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MSC 134 Fishing Gear Technology II Gill Nets: Concepts and Design.

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1 MSC 134 Fishing Gear Technology II Gill Nets: Concepts and Design

2 Gill Net Design: Class Example We would like to construct a gill net 150 yards long. We will be using a #6 (#139) monofilament webbing with a 1¾-inch square mesh. We would like to fish the net on the bottom (sink net) and would like the net to be approximately 7½ feet deep when hung. The primary hanging ratio should be 50%. We will use a “Sponge” SB-2 float with 3/16 -inch diameter hollow braided polypropylene rope. The rope will have a buoyancy factor of approximately.02(.0163) ounces per foot of rope. We will also consider the “weight” of the webbing in our “design” calculations. How did we decide what mesh size to use? * The mesh size of gillnets can be calculated as shown in the Fisherman’s Workbook, Pg. 98 or by referring to the handout “Entangling Nets, Gillnets and Seine Nets.”

3 “There is a ratio between the body girth or the length of a fish one wants to catch, and the gillnet meshsize which will be effective for that fish.”* Choice of Meshsize (Textbook, Pg. 98) OM = L (fish) / K OM = mesh opening (mm) L (fish) = average length (mm) of fish one wants to catch K = coefficient, according to species K = 5 for long, thin fish K = 3.5 for average-shaped fish (neither very thick nor thin) K = 2.5 for very thick, wide or high (shaped) fish * Fisherman’s Workbook compiled by J. Prado, Fishing News Books, Oxford, England:1990. Pg. 98

4 OM = L (fish) / K K = 5 for long, thin fish K = 3.5 for average-shaped fish (neither very thick nor thin) K = 2.5 for very thick, wide or high (shaped) fish If asked to design and build a gillnet capable of catching a quantity of Bluefish ( Pomatomus saltatrix ) with an average length of 12 inches,use the formula from your text to decide on a suitable mesh size. Mesh Opening = 12” ÷ 3.5 = 3.42” (3½”) Examples:

5 Mesh selection factor based on known values obtained by local sampling experience and/or historical data. Mo = L / Km (L ÷ Km) If a gill net with the mesh size M 1 has caught fish of the length L 1 and a gill net with the mesh size M 2 catches fish of the length L 2, then: L 2 / L 1 = M 2 / M 1 (L 2 ÷ L 1 =M 2 ÷ M 1 ) Therefore, L 2 = L 1 x M 2 ÷ M 1 and M 2 = M 1 x L 2 ÷ L 1 The numerical value of the ratio L 1 ÷ M 1 = Km The Km is specific for each species of fish. Net selectivity data includes the hanging ratios, twine material and diameter, and the ballast and floatation specifications. File the net selectivity data and mesh selection factors for future reference.

6 MO = L / Km L 2 / L 1 = M 2 / M 1 (L 2 ÷ L 1 =M 2 ÷ M 1 ) Therefore, L 2 = L 1 x M 2 ÷ M 1 and M 2 = M 1 x L 2 ÷ L 1 If asked to design and build a gillnet capable of catching a quantity of Bluefish ( Pomatomus saltatrix ) with an average length of 12 inches,use the formula from your handout and refer to historical data from your sampling area to decide on a suitable mesh size and net design. 12.2” / 10.3” = 3.5” / 3” Therefore L 2 = L 1 x M 2 ÷ M 1 L 2 = 10.3” x 3.5” ÷ 3” L 2 = 10.3” x L 2 = 12.02” (12”) Examples: OR MO = L / Km L 1 ÷ M 1 = Km 10.3” ÷ 3” = ” ÷ 3.5” = 3.49 Therefore average Km = 3.46 So - MO = 12”/3.46 MO = 3.47” (3½”) L 2 / L 1 = M 2 / M ” / 10.3” = 3.5” / 3” Therefore M 2 = M 1 x L 2 ÷ L 1 M 2 = 3” x 12.2” ÷ 10.3” M 2 = 3” x M 2 = 3.56” (3½”)

