Fishing Gear Design and Hydrodynamics PDF

Fishing Gear Design and Hydrodynamics Module 3 – Week 3 Fish 119 Fisheries Engineering  Estimate cutting rates and taper ratio of netting; By the end of Calculate twine surface area of trawl nets; this module, Estimate hanging ratio; students are Es...

Fishing Gear Design and Hydrodynamics Module 3 – Week 3 Fish 119 Fisheries Engineering  Estimate cutting rates and taper ratio of netting; By the end of Calculate twine surface area of trawl nets; this module, Estimate hanging ratio; students are Estimate trawl net, otter boards, warps, floats and friction hydrodynamic resistance expected to: 2  Net cutting Source: https://www.researchgate.net/figure/Net-plan-of-the-commercial-trawl- 3 used-as-control-during-the-comparative-fishing-trial-in_fig2_242366326 Vertical mesh count Net cutting Important in shaping fishing gear netting 4 Net cutting Horizontal mesh count Cutting rates 5 Net cutting Sideknots/N-cut/Point cut (N) Bars/B-cut/Bar cut (B) Meshes/T-cut/Mesh cut (T) N cuts are vertical B cuts are diagonal T cuts are horizontal 6  Net cutting 7 Source: Fisherman’s Workbook Net cutting 3N 3B 3T 8 Net cutting Cutting rates are only ideal when combining T with B or N with B. 1T2B 1N2B Combining T with N is inefficient, it is better to just use the All B cuts (AB). In this figure, we compare cutting rates of 1T2B (1 T cut then 2 B cuts) and 1N2B (1 N cut then 2 B cuts). 1T2B 1N2B 9 Net cutting a combination of T and B in 1T2B results to a longer T-direction compared to its N-direction. the N and B combination results 1T2B 1N2B to a longer N-direction compared to T-direction. These differences can be quantified using the taper ratio (R), which is simply a ratio between the number of meshes in the N- and T-direction. 1T2B 1N2B 10  Bars Sideknots Meshes Calculating B N T 𝑇𝑛 0.5 0 1 taper ratio 𝑁𝑛 0.5 1 0 𝑇 𝑅 = 𝑛ൗ𝑁 1 0 undefined 𝑛 𝑇𝑛 Number of T-cuts 𝑅= 𝑁𝑛 Number of N-cuts 11  Solving for 1N1B taper ratio: Calculating taper ratio Convert 1N1B to 1N + 1B Treat 𝑇𝑛 = 1𝑁 + 1𝐵 and 𝑁𝑛 = 1N + 1B Bars Sideknots 1N1B B N 𝑇𝑛 0.5 0 (1*0)+(1*0.5) = 0.5 𝑁𝑛 0.5 1 (1*0.5)+(1*1) = 1.5 𝑇𝑛 1 0 0.5 1 𝑅 = ൗ𝑁 = = 0.333.. 𝑛 1.5 3 12 Taper ratio sample problem Bars Sideknots Meshes 1N2B 1T2B 2T1B 2N1B 2T4B B N T 𝑇𝑛 0.5 0 1 ? ? ? ? ? 𝑁𝑛 0.5 1 0 ? ? ? ? ? 𝑇𝑛 1 0 Und. ? ? ? ? ? 