Below we want to show some screen dumps that clearly show how good indication of fill rate is achieved by the use of an Angle sensor (filling indicator) on the bag.
Anyone who has used the Angle sensor says that the filling pattern repeats itself in every haul, if not at the same speed (depending on the fish inflow), and therefore provides reliable measurements.
Fluctuations in the angle may be due to the precision of the measurements, but they can easily be smoothed by the use of filters. The curves give in any case a clear indication of the fill rate.
We will not comment on every part of the picture, but rather point out that a combined Catch / filling indicator is fitted exactly on top of the bag. Note that the
scale shows an increasing degree (top view) from minus to plus and a shift from port to starboard, from minus to plus.
Both angles are approximately 0 degrees when the haul begins. The yellow curve shows the pitch angle (longitudinal). The angle increases gradually when the bag is filled behind the sensor. The red curve shows the twist (twist angle) and goes from 0 to 70 degrees starboard when the bag begins to fill in the back. The bag straightens up gradually when it is filled and is about 30 degrees when the Catch sensor kicks in (large inflow just before). See the top line that changes from green to red.
Here the roll angle is displayed, showing the twisting of the bag in a shrimp haul.
At the beginning of the haul the bag is twisted about 30 degrees to starboard.
As the bag fills it straightens up, and when the Catch sensor kicks in it is
twisted 20-30 degrees to port. This was repeated haul after haul.
Here we can see the angle impact on a small research trawl where
the catch is 50 kg. The roll angle changes from 60 to 24 degrees
(the bag straightens, having started with a significant twist to starboard), and pitch changes from being horizontal to pointing 10 degrees down when the bag is filled behind the sensor.
Below are two screen images from two different hauls on a 14 m bottom trawl. Notice how the pitch angle follows the same curve in both hauls even though the fish entrance does not happen in exactly the same time in the haul.
Also notice the impact on the curve; it shows when the fish pass
the spot where the sensor is mounted (there is a small bucket effect).
This image displays the same as the two images above, but we can also see the twist impact (red curve). It is very surprising and we have no explanation for why it happens. Nevertheless, it is important to be aware of the phenomenon because it reduces the water flow and can create a bucket effect further ahead in the trawl, causing the fish to escape.
Note that when the bag is twisted, it can easily turn completely around and cause the trawl to not fish. SuperCatch can be programmed with a function that shows whether the bag is turned upside down.