7 Examples: If asked to design and build a gillnet capable of catching a quantity of Bluefish ( Pomatomus saltatrix ) with an average length of: MO = L / Km 14 inches then MO = 14”/3.46 so the mesh opening = 4.04” (4”) 16 inches then MO = 16”/3.46 so the mesh opening = 4.62” (4½-4¾”) 18 inches then MO = 18”/3.46 so the mesh opening = 5.20” (5 -5¼ ”) 10 inches then MO = 10”/3.46 so the mesh opening = 2.89” (2¾-3”) 8 inches then MO = 8”/3.46 so the mesh opening = 2.31” (2¼”) Remember: The Km is specific for each species of fish. Net selectivity data includes the hanging ratios, twine material and diameter, as well as the ballast and floatation specifications. File the net selectivity data and mesh selection factors for future reference.

8 A spread-sheet designed to file your net selectivity data and mesh selection factors may look similar to the example shown below.

9 Gill Net Design: Class Example We would like to construct a gill net 150 yards long. We will be using a #6 (#139) monofilament webbing with a 1¾-inch square mesh. We would like to fish the net on the bottom (sink net) and would like the net to be approximately 7½ feet deep when hung. The primary hanging ratio should be 50%. We will use a “Sponge” SB-2 float with 3/16 -inch diameter hollow braided polypropylene rope. The rope will have a buoyancy factor of approximately.02(.0163) ounces per foot of rope. We will also consider the “weight” of the webbing in our “design” calculations. What is the “twine ratio” selected for this gillnet?

10 Calculating the Twine Ratio When selecting a twine diameter for gillnets, the diameter should be proportional to the mesh size. The ratio should be between and for calm waters and/or low catches..01 for rough waters and/or bottom set nets. An average ratio is * The twine ratio can be calculated as shown in the Fisherman’s Workbook, Pg. 99 or by referring to the handout “Entangling Nets, Gillnets and Seine Nets.” Ratio = Twine Diameter ÷ Stretch Mesh Size (always use the same units of measurement to compare the two variables) Twine Diameter =.40mm and.40mm = in. (1mm ÷ 25.4mm = so.40mm =.03937in. x.40mm = inches) Stretch Mesh Size = 3½ in. and 3½ in. = 88.9mm (1in. = 25.4mm so 3½ in. = 3½ in x 25.4mm =88.9mm).40mm ÷ 88.9mm = =.005 Or in. ÷ 3.5in. = =.005

11 Exactly how much rope do I need to complete this net? 935 Feet (920’ to 950’)

12 Exactly how much rope do I need to complete this net? How much “Classic” hollow braided polypropylene rope would you order? What would the rope cost? 935 Feet (920’ to 950’) One 1200’ reel cost $ Two 600’ reels cost $26.00 ($13.00 ea.) Since we need two lengths of rope - is it worth $1.30 not to separate and measure the ropes, a job that would take approximately 30 to 60 minutes? 1200 Feet $26.00 (Discretionary Decision – Why?)

13 How many meshes deep should I order the webbing? E 1 = L/Lo. E 1 is the Primary Hanging Ratio. L is the length of rope on which a net panel is “hung”. Lo is the length of stretched netting before hanging. E 2 = H/Ho. E 2 is the Secondary Hanging Ratio. H is the actual height of a “hung” net. Ho is the height of the stretched netting before hanging. Meshes Deep is a function of E 2

14 How many meshes deep should I order the webbing? 1 Mesh = 1¾” Square = 3½” Stretch E 1 = 50% (.50) therefore E2 = 87% (.87)** Finished Gill Net = Approximately 7½ feet deep. ** Refer to Fisherman’s Workbook, pg.38; the handout “Introduction to Netting Theory”or use the formula E 2 = 1 – E 1 ² E 2 = H ÷ Ho therefore H = E 2 x Ho and Ho = H ÷ E 2 The answer can be found by mathematically using the known variables and then referring to the “materials available” in our catalog.