𝑅= ൗ𝑁 𝑛 13 Taper ratio sample problem B N T 1N2B 1T2B 2T1B 2N1B 2T4B 𝑇𝑛 0.5 0 1 (1*0)+(2*0.5) (1*1)+(2*0.5) (2*1)+(1*0.5) (2*0)+ (2*1)+ (1*0.5) (4*0.5) 𝑁𝑛 0.5 1 0 (1*1)+(2*0.5) (1*0)+(2*0.5) (2*0)+(1*0.5) (2*1)+ (2*0)+ (1*0.5) (4*0.5) 𝑇𝑛 1 0 Und. ½ or 0.5 2 5 1/5 or 0.2 2 𝑅= ൗ𝑁 𝑛 14 Twine surface area 15  Twine surface area Measured in 𝑚2 N = no. of meshes above N = no. of meshes below H = no. of vertical meshes a = stretched mesh (mm) Ø = twine diameter (mm) 16 Twine surface area sample problem A piece of netting has a stretch mesh diameter of 80 mm and a twine diameter of 1.5 mm. Calculate the twine surface area. N = 16 n=6 H=6 17 Twine surface area sample problem 𝑁+𝑛 ∗ 𝐻 ∗ 2 ∗ (𝑎 ∗ ∅) 2 𝑆= 1000000 16 + 6 ∗ 6 ∗ 2 ∗ (80 ∗ 1.5) 2 𝑆= 1000000 22 ∗ 6 ∗ 2 ∗ (120) 2 = 1000000 11 ∗ 6 ∗ 2 ∗ (120) = 1000000 66 ∗ 2 ∗ 120 = 1000000 15,840 = 1000000 S = 𝟎. 𝟎𝟏𝟔 𝒎𝟐 18 Twine surface area sample problem Calculate the twine surface area of trawl as illustrated to the right: Given: All values vary. Find: S 19 Twine surface area sample problem (Trawl) Panel No. of N+n/2 H N+n/2*H a(mm) Ø(mm) 2*(a*Ø) Twine TOTAL surface panels area A 4 21 24 504 80 1.13 181 0.091 0.364 B 2 61 90 5490 80 1.13 181 0.993 1.985 C 1 279 30 8370 60 0.83 100 0.834 0.834 D 2 194 140 27160 60 0.83 100 2.705 5.410 E 2 136 100 13600 40 0.83 66 0.903 1.806 F 2 54 90 4860 80 1.13 181 0.879 1.757 G 2 97 30 2910 60 1.13 100 0.290 0.580 J 2 86 150 12900 40 1.13 90 1.166 2.332 7.860 15.069 20 Hanging ratio Calculated using the formula: 𝐿 𝐸= 𝐿𝑜 Where: L = length of rope on which a net panel is mounted 𝐿𝑜 = length of stretched netting hung on the rope 21  A 200 meshes net in the T-direction with Sample stretched mesh size of 50 mm is hung on a hanging ratio rope with length 8 m. Find the hanging ratio. problem Given: L = 8 m, Lo = 50 mm * 200 = 10,000 mm or 10 m Find: E 22  A 200 meshes net in the T-direction with Sample stretched mesh size of 50 mm is hung on a hanging ratio rope with length 8 m. Find the hanging ratio. problem Solution: 8 = 10 E =0.8 23  Note that the maximum surface area covered is achieved when Surface area by E = 0.71. Why is that? hanging ratio 24  The calculation of the surface area covered using E is given by the formula: Surface area S = E ∗ 1 − E 2 ∗ L ∗ H ∗ a2 by hanging ratio Where S = surface area of the netting in meters E = horizontal hanging ratio L = # of horizontal meshes H = # of vertical meshes a = stretch mesh size in meters 25  A netting panel having mesh count of 10,000 x 500 was calculated to have a hanging ratio 0.9. Surface Area Calculate the surface are occupied if the stretched mesh size is 30 mm. by Hanging Ratio Sample Given: E = 0.9, L = 10,000, H = 500, a = 0.030 m Problem Find: S 26  Solve for S 𝑆 = 𝐸 ∗ 1 − 𝐸 2 ∗ 𝐿 ∗ 𝐻 ∗ 𝑎2 𝑆 = 0.9 ∗ 1 − 0.92 ∗ 10000 ∗ 500 ∗ 0.032 𝑆 = 0.9 ∗ 1 − 0.81 ∗ 10000 ∗ 500 ∗ 0.0009 Surface Area 𝑆 = 0.9 ∗ 0.19 ∗ 4500 by Hanging 𝑆 = 0.9 ∗ 0.436 ∗ 4500 𝑺 = 𝟏, 𝟕𝟔𝟓. 