J
.
274
THE SEAS
but a difference lies in the means by which the mouth of
the net is kept open as it sweeps over the bottom.
In the front of the net in the beam—trawl is a frame,
consisting of two D-shaped iron runners, known as “ shoes ”
or “ trawl heads,” joined together above by along and very
stout wooden beam.
To this beam the upper edge of the
mouth of the net,is attached, the Short side of the mouth
being xed to the runners while the heavy foot-rope,
curving backwards at the centre (Fig. 57), drags along the
_
ground.
The opening of the net is therefore determined
by the size of this frame, its width being the length of the
beam and its height the same as that of the shoes.
The
length of.- the beam may vary from forty-ve to fty feet
.....…………«—««W
\'
_
Fm. 57.—Beam-traw], showing frame and front portion of net.
down to much smaller dimensions to suit the size ofthe
boat in which it
The height of the shoes for a ‘
-
full sized trawl is three to three and a half feet, so that the
largest opening a net Could have would be a rectangle .
'
fty feet by three and a half feet.
The net itself may
-
extend _backwards up to 100 feet in length.
The principle upon which the mouth of the net is kept
open in the otter-trawl is entirely different. ,In this case
there is no frame to which the front of the net can be
attached.
Advantage is here taken of the fact that if a
'
,
kite or any at object set at an oblique angle be drawn.