15 How many meshes deep should I order the webbing? 30 Meshes Deep 1 Mesh = 3½” Stretch …. E2 = 87% (.87)*…. 7½ feet deep. E 2 = H ÷ Ho therefore H = E 2 x Ho and Ho = H ÷ E 2 H =.87 x 3.5” therefore the “hung” height of one mesh = 3.045” and 7.5 ft. x 12 in. = 90 inches so 90” ÷ 3.045” = Meshes obviously we will look for 30 Meshes Deep in our catalog. Proof: 30 meshes x 3.5” = 105 str.in. H = E 2 x Ho so H =.87 x 105” = 91.35” ÷ 12” = 7.61 ft. E 2 = H ÷ Ho so E 2 = 91.35” ÷ 105” =.87 (87%) Ho = H ÷ E 2 so Ho = 91.35” ÷.87 = 105”

16

17 How many pounds of webbing will I need to complete this net? 7.2 Pounds E1 = L ÷ Lo 150 yd. Net x 3 ft. = 450 foot long Net 125 stretch feet per pound (Stk. #N221A) 125 str. ft.(Lo) x.50 (E 1 ) = 62.5 hung Ft./Lb. (L) 450 ft. net ÷ 62.5 hung Ft./Lb. = 7.2 Pounds

18 What would the total cost of this webbing be? How many pounds of webbing would you order? 8 Pounds $ thru 24 Lbs. = $8.85 Lb. therefore 8 Lb. x $8.85 = $70.80 Can’t order partial poundage unless ordering a “hank”. The catalog presents a hank as the “standard” most people would base their gill net calculations with: A 100 yard net hung on a “half” would require 4.8 pounds of stk. # N221A webbing. 125 str.ft.(Lo) x.50 (E1) = 62.5 hung ft./lb. (L) 300 ft. net ÷ 62.5 hung ft./lb. = 4.8 Pounds How many feet of repair material would you have left if you order 8 pounds of webbing?.8 lbs. x 62.5 hung ft./lb. = 50 hung feet for repairs.

19 When hanging the webbing to the headrope and footrope, how many meshes will you insert into every “pickup”? When hanging the webbing to the headrope and footrope, what will the distances of your “pickups” be? Options: 1 mesh = 3.5” str. E 1 =.50 or 50% L =.50 x 3.5” = 1.75” per mesh 2 meshes = 3.5” 3 meshes = 5.25” 4 meshes = 7” Refer to standards discuss in the handout “Entangling Nets, Gillnets & Seine Nets”

20 Complete a schematic of the gill net showing a “one unit” section representing the distance and number of pickups between floats and the number of pickups between leads. *Complete the schematic in detail, all answers concerning floats and leads are based on this schematic. “Unit” Size? “Pickup” Size? Meshes per “Pickup”? Floatation per “Unit”? # of Leads per “Unit”? Ballast per “Unit”? Label “Pickup” Size Label “Unit” Size Show Lead Placement Show Float Placement # of meshes Gill Net Schematics

21 Complete a schematic of the gill net showing a “one unit” section representing the distance and number of pickups between floats and the number of pickups between leads. *Complete the schematic in detail, all answers concerning floats and leads are based on this schematic. “Unit” Size? “Pickup” Size? 7” Meshes per “Pickup”? 4 Floatation per “Unit”? # of Leads per “Unit”? 2 Ballast per “Unit”? ” Unit 7” Option 1: 4 7 inches Units: This net is designed to be 7½’ (90”) deep. 50% of 90”= 45” which we have defined as the maximum distance between floats. 45” ÷ 7” = 6.42 “pickups” between floats. We can’t have partial “pickups” so 6 x 7” = 42” Refer to standards discuss in the handout “Entangling Nets, Gillnets & Seine Nets” 42”

22 Complete a schematic of the gill net showing a “one unit” section representing the distance and number of pickups between floats and the number of pickups between leads. *Complete the schematic in detail, all answers concerning floats and leads are based on this schematic. “Unit” Size? “Pickup” Size? 5.25” Meshes per “Pickup”? 3 Floatation per “Unit”? # of Leads per “Unit”? 2 Ballast per “Unit”? ” Unit 5¼” Option 2: 3 5¼ inches Units: This net is designed to be 7½’ (90”) deep. 50% of 90”= 45” which we have defined as the maximum distance between floats. 45” ÷ 5¼” = 8.57 “pickups” between floats. We can’t have partial “pickups” so 8 x 5¼” = 42” Refer to standards discuss in the handout “Entangling Nets, Gillnets & Seine Nets” 42”

