Materials
and accessories

Density of materials

STRENGTH OF HARDWARE

Safe working load, breaking load, safety factor

∎ Definitions

—  Safe working load (SWL), is the maximum load that an item is certified to lift in service. Another equivalent term in use is Working load limit.

—   Breaking load (BL) is the maximum load that an item can hold with a static load before it breaks. Another equivalent term in use is Breaking strength.

—   Safety factor

Very important : The loads used in these calculations are static loads. Dynamic or shock loads increase the stress considerably, and thus increase the possibility of breakage.

∎ Values of the safety factor

(a) For ropes

(b)  For wire ropes and metal hardware : safety factor about 5-6.

∎ Safe working load

SYNTHETIC FIBRES

Synthetic fibres and commercial names

∎ Polyamide (PA)

Amilan (Jap)
Anid (USSR)
Anzalon (Neth)
Caprolan (USA)
Denderon (E. Ger)
Enkalon (Neth, UK)
Forlion (Itd)
Kapron (USSR)
Kenlon (UK)
Knoxlock (UK)
Lilion (Ital)
Nailon (Ital)
Nailonsix (Braz)
Nylon (many coun.)
Perlon (Ger)
Platil (Ger)
Relon (Roum)
Roblon (Den)
Silon (Czec)

∎ Polyethylene (PE)

Akvaflex (Nor)
Cerfil (Port)
Corfiplaste (Port)
Courlene (UK)
Drylene 3 (UK)
Etylon (Jap)
Flotten (Fran)
Hiralon (Jap)
Hi-Zex (Jap)
Hostalen G (W. Ger)
Laveten (Swed)
Levilene (Ital)
Marlin PE (Ice)
Norfil (UK)
Northylen (Ger)
Nymplex (Neth)
Rigidex (UK)
Sainthene (Fran)
Trofil (Ger)
Velon PS (LP) (USA)
Vestolen A (Ger)

∎ Polypropylene (PP)

Akvaflex PP (Nor)
Courlene PY (UK)
Danaflex (Den)
Drylene 6 (UK)
Hostalen PP (Ger)
Meraklon (Ital)
Multiflex (Den)
Nufil (UK)
Prolene (Arg)
Ribofil (UK)
Trofil P (Ger)
Ulstron (UK)
Velon P (USA)
Vestolen P (Ger)

∎ Copolymers (PVD)

Clorene (Fran)
Dynel (USA)
Kurehalon (Jap)
Saran (Jap, USA)
Tiviron (Jap)
Velon (USA)
Wynene (Can)

∎ Polyester (PES)

Dacron (USA)
Diolen (Ger)
Grisuten (E. Ger)
Tergal (Fran)
Terital (Ital)
Terlenka (Neth, UK)
Tetoron (Jap)
Terylene (UK)
Trevira (W. Ger)

∎ Polyvinyl alcohol (PVA)

Cremona (Jap)
Kanebian (Jap)
Kuralon (Jap)
Kuremona (Jap)
Manryo (Jap)
Mewlon (Jap)
Trawlon (Jap)
Vinylon (Jap)

∎ Commercial names of combined twines for netting

 Synthetic fibres : physical properties

 Synthetic fibres : identification

TWINE

Twine : number, tex, denier, meters/kg, diameter

∎ Simple fibres

Titre (denier)  : Td = weight (g) of 9000 m of fibre
Metric number : Nm = length (m) of 1 kg of fibre
English number for cotton : Ne_c = length (in multiples of 840 yd) per lb
International  system:  tex  =  weight (g) of 1000 m of fibre

∎ Finished twine

Runnage, metres/kg : m/kg = length (m) of 1 kg of finished twine
Resultant tex : Rtex = weight (g) of 1000 m of finished twine

∎ Equivalents and conversions

∎ Estimating the diameter of twine

In addition to precise measurements from instruments such as micrometer, magnifying glass and microscope, there exists a quick method of estimation. Roll 20 turns of the twine to be measured around a pencil and measure the total length of the turns.

