Fishing in slope, seabed conditions, underwater currents etc. have a great impact on the trawl doors so that they are often significantly less efficient than they should be. Underwater currents, whether they come from ahead, behind or from the side, create big problems for the trawl’s ability to catch, either because bucket effects form in the trawl opening and in the trawl, or because the trawl is not symmetrical in relation to the water current, which again leads to fish escaping through the side panels in the front of the trawl where the mesh is bigger.

That trawl geometry is not only the trawl’s horizontal and vertical openings, but also the trawl’s symmetry around the water current, which has an even larger significance, is a more and more widespread perception. We see an array of, even quite small vessels, both single and twin rigs that use the Symmetry sensor, often together with the Distance sensor, as their most important information source for efficient fishing.  

This is not very surprising really because it immediately affects the amount of catch if the trawl is skewed when towed through the water current.  

Seeing as many use combined Trawlspeed/Symmetry sensors they have realized the importance of correct towing speed. Then the question arises; what do the trawl door angles mean for Symmetry and Towing speed, and not to mention for the fuel consumption? 

Most people understand that when the door is not vertical it is not as efficient as it should be, but how important is that? And what angles do the doors have? On the basis of what one learns by using the Trawlspeed and Symmetry sensors one really begins to understand the importance of Door angles, and especially the roll angle, for efficient fishing.  

Many have therefore bought or tried the DoorAngle sensor, and the truth is that most, even though they are aware of the sensor’s importance, experience that the significance is much greater than expected. Many believe that the DoorAngle sensor is the most important sensor Scanmar has developed.

What perhaps baffles most people, us included, is how sensitive the doors are under towing. The accuracy of the sensor readings is therefore crucial for a good result. The measuring head on the Trawlspeed/Symmetry sensor is made from special components and the sensors are put through extensive calibrating tests in a special flume tank before they enter the market.  

Likewise the accuracy is extremely important for the DoorAngle sensors; Scanmar has constructed them so that they can be mounted directly on the door blade, parallel with the shoe, and calibrating is done in a hand turn with an instrument that is included.

(1) reduced trawlspeed leads to (2) the doors laying down inwards and (3) reduced door distance.

The interaction between the Towing speed (water current into the trawl), the trawl doors’ roll angle and the warp length makes it possible to adjust the gear much more accurately than one would think. Especially when a side current comes into the picture, it could otherwise present problems. Uneven seabed, in slope and poor weather also make it difficult.

We see that more and more are aware of the combination of Trawlspeed/Symmetry sensor and DoorAngle sensor, and we receive feedback that is very encouraging to us.

The fishing is occurring in very strong current (1): GPS 4.9 kn., (2) TS 2.9 kn. This makes the doors unstable (3), but the twin rig and gear press hard in the seabed (4), allows the bottom contact to be kept.