23 Complete a schematic of the gill net showing a “one unit” section representing the distance and number of pickups between floats and the number of pickups between leads. *Complete the schematic in detail, all answers concerning floats and leads are based on this schematic. “Unit” Size? 49” “Pickup” Size? 7” Meshes per “Pickup”? 4 Floatation per “Unit”? # of Leads per “Unit”? Ballast per “Unit”? ” Unit 7”7” Option 3 (Discretionary): 4 7 inches This schematic utilizes a “unit” that exceeds the “50% of hung depth” rule summarized in the “handout”. However, it does not exceed the general rule of “75% of the hung depth” and thus becomes a discretionary decision and as such should have an attached explanation. Refer to standards discuss in the handout “Entangling Nets, Gillnets & Seine Nets”

24 How many floats will you need to order? What is the total cost of those floats? Actual Floats Needed:Floats Ordered: Total Cost: $41.60 Option 1: One float every 42” = Floats (128 or 129 Floats) [450’ (length of net) x 12” = 5400” ÷ 42”(units) = floats] Option 2: One float every 42” = Floats (128 or 129 Floats) Option 3 (Discretionary): One float every 49” = Floats (110 or 111) [450’ (length of net) x 12” = 5400” ÷ 49”(units) = floats] [Catalog states 50 or more SB2 Floats = $.32 each = 130 floats x $.32 = $41.60]

25 What size lead are you planning to use? Stk. # How many leads per pound? How many leads per unit? How many pounds of lead will you need? Leads are designated by Hole Diameter, Length and Number of Leads per Pound. Diameter of the lead hole must be approximately 1/8” larger than rope diameter. Stk. LS6 (1/2”) = 6 Leads per Pound = 2.67 ounces each (16 oz. ÷ 6 = ) Stk. LS8 (1/2”) = 8 Leads per Pound = 2 ounces each (16 oz. ÷ 8 = 2) Stk. L8 (3/8”) = 8 Leads per Pound = 2 ounces each (16 oz. ÷ 8 = 2) Stk. L10 (7/16”) = 10 Leads per Pound = 1.6 ounces each (16 oz. ÷ 10 = 1.6) Stk. L13 (3/8”) = 13 Leads per Pound = 1.23 ounces each (16 oz. ÷ 13 = ) Stk. L16 (9/32”) = 16 Leads per Pound = 1 ounce each (16 oz. ÷ 16 = 1) The “handout” specifies a spacing of leads not to exceed 2 to 4 per float. A “sink gillnet” would need a minimum ¾ to 2 ounce ballast per unit. A “floating gillnet” would need a minimum ¾ to 2 ounce buoyancy per unit. 2 #L8 Leads = 4 oz #L10 Leads = 3.2 oz #L13 Leads = 3.69 oz. Number of Leads per unit x # of units in the net ÷ # of leads per pound = Pounds

26 “Unit” Size? 42” “Pickup” Size? 7” Meshes per “Pickup”? 4 Floatation per “Unit”? 2.64 oz. # of Leads per “Unit”? 2 (#L8) Ballast per “Unit”? ” Unit 7” Option 1: 4 7 inches Floatation per “Unit” = 2.64 ounces Floats = 2½ oz. (catalog) Rope =.02 oz. per ft. (approximate given).0163 oz. per ft.(actual calculation) One unit = 42” therefore 84”(7’) of rope per unit, so 7’ x.02oz. =.14 oz. per unit (approx.) or 7’ x.0163oz. =.1141 oz. (actual) 2.5oz. (float) +.14oz. (rope, approx.) = 2.64 oz. (2.6141, actual)

27 Rope: The handout “Ropes and Fibers” from the MSC 132 class contains a Fiber Cordage table* which indicates the “typical weights and minimum strengths”. * Similar information is shown in the table “Synthetic Fiber Rope” in Fisherman’s Workbook, Pg Pound = 16 ounces 16 oz. ÷ 137 ft. = oz. per ft. of rope or 16 oz. X.73 lbs. = oz. ÷ 100 ft. = oz. per foot However To obtain the weight in water of a certain quantity of material, you must multiply its weight in air by the factor given in the “Density of Materials” table found in your textbook on page 3. Obviously, polypropylene(PP) is listed as a “Floating Material”. Polypropylene(PP) = (Multiplication factor in sea water) Therefore oz. X.14-= oz. per foot of rope (approx oz.)

