About Simrad's Catch Monitoring Systems

How to stay in full control of your fishing gear during trawling and seining

Before the arrival of the catch monitoring systems - also known as "net instruments" - even the professional fishermen were practically "blind". At the time, there was no way of telling the position of the trawl or seine. Expensive nets would be destroyed on uneven seabed, schools would be missed, and time would be wasted – all adding extra stress to an already stressful job!

It was obvious to Simrad that the fisherman needed to "see"’ the gear under the water. He needed to know the net’s position in relation to the bottom, the surface, the fish and the vessel. He would also need to know the amount of fish in the net, and at what rate the net is filled.

Simrad started to tackle these problems in the early 1960s, and in 1965, the company released the cable based FH Trawl Eye. By means of a single cable, this early system was able to offer a wealth of information about the gear. However, the real revolution was yet to come.

The wireless revolution

The trawl is often towed at great distances from the vessel. This makes cable based net instrumentation too expensive for bottom trawlers. In 1969, Simrad introduced a brand new acoustic system; the FL Trawl Link.

The FL Trawl Link was the world's the first wireless based catch monitoring system. Its lack of cable made it a viable option for the smaller operator. It offered all the functionality of the earlier Trawl Eye system without the expense of a cable.

The Trawl Link didn’t kill off cable based systems – they are still around today – but cable free set-ups are less prone to damage, making them the obvious choice for bottom trawlers.

The first Catch Indicator

Simrad EQ/EX Catch indicator

Catch monitoring in the late
seventies with Simrad EX and EQ.
The catch sensor is shown in the front.

Throughout the seventies, Simrad came up with a multitude of ideas and innovations that form the basis of the high-tech net instrumentation we have today. A particular problem that arose in the Blue Whiting fishing grounds to the West of Ireland would be the catalyst for one of Simrad’s most notable achievements. Fishermen were complaining of damage to expensive nets as fish expanded on coming to the surface, in turn causing a full net to practically explode, showering fish everywhere!

A catch indicator was required to measure how full the net was. Simrad established a research team who realised that the mesh opening in the cod end would change depending on how full it was. With this knowledge, the team created a small device that used rubber bands connected to a sensor: These measured the opening of the meshes, and thus became the first ever catch indicator.

The Catch Indicator, and indeed net instrumentation technology, reached a high in 1980 with the release of the Simrad FR500. This cable system featured an up/down transducer, temperature/depth sensor, a true motion display and a cable free FA100 catch sensor. It was the birth of the modular ”pick & play” systems used today.

Simrad FA100

Simrad FA100 - "the egg" - from 1979

Commonly known as ”Eggs”, the FA100 sensors were completely sealed, making them highly durable. This raised the problem of how to power them, so Simrad introduced a rechargeable battery and charging cabinet to solve this particular problem. Simrad’s PI system launched in 2000, is the natural progression of the FA100. The general idea of a fully sealed unit remains the key but many new features such as a seawater switch and even easier recharging reinforce the fact that Simrad is still the leading innovator in net instrumentation.

Leading the way

Today, Simrad can provide three different catch monitoring systems to provide all necessary information about your net and your catch.

  • Simrad PI
  • Simrad ITI
  • Simrad FS

The Simrad PI Systems obtain information from a number of sensors mounted on the trawl or purse seine. The data collected by the sensors are relayed acoustically back to your vessel. Once received and processed, the data are displayed on the operator unit. The PI Systems also include a small echo sounder. The data from the sensors can be added to the echogram, and the entire underwater situation can be monitored on a coloured graphic presentation.

The Simrad ITI System also works with a number of sensors mounted on a trawl. However, the ITI presents the information from the sensors in a graphical manner, and monitors the range and position of the trawl.

The Simrad FS System trawl sonars operate with a small sonar transducer inside a subsea unit, and this unit in mounted above the trawl opening. From this position, it will give you a vertical picture of the whole trawl opening. Communication with the operator unit is made through a cable. The latest product, Simrad FS70, will also communicate with the PI sensors!

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