US-20260123615-A1 - SPREADING DEVICE

US20260123615A1US 20260123615 A1US20260123615 A1US 20260123615A1US-20260123615-A1

Abstract

A spreading device for spreading gear, including fishing gear or seismic survey gear, towed behind a vessel in water, comprising a hollow body of concavo-convex shape and made of plastics material. The body has a general mirror symmetry about a plane which is substantially mid-height and/or mid-length in the body in use. The body has a fore-and-aft to top-to-bottom aspect ratio of between 1:2 and 4:1, and an inner concave side and an outer convex side. The device has a forward towing point on the inner concave side for a tow line to the vessel and aft towing point for attachment of the gear to be towed. The plastic material of the hollow body renders the body buoyant in water and enables ballast or additional buoyancy to be added.

Inventors

Atli Mar Josafatsson

Assignees

Atli Mar Josafatsson

Dates

Publication Date: 20260507
Application Date: 20251229
Priority Date: 20200422

Claims (13)

1 . A spreading device for spreading gear towed behind a vessel in water comprising: a hollow body of plastics material, the body being of concavo-convex shape and having: general mirror symmetry about a plane which is substantially mid-height and/or mid-length in the body in use; a fore-and-aft to top-to-bottom aspect ratio of between 1:2 and 4:1′ an inner concave side; and an outer convex side; at least one forward towing point on the inner concave side of the body for a tow line to the towing vessel; at least one aft towing point for the towed gear or a line to it; wherein the forward and aft tow points are interconnected through the body; wherein the plastics material of the body renders the spreading device buoyancy in water; wherein the body is moulded by rotational moulding or extrusion or 3D printing; wherein the device further includes righting ballast at least in a lower part of the device, whereby in use the spreading device is deployable outwards of a launching side of the vessel, spreading the gear in the direction of the convex outer side opposite from the forward towing point on the inner concave side, the righting ballast being ballast material arranged inside the body of plastics material or on the outside of the body.
2 . The spreading device as claimed in claim l, wherein the at least one forward towing point is substantially at or symmetrically positioned with respect to the mid-height plane.
3 . The spreading device as claimed in claim l, wherein the at least one aft towing point is substantially at or symmetrically positioned with respect to the mid-height plane.
4 . The spreading device as claimed in claim l, wherein the at least one aft towing point is on the outer convex side of the body.
5 . The spreading device as claimed in claim 1 , wherein the at least one aft towing point is on the inner concave side of the body.
6 . The spreading device as claimed in claim l, wherein the towing points are provided with load spreading plates on the opposite side of the body and bolts through the body for transferring the load to the plates.
7 . The spreading device as claimed in claim 5 , wherein at least one of the load spreading points on one side of the body is connected to at least one of the towing points on the same side of the body for towing load transfer from the towing point bolted to the load spreading plate to the connected towing point, the connection being an integral metal connection or a bolted metal to metal connection.
8 . The spreading device as claimed in claim 1 , in combination with at least two strops for forward ones of the towing points or for aft ones of the towing points for connection to the tow line or the gear line.
9 . The spreading device as claimed in claim l, wherein: the body is moulded of thermo-softening plastics material by rotational moulding or extrusion or 3D printing and is hollow and provides the device with additional buoyance over and above inherent buoyancy of the plastics material; and wherein the spreading device is provided with additional ballast to counteract the additional buoyancy.
10 . The spreading device as claimed in claim 1 , wherein: the body is moulded of thermo-softening plastics material by rotational moulding or extrusion or 3D printing and is hollow and provides the device with additional buoyance over and above inherent buoyancy of the plastics material; and wherein the body is provided with apertures in the wall of the plastics material body to enable water to fill the hollow interior of the body.
11 . The spreading device as claimed in claim l, wherein the body is of wood fibres or a blend of wood fibres and polymer.
12 . The pair of spreading device, each as claimed in claim l, wherein one is a starboard device and the other is a port device, the bodies of the pair of spreading devices being from the same mould, the bodies of the two devices: being arranged oppositely fore and aft with respect to their mid-length plane; being thickest substantially at their mid-length plane; and preferably having their sides substantially circularly curved with the inner concave sides being less curved than the outer convex sides.
13 . The pair of spreading device, each as claimed in claim 1 , wherein one is a starboard device and the other is a port device, the bodies of the pair of spreading devices being from the same mould, the bodies of the two devices: being the arranged oppositely top to bottom with respect to their mid-height plane and preferably having rounded forward edges, greatest thickness forward their mid-length plane, and tapered aft edges.