28 “Unit” Size? 42” “Pickup” Size? 7” Meshes per “Pickup”? 4 Floatation per “Unit”? 2.64 oz. # of Leads per “Unit”? 2 (#L8) Ballast per “Unit”? 3.73 oz ” Unit 7” Option 1: 4 7 inches (2 #L8’s) Ballast per “Unit” = 3.73 oz. Leads = 2 oz. each (catalog) 1.82 oz. (actual weight in seawater) Webbing =.09 oz. per “unit” (approximate) oz. Per”unit”(actual calculation) 4 oz. (leads approx.) +.9oz. (webbing approx.) = 4.9 oz. (Air Weight) 3.64oz. (leads approx.) +.09oz. (webbing approx.) = 3.73 oz. ( actual in seawater) “The weight in water, with examples for materials and for a rigged gillnet” is shown in the Fisherman’s Workbook, Pg. 04.

29 Ballast: To obtain the weight in water of a certain quantity of material, you must multiply its weight in air by the factor given in the “Density of Materials” table found on page 3 of your textbook. Obviously, lead is listed as a “Sinking Material”. Nylon or polyamides(PA) are also listed as a “Sinking Material”. Lead = (Multiplication factor in sea water) Webbing, Polyamide(PA) = (Multiplication factor in sea water) Each #L8 lead has an air weight of 2 ounces (given in catalog) Therefore 2.0 oz. X.91+ = 1.82 oz. per lead of actual ballast in seawater And This gillnet contains 62½ hung feet of webbing per pound (16 oz.) So One “unit” on this net is 42” (3½’) which means: 62½’ ÷ 3½’ = units per pound of material. 16 ounces ÷ units =.896 oz. per unit of webbing. Therefore.896 oz. X.10+ =.0896 oz. of actual ballast per “unit” of webbing in seawater.

30 What size lead are you planning to use? Stk. #L8 How many leads per pound? 8 How many leads per unit? 2 How many pounds of lead will you need? Leads are designated by Hole Diameter, Length and Number of Leads per Pound. Diameter of the lead hole must be approximately 1/8” larger than rope diameter. Stk. L8 (3/8”) = 8 Leads per Pound = 2 ounces each (16 oz. ÷ 8 = 2) The “handout” specifies a spacing of leads not to exceed 2 to 4 per float. A “sink gillnet” would need a minimum ¾ to 2 ounce ballast per unit. 2 #L8 Leads = 4 oz. (Air Weight) Number of Leads per unit x # of units in the net ÷ # of leads per pound = Pounds (2) x (5400” ÷ 42” = 128.6) ÷ (8) 2 x = leads ÷ 8 leads per lb. = Pounds Option 1: 4 7 inches (2 #L8’s) 32.15

31 Is this net designed to sink or float? What is the average buoyancy per “unit”? What is the average ballast per “unit”? What is the average “positive” (floats) or “negative” (sinks) factor you have calculated for each “unit”? Sink Option 1: 4 7 inches Original Specifications: “ We would like to fish the net on the bottom (sink net) and would like the net to be approximately 7½ feet deep when hung.” 2.64 oz. Floatation Calculations: 2.5oz. (float) +.14oz. (rope, approx.) = 2.64 oz. ( oz. actual) 3.73 oz. Ballast Calculations: 3.64oz. (leads approx.) +.09oz. (webbing approx.) = 3.73 oz. ( actual in seawater) 1.09 oz. “negative” Calculation: Average ballast per unit – average buoyancy per unit oz. – 2.64 oz. = 1.09 oz.

