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MSC 134 Fishing Gear Technology II

MSC 134 Fishing Gear Technology II. Trawl Plan Conversions. 3P2B. Standard Net Plan Layout: Cutaway View. 3P2B. Net Plan with Hidden Lines: Uncommon. 3P2B. 3P2B. Full Net Plan Layout: More Detail but not commonly used. You CAN! Change Mesh Sizes. Change Mesh Counts. You CANNOT!

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MSC 134 Fishing Gear Technology II

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  1. MSC 134Fishing Gear Technology II Trawl Plan Conversions

  2. 3P2B Standard Net Plan Layout: Cutaway View

  3. 3P2B Net Plan with Hidden Lines: Uncommon

  4. 3P2B 3P2B Full Net Plan Layout: More Detail but not commonly used.

  5. You CAN! Change Mesh Sizes. Change Mesh Counts. You CANNOT! Change Hanging Ratios. (except within ± 2.5%) Change tapers. Change Net Orientations. (E1 & E2 alignment) When converting net plans: Always pay attention to the Do’s and Don’ts! Double Check all work Before Beginning Construction

  6. 3P2B

  7. Trawl Plan Conversion: Class Exercise In the handout “Traditional Trawls” you have a set of plans for a 50 ft., 4-seam flat shrimp trawl which specifies a #15 nylon twine and a 1.875 inch stretch mesh. We will convert the original trawl plans to facilitate building a 32 foot, 4-seam flat trawl. Our new trawl will be built with a #15 nylon twine and a 1.5 inch stretch mesh. We will do the calculations and answer the following questions before completing a revised trawl schematic. The first thing we should do is calculate the hanging ratio (E 1) used in the “original” 50 ft. trawl plans?

  8. Calculating the Hanging Ratio • Determine which variables are known and utilize the equation E1 = L/Lo. • E1 is the Primary Hanging Ratio. • L is the “hung” distance along the top or bottom of the net. • Lo is the number of meshes multiplied by the stretch size of the mesh in a given distance.

  9. E1 = L ÷ Lo E1 = 4.125” ÷ 5.625” (3 meshes x 1.875”) E1 = 0.73333 (.73333 x 100 = 73.333%) E1 = 602.16” (50.18’ x 12”) ÷ 821.25” (438 meshes x 1.875”) E1 = 0.73322 (.73322 x 100 = 73.322%)

  10. E1 = L ÷ Lo E1 = 668.16” (55.68’ x 12”) ÷ 911.25” (486 meshes x 1.875”) E1 = 0.73323 (.73323 x 100 = 73.323%)

  11. The hanging ratio (E 1) used in the “original” 50 ft. trawl plans is 73.3%. What hanging ratio (E 1) should you plan to use in the “new” 32 ft. trawl? 73.3% or as close as physically possible (Calculate the new hanging specifications) 32 ft., 4-SEAM FLAT TRAWL 1 1/2 INCH STRETCHED MESH, NO. 12 THD.; NYLON HANGING SPECIFICATIONS: 3 MESHES ON ? TIES • You CANNOT Change Hanging Ratios. (except within ± 2.5%)

  12. 32 ft., 4-SEAM FLAT TRAWL 1 1/2 INCH STRETCHED MESH, NO. 12 THD.; NYLON HANGING SPECIFICATIONS: 3 MESHES ON ? TIES E1 = L ÷ Lo and the original plans indicate .7333 = 4.125” ÷ 5.625” Therefore the new Lo is 4.5”(3 meshes x 1.5”) and the desired E1 is 73.3%(.7333). TheL value in this problem would represent the measurement of the ties. Solve the problem by using the equation with the known variables E1 and Lo: L = E1 x Lo. L = .7333 x 4.5” which mathematically indicates anL value of 3.299” Of course a measurement of 3.3” is not necessarily practical when using a standard tape measure to lay out the distance of the ties (pick-ups).