Example :

If 20 turns of the twine measure 6 cm, then the diameter of the twine  = 60 mm/20 turns = 3 mm

Note : The strength of twine or rope depends not only on its thickness, but also on the method ond degree of twisting or braiding its yarns.

Twine : calculation of tex

∎ Calculation of Resultant tex (Rtex) of twine

Case 1 : When the structure of the twine is known

Example :
Netting twine made of nylon (polyamide), with 210 denier single yarns, 2 single yarns in each of the 3 folded yarns (strands) which make up the twine.

To find the Resultant tex (Rtex) we have to apply a correction to the calculated value, taking into account the structure of the finished twine (twisted, braided, hard lay, degree of twist, etc.). A rough estimation of Rtex can be found by adding 10% to the value calculated above:

138 tex + 10% = R 152 tex (estimate)

Note : In view of the complex structure of braided twines, it is the general practice in fisheries for the gear designer to use the Rtex value without going into detail.

Case 2: A sample of twine is available for evaluation

Example :
5 m of twine, placed on a percision scale, weigh 11.25 g.
We know that twine of R 1 tex weighs 1 g per 1000 m, and the weight per meter of the sample twine is 11.25/5 = 2.25 g/m. So, 1000 m of the sample would weigh 1000 x 2.25 = 2250g, or R 2250 tex

Note : The strength of twine or rope depends not only on its thickness, but also on the method and degree of twisting or braiding its yarns.

Twine : equivalents of numbering system

Eg.: twisted nylon (polyamide) twine

Note : 210 denier = 23 Tex

Twine : nylon (polyamide PA), multifilament twisted or braided

A = breaking load, dry without knots (single twine)

B = breaking load, wet, knotted (single twine)

∎ Twisted, continuous filament

∎ Braided, continuous filament

Twine, nylon (polyamide PA) monofilament and multimonofillament, japanese numbering system

A = breaking load, dry without knots (single twine)

B = breaking load, wet, knotted (single twine)

Japanese numbering system for Monofilament

∎ Multimonofilament

* for monofilament, tex and Rtex are the same.

Twine : polyester (PES), polyethylene (PE), polypropylene (PP)           

A = breaking load, dry without knots (single twine)

B = breaking load, wet, knotted (single twine)

POLYESTER (PES)

∎ twisted, continuous filaments

POLYETHYLENE (PE)

∎ twisted or braided thick filaments

POLYPROPYLENE (PP)

∎ twisted, continuous filaments

∎ twisted staple fibres

ROPE

Vegetable fibre ropes*

** In English-speaking countries the size of a rope is sometimes measured by its circumference in inches (in.) or by its diameter in inches Diameter of rope 0 (mm) = approx. 8 x c (inch)

Example: 0 (mm) of a rope of 2.25 inch circumference 0 (mm) = 2.25x8 = 18 mm (approximate)

Synthetic fibre rope*

R = breaking strength, dry

Direction of twist of twines, ropes and cables

* Safe working bad, see page 5
**Conversion inch-mm, seepage 15

Rope : joining knots and loops

Some knots are used more than others. In selecting which knot to use the following points should be considered : — the use of the knot — the type of rope — whether the knot will slip — whether the knot is permanent.

∎ Joining two cords

Two cords of the same diameter, multifilament

Two cords of same diameter, monofilament

Two cords of different diameters or different types

Sheet bends are also useful for joining two identical cords

∎ Loops

Fixed loop

Running loop

Knots for stoppers and mooring

Some knots are used more than others. In selecting which knot to use the following points should be considered : — the use of the knot — the type of rope — whether the knot will slip — whether the knot is permanent.

∎ For stopping a rope from running through a narrow space (i.e. sheave)

∎ Knots for mooring

∎ To close the codend of a trawl
(codend knot)

∎ To shorten a rope

Knots for hitches and stoppers

Some knots are used more than others. In selecting which knot to use the following points should be considered : — the use of the knot — the type of rope — whether the knot will slip — whether the knot is permanent.