32 Other Design Options and Discretionary Decision Making Gill Nets: Concepts and Design

33 “Unit” Size? 42” “Pickup” Size? 7” Meshes per “Pickup”? 4 Floatation per “Unit”? 2.64 oz. # of Leads per “Unit”? 2 (#L10) Ballast per “Unit”? 2.99 oz ” Unit 7” Option 1: 4 7 inches (2 #L10’s) Floatation per “Unit” = 2.64 ounces Ballast per “Unit” = 2.99 oz. Leads = 1.6 oz. each (catalog) oz. (actual weight in seawater) Webbing =.09 oz. per “unit” (approximate) oz. Per”unit”(actual calculation) 2.9 oz. (leads approx.) +.09oz. (webbing approx.) = 2.99 oz. ( actual in seawater)

34 Is this net designed to sink or float? What is the average buoyancy per “unit”? What is the average ballast per “unit”? What is the average “positive” (floats) or “negative” (sinks) factor you have calculated for each “unit”? Sink Option 1: 4 7 inches (2 #L10’s) Original Specifications: “ We would like to fish the net on the bottom (sink net) and would like the net to be approximately 7½ feet deep when hung.” 2.64 oz. Floatation Calculations: 2.5oz. (float) +.14oz. (rope, approx.) = 2.64 oz. ( oz. actual) 2.99 oz. Ballast Calculations: 2.99oz. (leads approx.) +.09oz. (webbing approx.) = 2.99 oz. ( actual in seawater).35 oz. “negative” Calculation: Average ballast per unit – average buoyancy per unit oz. – 2.64 oz. =.35 oz. Will this Design Work? No – Not enough ballast!

35 “Unit” Size? 42” “Pickup” Size? 7” Meshes per “Pickup”? 4 Floatation per “Unit”? 2.64 oz. # of Leads per “Unit”? 3 (#L13) Ballast per “Unit”? 3.49 oz ” Unit 7” Option 1: 4 7 inches (3 #L13’s) Floatation per “Unit” = 2.64 ounces Ballast per “Unit” = 3.49 oz. Leads = oz. each (catalog) 1.12 oz. (actual weight in seawater) 3 x 1.12oz. = 3.36 oz. (3.4 oz.) Webbing =.09 oz. per “unit” (approximate) oz. Per”unit”(actual calculation) 3.4 oz. (leads approx.) +.09oz. (webbing approx.) = 3.49 oz. ( actual in seawater)

36 Is this net designed to sink or float? What is the average buoyancy per “unit”? What is the average ballast per “unit”? What is the average “positive” (floats) or “negative” (sinks) factor you have calculated for each “unit”? Sink Option 1: 4 7 inches (3 #L13’s) Original Specifications: “ We would like to fish the net on the bottom (sink net) and would like the net to be approximately 7½ feet deep when hung.” 2.64 oz. Floatation Calculations: 2.5oz. (float) +.14oz. (rope, approx.) = 2.64 oz. ( oz. actual) 3.49 oz. Ballast Calculations: 3.4 oz. (leads approx.) +.09oz. (webbing approx.) = 3.49 oz. ( actual in seawater).85 oz. “negative” Calculation: Average ballast per unit – average buoyancy per unit oz. – 2.64 oz. =.85 oz. Will this Design Work? YES?? – Discretionary ballast!

37 “Unit” Size? 42” “Pickup” Size? 7” Meshes per “Pickup”? 4 Floatation per “Unit”? 2.64 oz. # of Leads per “Unit”? 2½(#L8) Ballast per “Unit”? 4.69 oz ” Unit 7” Option 1: 4 7 inches (2½ #L8’s) Floatation per “Unit” = 2.64 ounces Ballast per “Unit” = 4.69 oz. Leads = 2 oz. each (catalog) 1.82 oz. (actual weight in seawater) 2.5 x 1.82oz. = 4.55 oz. (4.6 oz.) Webbing =.09 oz. per “unit” (approximate) oz. Per”unit”(actual calculation) 4.6 oz. (leads approx.) +.09oz. (webbing approx.) = 4.69 oz. ( actual in seawater)