  13. What could a practical discretionary answer to the questions be?Instead of 3 MESHES ON3.299” TIES = E1 of 73.3%A more practical approach may be: 3 MESHES ON3.25”(3¼”) TIES = E1 of 72.22%(within ± 2.5%) E1 = 3.25” ÷ 4.5” (3 meshes x 1.5”) E1 = 0.7222 (.7222 x 100 = 72.22%) 3 MESHES ON3.3125”(35/16”) TIES = E1 of 73.61%(within ± 2.5%) E1 = 3.3125” ÷ 4.5” (3 meshes x 1.5”) E1 = 0.7361 (.7361 x 100 = 73.61%)

  14. The original 50 ft. trawl plans utilized a 1.875 inch stretch mesh. The new 32 ft. trawl plans will be using a 1.5 inch stretch mesh. What percentage of decrease does this change in mesh size represent? • Percentage is a part of a whole expressed in hundredths. • The equations we use for finding E1 and E2 values are basic percentage problems. • Percentage gives us a method of comparing quantities. It helps us make a comparison where the relationship is not easy to see at once. • Percentages will be used in every aspect of fisheries related work.

  15. In this case you want to find what per cent of 1.875” (17/8”) the measurement 1.5” (11/2”) represents. First, write the problem in the form 1.5” = ? x 1.875”. You can find the missing factor by dividing 1.5” by 1.875”. 1.5” ÷ 1.875” = 0.80 therefore 1.5” = .80 x 1.875” Generally speaking the relationship we have just calculated shows us that a 1.5” stretch mesh is 80% of the size of a 1.875” stretch mesh. This represents a 20% decrease in mesh size. Another way we could have accomplished this is: 1.875” – 1.5” = .375” therefore .375” = ? x 1.875” so .375” ÷ 1.875” = 0.20 • You CAN Change Mesh Sizes.

  16. If you left all the “mesh counts” the same as on the original 50 ft. trawl plans but utilized the 1.5 inch stretch mesh size, how big would the trawl be? We just determined the new mesh size is 20% smaller than the original mesh size therefore we can safely assume the new trawl will be 20% smaller than the original trawl. Original Trawl Plans = 50.18’ Headrope New Trawl Plans = 20% smaller or 80% of the original Headrope Therefore ? = .80 x 50.18’ which means the new trawl would be 40.14’ What percentage will you have to decrease all the “mesh counts” from the smaller net in order to yield a 32 ft. trawl using a 1.5 inch stretch mesh? • You CAN Change Mesh Counts.

  17. Based on our previous use of percentages to make comparisons of differentials in mesh size, why not use percentages to make comparisons to “mesh counts”. New Mesh Size = 40.14’ Headrope with a 1.5” stretch mesh. We Want a 32’ Headrope with a 1.5” stretch mesh. 32’ = ? x 40.14’ or ? = 32’ ÷ 40.14’ therefore .7972 = 32’ ÷ 40.14’ in order to yield a 32 ft. trawl using a 1.5 inch stretch mesh? Generally speaking the relationship we have just calculated shows us that a 32’ trawl is 79.7% of the size of a 40.14’ trawl. This will represent a need to decrease the mesh countby20.3%. Another way we could have accomplished this is: 40.14’ – 32’ = 8.14’ therefore 8.14 = ? x 40.14’ so 8.14’ ÷ 40.14’ = 0.2028 • You CAN Change Mesh Counts.

  18. Decrease several of your key “mesh counts” by the percentage you just calculated and check your plans to see if the body tapers will remain the same when the new mesh counts are used. 292 meshes x .7972 = 232.78 meshes 92m x .7972 = 73.34 meshes 200m x .7972 = 159.44 meshes Obviously we can’t have .78 meshes or .34 meshes, etc. so we must discretionarily round off the mesh counts. 3P2B Do the new mesh count tapers match the original mesh count tapers? If your answer is no, recalculate your answers and make corrections before continuing! YES • You CANNOT Change tapers.