Loss of breaking strength due to knots and splices

Combination wire (1)*

∎ Steel - Sisal 3 strands

∎ Steel - Sisal 4 strands

R = Breaking strength dry

* Safe working loads, see page 5

Combination wire (2)*

∎ Steel -Manilla B, 4 strands

∎ Steel - Polypropylene

R = Breaking strength dry

* Safe working loads, see page 5

Flatline and leadline

∎ Floatline (with floats inside)

Principal advantages (1) and disadvantages (2)

1. Ease of rigging; less entanglement in the meshes.
2. Need to calculate the rigging as a function of the distance between the floats; fragility of some types of float when passing through certain gillnet haulers.

Floatline (with floats inside)

∎ Leadline (with leads inside)

Principal advantages (1) and disadvantages (2)

1. Ease of rigging; uniform weight of leadline; better hanging; no entanglement in meshes.
2. In the case of breaking, loss of leads; difficult to repair; high cost.

Braided with a centre core of lead

Rope with a lead core in three strands

R = breaking strength

there are also leadlines of 0.75; 0.90; 1.2; 1.5; 1.8 kg/100m

WIRE ROPE

Steel wire rope : structure, diameter and use

Examples of common marine wire rope

Type	Structure and diameter	Example of Use	S
	7 x 7 (6/1) central heart: steel Ø 12 to 28 mm	Standing rigging	+
	6 x 7 (6/1) Central heart: textileØ 8 to 16 mm	Standing rigging Warps for small trawlers Small coastal vessels	+
	6 x 12 (12/fibre) Central heart, strand cores, fibre Ø 8 to 16 mm	Bridles and warps for small trawlers moorings and running rigging	++
	6 x 19 (9/9/1) Central heart of steel or textileØ16 to 30 mm	Trawler warps	+
	6 x 19 (12/6/1) Central heart of textile Ø 8 to 30 mm	Trawler's sweeps and warps running rigging	+
	6 x 24 (15/9/fibre) Central heart and strand cores of textile Ø 8 ta 40 mm	Purse wire bridles and otter board strops, running rigging moorings and towing	++
	6 x 37 (18/12/6/1) Central heart of textile Ø 20 to 72 mm	Purse wire moorings and running rigging mooring	++

S = flexibility
+ = poor or average
++ = good

As a general rule, the greater the number of strancs, and the greater the number of filaments per strand, the greater the flexibility of the cable.

Galvanised steel wire rope : runnage, breaking strength*25

(for structure, see page 24) examples

R = Breaking strength
(steel 145 kgf/mm²)

*Safe Working Loads, see page 5

Handling wire rope

NO	YES

∎ Winding onto a drum depending on the direction of lay in a wire.

Matching wire ropes with drums and sheaves

∎ Drums:	the diameter of a drum (D) relative to the diameter of the wire rope (Ø) to be held on the drum — D/Ø depends on the structure of the wire rope, and depending on the particular situation, D should range from 20Ø to 48Ø. In practical use on board fishing vessels, depending on the space available, the following values are common : D = 14Ø or more
∎ Sheaves :	The diameter of a sheave (D) relative to the diameter of the wire rope (Ø) to be used with the sheave — D/Ø depends on the structure of the wire rope, and depending on the particular situation, D should range from 20Ø to 48Ø. In practical use on board fishing vessels, depending on the space available, the following values are common: D = 9Ø or more

Width of sheave relative to the diameter of the wire rope

∎ Location of sheave relative to drum

Maximum fleet angle of a steel wire between a fixed sheave and a drum with manual or automatic spooling gear:

L = C x 5 (or more); C x 11 is recommended

(In order to let a sheave shift with changing wire angles, it is often better to use a flexibly attached block rather than a fixed sheave.)

∎ Cable clamps should be fastened with nuts on the standing part of the wire

Steel wire rope, small diameter

∎ Stainless steel, heat treated and painted (examples)

∎ Galvanised steel, not lubricated

R = breaking strength

NET WEBBING

Meshes : Definition

∎ Types of mesh nets

b - bar length

∎ Dimension of mesh, stretched mesh (a), and mesh opening (OM)

Meshes of metallic or plastic netting
see page 107

Systems of measuring net meshes in different countries

* Note that stretched meshsize is not the same as mesh opening, which is considered in many fisheries regulations.