38 Is this net designed to sink or float? What is the average buoyancy per “unit”? What is the average ballast per “unit”? What is the average “positive” (floats) or “negative” (sinks) factor you have calculated for each “unit”? Sink Option 1: 4 7 inches (2½ #L8’s) Original Specifications: “ We would like to fish the net on the bottom (sink net) and would like the net to be approximately 7½ feet deep when hung.” 2.64 oz. Floatation Calculations: 2.5oz. (float) +.14oz. (rope, approx.) = 2.64 oz. ( oz. actual) 4.69 oz. Ballast Calculations: 4.6 oz. (leads approx.) +.09oz. (webbing approx.) = 4.69 oz. ( actual in seawater) 2.05 oz. “negative” Calculation: Average ballast per unit – average buoyancy per unit oz. – 2.64 oz. = 2.05 oz. Will this Design Work? NO?? – Discretionary ballast!

39 “Unit” Size? 42” “Pickup” Size? 5.25” Meshes per “Pickup”? 3 Floatation per “Unit”? 2.64 oz. # of Leads per “Unit”? 2½(#L10) Ballast per “Unit”? 3.69 oz ” Unit 5¼” Option 2: 3 5¼ inches (2½ #L10’s) Floatation per “Unit” = 2.64 ounces Ballast per “Unit” = 3.69 oz. Leads = 1.6 oz. each (catalog) oz. (actual weight in seawater) 2.5 x 1.456oz. = 3.64 oz. (3.6 oz.) Webbing =.09 oz. per “unit” (approximate) oz. Per”unit”(actual calculation) 3.6 oz. (leads approx.) +.09oz. (webbing approx.) = 3.69 oz. ( actual in seawater)

40 Is this net designed to sink or float? What is the average buoyancy per “unit”? What is the average ballast per “unit”? What is the average “positive” (floats) or “negative” (sinks) factor you have calculated for each “unit”? Sink Option 2: 3 5¼ inches (2½ #L10’s) Original Specifications: “ We would like to fish the net on the bottom (sink net) and would like the net to be approximately 7½ feet deep when hung.” 2.64 oz. Floatation Calculations: 2.5oz. (float) +.14oz. (rope, approx.) = 2.64 oz. ( oz. actual) 3.69 oz. Ballast Calculations: 3.6 oz. (leads approx.) +.09oz. (webbing approx.) = 3.69 oz. ( actual in seawater) 1.05 oz. “negative” Calculation: Average ballast per unit – average buoyancy per unit oz. – 2.64 oz. =1.05 oz. Will this Design Work? YES!

41 “Unit” Size? 49” “Pickup” Size? 7” Meshes per “Pickup”? 4 Floatation per “Unit”? 2.663oz. # of Leads per “Unit”? 3 (#L10) Ballast per “Unit”? 4.6 oz ” Unit 7”7” Option 3 (Discretionary): 4 7 inches Floatation per “Unit” = 2.66 ounces Ballast per “Unit” = 4.6 oz. Leads = 1.6 oz. each (catalog) oz. (actual weight in seawater) Webbing =.10 oz. per “unit” (approximate) oz. Per”unit”(actual calculation) 4.5 oz. (leads approx.) +.1oz. (webbing approx.) = 4.6 oz. ( actual in seawater)

42 Is this net designed to sink or float? What is the average buoyancy per “unit”? What is the average ballast per “unit”? What is the average “positive” (floats) or “negative” (sinks) factor you have calculated for each “unit”? Sink Option 3 (Discretionary): 4 7 inches Original Specifications: “ We would like to fish the net on the bottom (sink net) and would like the net to be approximately 7½ feet deep when hung.” 2.66 oz. Floatation Calculations: 2.5oz. (float) +.164oz. (rope, approx.) = oz. ( oz. actual) 4.6 oz. Ballast Calculations: 4.5oz. (leads approx.) +.10 oz. (webbing approx.) = 4.6 oz. ( actual in seawater) 1.94 oz. “negative” Calculation: Average ballast per unit – average buoyancy per unit. 4.6 oz. – 2.66 oz. = 1.94 oz. Will this Design Work? Yes

