Mechanical Advantage (MA) and Velocity Ratio (VR) of a Double Purchase Crab Winch under Varying Loads and Efforts

Abstract

This study explores a double purchase crab winch\'s mechanical advantage (MA) and velocity ratio (VR) under various load and effort scenarios. In order to provide a view on the winch\'s effectiveness and operational features, the study intends to test how these parameters are impacted by variations in the applied load and effort. The effort needed to lift various loads, as well as the corresponding distances moved by the effort and the load, were measured using a specially created experimental setup. Although the mechanical advantage changed with the applied load, suggesting the impact of frictional forces, the results show a constant velocity ratio, which is theoretically determined by the winch\'s geometry. The results help to clarify the practical uses and performance constraints of double purchase crab winches.

Introduction

The study investigates the mechanical performance of a double purchase crab winch, a device used for lifting heavy loads with reduced effort. It focuses on experimentally measuring the mechanical advantage (MA), velocity ratio (VR), and efficiency of the winch under varying load conditions.

Key Objectives:

1. Measure the mechanical advantage (MA) when lifting different loads.

2. Calculate the velocity ratio (VR) from the winch’s physical dimensions.

3. Analyze the relationship between applied effort and load lifted.

4. Determine the efficiency of the winch under various load conditions.

5. Compare experimental MA with the theoretical VR and explore discrepancies.

Literature Review Highlights:

• MA and VR are well-documented in machine theory.

• Real-world MA is often lower than theoretical VR due to friction and other losses.

• Prior research lacks detailed experimental analysis of double purchase crab winches, a gap this study aims to fill.

Methodology Overview:

• A double purchase crab winch with known gear ratios and drum sizes was used.

• Loads were applied via calibrated weights.

• Effort was measured using a spring balance.

• Distances for effort and load were recorded to calculate MA and VR.

• Efficiency was computed using the formula:

  Efficiency(η)=MAVR×100%\text{Efficiency} (\eta) = \frac{\text{MA}}{\text{VR}} \times 100\%Efficiency(η)=VRMA?×100%

Key Experimental Results:

• Theoretical VR = 3.12 (based on gear and drum dimensions)

• MA ranged from 1.0 to 1.2

• Efficiency ranged from 34.3% to 38.5%

• MA and efficiency showed slight variation with increased load but remained generally low

• Plots showed:

  • Linear increase of effort with load

  • Decrease in efficiency and MA with higher loads

Discussion and Insights:

• The winch offers modest force amplification, suggesting it's not highly efficient.

• VR remained constant, indicating a fixed mechanical setup.

• Efficiency is consistently low, likely due to frictional losses and design limitations.

• The study confirms the general principle that real MA < theoretical VR.

Limitations:

• Results are specific to the tested winch design.

• Experiments were static—dynamic loading and lubrication effects were not evaluated.

Conclusion

This study experimentally examined the mechanical advantage and velocity ratio of a double purchase crab winch under different load and effort conditions. The study verified that while the mechanical advantage is load-dependent and decreases as the applied load increases because of internal frictional losses, the velocity ratio is a constant that is set by the geometry of the winch. As a result, as the load increases, it also affects the winch\'s efficiency. Limited force amplification is indicated by the machine\'s low and almost constant mechanical advantage (1.0–1.2). A constant design is confirmed by the velocity ratio, which remains constant at 3.12. The efficiency ranges from 34.3% to 38.5%, indicating significant energy losses that are probably caused by friction. When all factors considered, the machine is appropriate for light loads or educational purposes but not for heavy-duty or effective uses. To improve performance and lower energy losses, design changes are required.

References

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Copyright

Copyright © 2025 Suhas U. Misal, Vinayak C. Gavali, Abhijeet P. Kothali, Shafik S. Mullani, Swapnil K. Hingangave. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.