A simple method of measuring stretched meshsize is as follows: extend a panel of twine fully in the N direction (see page 32 for N direction), and measure the distance between the entres of 2 Knots (or connexions) separated by 10 meshes. Then divide this measure by 10.

Knots and edges or selvedges

∎ Knots

The height of the single knot is approximately equal to three times the diameter of the twine.

∎ Edges and selvedges

Definition of cuts

Cutting rate

∎ Cutting rate

∎ Values of the parts of a cut

Common cutting rates and tapers

Number of meshes decreasing (or increasing) in width

N = Sideknots
T = Meshes
B = Bars

Estimation of weight of netting

∎ Knotless netting

∎ Knotted netting

Where

W = estimated weight lg) of netting
H = number of rows of knots in the height of the netting 2 x number of meshes
L = Stretched length (m) of netting

Rtex and m/kg — the size of twine in the netting

K = knot correction factor to take into account the weignt of the knots (single knot); see table below

K = (knot correction factor) for different netting panels

Example : Knotted netting of twisted nylon twine, R1690 tex (590 m/kg), 100 mm bar length (200 mm stretched mesh length), height 50 meshes, length 100 meshes

50 meshes = 100 rows of knots in height

Stretched length = 100 meshes x 0.200 m = 20 m

Diameter of twisted polyamide twine 1690 Rtex = 1.5 mm (see page 12)

K in the table above = 1.12 (stretched mesh 200 mm; diameter 1.5 mm)

W = 100 x 20 x (1690/1000; x 1.12 = 3785 g = about 3.8 kg

Calculating twine surface area

The drag of a net is proportional to the number and type of meshes in the netting, and to the orientation of the net panel(s) in the water.

Where

Example : In the piece of netting shown above on the right, if N = 16; n = 6; H = 6; a = 80 mm; = 1.5 mm

Calculating twine surface area of trawl

∎ NET WEBBING: CALCULATING TWINE SURFACE AREA OF A TRAWL

In order to compare the twine surface areas of two trawls, the trawls should be as nearly the same shape as possible. In the case of such comparisons the surfaces of the lengthening pieces and the codend (parts without oblique orientation), will cause no significant drag, and can be disregarded.

Hanging ratios, definition and calculation

∎ Hanging ratio (E) is commonly defined as :

Example : 200 meshes of 50 mm stretchea mesh size hung on a rope of 8 m

∎ Other expressions used for hanging ratio :

1. Also called external hanging co-efficient
2. Also called percentage of hanging in — Setting in x 100— Looseress percentage of hanging — hang in (Asia, Japan)
3. Also called Hang in ratio (Scandinavia)

Note : It is recommended that only the hanging ratio E be used

Surface covered at differnt hanging ratios

∎ Examples of common horizontal hanging ratios

∎ Calculation of the surface covered by a piece of netting

Where

Example :

Note : The surface covered ¡s at a maximum when E = 0.71, that is when each mesh forms a square

Mounted height of a net

∎ Calculation of mounted height

The actual height of a mounted (rigged or hung) net depends on the stretched height and the hanging ratio.

The general formula permitting estimation in all cases is :

where  E² = horizontal hanging ratio multiplied by itself

Example : Given the piece of netting described on the preceding page with hanging ratio of 0.90 :

∎ Table for estimating mounted height

Example :
Given the piece of netting described on the preceding page, mounted with the horizontal hanging ratio 0.90, we can deduce from the table above (E to A to H) that its mounted height is 44% of the stretched height.

Stretched height = 500 meshes of 30 mm = 500 x 30 mm = 15 m

Mounted height = 44% of 15 m = 6.6 m

Joining panels of netting

∎ Netting with straight edges (i.e. AB, AT, and AN)

Netting having the same number of meshes, and meshes of the same size, or approximately the same size.

