3.2 The disadvantages of conical tow nets are as follows:
3.2.1 They are effective only where drawn through a stratum of water having considerable thickness. They are not suitable for collecting samples from a small or restricted region.
3.2.3 They collect only qualitative samples, or semiquantitative samples when used with a flowmeter.
3.3 There are several special considerations that shall be observed when using conical tow nets. They are as follows:
3.3.1 The conical net samplers are designed to be towed at speeds less than 3 knots; however, greater speeds have been used for the larger nets with a concomitant increase in capture.
3.3.2 Although there is a tendency to use the smallest mesh size available, there is the liability of small mesh sizes reducing the collection efficiency and increasing equipment failure through tearing.
3.3.3 If discrete depth samples are required, an opening and closing net device should be installed on the sampler.
1.1 This practice covers the pro......
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