43 Weight in Water – Overview of Options Option 1: 4 7” 42” unit,2x #L8 Option 1: 4 7” 42” unit, 2x #L10 Option 1: 4 7” 42”unit, 3x#L13 Option 1: 4 7” 42” unit,2.5x #L8 Rope & Floats 2.64 oz. / unit Leads & Webbing 3.73 oz. / unit 1.09 oz. Ballast/unit 150 yard Gillnet “units” lbs. Buoyancy lbs. Ballast 8.75 lbs. Ballast (not including anchors) Rope & Floats 2.64 oz. / unit Leads & Webbing 2.99 oz. / unit.35 oz. Ballast/unit 150 yard Gillnet “units” lbs. Buoyancy lbs. Ballast 4.5 lbs. Ballast (not including anchors) Rope & Floats 2.64 oz. / unit Leads & Webbing 3.49oz. / unit.85 oz. Ballast/unit 150 yard Gillnet “units” lbs. Buoyancy lbs. Ballast 8.46 lbs. Ballast (not including anchors) Rope & Floats 2.64 oz. / unit Leads & Webbing 4.69 oz. / unit 2.05 oz. Ballast/unit 150 yard Gillnet “units” lbs. Buoyancy lbs. Ballast lbs.Ballast (not including anchors)

44 Weight in Water – Overview of Options Option 1: 4 7” 42” unit, 2x #L8 Option 1: 4 7” 42” unit, 3x #L13 Option 2: ” 42” unit, 2½x #L10 Option 3: Discretionary 4 7” 49” unit, 3x #L10 Rope & Floats 2.64 oz. / unit Leads & Webbing 3.73 oz. / unit 1.09 oz. Ballast/unit 150 yard Gillnet “units” lbs. Buoyancy lbs. Ballast 8.75 lbs. Ballast (not including anchors) Rope & Floats 2.64 oz. / unit Leads & Webbing 3.49oz. / unit.85 oz. Ballast/unit 150 yard Gillnet “units” lbs. Buoyancy lbs. Ballast 8.46 lbs. Ballast (not including anchors) Rope & Floats 2.64 oz. / unit Leads & Webbing 3.69oz. / unit 1.05 oz. Ballast/unit 150 yard Gillnet “units” lbs. Buoyancy lbs. Ballast lbs. Ballast (not including anchors) Rope & Floats 2.66 oz. / unit Leads & Webbing 4.66 oz. / unit 1.94 oz. Ballast/unit 150 yard Gillnet “units” lbs. Buoyancy lbs. Ballast lbs. Ballast (not including anchors)

45 The average buoyancy and ballast values will change depending on local experience and gear applications. How do our net designs compare with examples given in our text and why might they differ? Comparisons Option 1: 4 unit, 2x #L lbs. Buoyancy lbs. Ballast 8.75 lbs. Ballast Ratio 1 to 1.41 Option 2: 3 unit, 2½x L lbs. Buoyancy lbs. Ballast lbs. Ballast Ratio 1 to 1.52 Option 3: 4 7” 49” unit, 3x #L lbs. Buoyancy lbs. Ballast lbs. Ballast Ratio 1 to 1.81 The text generally recommends a buoyancy to ballast ratio for a bottom set gillnet at approx. 1 to 2. Rationale The weights do not include anchors which add considerably to our overall weight and brings our ratios in line with the text. Both our ballast and buoyancy values were based on sea water – we generally are working in brackish waters. We generally use shorter length nets with smaller catches than commercial gear. Our nets are generally used in shallow waters without excessive currents. We can add ballast easier than subtracting ballast. Discretionary Decision Making “Average buoyancy and ballast of gillnets and trammel nets” is shown in the Fisherman’s Workbook, Pg. 103.

46 E 1 = L ÷ Lo.50 = 50 ÷ (320mm x 313) Pickups: 2 320mm Units:1 1600mm (5 pickups x 320mm) 32 floats: 50 M ÷ 1.6 M (31.25) 156 leads: 50 M ÷.32 M (156.25) Buoyancy: 1600gf (floats only) Ballast: 7098g -(leads only-seawater weight) 5498 grams ballast (12.14 lbs.) Ratio 1 to 4.44


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