TWIN-RIG trawling has swept through the Scottish fleet in the last five years having proven successful for vessels from ten to 40 metres fishing in 20 to 500 fathoms, reports David Linke.

Just ten years ago Scottish groundfish was mainly caught by 18 to 22 metre pair-trawlers. Targeting cod, haddock and whiting, their run of successful was ended by quota cuts on traditional species.

These cuts led to reduced processing capacity ashore, with associated falls in market demand.

Faced with inflation-fuelled running costs and diminishing returns, skippers looked at alternative methods. East coast Scottish skippers, particularly those at Fraserburgh with 15 to 20 metre trawlers, turned to nephrops, helped by underfished Fladen grounds stocks.

Although prawn trawling was not new at Fraserburgh, it did not have a high profile.

Skippers recognised that ground contact through the belly of the net, rather than by simple gear spread, was beneficial in taking larger hauls of nephrops and groundfish.

As a result, several net-makers produced single trawls with double crowns. Skippers found that these two bosum nets could out-fish single prawn trawls.

At the same time, skippers started to tow together two conventional low- opening 20 to 30 fathom prawn trawls, with the two inner wings connected to a central chain weight or clump. Most boats worked split wires to compensate for having only a two-drum winch.

Twin-rig trawls provided vastly increased ground contact and became popular with prawn skippers. Two vessels built pointed the way ahead: the 16 metre E'phriam (Gerrards 1987) featured a three-drum winch forward on the main deck and a split net drum. Similarly rigged, the 20 metre James Miller- built Celnius II powered by a 550hp Deutz engine had her middle warp passing under the wheelhouse.

Steel boats were gradually replacing timber, enabling a semi-bulbous bow to be incorporated into a fairer waterline entry. There could also be a larger propeller aperture, providing the increased bollard pull skippers needed.

The 18.6 metre twin-rig Heather Sprig with a 550hp Deutz engine blazed the trail for the succession of 70 to 90 ft. twin-riggers the Macduff yard is producing today.

Skippers of larger groundfish boats had switched to single boat trawling, fishing west and north of Scotland, with a few edging down the continental slope into underfished deeper water.

Catches included higher value groundfish, such as monks and megrim, plus non-quota deepwater blue-ling and grenadiers.

Skippers pioneering these grounds down to 250 fathoms needed fuller and deeper bodied boats, with the full-length shelterdecks now commonplace, as shown by the 23 metre single trawler Westro from Macduff Shipyards in 1992.

Westro was powered by a 650 hp Deutz engine and had 12-tonne split winches arranged abaft her wheelhouse and a 12 tonne plain and 2 x 7.5 tonne split net drums arranged at main deck level aft, working the gear through transom hatches.

Her trawl gear included a 166 metre scraper net and two heavy rockhopper trawls rigged on 61 metres and 29 metres of ground gear.

Twelve months later the 27.5 metre Marantha III showed development, with a 980 hp engine and more powerful winches giving increased warp capacity to go deeper.

Other powerful trend-setting single trawlers arriving in 1994 included the 26 metre Mizpah fitted out by Jones of Buckie, Scotland, as a stern- ramp trawler. Twenty tonne split winches hauled the gear forward along a net area atop the shelterdeck under the wheelhouse - an innovation repeated on the 21 metre twin-rigger Crystal River from the same yard.

The 28 metre Macduff-built single trawler Challenge II illustrated current thinking with a whaleback atop the shelterdeck providing protection for two sweepline winches located at the fore end of a full-length net area, which was by now becoming a standard feature.

Yards were pioneering designs in the 21 metre class, where the explosion in twin-rig trawling was under way. Vessels got greater beam and depth to fit three-drum trawl winches and double split net drums for increased towing performance and carrying capability.

One of the first of these twin-rig trawlers, which performed well off Rockall, was the 20.75 metre Solstice with a 14-tonne triple-barrel winch. Her trawl gear included two scraper nets with 95 metres of ground gear, and two groundfish trawls with 57 metres of hoppers.

