Trials with Pluto doors on board a coastal boat in Iceland look promising, putting to work the first pairs of doors engineered for small-scale trawlers, while also being made using recycled plastic.
Polar Fishing Gear has been working on this initiative for some years, and the first pair of Pluto doors have been tested on board Westman Islands trawler Andvari VE-100 with promising results.
‘There are very few trawlers in this size bracket in Iceland, as small-scale fishing is generally done with hooks or gill nets,’ said Atli Már Jósafatsson of Polar Fishing Gear, who has been driving this, in a move that diverges from the steel trawl doors that the company produces for larger fishing vessels.
‘Skipper Hafthór Halldórsson is an imaginative fisherman and he had even made his own small Vee doors to spread Andvari’s trawl. Then we made him a pair of 0.9 square metre Neptune doors so that we would have a comparison, and produced two pairs of 1.1 square metre Pluto doors for him, one made with virgin plastic and one with 50% recycled plastic to evaluate the performance of each.’
The Neptune doors with a 32° angle of attack returned a 19 metre door spread at 2250rpm, while the Pluto pair with a 27° angle of attack generated a 26 metre door spread. With the doors rigged for minimum spread and a 24° angle of attack, the door spread was a very respectable 25 metres – but with the main engine running at only 1900rpm.
‘We were towing at a depth of 38 fathoms and with 125 fathoms of warp. By the time we had shot away 70 fathoms of warp, the doors had already achieved full spread, showing that the Pluto doors do not need direct impact to the bottom to spread,’ Atli Már Jósafatsson said.
‘Further tests will be carried out with these doors, with less angle of attack and also with reduced weight on the doors to lift them off the seabed during fishing.’
The Pluto doors are rotomoulded from plastic, which he commented provides ‘practically endless design possibilities’ compared to steel or wood. There is no steel inner frame, but there are steel attachment points for bridles and warps, as well as keels that serve as protection and to provide balance – but a key aspect of the design is to eliminate the need to rely on ground contact to square the doors.
‘Wooden doors that are used throughout Africa and Asia are not expensive to produce, but they are towed hard on the ground and so need regular repairs due. So over their working lifetime, these become expensive doors. In contrast, if a skipper can use the Pluto doors without ground contact, there’s no reason they should not last for years,’ he said, commenting that this is a market that has not been served by trawl door manufacturers.
‘Pluto doors are designed to meet the needs of the close to a million motorised fishing boats in the 8-24 metre range – and this is a market that has been completely ignored,’ he said.
‘We aim to get the doors completely off the bottom. There is the substantial reduction in towing resistance and consequently a fuel saving that can be achieved switching to hydrodynamically designed doors towed clear of the sea bed, compared to old-style doors that rely on ground contact for much of their spreading force.’
The trials pairs of Pluto doors have been produced in Iceland, but the aim is to manufacture these closer to where they will be used, and using raw materials available there, as recycling is a key aspect of all this.
‘We are making doors from old nets,’ he said.
The first pairs have been made using 50% recycled plastic, sourced from Danish company Plastix, which specialises in recycling fishing gear into usable plastic raw material. At the end of their working life, the Pluto doors can be returned to the cycle of recycling.
‘Right now we are completing production of three pairs of Pluto doors that are going to be tested in England, and we’re expecting to send more pairs to Scotland and Ireland to be tried out,’ Atli Már Jósafatsson said.
‘There are all kinds of opportunities that these plastic doors offer, as working with plastic provides us with design possibilities that simply aren’t there with steel. In addition, there are the possibilities offered by sound and light that have barely been explored, such as using whale noises to herd fish into the gear, or directional lights mounted on the trawl doors or the gear itself that generate a barrier, which also provide incentives for fish to go in a particular direction.’