forth in the preamble of claim 4, and is, according to the present invention, characterized by proceeding in the manner set forth in the characterizing clause of claim 4. Advantageous embodiments of the float and the method are set forth in claims 2, 3, and 5-8, respectively, and the effects of these embodiments are explained in more detail in the following detailed portion of the present specification.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed specification, the present invention is explained in more detail with reference to the drawings, in which

Figure 1 shows a trawl float of a known type, and

Figure 2 shows an exemplary embodiment of a trawl float according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In order to illustrate the prior art, Figure 1 shows a trawl float 1 consisting of two float halves 2 and 3. Internally in each of the float halves 2 and 3 a tube half 4 and 5, respectively, is formed integral with the float half in question, in such a manner that the bore of each tube half opens to the outside of the float half in question. The two float halves 2 and 3 are, together with their respective tube halves 4 and 5, respectively, joined by welding so as to form the liquid-tight hollow body shown in Figure 1, said body being capable of serving as a float for a line, rope or cable, e.g. a head rope on a fishing net or a trawling net, the line, rope or cable in question extending through the tube, in the trade referred to as the "center tube", consisting of the two halves 4 and 5.

The two float halves 2 and 3, together with their respective tube halves 4 and 5, preferably consist of synthetic plastic material and are produced by casting or moulding. A thermoplastic material is preferred, since it can be welded relatively easily.

Practical experience has shown that when the trawl float 1 is subjected to great loads, the center tube 4, 5 is usually the first part to go to pieces. For this reason, a trawl float of the kind shown in Figure 1 is not well suited for deep-sea trawling.

Figure 2 shows an exemplary embodiment of a trawl float 11 according to the present invention, this float being shown with the two float halves 12 and 13 facing each other, but somewhat spaced before being welded to each other. The trawl float 11 also has two tube halves 14 and 15, respectively, and is con¬ structed substantially in the same manner as the trawl float 1 shown in Figure 1.

The trawl float 11 shown in Figure 2 does, however, differ from the float 1 shown in Figure 1 by accord¬ ing to the present invention being provided with two sleeves 16 and 17, respectively, force-fitted on the two tube halves 15 and 15, respectively. The sleeves 16 and 17 consist of a material with substantially higher tensile strength and modulus of elasticity than the material, of which the remainder of the trawl float 11 consists. Practical experience has shown that sleeves 16 and 17 consisting of steel provide a strengthening of the center tube 14, 15 to such a degree, that the risk of the latter going to pieces is substantially reduced. It is, of course, possible to use other materials than steel, thus e.g. other metals or even fibreglass-reinforced synthetic resin may come under consideration.

In the exemplary embodiment shown in Figure 2, the welding of the two float halves 12 and 13 to each other is not accompanied by any corresponding welding of the two tube halves 16 and 17 to each other - at least not if they consist of metal - but in spite of this, the sleeves have proved to cause a considerable stiffening of the center tube 14, 15.

It is, however, also possible to contemplate the present invention being carried out by means of a single sleeve, having e.g. twice the length of each of the sleeves 16 and 17, said single sleeve being fitted on one, e.g. 14, of the tube halves before assembling the two float halves 12 and 13, after which the free end of the "double" sleeve is force-fitted on the other tube half 15 during the operation of assembling the two float halves. In that case, the requisite energy for welding the two tube halves 14 and 15 to each other may be provided through the bore of one of the tubes.

It is also possible to use more than one single sleeve on each tube half and it is equally possible in a manner similar to what is shown in Figure 2 to use two sleeves of a shape similar to the sleeves 16 and 17, but provided with coupling means, e.g. screw threads, with which they may be coupled to each other to form a single sleeve during the operation of assembling the float halves 12 and 13. To avoid local stress concentrations, which could in time lead to fatigue failure, it is preferred that the edges of the sleeves facing the center tube are chamfered or - preferably - rounded. Such a shape will also make it easier to fit the sleeves on the tube halves in question.

