Scanmar has delivered tens of thousands of sensors for monitoring of trawl and trawl doors. In addition to that we have helped thousands of fishermen to fish more efficiently and have received experience and feedback from fishermen that have made that have provided extensive interesting knowledge about how the trawl and trawl doors behave during fishing.
Much of what we have learned we expected, but some things were quite surprising. We begin with trawl doors:
1. Trawl doors
- Door importance for efficient fishing can hardly be overstated, in addition to opening the trawl, the stability of the doors and the movement influences the effectiveness of the sweep lines and trawl gear because any problem with the door propagate backward and increases the problems.
- When acquiring trawl doors it is common for fishermen to consider their own experiences and advice from other fishermen who are doing well, but the results are not always as expected. Emphasis is placed on the doors’ area, weight and construction, and they arranged as specified by the manufacturer to obtain an optimal ratio between the doors spreading effect and towing resistance.
- The trawl and trawl doors behave differently on different bottoms, at different depths and in different conditions affecting the vessel and gear. Moreover, it is not likely that the trawl and trawl doors are precisely matched, and the trawl properties change when the trawl is used for a while, when the bag is full, etc.
- Through personal experience and experience of fishermen who have used Scanmar for many years, we have discovered a number of other conditions that many may not have thought of.
- If you study the different trawl doors carefully, one sees perhaps in trawl doors that at first glance seem the same small differences that can lead to major differences in practical fishing. We are talking in particular about:
- Size and weight
- Size and shape of the upper and lower part of the door
- Curve
- Foils
- Fixing the warp and the backstops, etc.
- Several factors could be mentioned, but in essence doors of different types must be arranged with a different approach, especially roll and pitch angle. Precise attachment of the warp and precise adjustment of the backstops / sweep of the trawl doors shall be stable, optimize performance, and trawl fisheries effectively.
2. Trawl
- To go straight to the point, water flow is the alpha and omega of the trawl to fish effectively and with minimal towing resistance and fuel consumption.
- That the water velocity in the trawl opening must be correct and the trawl must be pulled so that the flow is 90 ° on the trawl opening is something most people have understood (look at the use of trawl Speed Sensors and Symmetry).
- What happens behind the trawl, in the belly, in the extension and in the cod end is something few who enough about. A wide belly, long extension, and long cod end ensure that the bucket effect is reduced and the fish end up back in the bag instead of escaping through the panels in the trawl.
- However, there is one thing that we were not aware of, and that is that, almost without exception, at twist occurs in the trawl and in particular in the bag (60 ° or more), varying with the filling of the bag. Twist leads to closure of the measures and a bucket effect that reduces water flow.
- The bucket effect that causes fish that have entered the trawl to disappear through the panels instead of ending up in the cod end may be costing fishermen because it leads to increased towing time, fuel consumption, and wear.
It was not so easy for Scanmar to gain acceptance for the use of distance sensors, Trawl and Symmetry sensors, and some other sensors, but when the first fishermen had great success with the products the others were not slow to follow. Today, most will probably argue that these are important to efficiency and profitability.
In our opinion, control of the factors mentioned above is perhaps the most important thing that most people can do to achieve significant efficiency and cost improvements.