Description

CROSS REFERENCE TO RELATED APPLICATION This application is for entry into the U.S. National Phase from which priority is claimed under all applicable sections of Title 35 of the United States Code including, but not limited to, Sections 120, 363, and 365 (c) to International Application No. PCT/EP2021/060274 filed on Apr. 20, 2021, and which in turn claims priority under 35 USC 119 to Great Britain Patent Application No. 2005885.5 filed on Apr. 22, 2020 and U.S. patent application Ser. No. 63/028,089 filed on May 21, 2020. BACKGROUND The present invention relates to spreading devices for spreading gear towed in the sea or other bodies of water, in particular but not exclusively trawl doors for trawl fishing in general and deflectors for seismic survey operations. Whilst spreading devices have other uses such as in seismic surveys, their primary use is as trawl doors, i.e. spreading devices towed by a trawler for spreading a trawl fishing net, that is holding it open. Trawl doors control opening of the fishing trawl, or plurality of trawl doors operating plurality of fishing trawls to optimize the fishing ability of the total fishing gear. Deflectors spread the seismic system with number of streamers or cables towed behind the seismic vessel. They are used in pairs, one at one side of the trawl net and the other at the other. Water acts on their inner sides, which are oblique to their towed direction through the water and forces them apart. Traditional trawl doors have been flat. Increasingly for pelagic fishing in particular, curved trawl doors have been used. Forming trawl doors with complementary concave inner and convex outer surfaces, in the manner of an aerofoil, increases their efficacy, i.e. their net opening action per unit area. This form of door is readily manufactured for large doors by fabrication from sheet steel. However, such doors are expensive, heavy and disadvantageous for shallow water, bottom trawling with light gear. For such trawling, flat, relatively heavy, conventional trawl doors are still widely used. They have a damaging effect to the seabed. SUMMARY According to the invention there is provided a spreading device for spreading gear towed behind a vessel in water comprising: a hollow body of plastics material, the body being of concavo-convex shape and having:general mirror symmetry about a plane which is substantially mid-height and/or mid-length in the body in use,a fore-and-aft to top-to-bottom aspect ratio of between 1:2 and 4:1,an inner concave side andan outer convex side;at least one forward towing point on the inner concave side of the body for a tow line to the towing vessel;at least one aft towing point for the towed gear or a line to it, wherein:the plastics material of the body renders the spreading device buoyant in water. Preferably the spreading device includes righting ballast at least in a lower part of the device, whereby in use the spreading device is deployable outwards of a launching side of the vessel, spreading the gear in the direction of the convex outer side opposite from the forward towing point on the inner concave side. In the preferred embodiments, the righting ballast is a shoe of material denser than water fitted to a lower edge of the device, with the lower edge preferably being locally thickened to fit a constant width of the shoe. The shoe can be of: metal mechanically fitted to the body, conveniently of a plurality of channel sections of constant width, the body being locally swollen at least at its lower edge for location in the shoe orplastics material filled with non-buoyant filler, bonded or mechanically fitted to the body. Alternatively, the righting ballast is ballast material arranged inside the body of plastics material or on the outside of the body. Normally, the or each forward towing point is substantially at or symmetrically positioned with respect to the mid-height plane. Similarly, the or each aft towing point is normally substantially at or symmetrically positioned with respect to the mid-height plane. The or each aft towing point can either be on the outer convex side or the inner concave side of the body. In use the tow line and the net or net line can be connected directly to the respective towing points. Alternatively, strops can be provided between the towing line and the net or net lines. A single forward and a single aft tow point can be provided. Normally at least one forward and two aft towing points are provided, with the aft towing points being on the outer side or at the inner side. Other simple alternatives are two forward & two aft towing points and two forward & one aft towing points envisaged. Further in the interests of spreading load to the plastics material body more towing points, with appropriate length of strops to common points of attachment to a towing line and/or a net or net line, are also envisaged. The forward and aft tow points can be interconnected through the body or by external plates. Normally the p