SYM 7 AutoTrawl - Symmetry Control
Are you losing Catch when Towing along a Slope or in Difficult Tide Conditions?
KEEP YOUR NETS SQUARE – ALWAYS - With Scantrol Symmetry Control
SYM 7 Symmetry Control monitors the direction of water flow into the trawl and adjusts the wire tensions automatically to get the water flow directly into the trawl. This makes the net symmetric and well spread even when towing in strong tides and along slopes.
Towing of multiple trawls is becoming more common in many fisheries due to catch efficiency and fuel economy. The biggest challenge is to keep the trawls symmetrical in varying operating conditions, so we have expanded Scantrol Symmetry Control to handle up to 7 trawls.
Scantrol’s unique Symmetry Control is well recognized in the industry. You can select SYM 7 to square all your nets automatically or select towing mode where you decide length/tension offsets for one trawl and leave SYM7 Symmetry control to do the rest.
SYM 7 lets the skipper choose towing modes for different towing conditions. It is for example possible to choose SYNCRO towing mode when towing on flat bottom, and Symmetry Control when towing along a slope.
For all Towing modes, SYM 7 Symmetry Control will show you if your nets are square. Your nets shall always be green and symmetric.
Symmetry Control for Single Trawl
Ordinary autotrawls try to keep the trawl square by keeping equal tension in the trawl wires (SYNCRO).
Scantrol Symmetry Control focuses on the trawl, working after a simple principle: The trawl is square and fishes most efficiently when the water flows directly into the opening.
When the water flows straight into the opening, the water forces inside the trawl will be equally distributed, making the trawl symmetric with correct geometry.
SYM7 will keep your net square even when fishing in difficult conditions such as slopes or strong tides, and you will be less dependent on perfect winches and wire spooling.
Challenge: Towing in SYNCRO mode along a Slope
The net gets skewed because the direction of the water flow is not correct. Lower tension on the port winch is required to square up the net and get the port door on the bottom (port side is deepest).
The SYM7 display shows the skipper that the trawl is skewed. Towing a skewed net is waste of towing time and fuel.
Solution: Towing in Symmetry Control mode along a Slope
The winches are automatically controlled to get the waterflow directly into the trawl opening. The net will be symmetric even when towing along steep edges.
The SYM7 display shows that the net is all green and symmetric.
Symmetry Control for Multiple Trawls
Symmetry Control was originally developed for single trawl, but it was not until twin- rigging started that fishermen really discovered the benefits of controlling the trawl according to the water flow.
It is easy to see if one net is catching more fish, and if this is caused by how the nets are controlled. SYM7 makes it easy to choose the towing mode that is most suitable for the fishing conditions and fishing gear.
Challenge: Twin-rigging in SYNCRO mode with Manual Centre Winch Offset
Starboard and port winches are synchronized on tension, and the skipper can set the offset length of the middle winch. If the offset length of the middle winch is not correct, both trawls will be skewed and catching efficiency is reduced.
Solution: Twin-rigging in SYNCRO mode with Automatic Symmetry Control for positioning the Middle Winch
Starboard and port winches are synchronized on tension, and the position of the middle winch is adjusted by an asymmetry sensor in either starboard or port trawl. In the example below, the symmetry sensor in the starboard trawl is controlling the middle wire.
Twin and Triple Rigging along Slopes
Towing along a slope in SYNCRO mode can give very undesirable results. SYNCRO keeps equal tension on the trawl doors, while you will need less tension on the lower door to make sure it has bottom contact.
Making the middle winch the master and control each side winch individually by the water flow can significantly increase catching results.
Challenge: Twin-rigging in SYNCRO mode along a slope
When towing with SYNCRO along a slope (port side is deepest). The tension in the port wire must be lower than the STB to get the port door on the bottom. This is impossible as long as STB and port winches have equal tension (Syncro). Both nets are skewed, wasting both towing time and fuel.
Using one symmetry sensor for controlling the middle wire does not solve this problem. The Symmetry Control will make one net square (the net with the sensor), but the other nets become even more skewed.
Solution: Clump as master and symmetry sensor controlling STB and PRT doors
Switching off the Synchro function and making the middle winch the master, solves the problem. Starboard and port winches are controlled automatically by one symmetry sensor in each net.
This will keep both nets symmetric in all situations. Note the wire lengths that are needed to get both nets symmetric when towing along a slope.