One thing about towing a net behind your boat is that once the net and doors drop beneath the surface and head toward the bottom, it’s pretty much a crapshoot as to what’s happening.
You can overspread the gear and not know it. A sweep can break, and you won’t discover it until you haul the gear aboard. Everybody else can be catching fish, and even though the shine on the doors looks just right, you’re just dragging water.
Headaches like these would be a thing of the past if you could constantly track the trawl’s geometry. How far apart the doors are and the relationship of the doors to each other is especially important.
Notus Electronics’ Trawlmaster does just this, monitoring bottom or pelagic trawls, single rig up to a quad rig. The Trawlmaster has been sold to European and Canadian fishermen but is just being introduced to U.S. fishermen.
The Trawlmaster’s most important feature is acoustic sensors on the doors that measure door spread and the distance between the doors from the boat. In the wheelhouse, these measurements, as well as the trawl, doors, and warp show up on a color 3-D screen display, along with other data, such as headrope height.
“The system is accurate to within 1 1/2 feet,” says Francis Parrott, marketing manager for Notus. However, he adds, “The relative accuracy is dead on.” Thus, if you have 500 feet of trawl warp in the water, the sensor on the port door might read 502 feet, but the starboard sensor will also read 502 feet, showing that the doors are aligned.
The Trawlmaster indicates if one door is ahead of the other, if doors have crossed or fallen over, or if the trawl has closed up in a cross current.
In the case of twin trawls, where the third or middle wire isn’t the same length as the outside trawl warps, there is a separate adjustment for the third wire to calculate how much wire has to go out to keep it aligned with the two outer doors.
Other sensors in the system include a catch, depth, temperature, sorting-grid angle and one that measures the ratio of wire that’s out to the depth.
The door sensors have an omnidirectional acoustic signal, so even if the trawl is out to the side of the boat, the signal will still be picked up.
Spread and warp sensors for a single-rig trawl are about (U.S.) $20,000. Contact: Notus Electronics, 40 O’Leary Ave., St. John’s, Newfoundland A1B 2C7, Canada; tel. (888) 265-6173; www.notus.nf.ca.