Trawl gear performance and net drag analysis with application to small trawls and vessels

Smith, David A. (David Abram) (1986) Trawl gear performance and net drag analysis with application to small trawls and vessels. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (15MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

In the following thesis a procedure is developed to determine the engineering performance of an inshore trawling system from an analysis of the forces acting on the towing warps and bridle system. Equilibrium force balance equations are derived for each warp and solved using a fourth-order Runge kutta numerical analysis method. The procedure is then applied to an inshore trawl and the results are used in the comparison of vessel power and gear drag. -- In addition towing tank drag measurements were made on small polyethylene nets. The effect of the development of turbulent flow around the net on the drag of the net is investigated. Empirical drag coefficients are also derived for polyethylene netting from these measurements. The coefficients are then used in empirical trawl net drag calculations using methods developed by Dickson, Kowalski and Fridman. In addition the relationship between the orientation of a mesh and the drag of the net is investigated. It is shown how mesh orientation can explain the reduced drag of a square mesh net as compared to a diamond mesh net.

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