Netting having a different number of meshes or meshes of a different size

∎ Netting cut obliquely with a combination of cuts B and N or Τ Pieces having a different number of meshes and different cuts

Mounting (Hanging or rigging) panels of netting

Examples

FISH HOOKS

Terms for describing fish hooks

∎ - Examples of fish hook characteristics

Principal types of fish hooks

∎ Straight hooks 'J' shape, ring eye

∎ Kirbed (offset) hooks

∎ Reversed hooks

∎ Double and treble hooks

∎ Specialised hooks for particular species or fishing methods

Trolling

Longlines

Pole and line

Lures, knots for fish hooks

∎ Lures

∎ Knots for ring-eyed hooks

∎ Knots for flatted shank hooks

LINE FISHING ACCESSORIES

Swivels, snaps, knots for longlines

∎ Swivels

∎ Three-way swivels

∎ Snaps

∎ Knots for joining branditine or snood to mainline

∎ Knots for joining branditine to snood

FLOATS

Floats for seines : examples

There are a great variety of seine floats, with L ranging from 100 to 400 mm; Ø from 75 to 300 mm; and buoyancy from 300 to 22000 gf.

Durability is a most important characteristic of a seine float.

Examples : In expanded PVC, two types of manufacture

For the dimensions given, the buoyancy varies depending on the material.

Rough estimation of the buoyancy-may be found by measuring the float.

Estimation of the number of floats necessary for a seine :

Flats for gillnets and seines (1)

Examples

Estimating the buoyancy from the size of the float :

buoyancy (in gf) = 0.67 x L (cm) x ² =(cm)²

Estimation of the buoyancy from the size of a float

buoyancy (in gf) = 0.5 x L (cm) x ز (cm)² ز = external diameter multiplied by itself

Flats for gillnets and seines (2)

Examples

Spherical floats and trawl floats

Examples from suppliers' catalogues

	Diameter (mm)	Volume (litres)	Buoyancy kgf	Maximum depth (m)
	200	4	2.9	1 500
	200	4	3.5	350
	280	11	8.5	600
	75	0.2	0.1	400
	100	0.5	0.3	500
	125	1	0.8	400-500
	160	2	1.4	400-500
	200	4	3.6	400-500
	203	4.4	2.8	1 800
	200	4	3.5	400
	280	11-11.5	9	500-600
	152	1.8	1.3	1 190
	191	3.6	2.7	820
	203	4.4	2.8	1 000
	254	8.6	6.4	1 000

The table below shows that, for floats of equal diameter (200 mm in this case), the volume and buoyancy may vary a great deal, depending on the material and placement of holes or lugs.

* Note : The maximum effective depth of a float depends on the manufacture, and should be specified by the supplier. It cannot be deduced from the appearance, shape or colour

Floats (buoys) for marking nets, lines and traps

Examples:

1/  Solid floats (PVC)

2/ Inflatable floats

SINKERS

Groundrope leads and rings

Examples

∎ Leads for ropes

∎ Leads for lines, examples of shapes

∎ Example of mould for leads

∎ Example of groundrope rings for a gillnet

Ex:

HARDWARE

Chains and thimbles*

∎ Chains

High tensile steel

∎ Thimbles

∎ Clips for wire rope

* Safe Working Load see page 5

Steel accessories for joining : shackles, links and cilps*

∎ Shackles

∎ Links and Clips

* Safe Working Load see page 5

Swivel

∎ Swivel, forged steel

∎ Swivel, tempered steel and hot galvanized

∎ Swivel, high tensile stainless steel

* Safe working load see page 5
** Breaking strength, see page 5

Hooks and 'G' links*

* Sale working load and breaking  strength see page 5

Spreaders, codend realease and purse rings

∎ For trawl

∎ For seine : Opening purse clips or rings

Elements of trawl groundropes : steel bobbins

Examples

Elements of trawl groundropes : rubber bunts, bobbins, spacers and rings

Examples

∎ Spacers

∎ Rings or "cookies" (made from old tyres)

* Weight in air

LIFTING

Silings and tackles