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MISSION DISPATCH 3 June 4, 2005 | Dr. Tammy Frank | San Clemente Basin (off the coast of S. California) 
After some trying times, attempting to get all the kinks worked out of the new net
(nothing ever works the first time you deploy it into the ocean, and if it comes back,
you've won half the battle), we're now falling into a groove with our deployments and
recoveries. There are a number of factors involved in safely launching and recovering
a net of this size.
First off, the trigger on the cod-end has to be put in place, making sure that the 70 ft. line attached to the trigger doesn't get wrapped around any other parts of the net. The cod-end is a specially designed collecting vessel on the end of the net, consisting of a thick, temperature insulated PVC cylinder with a mesh bag inside. The trigger pin keeps two ball valves open, so the cod-end goes down open, and as the net fishes, animals end up on the cod-end. The other end of the trigger pin line is attached to the top bar of the net, so when the top bar drops (it's held open with a timing mechanism), it pulls the trigger pin out of the cod-end, snapping the ball valves closed, and allowing us to bring the animals to the surface in cold water, and, most importantly for our visual ecology work, protected from light. As the net is deployed, the trigger pin line has to be fed out carefully to make sure it doesn't get caught on something and pull out at the surface. 
Once the majority of the fabric portion of the net is overboard, coordinated teamwork is needed to get the frame with the rest of the net launched safely. The A-frame operator operates the A-frame controls to start moving the A-frame out. The A-frame operator, together with the winch operator (always a member of the ship's crew - scientists shouldn't be trusted with heavy machinery), need to watch carefully to make sure that the net tow bar isn't dragged up through the block and tackle, which would be a disaster. In addition to the winch line, there are four other lines that need to be operated (and carefully monitored) as the net is deployed and recovered. The two lines running through blocks on either side of the main block are attached to the weight bar, and pulled up using the capstan so there's enough room for the net to go through the A-frame. The capstan actually requires two operators - one to operate the on-off controls, and one to haul in the line as the capstan turns. 
Two tag lines are also attached to the net as it is deployed and launched, to keep the bars from swinging wildly as they're raised in the air. Once the net is deployed, its progress has to constantly monitored (particularly during the long deep day trawls, to make sure we don't hit the bottom) using real time data sent up the wire from sensors attached to the tow bar. The net is recovered in essentially the same way, with the exception of the recovery of the fabric portion of the net. While the ocean is very helpful in dragging the net off the deck, she isn't quite as helpful in bringing it back onboard, so the net has to be manually hauled once the frame is onboard. Once the net is onboard, the cod-end is detached and carried to a light tight room, where the catch is sorted out under dim red light. 
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