In 2010 we compared the performance of the locally designed Cushman trawl constructed from 3.0 mm diameter, 6.0" polyethylene mesh with the same trawl constructed from 2.1 mm diameter, 7.0" sapphire mesh. The strength of the sapphire mesh was little different to the polyethelyne mesh. A model of each trawl was constructed and tested in a flume tank to provide useful information about the expected performance and important rigging detail.
Next, we compared the full-scale performance of both trawls over several days on the F/V Lauren Dorothy. After some initial difficulties we replaced the No 7 Bison doors with smaller No 6 Bison doors and collected trawl performance and catch data from 10 one-hour tows.
We found that:
- Using the large-mesh experimental trawl, wingend spread and headline height were on average 13% and 26% larger than the traditional Cushman trawl respectively (Fig. 1)
- The mean rate of fuel consumption per square meter of trawl-mouth area was 29% less than that for the traditional trawl (Fig. 2)
- Catches were modest in the test location, however, there was little difference in catches of cod and monkfish between trawls
Figure 1: Average trawl geometry for each tow.
Figure 2: Average fuel use (gph) per square meter of trawl-mouth area.