  19. CALCULATION OF TAPERS Body Taper = 2 Cut ÷ Depth – Cut Answer given in Bars/Points Jib Taper = (2 x Depth) – 2 ÷ Length –Depth + 1 Answer given in Bars/Meshes 1 • Cut = Top – Bottom ÷ 2 • = 292 – 92 ÷ 2 • = 100 • Body Taper = 2 x 100 ÷ 200 – 100 • = 200 ÷ 100 • = 2 Bars 1 Point 3P2B New Calculations: 292 meshes x .7972 = 232.78 meshes = 232 or 233 meshes 92m x .7972 = 73.34 meshes = 73 or 74 meshes 200m x .7972 = 159.44 meshes = 159 or 160 meshes Therefore: Cut = Top – Bottom ÷ 2 so 233 – 73 ÷ 2 = 80 Body Taper = 2 x 80 ÷ 160 – 80 = 160 ÷ 80 = 2 Bars 1 Point Do all the new mesh count tapers match all the original mesh count tapers?

  20. The size of a trawl is defined by its’ headrope. Check the newly calculated mesh count along your headrope and by using your new mesh size (1.5”) and the intended primary hanging ratio, verify whether or not you will yield a 32’ trawl. 3 MESHESON3.3125” TIES = E1 of 73.61% E1 = 3.3125” ÷ 4.5” (3 meshes x 1.5”) E1 = 0.7361 (.7361 x 100 = 73.61%) E1 = 384.24” (32.02’ x 12”) ÷ 522” (348 meshes x 1.5”) E1 = 0.7361 (.7361 x 100 = 73.61%) E1 = L ÷ Lo 116 meshes x 3 = 348 meshes along the headrope. 348M x 1.5” = 522” and 522” ÷ 12” = 43.5 stretch feet (Lo) 43.5 stretch feet x .7361 (E1) = 32.02 feet (L) Do your calculations check out correctly?

  21. Convert the plans: Calculate all the new mesh counts by applying the percentage indicated previously (.203 or .7972) and label the schematic accordingly. (note: use only whole numbers for mesh counts, round as necessary) Label the Top, Bottom & Stretched Mesh Length dimensions with the new linear measurements. Double check all work before beginning construction!

  22. How many pounds of nylon webbing would you need to order so you could build the 32’ four seam flat trawl you just converted/designed? • Supplies can be purchased: • Through local suppliers • New River Net Company, Sneads Ferry, NC • Ed’s Net Shop, Brunswick County • Through Catalogs and/or Internet • Memphis Net & Twine - Catalogs • Nylon Net Company – Catalogs • http://www.nylonnet.com/

  23. Ordering: • You will be ordering • #15 Nylon Twine with a 1-1/2” Stretch Mesh • Material is priced by the pound • Check your catalog for the “stretch feet to the pound”

  24. Ordering: How many meshes would we have if we ordered 1 pound of the webbing we plan to use? (E1 & E2) E1 = L ÷ Lo therefore 100% = 24” ÷ 24”str. in. per pound So 24 str. in. ÷1½str. in. = 16 meshes per pound E2 is given as 200 meshes deep. ∞ E1 = 2 Stretch Feet per Pound E2= 200 meshes The values given in the catalog for the “depth in feet” of a particular mesh size of webbing used in the construction of “hydro-dynamic gear” is generally based on an E1 value of 71%.