By 1994 a trend was emerging: below 21 metres twin-rig and 25 metre + single trawl for deeper water. As twin-trawls could out-fish single trawls, it was inevitable there would soon be a vessel capable of twin-rigging in deeper water. One of the first - the 26 metre Crusader - came from Armon of Navia, Spain, in 1995.

Of conventional Scottish layout and with 20 tonne split trawl winches, the third winch was located forward atop the shelterdeck, with the gear being worked off 20-tonne split net drums in the quarter tween space through transom hatches.

Similar vessels followed, including the 24 metre Vela, but some skippers still opted for single trawling, such as the 28 metre Victoria May and 27.5 metre Seagull.

It was found that the greatest operational efficiency was achieved by working one set of gear from sweepline winches forward atop the shelterdeck, with a second full set of trawls wound on to net drums in the maindeck 'tween space aft.

Slightly smaller vessels continued to favour a three-drum winch forward on the main deck and double split net drums aft. Both types took the cod- end aboard forward, starboard side.

The success of twin-riggers led to relatively new single boat trawlers, including Marantha III, Seagull, Victoria May and Challenge III, fitting a third winch for twin-rigging.

While a twin-rig trawler may out-fish a single trawler by 40 boxes to 20 each tow, this 2:1 differential can be 20:1 in the event of vessels badly damaging one net each. Then the twin-rig skipper would still have one cod-end fishing!

A central issue hindering twin-rig development was the true capability of fishing well in deep Atlantic waters. The hull had to provide a stable platform to cope with the strains involved, as deepwater twin-rig trawls were approaching 30 tonnes.

The UK's 24 metre registered length restriction, above which extra crew certification is needed, was proving a barrier to vessel design, too.

In 1997 two vessels joining the Shetland fleet showed new ideas. Macduff Shipyards delivered Andromeda III to plans developed by Macduff Ship Design. This 28.5 metre trawler was the first in the UK traditional inshore sector with a stern ramp slipway.

Sweepline winches were positioned forward on Andromeda III's upper deck to take the gear aboard in one continuous hauling process. There were also additional net drums and three 27 tonne split trawl winches.

Spain's Zamankona yard then delivered the 44 metre stern trawler Sunbeam, designed by Johnson and Smart (Projects) of Aberdeen, Scotland. With a moulded breadth of 10.5 metres and a 2610 hp MAN-B&W engine, she went twin-rigging with three 31-tonne split trawl winches and six 13-tonne sweepline winches. A second generation deep water twin-rigger had arrived!

Last year saw another three vessels with similar specifications: the 34 metre Russa Taign and Victory, and 40 metre Solstice II. These ships have split trawl winches over 32 tonnes and 10 tonne sweepline winches pulling at least two sets of twin trawls the full length of the vessel.

Experience is showing that the extra five metres between a 28 and a 33 metre long vessel makes a significant difference - especially when gear- handling in deep water. Endurance is increased, too, but this size vessel is a more difficult financial hurdle.

This year another three similar vessels, including the 40 metre Atlantic Challenge (PD 197) and 34 metre Audacious III, will join the UK fleet, while two 34 metre trawlers are set for delivery in 2000.

Despite the higher operating costs and the increased spending on gear, bigger twin-riggers have made a successful start. They fish up to ten days out into the Atlantic to the Hatton Bank, Rockall and along the deep water slopes to 500 fathoms.

They land black halibut, redfish, grenadiers and blue ling in bins into Scrabster, Lochinver or Ullapool. Tows typically last five hours, while hauling and shooting can take up to 90 minutes, given the complexities of layered tidal currents which cause the gear to take longer to reach the bottom.

While skippers have taken the plunge into deep waters, their initiatives have to be mirrored ashore by buyers and processors.

They need to continue to build up a strong demand for new species, an issue central to this fishery's long term future.

Other skippers, who do not intend to fish so deep, are opting for scaled down stern-ramp designs such as Just Reward, Marigold and Polaris, which typically have trawl winches of 25 tonnes and work twin-rig gear from 10-tonne sweepline winches forward on the trawl deck.

It is inevitable that the future will see a fine tuning of ideas, with more thought given to positioning the deck machinery which can weigh up to 80 tonnes on the largest vessels, rather than radical changes in hull design.

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