Fish 119: Fishing Gear Design and Hydrodynamics

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Questions and Answers

What is the formula used to calculate Netting Resistance (Rr)?

$Rr = \frac{dr}{Sr} * (1 + \frac{Lr + Hr}{6.6})$

$Rr = \frac{Sr}{dr} * (1 + \frac{Lr * Hr}{6.6})$

$Rr = Sr * \frac{dr}{125} * (1 + \frac{6.6 * Lr * Hr}{Sr})$ (correct)

$Rr = \frac{6.6 * Sr * dr}{Lr * Hr}$

What is the calculated value of Netting Resistance (Rr) in tonnes?

4.50 tonnes

3.00 tonnes

2.50 tonnes

3.83 tonnes (correct)

How is the Netting Resistance (Rr) converted from tonnes to newtons?

Rr is multiplied by 1,000 and divided by 9.8 m/s²

Rr is multiplied by 1,000 and then multiplied by 9.81 m/s² (correct)

Rr is multiplied by 9.81 m/s²

Rr is divided by 1,000 and then multiplied by 9.8 m/s²

What does 'dr' represent in the calculations?

Diameter of the ring or netting in meters Signup and view all the answers

What is the significance of the term 'Sr' in the formula?

It represents the standard reference area. Signup and view all the answers

What is the formula for the taper ratio 𝑅?

𝑅 = 𝑇𝑛 / 𝑁𝑛 Signup and view all the answers

In the taper ratio calculations for a 1N2B configuration, what value is assigned to 𝑇𝑛?

0.5 Signup and view all the answers

What is the value of the hanging ratio (E) calculated from a rope length of 8 m and stretched mesh size of 50 mm with 200 meshes?

0.8 Signup and view all the answers

For the taper ratio of 2T1B, what is the computed value for 𝑁𝑛?

1 Signup and view all the answers

What is the correct simplification for the taper ratio 𝑅 in the context of 1N1B?

0.333... Signup and view all the answers

For surface panel C, what is its calculated total surface area?

0.834 Signup and view all the answers

Which surface panels share the same dimension for the Ø(mm) parameter?

D and J Signup and view all the answers

When converting 1N1B, what is the correct treatment for 𝑇𝑛?

𝑇𝑛 = 1N + 1B Signup and view all the answers

What value represents 𝑇𝑛 in a configuration of 2T4B?

Undefined Signup and view all the answers

What is the role of the coefficient CD in the formula for calculating Rp?

It reflects the otter board type and angle of attack. Signup and view all the answers

What is the calculated 'Total area' for surface panel E?

1.806 Signup and view all the answers

Which statement is true regarding the maximum surface area covered and the value of the hanging ratio?

It can never exceed E = 0.71. Signup and view all the answers

Which configuration yields a taper ratio 𝑅 that cannot be determined?

1T2B Signup and view all the answers

Which formula correctly calculates the area Sp of a trawler’s Süberkrub if Rp is known?

Sp = 2 * Rp / (ρw * v^2 * CD) Signup and view all the answers

If the towing speed is increased while other factors remain constant, what happens to the resistance Rp?

Rp increases due to the square of the velocity. Signup and view all the answers

For the configuration 2N1B, how is 𝑇𝑛 calculated?

(20)+(10.5) Signup and view all the answers

What is the formula used to calculate the hanging ratio E?

E = L / Lo Signup and view all the answers

If the stretched mesh size is 50 mm and the number of meshes is 200, what is the value of Lo in meters?

10 m Signup and view all the answers

Which type and angle of attack for an otter board has the lowest approximate Rp according to the data?

Süberkrub board at 15 degrees. Signup and view all the answers

Considering the surface panels, which panel has the largest total area?

Panel D Signup and view all the answers

In the given context, what primarily affects the resistance of warps and ground ropes?

The length and diameter of the line. Signup and view all the answers

What is the correct formula to calculate the surface area using the hanging ratio?

$S = E imes 1 - E^2 imes L imes H imes a^2$ Signup and view all the answers

If the hanging ratio (E) is equal to 0.9, what effect does it have on the total surface area (S)?

The surface area is maximized at E = 1. Signup and view all the answers

Given E = 0.9, L = 10000, H = 500, and a = 0.030 m, which of the following values is correct for the calculated surface area S?