  25. Configure the parts of the trawl to be cut: E1 = 2 Stretch Feet per Pound 517 MESHES 80M 233M 80M 56M 12M 56M 78M 176M E2= 200 meshes 1P2B 160M 1P2B 3P2B 176M 78M 80M 36.5M 73M 36.5M 80M 56M 73M 320M 19M 58M 116M 58M 54M WASTE 12M 56M WASTE 1M2B 1M2B 54M 30M 30M 19M 19M 73M 116M 116M 54M

  26. Calculate the quantity of webbing needed. Based on our previous work we decided we would need a section of webbing that was 517 meshes long (E1) by 200 meshes deep (E2). The webbing cited above would not allow for waste and/or future repairs Nor does it include the material needed for the codend bag. Therefore 517 meshes ÷ 16 meshes per pound = 32.3125 pounds (33 lbs.) or 517M x 1.5” = 775.5 st.in. ÷ 24 st.in. per lb. = 32.3125 pounds (33 lbs.) ∞ 2 Stretch Feet per Pound 200 meshes

  27. What is the total twine surface area(not including Codend Bag)of the original net? The plans calls for a #15 Nylon twine (.051” diameter) with a 1.875” stretch mesh? (see pg. 36 of textbook) Prepare to calculate the twine surface area by: • Sketch each individual trawl part. • Include: • # of meshes at the top of the part (N) • # of meshes at the bottom of the part (n) • # of meshes in the height of the part (H) • Determine stretched mesh size • Use appropriate measurement system • Determine diameter of the twine* • Use appropriate measurement system *The twine diameter can be calculated as shown in the Fisherman’s Workbook, Pg. 9 or by referring to a “Twisted Twine Specifications” table found in various net catalogs.

  28. 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.” (N+ n x H) 2 1000000 S = x 2 (a x Ø ) Where S = twine surface area (square meters) N = number of meshes at the top of the panel n = number of meshes at the bottom of the panel H = number of meshes in the height of the panel a = stretched mesh (mm) Ø= diameter of twine (mm) For use with the Metric or International System of Measurements (ie. Square Meters) Fisherman’s Workbook, compiled by J. Prado, Fishing News Books, Oxford:1990 - Pgs. 36-37

  29. Calculating Twine Surface Area:When the values to be compared are given in “square feet” adjust the formula accordingly. (N+ n x H) 2 144 x 2 (a x Ø ) S = Where S = twine surface area (square feet) N = number of meshes at the top of the panel n = number of meshes at the bottom of the panel H = number of meshes in the height of the panel a = stretched mesh (inches) Ø= diameter of twine (inches) For use with the English or Customary System of Measurement (ie. Square Feet) Fisherman’s Workbook, compiled by J. Prado, Fishing News Books, Oxford:1990 - Pgs. 36-37

  30. Original 50’ Trawl Top & Bottom Body Parts: Customary System (N+ n x H) 2 144 x 2 (a x Ø ) S = 292M S = (292+ 92 x 200) 2 144 x 2(1.875” x .051”) 1P2B 1P2B 200M S = x 2(.0956”) 92M (192 x 200) 144 S = x0.1913” = 38400 144 7345.92 144 2 parts = 2 x 51.013 sq.ft. TOTAL = 102.027 sq.ft. S = 51.013sq.ft. per part

  31. Original 50’ Trawl Top & Bottom Body Extension Parts: Customary System (N+ n x H) 2 144 x 2 (a x Ø ) S = 92M S = (92+ 68 x 24) 2 144 1P2B 1P2B x 2(1.875” x .051”) 24M S = x .1913 68M (80 x 24) 144 S = x0.1913” = 367.296 144 1920 144 2 parts = 2 x 2.5507 sq.ft. TOTAL = 5.101 sq.ft. S = 2.5507sq.ft. per part

  32. Original 50’ Trawl Remaining Parts: Customary System (N+ n x H) 2 144 x2 (a x Ø ) 68M S = Top Extension Part: 1 Part = 2.17 sq.ft 24M 68M 70M 70M Front Side Extension Part: (11.25sq.ft.) 2 Parts =22.5 sq.ft. 121M 3P2B 200M 70M Side Tapered Part: (11.16sq.ft.) 2 Parts =22.32 sq.ft. 146M 1M2B 1M2B 36½ M Jib Corner Part: (3.56sq.ft.) 4 Parts =14.24 sq.ft. 14M CODEND BAG NOT INCLUDED