𝟖𝒎𝟐 Ratio Sample Problem 27 Fishing gear resistance 28 Calculating Netting Resistance (Rr) There are several ways to calculate netting resistance (in tonnes). In our case, we will use the W. Dickson Method with the formula: 𝑑𝑟 6.6 ∗ Lr ∗ Hr R r = Sr ∗ ∗ (1 + ) 125 Sr Where Sr = twine surface area of the trawl (in m2) (refer to slide #15) dr = average diameter of twine (in mm) Lr = horizontal opening of the net (in m) Hr = vertical opening of the net (in m) 29 Netting Resistance (Rr) Sample Problem Calculate the netting resistance in Newtons if the trawl in slide #19 has an average twine diameter of 0.98 mm, horizontal and vertical opening of 10 m and 7 m, respectively. Given: S = 15.08 m2, dr = 0.98 mm, Lr = 10 m, Hr = 7 m Find: Rr 30 Netting Resistance (Rr) Sample Problem Solve for Rr: 𝑑𝑟 6.6 ∗ Lr ∗ Hr R r = Sr ∗ ∗ (1 + ) 125 Sr 0.98 6.6 ∗ 10 ∗ 7 R r = 15.08 ∗ ∗ (1 + ) 125 15.08 462 Note: 𝑅𝑟 = 15.08 ∗ 0.008 ∗ 1 + 15.08 no conversion of values 𝑅𝑟 = 0.121 ∗ 1 + 30.637 𝑅𝑟 = 0.121 ∗ 31.637 in here. Calculations are R r = 3.83 tonnes carried out irrespective of measurement units. Convert tonnes to newtons (N): 1000 kgs 3.83 tonnes ∗ ∗ 9.8 m/s 2 = 37,534 N 1 tonne 𝐑 𝐫 = 𝟑𝟕, 𝟓𝟑𝟒 𝐍 31 Calculating Otter Board Resistance (Rp) Otter boards are used to stabilize the trawl net during towing. The formula for calculating Rp is given by the formula: 1 R p = ∗ ρw ∗ Sp ∗ v 2 ∗ CD 2 Where ρw = density of seawater: 1025 kg/m3 Sp = area of the otter board (in m2) v = towing speed (in m/s) CD = coefficient of otter board type and angle of attack 32 Calculating Otter Board Resistance (Rp) CD values are given in the table Type of board Attack angle 𝑪𝑫 Behavior Approximate 𝑹𝒑 Rectangular flat 40 0.72 Good in bottom 0.25 Oval diedric 35 0.74 Very good in 0.20 bottom Süberkrub 15 0.25 Very good in 0.15 midwater 33 Otter Board Resistance (Rp) Sample Problem Calculate the area of a trawler’s Süberkrub if the towing speed observed when deployed in the Western Visayan Sea was 2.5 meters per second. Given: ρw = 1025 kg/m3, v = 2.5 m/s, CD = 0.25, Rp = 0.15 Find: Sp 34 Otter Board Resistance (Rp) Sample Problem Solve for Sp: 2 ∗ Rp Sp = ρw ∗ v 2 ∗ C D 2 ∗ 0.15 Sp = 1025 kg/m3 ∗ 2.5 2 ∗ 0.25 2 ∗ 0.15 N Sp = 1025 kg/m3 ∗ 2.5 m/s 2 ∗ 0.25 𝐒𝐩 = 𝟏. 𝟖𝟕𝐱𝟏𝟎−𝟒 𝐦𝟐 35  The resistance of warps and ground ropes are largely dependent on the length and diameter of the line. Hence the formula for Rc is given by the following: Calculating Rc = 55 * cos2 θ * Lc * d * v2 Warps and Where Ground Rope θ = angle of the warp with respect to the horizontal bottom Resistance (Rc) Lc = length of the warp (in m) dc = warp diameter (in m) v = towing speed (in m/s) 36  Determine the resistance caused by the warps of a trawler if the length of the warp is 10 meters, Warps and the diameter is 0.016 m, the towing speed is 4 meters per second, and the angle produced with Ground Rope respect to the horizontal substrate is 30°. Resistance (Rc) Given: