The ‘Arnold Schwarzenegger of polytunnels’

by Tom Morton -

It is known as ‘the Arnold Schwarzenegger of polytunnels’, and can survive 120 mph winds with ease, in locations as far flung as the Falkland Islands. And now the Polycrub - the name is copyright - invented in Shetland, designed and produced by a local community development company using recycled pipe from dismantled salmon farms - is being marketed and built-on site in the Western Isles by local firm AMK.

The units have also now been approved for rural payments under the Crofting Agricultural Grants Scheme, with a support rate of 60% on materials and labour, and 80% for crofters under 41. And they have received the ultimate horticultural accolade - enthusiastic discussion on BBC Radio Four’s Gardener’s Question Time show.

In Shetland, no stranger to DIY recycling by crofters, you can easily find boat trailers and slipways made using old plastic salmon pipe as rollers and supports. But Nortenergy, part of the Northmavine Community Development Company, has so far taken 30km of used High-Density Polyethylene (HDPE) salmon-feed pipe and turned it into a product which is achieving worldwide success. Over 1.2 acres of Shetland is now under cultivations using Polycrubs.

The word ‘crub’ or ‘crö’ refers to a traditional Shetland structure used most commonly to gather or shelter sheep but also, with a variation in design, to nurture young kale plants (which would, when strong enough, be transferred to an open yard and grown for human and animal feed). In its traditional form a ‘planticrub’ was a round, open enclosure of dry-stone construction. Its circular walls would often slope inwards slightly towards the top, like a broch, in order to provide further protection from some of Europe’s strongest and most destructive gales. Planticrubs can still be seen throughout the isles and indeed are sometimes still used for their original purpose.

Their modern descendant, the Polycrub, has been designed and produced by Nortenergy, wholly owned by NCDC, a charity which aims at developing and sustaining its home parish of Northmavine. Tunnels can be erected on site by the company, locally and have been around the UK. But Polycrubs have also been made available in kit form, with full building instructions, and can now be obtained from Western Isles based plant hire and construction company AMK.

Nortenergy chair Drew Ratter was delighted to have come to an agreement with AMK:

“Alec John and Jayne of AMK are now stocking materials for the polycrubs, and their staff have been trained in kit assembly and erection,” he said. “Anybody looking for a Polycrub anywhere in the Outer Hebrides can now get in touch with AMK directly to make their arrangements. The arrangement makes the whole process a lot easier for us, getting rid of the need to freight materials to Shetland and then out again.”

Can survive 120 mph winds with ease, in locations as far flung as the Falkland Islands...

The Hebrides already have quite a few polycrubs, as their qualities in providing a gale-proof growing environment have been well proven. Martin Adil-Smith is looking forward to making use of his Polycrubs, on his croft at Seaview in Knockaird, near the Butt of Lewis, reckoned to be the windiest place in Britain. He regards the grant aided polycrubs as vital to his development plans:

"That Rural Payments have now acknowledged the unmitigated benefit that the Polycrub brings to crofters is testament to the fortitude and diligence of both Nortenergy and Rob Black at SAC consulting who successfully navigated the CAGS progress on our behalf,” he said. “The Polycrub is an essential part of croft diversification and offers a substantial horticultural opportunity to all.".

The Polycrub design, which tensions twin-walled polycarbonate sheeting against the recycled feed pipes, has been developed over the past nine years so that it is now capable of withstanding “strong winds, snow and frost, collisions from airborne debris and vandalism”. Even the earliest, experimental examples are still proudly in use, having dealt with everything from full-on hurricanes to accidental collisions with flying wheelbarrows.

So how did it all begin? Drew remembers that NCDC was “casting around for something that would produce a bit of revenue”, when the idea of producing some kind of polytunnel came up. But what would be strong enough to handle the extreme weather conditions of Shetland? There had been many instances of traditional polytunnels “losing their skins” in the teeth of a gale, and something stronger was evidently required.

“I remember a group of us went off in a minibus one weekend to look at polytunnels round and about Shetland,” says Drew. “We didn’t see anything that was quite what we had in mind but one had used polycarbonate sheets and one had recycled salmon pipe as supporting hoops.

“We came back and designed something which used those ideas, and the notion of using second-hand salmon-farm pipe to make the hoops in the Polycrub was especially appealing, because there was a surplus in Shetland of used salmon pipe. And that was the original design.”

The pipes used in the Polycrub design come from feeding systems. In their original role, after a certain period of time feed pipes’ insides become rough and eroded, and so unsuitable for highly precise feed-supply work. They do remain very robust, though – indeed almost indestructible. The pipes, all donated freely to the project by the salmon industry in Shetland, also act as a thermal store for heat absorbed through the polycarbonate surface of the ’crub.

The original Polycrubs were built, says Drew, “according to an idea rather than an actual design”, but there have been constant improvements over the years.

“Through I guess basically word of mouth, news of them just got out. The most remote and distant ones we have now are in the Falkland Islands – we’ve sent two to the Falklands and there have been more enquiries from as far away as Tristan Da Cunha. There’s a lot in Orkney and the Western Isles – they’re just incredibly suitable for places that experience high winds.”

So what is the basic design of a Polycrub? Essentially, the salmon pipe is cut to lengths suitable for providing a hoop-shaped support for four- or three-metre wide units. They’re the ‘rafters’ of the structure. Longitudinal wooden purlings support the polycarbonate sheets and are attached to the plastic pipes. At the end hoops, round posts are inserted into the pipes and concreted into the ground. The bottom edges are finished in wood, the ends and the doors with wood and polycarbonate. The result is in the shape of a Nissen hut, which was specifically designed so that the wind pushes it down rather than lifts it up.

There’s no sign that the supply of recyclable salmon feed pipes – around 25 kilometres of which have so far been saved from landfill – will dry up. According to Drew: “The salmon industry is in the Western Isles and down the western seaboard of Scotland too, so it looks as if, unless they change the way they do things radically, I would think there will be a good supply ongoing in the future. You could buy new pipe, obviously, but it seems ecologically sound and more in the spirit of combatting climate change if you can use recycled material.”

Further details:
Read more about Polycrubs at nortenergy.co.uk and follow Nortenergy on Facebook –
Facebook.com/polycrub. AMK is at amkplantandtipperhire.co.uk

The Polycrub will be on display at this Year's Orkney County Show, the Black Isle Show, and at other shows in Harrogate and beyond.
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