The studies were carried out to measure the drag and lift components of hydrodynamical resistance of the trawl-knotted and knotless nettings, both of which were equally composed from the same size of nine meshes, made of the same polyethylene twine.
The results obtained were as follows:
1. Hydro-dynamical resistance of the drag-coefficient (
CD), the lift-coefficient (
CL) and the frictional-drag-coefficient (
CF) on both nettings were denoted by the following empirical equations.
CD=
CD90sin
2/5θ
CL=
CD90sin
3/2θcosθ
CF=
CF0cosθ+
Ksinθcosθ
Where θ was the attack angle of the netting,
CD90 was the value of drag-coefficient on 90° of θ,
CF0 was the frictional-drag-coefficient on 0° of θ, and
K was the constant depending on characteristic of netting.
2. The value of pressure-drag-coefficient (
CD and
CL) of the trawl-knotted netting was noted to be about 10% bigger than the knotless netting.
The frictional-drag-coefficient (
CF) of the trawl-knotted netting was equal or a little bigger than the knotless netting, and the hydro-dynamical resistance of the netting was proportional to the projective area of the netting twine.
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