Due to the great loads, to which a trawl float of this kind may be subjected, it is preferred to use substan- tially compact plastic material for the float halves 12 and 13 and their associated tube halves 14 and 15, but it is also possible, especially for less demanding tasks, to use plastic material that is foamed to a greater or lesser degree.

A trawl float that has given good results in practical trials has the following dimensions (approximate measurements in millimetres):

Outside diameter of float 203 Wall thickness of float 11 Outside diameter of center tube 39⁺ Wall thickness of center tube 10

Inside diameter of sleeves 39⁺

Wall thickness of sleeves 2.5

Length of sleeves 60 Material of sleeves steel

⁺ tight fit

Further, tests have been carried out with a float of polystyrene constructed according to Figure 2, reinforced with two sleeves of polyamide, as follows (linear dimensions in millimetres): Sleeves:

Length 65

Outside diameter 62 Inside diameter 38 Material: polyamide ("ERTALON 6PLA") tensile yield stress (DIN 53455) 82 N/mm² tensile modulus of elasticity (DIN 53457) 3300 N/mm²

Float sphere:

Diameter 200

Material: polystyrene tensile yield stress 30-40 N/mm² tensile modulus of elasticity 2550 N/mm²

The sleeves were inserted with a press fit on the center tube.

A pressure test showed that the first part to fail was the shell of the sphere - in contrast to the previously known floats, in which the center tube was the weakest component.

Claims

CLAIMS :

1. A float, especially for fish-trawling nets, of the kind consisting of a liquid-tight hollow body (11) of plastic material with a through-going tube (14, 15) of plastic material, said tube in the locations where it adjoins the wall of the hollow body being connected in a liquid-tight manner with the wall of the hollow body in such a manner, that a line, rope or cable may run through the bore of said tube (14, 15), c h a r a c t e r i z e d in that the tube (14, 15) is closely embraced by at least one sleeve (16, 17) of a material having a high tensile strength and a high modulus of elasticity.

2. A float according to claim 1, c h a r a c¬ t e r i z e d in that the material in the sleeve or sleeves (16, 17) is steel.

3. A float according to claim 1, c h a r a c¬ t e r i z e d in that the material in the sleeve or sleeves (16, 17) is fibreglass-reinforced plastic.

4. A method of manufacturing a float according to any one or any of the claims 1-3, said method being of the kind comprising the following steps a and b, carried out in the order mentioned: a) for each float two float halves (12, 13) of plastic material are produced, each such half consisting of a bowl, from the bottom to the open side of which extends a tube half (14, 15), the wall of which is connected in a liquid-tight manner to the wall of the bowl, and the bore of which opens through or outside of the bottom of said bowl, b) the two float halves (12, 13) are moved towards each other and joined in such a manner, e.g. by welding, that the two bowls of said two float halves with their associated tube halves (14, 15) cooperate in forming a hollow body as set forth in the preamble of claim 1, c h a r a c t e r i z e d in c) that prior to the above-mentioned step b, at least one sleeve (16, 17) of a material with a high tensile strength and a high modulus of elasticity is placed with a close or tight fit on at least one of the tube halves (14, 15).

5. A method according to claim 4, c h a r a c- t e r i z e d in that on each tube half (14, 15) a single sleeve (16, 17) is placed extending along a substantial proportion of the length of the tube half and ending close to or flush with the end of the tube half facing away from the associated bowl.

6. A method according to claim 4, c h a r a c¬ t e r i z e d in that a sleeve is placed solely on one of the tube halves, said sleeve protruding beyond the free end of said tube half, the protruding part of said sleeve being fitted onto the tube half of the other float half during the operation of moving the two float halves towards each other.

7. A method according to claim 4, c h a r a c¬ t e r i z e d in that a sleeve is placed on each of the two tube halves, said sleeves being constructed in such a manner, that when the two float halves are moved towards each other, the two sleeves are coupled to each other, the sleeves being used having appropriate coupling means, such as screw-thread or plug-and-socket components.

8. A method according to any one or any of the claims 1-7, c h a r a c t e r i z e d in that at least one sleeve is used having its inwardly facing end edges chamfered or rounded.