θ = 30°, Lc = 10 m, dc = 0.016 m, v = 4 m/s Sample Problem Find: Rc 37  Solve for Rc: Warps and Rc = 55 * cos θ2 * Lc * d * v2 Ground Rope Rc = 55 * (cos 30)2 * 10 m * 0.016 m * (4 m/s)2 Resistance (Rc) 𝑅𝑐 = 55 ∗ 0.867 2 ∗ 10 𝑚 ∗ 0.016 ∗ 16 𝑚ൗ 2 𝑠 𝑅𝑐 = 55 ∗ 0.752 ∗ 10 𝑚 ∗ 0.016 ∗ 16 Sample 𝑹𝒄 = 105.882 N Problem 38  Floats and sinkers balance each other by providing both lift and downward drag depending on the type of trawl net being used. Rfl is given by the formula Calculating Rfl = Kf * dfl2 * v2 * n Floats and Where Sinkers Kf = coefficient of the floats or sinkers, given Resistance (Rfl) dfl = diameter of the floats or sinkers (in m) v = towing speed (in m/s) n = number of existing floats or sinkers 39 Floats and Sinkers Resistance (Rfl) Sample Problem Determine the resistance caused by 300 trawl floats if its diameter is 0.28 m, towing at a speed of 3.5 m/s, and a float coefficient of 0.2. Given: Kf = 0.2, dfl = 0.28 m, v = 3.5 m/s, n = 300 Find: Rfl 40 Floats and Sinkers Resistance (Rfl) Sample Problem Solve for Rfl: Rfl = Kf * dfl2 * v2 * n Rfl = 0.2 * (0.28 m)2 * (3.5 m/s)2 * 300 𝑅𝑓𝑙 = 0.2 ∗ 0.078 ∗ 12.25 ∗ 300 Rfl = 57.330 N 41  When using a bottom trawl, the friction resistance (Rf) between the sediment and sinkers (and even otter boards) must be taken into consideration. Rf is calculate using the formula: Rf = f * G Calculating Where Friction G = weight of the sinkers/otter boards in Resistance (Rf) water (in kg) f = coefficient of frictional resistance which value depends on the material and the type of sediment. 42 Calculating Rf The table shows possible f values to various materials with corresponding sediment grain size. Note that comma (,) = dot(.) in this table. Therefore, all values displayed here are decimals. 43 Friction Resistance (Rf) Sample Problem It was observed that the 50 sinkers of a bottom trawler that weighs 0.5 kilograms (in water) each, are being dragged on fine sand with exerted friction resistance of 15.25 newtons. Determine the type of material used in each sinker. Given: G = 50*0.5 kgs, Rf = 15.25 N Find: material used through f 44  Solve for f: Friction f= Rf G Resistance (Rf) f= 15.25 N 0.5 kgs ∗ 50 Sample 𝐟 = 𝟎. 𝟔𝟏 ∴ the material used was melted iron Problem 45  Prado J. 1990. Fisherman’s Workbook. Food and Agriculture Organization of the United Nations. 185 pp. Available from: http://www.fao.org/3/ah827e/AH827E00.htm Papanikolaou AD. 1994. Estimation of General References Characteristics of Fishing Vessels. WEGEMT 20th Graduate School. Vol. 1. 997 pp. Polytechnic University of Madrid. Available from: https://www.pdfdrive.com/fishing-vessel- technology-e50975561.html 46  Answer the problem sets sent by your instructor in your LMS site. Task 47