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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.
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.
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.