Multi Rig Trawl - Nephrops triple rig
- triple rig
- multi rig
In this rig, three trawls are towed side by side using four trawl warps. Two pairs of trawl doors are used to spread this rig. The outer pair being standard trawl doors, the inner two being smaller but with added weight as they partly act as a trawl door and partly as a clump weight.
There will be the usual seabed impact from the four trawl doors but the trawl doors use din any multi rig system are considerable smaller than used in an equivalent single net rig. The inner doors on this rig are small heavy doors but the increased weight is there to manage the increased drag of the two nets behind each one. The weight of each door on the seabed would be no more than a similar sized door used in a single rig trawling set up. As a result of the increased in area swept by the nets, the sweeps and bridles are reduced in length for this rig. Any of the selective measures for a single trawl can be included in a quad rig trawl to improve its selectivity and reduce discards. Although this fishing method may appear dramatic it can be quite environmentally friendly.
Several scientific trials of quad rig have evidenced that it catches much less round fish bycatch than a single or twin rig on the same fishing grounds. Used properly four door triple rig should use less fuel for the same financial returns. Despite having many more nets the overall swept area and interaction with the seabed is usually less than or similar to that of a comparable twin rig vessel. The nets used in this rig are very small with a very low headline height that restricts the number of round fish entering the trawl making them a good choice to target bottom living species without much by catch of round fish
Some of the more ambitious skippers in the UK have opted to experiment with a method of towing three trawls (triple rig) using two sets of trawl doors. The method originated in the Danish nephrops fishery and requires the vessel to be fitted with a four barrelled trawl winch and four trawl warps. For this reason many of the vessels experimenting with this rig are purpose built vessels.
The rig requires two sets of trawl doors, a set of standard doors on the outsides of the two outside trawls, and a small heavy set at the point where the inside wings of the two outside nets meet up with the wings of the centre net. These small doors are acting as a trawl door (spreading device) for the centre trawl and a clump weight for the two outside trawls.
This method of multi rigged trawling, rigged with sweeps and bridles, similar to the nephrops three warp twin rig but usually shortened by about 40% in length. It has proved very effective at targeting bottom living demersal fish and nephrops in certain areas of the North Sea. There has not been much take up of this method in the UK as it does require extensive modifications to an existing vessel to operate the two extra warps and the two sets of trawl doors simultaneously.
There are restrictions in the use of more than two trawls in multi rig trawling that prohibits vessels using this rig in certain areas of UK waters. As a result of these regulations being introduced most of the vessels rigged for this method have reverted to twin rig trawling.
Multi rig trawling in its many forms is used throughout the world to target bottom living demersal fish and shellfish. If used properly when compared to the alternative fishing methods multi rig trawling should;
A. Be more efficient in species selection due to the lower headline height of trawls
B. Be more fuel efficient due to decreased drag of gear by using three smaller nets
C. Show no increase in discard rates, indeed in most situations with proper measures in place it should help to decrease the fishery’s discard figures.
Danish Prawn Trawl Multi Rig
More prawns and fewer cod caught in trials with multi-rig prawn trawl (2009)
Main target species (UK)
- Any demersal species
- Immature round fish