  33. Original 50’ Trawl What is the total twine surface area (not including Codend Bag) of the original 50 ft. net which uses a #15 Nylon twine with a 1.875” stretch mesh? Top & Bottom Body Parts: 102.027 sq.ft. Top & Bottom Body Extension Parts: 5.101 sq.ft. Remaining Parts: 61.23 sq.ft. TOTAL TWINE SURFACE AREA: 168.358 sq.ft. (Not including Codend Bag or Knot correction factor)

  34. Prepare to calculate the twine surface area of the 32’ trawl by: • Sketch each individual trawl part. • Include: • # of meshes at the top of the part (N) • # of meshes at the bottom of the part (n) • # of meshes in the height of the part (H) • Determine stretched mesh size • Use appropriate measurement system • Determine diameter of the twine* • Use appropriate measurement system *The twine diameter can be calculated as shown in the Fisherman’s Workbook, Pg. 9 or by referring to a “Twisted Twine Specifications” table found in various net catalogs.

  35. 32’ Trawl Top & Bottom Body Parts: Customary System (N+ n x H) 2 144 x 2 (a x Ø ) S = 233M S = (233+ 73 x 160) 2 144 1P2B 1P2B x 2(1.5” x .051”) 160M S = x 2(.0765”) 73M (153 x 160) 144 S = x0.153” = 24480 144 3745.44 144 2 parts = 2 x 26.01 sq.ft. TOTAL = 52.02 sq.ft. S = 26.01sq.ft. per part

  36. 32’ Trawl Top & Bottom Body Extension Parts: Customary System (N+ n x H) 2 144 x 2 (a x Ø ) S = 73M S = (73+ 54 x 19) 2 144 1P2B 1P2B x 2(1.5” x .051”) 19M S = x .153 54M (63.5 x 19) 144 S = x0.153” = 184.595 144 1206.5 144 2 parts = 2 x 1.2819 sq.ft. TOTAL = 2.56388 sq.ft. S = 1.2819sq.ft. per part

  37. 32’ Trawl Remaining Parts: Customary System (N+ n x H) 2 144 x2 (a x Ø ) 54M S = Top Extension Part: 1 Part = 1.0901 sq.ft 19M 54M 56M 56M Front Side Extension Part: (4.641sq.ft.) 2 Parts =9.282 sq.ft. 78M 3P2B 178M 56M Side Tapered Part: (6.4303sq.ft.) 2 Parts =12.8606 sq.ft. 116M 1M2B 1M2B 30 M Jib Corner Part: (1.849sq.ft.) 4 Parts =7.395 sq.ft. 12M CODEND BAG NOT INCLUDED

  38. 32’ Trawl What is the total twine surface area (not including Codend Bag) of the new 32 ft. net which uses a #15 Nylon twine with a 1.5” stretch mesh? Top & Bottom Body Parts: 52.02 sq.ft. Top & Bottom Body Extension Parts: 2.56388 sq.ft. Remaining Parts: 30.6277 sq.ft. TOTAL TWINE SURFACE AREA: 85.21158 sq.ft. (Not including Codend Bag or Knot correction factor)

  39. Comparisons Original Net: 50 ft. 1.875”str.mesh,#15 PA Twine Original Net = 168 sq.ft. Converted Net: 32 ft. 1.5”str.mesh,#15 PA Twine Converted Net = 85 sq.ft. 32’ net is 36% smaller than 50’ net 1.5” mesh is 20% smaller than the original 1.875” mesh. The square footage of the 32’ net is 49.4% less than the 50’ net Adjustments The trawl door size should be reduced by approx. 50%. A reduction in twine diameter (#15 to #12) could reduce the square footage (54.5% less than original) and the drag even more – allowing less H.P. Flotation and bridle lengths could be reduced. Winch requirements not as great as the original net. How does the total twine surface area of the two nets compare?What, if any, adjustments to the projected plans may be necessary based on your calculations?

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