1756.8 m² Signup and view all the answers

In the W. Dickson Method for calculating netting resistance, which variable represents the average diameter of twine?

dr Signup and view all the answers

What is the result of multiplying the twine surface area (Sr), average diameter (dr), and the ratio of openings in the net according to the W. Dickson Method?

An increase in resistance Signup and view all the answers

If the horizontal and vertical openings of the net are both 10 m and 7 m respectively, which values should be used in the equation for calculating netting resistance Rr?

10 m for Lr and 7 m for Hr Signup and view all the answers

When deriving netting resistance (Rr), what does the term $Sr$ represent?

Surface area of the net Signup and view all the answers

Based on the formula $Rr = Sr ∗ (6.6 ∗ Lr ∗ Hr / 125 ∗ Sr) ∗ (1 + dr / Sr)$, which term would increase resistance most significantly if increased?

Lr Signup and view all the answers

What is the calculated value of Rfl for the given parameters?

57.330 N Signup and view all the answers

Which formula correctly calculates the friction resistance (Rf) in water?

Rf = f * G Signup and view all the answers

What value does G represent in the calculation of friction resistance?

The weight of the sinkers in water Signup and view all the answers

How is the coefficient of frictional resistance (f) calculated?

f = Rf / G Signup and view all the answers

What was the calculated friction resistance (Rf) for the 50 sinkers dragged on fine sand?

15.25 N Signup and view all the answers

What does a calculated f value of 0.61 indicate about the type of material used in the sinkers?

The material is melted iron. Signup and view all the answers

If the weight of each sinker is increased, what would be the expected effect on the friction resistance (Rf)?

Rf would increase. Signup and view all the answers

In the Rfl calculation, which parameter is squared along with velocity?

dfl Signup and view all the answers

Study Notes

Fishing Gear Design and Hydrodynamics

This module covers fishing gear design and hydrodynamics, specifically within a fisheries engineering context (Fish 119).
Students will learn to estimate cutting rates and taper ratios of netting.
Students will calculate twine surface area for trawl nets.
Estimating hanging ratios is a key aspect of the module.
Calculating and estimating hydrodynamic resistance for trawl nets, otter boards, warps, and floats is part of the curriculum.

Net Cutting

Net cutting is crucial for shaping fishing gear and netting.
Key dimensions of a net are noted, including headline, fishing line length, and mesh sizes (nylon #21, 50 mm mesh size, nylon 2.0 mm, 50 mm mesh size).
Different types of cuts (N-cuts, B-cuts, T-cuts) are identified. N-cuts are vertical, B-cuts are diagonal, and T-cuts are horizontal.
Cutting rates are important in understanding netting design efficiency.
Combining different cuts (e.g., 1T2B, 1N2B) influence netting design and are discussed. A "taper ratio" (R) is used for comparing different cutting combinations. Formula for calculating taper ratio is provided.

Twine Surface Area

Students need to calculate and measure the surface area in square meters (m²).
Relevant variables include the number of meshes above (N), below (n), and the vertical meshes (H).
Twine diameters (Ø) and stretched mesh dimensions (a) are crucial to the calculation.
A sample problem using these variables is presented.

Hanging Ratio

This module defines hanging ratio as the relationship between the length of rope (L) supporting a net panel and the total length of the stretched netting panel (L₀).
The formula E=L/L₀ is presented.
A sample problem detailing calculating the hanging ratio (E) is provided. The sample problem utilizes the provided formula with specific given values.
Different hanging ratios (E values) affect surface area covered by the netting. The maximum surface area achieved occurs at E = 0.71.

Fishing Gear Resistance

Resistance (R) is a force in newtons (N) that opposes the thrust of a trawling vessel.
The total resistance (R₁) is the sum of several components: netting resistance (Rₙ), otter board resistance (Rₒ), warp resistance (Rₐ), float resistance (Rf₁), and friction resistance (Rₓ).
A formula, including variables such as twine surface area (S), average twine diameter (d), horizontal opening (L), and vertical opening (H), is presented for calculate netting resistance.
A sample problem illustrating the calculation of netting resistance is included.
Similar formulas (with different variables) are provided for calculating otter board resistance, warp resistance, and float/sinkers resistance.
These resistance calculations are presented with example problems and relevant data, including appropriate units.

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Description

This quiz focuses on fishing gear design and the principles of hydrodynamics in a fisheries engineering context. Students will explore net cutting techniques, estimate cutting rates, and calculate hydrodynamic resistance. Key concepts include taper ratios, twine surface area, and hanging ratios for trawl nets.