Discovery reports (1929) Discovery reports discoveryreports11929inst Year: 1929 PLANKTON NET SPECIFICATIONS 187 four in number, are attached to shackles at the junctions of the four sections. The frames for both these and the N 200 nets were made and galvanized by Messrs F. Braby of Ida Works, Deptford, London. The four bridles are of galvan- ized wire rope 6 mm. in diameter, each 20 ft. long. Section A is of netting with i| in. mesh (knot to knot), 15I ft. long. The tarpaulin canvas band D is 6 in. wide, but should have been considerably wider; it has fifteen 3 in. galvan- ized iron rings s
Discovery reports (1929) Discovery reports discoveryreports11929inst Year: 1929 PLANKTON NET SPECIFICATIONS 187 four in number, are attached to shackles at the junctions of the four sections. The frames for both these and the N 200 nets were made and galvanized by Messrs F. Braby of Ida Works, Deptford, London. The four bridles are of galvan- ized wire rope 6 mm. in diameter, each 20 ft. long. Section A is of netting with i| in. mesh (knot to knot), 15I ft. long. The tarpaulin canvas band D is 6 in. wide, but should have been considerably wider; it has fifteen 3 in. galvan- ized iron rings sewn on at equal intervals. The catching part of the net, BC, is 45 ft. long, tapering from a circumference of 50 ft. (4I m. diameter) to one of 3 ft. at the cod-end, where it joins the canvas cylinder, 3 ft. long, for attachment to the bucket. The netting in section B is in. mesh (knot to knot), and that in C of 7 mm. (knot to knot) mesh.'- It was found an improvement to line the 'cod-end' of the net with finer 4 mm. material. The longi- tudinal ropes, four in number, and two transverse ropes were, like those of the N 200, originally made of stout log line, but later were replaced by a soft 2 in. circum- ference rope of tarred hemp, known in Admiralty dockyards as 'Rumbo'. Experience showed, however, that any kind of twisted rope is liable to twist still further Fig. 12. Section and sketch of part of the stream-Hne frame for the N 450 net, showing the junction of two quadrants, a towing shackle, rings for the attachment of the net, and the fair-lead for the closing rope. in use, thus rolling the net up and decreasing its circumference. In consequence all the ropes had to be removed and sewn on again after the turns had been taken out. For roping large plankton nets a flat braided sennet would perhaps be suitable, if log line of sufficient strength cannot be obtained. The specifications of the five types of tow-net are summarised in the table on p. 188. Made by Messrs Stuar
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