MSC 132/134Fishing Gear Technology I & II

Calculating and Cutting Netting TapersExcerpts from:Calculations for Fishing Gear Designs, A.L. Fridman, Fishing News Books Ltd., Surrey, England. 1986

FAO Catalogue of Small Scale Fishing Gear, Edited by C. Nedelec, Fishing News Books Ltd. & Whitefriars Press Ltd., London, England. 1975

Fisherman’s Workbook, Compiled by J. Prado, Fishing News Books, Oxford, England. 1990

How to Make & Set Nets, John Garner, Fishing News Books Ltd., Surrey, England. 1986.

Machine Made Netting

Cutting and Shaping Netting

1. The number of meshes at the start of the cut.

2. The number of meshes required at the end of the cut.

3. The length or depth in meshes of the section to be cut.

All Meshes or Transverse E1 = Length (0º)

Base of right angle

All Points or “Siders”E2 = Depth (90º)

Normal Direction

All Bars45 degree angle

Resultant Angles for Net Tapers

Assuming Meshes Are Hung At 71% E1 Value of 50%

Common Cutting Rates & Taper Ratios

Cuts: Netting Example

Body TapersGuidelines and Formula

1. You can only cut or calculate a cut by evaluating one side of the intended shape or piece of netting .

2. Always establish which way your E values are oriented.

3. The body taper is only used if the material to be cut is less than the depth of the netting.

Body Taper = 2 x Cut

Depth - Cut=

BarsPoints

Cut = Bottom - Top2

Body Taper: Calculations

Body Taper = 2 x Cut

Depth - Cut=

BarsPoints

Cut = Bottom - Top2

180 meshes

140 meshes

30 mesh

2 Cut = 2 x 20 = 40 = 4 barsDepth – Cut 30 – 20 10 1 points

E1

Body TapersCalculating the Cut

1. For calculation purposes – when applying the cut formula, always assume the bottom of the netting piece is represented by the larger mesh count.

2. When using the cut formula - if only one side of the netting piece will be cut, do not divide by 2.

Cut = Bottom - Top2 180 meshes

140 meshes

30meshes

E1CUT CUT

180 – 140 = 40 = 20 2 2

Body Taper: Cuts

Body Taper = 2 x Cut

Depth - Cut=

BarsPoints

Cut = Bottom - Top2

2 Cut = 2 x 40 = 80 = 8 barsDepth – Cut 60 – 40 20 2 points

E1

180 meshes

140 meshes60 mesh

Cut = 180 – 140 = 40 = 40

When using the cut formula - if only one side of the netting piece will be cut, do not divide by 2.

Body Taper: Cuts

Body Taper = 2 x Cut

Depth - Cut=

BarsPoints

Cut = Bottom - Top2

2 Cut = 2 x 40 = 80 = 4 barsDepth – Cut 30 – 40 -10 -1 points

E1

180 meshes

140 meshes30 mesh

The body taper is only used if the material to be cut is less than the depth of the netting.

Cut = 180 – 140 = 40 = 40

3P2B

Body Tapers: Calculations3P

2B

Body Tapers: Calculations

200 M

Body Tapers: Calculations

200 M

Body Taper = 2 Cut Depth – Cut

Cut = Top – Bottom ÷ 2 = 340 – 100 ÷ 2 = 120

Body Taper = 2 x 120 ÷ 200 – 120 = 240 Bars 80 Points

= 3 Bars 1 Point

Body Taper = 3 Bars 1 Point – however, even tapers are easier and neater to sew. A 6 Bar to 2 Point Body Taper (4B1P, 2B1P) is the same as a 3Bar to 1Point taper.

=Bars

Points

Body Taper Examples

3 Bars1 Point

2 Bars1 Point 4 Bars

1 Point

Jib TapersGuidelines and Formula

1. You can only cut or calculate a cut by evaluating one side of the intended shape or piece of netting .

2. Always establish which way your E values are oriented.

3. The jib taper is only used if the material to be cut is greater than the depth of the netting.

4. Length replaces the cut on jib tapers.

Jib Taper = (2 x Depth) - 2Length -Depth + 1

BarsMeshes

=

Jib Tapers: Calculations

Jib Taper = (2 x Depth) - 2Length -Depth + 1

BarsMeshes

=

20 P

38 Meshes

E1

The base length of the right triangle represents the cut length.

(2 x 20) – 2 38 2 bars 38 – 20 + 1 19 1 mesh

= =

Jib Tapers: Calculations

Tapers do not always work out “perfectly”. Your critical thinking skills are essential to properly apply various tapers and/or cutting rates.

(2 x Depth) - 2Length -Depth + 1

JibTaper

BarsMesh

= =

(2 x 36.5) – 2 73 – 2 7173 – 36.5 + 1 36.5 + 1 37.5

1.89 Bars 2 1 Mesh 1

= =

=

All Bar TapersGuidelines and Formula

1. You can only cut or calculate a cut by evaluating one side of the intended shape or piece of netting .

2. Always establish which way your E values are oriented.

3. If the “cut” or “length” is equal to the depth of the netting – you would have an all bar (AB) taper.

4. If statement #3 is true there are no calculations necessary.

Prove the “Taper” which is indicated on the circled “panel” shown in the trawl plans (A15) to the right.

Tapers: Calculations

31M

35M

62M

AB

7P2B

4M

31M

2 Cut Depth – Cut

2 x 4 31 – 4

Keys to Finding and/or Proving the Taper:• You can only cut and/or calculate a cut by evaluating one side of the intended shape or piece of netting at a time.

• An All Bar (AB) taper will yield a 45 degree angle, which means the “Cut” is equal to the “Depth” of the netting.

Cut = Top – Bottom = 66 – 62 = 4

Body Taper =

Body Taper =8 Bars 27 Pts.

2 Bars 6.75 Pts.

2 Bars 7 Points

= = =

Taper Examples

Cutting Rate: 1N 2B(1 Point 2 Bars)

Cutting Rate: 1T 2B(1 Mesh 2 Bars)

Cutting Rate: 1N 2T(1 Point 2 Meshes)

Drop Tapers

5 Meshes to 7 Meshesor

1 1 1 11 2 1 2

Drop Loops Added

Identify the Tapers Shown Below

CUT LOSS