Topic: Sensible?...Spacing of frames on DIY tunnel

[chriscross1966]

I'm thinking of making a polytunnel for my plot using 32mm MDPE tube. To get a sensible width and height for the  semicircular (for strength) tunnel I'll get 7 frames from a 50m roll. What sort of gapping should I look to use on the frames?.... would I get away with a metre giving me a 6m  long x 4.5m wide tunnel (about 20 feet by 14) or would I have to space closer?

What's the best way to joint the cover?

I'm planning on using 720 gauge UVI stabilised polythene. For the record the poly should cost about 80 quid and the pipe about 50. I'll add some wooden bits to frame the doors etc and I think I'm looking at a budget of 150-175 all in..... which seems OK given the size.

Anchoring the frames in I'd planned on drilling a 6mm cross-hole about 50mm from the end of the pipe, inserting a piece of stainless steel rod into it to act as a bracing and then casting a bucket of cement around it and sinking these into the floor.

I'm hoping to have a central row (tall toms, climbing exotic beans, possibly a melon) and two outer rows (peppers, chillis, aubergines, maybe Oca, maybe a few big onions), would it make sense to lower the paths inside it for some extra head height but leave the beds high?

As I go to quite a few festivals (I have a hobby of doing projection effect lighting at them) during the summer I'd expect to arrange an autowatering system. I  note that 1000 litre bund tanks are cheap, the worst-case scenario for festivals (Glastonbury) can see me away from the lottie for nearly ten days. Given that growing space in the tunnel occupies 3/5 of the area (total 27msq so used area about 16msq) then it follows that two 1000l tanks will supply 12.5 cm (5") of water in total from full across 16msq.... this is the  equivalent of half an inch of water per day for ten days.... is that enough or should I increase my water provision? It wouldn't be hard to target the watering a bit more precisely though.... short sections of leaky hose for the peppers, circles for the beans, coils for the tomatos....

During winter I'd have a go at some salads, maybe a few xmas spuds etc plus the usual seed-raising orgy come the new year, but mostly it would be there to push the half-hardy season a month to six weeks either side of the outdoor times...

Does this seem rational?... or at least rational by A4A? :D

chrisc

[Deb P]

Blimey, that's a lot of questions at 2am Chris!

I know there have been several DIY polytunnel builders on here, so hopefully they will be able to help you with the specifics. My polytunnel 'hoops' are 1m apart, but it is only a short tunnel so I presume you will need more bracing the longer it gets.

As for watering, I've never had a really automatic reliable system, mine either got blocked on one side, or failed completely after five days.......the poor plants never did well after that! This was an autometed system linked to a timer/hose, which I'm just not using now, back to hand watering.... ::)

[chriscross1966]

Blimey, that's a lot of questions at 2am Chris!

I know there have been several DIY polytunnel builders on here, so hopefully they will be able to help you with the specifics. My polytunnel 'hoops' are 1m apart, but it is only a short tunnel so I presume you will need more bracing the longer it gets.

As for watering, I've never had a really automatic reliable system, mine either got blocked on one side, or failed completely after five days.......the poor plants never did well after that! This was an autometed system linked to a timer/hose, which I'm just not using now, back to hand watering.... ::)

Yeah.. once I start having thoughts like that I won't get to sleep until I've had a chance to "externalise" them :D. THe problem with our plots is that they aren't easily accessible to the general public anyway, plus I don't know that many of the other plotholders that well (I'm a pretty private person in RL) so I don't like to go around asking for favours... plus I'm up there at times few others are so it might well go a week between me seeing other people to ask.... and by then it might be too late..... My plan os for it to run off a small battery powered pump with the pumping kit hidden away so as not to be too obvious, I reckon a 100Ah leisure battery will do me for ten days, especially if I can give it a solar panel to recharge from a bit..... THe pump can be a small pond fountain one..... all I'll need to do is experiment with the timer to make sure that it gets its required water each day.... THat bit doesn't bother me much (I'm good at electronics and small-scale mechanical engineering)....

[lewic]

I've got similar watering issues. Would be very interested to see details of your system if/when you get it running!

[chriscross1966]

I've been having some more thoughts on both the design of the frame and the watering. I'll not go into the frame stuff as it's mostly about trying to keep costs down by reusing pallet wood instead of buying new timber.....

Watering... a tomato growing strongly in the maximal part of the season goes through about a gallon of water a day, call it 5 litres. A big cucumber/courgette/melon nearly that (4 litres). A pepper, aubergine or chilli about 2 litres, maybe three. Assume no evaporation loss from the soil as it will be mulched in plastic. 20 feet of row length will  take about 15 tomatos (75 litres), assume a couple of cucurbits of each type take a 20 foot row to themselves (24 litres) and 15  capsicums and aubergines are the third row, so that's another 30 litres..... so thats an estimate of maximal requirement of 130 litres, erring in the cautious side says 150 litres per day worst case.... That means my reqirement for tanking can be handled by two 1000 litre bund tanks easily (hurrah) and the header tank can be the waterbut I already have (hurrah 2).

From the point of view of pumping I know that a 370W motor on my dirty water pump will drive 80 litres a minute a fair distance uphill and that therefore lifting 50 litres a minute a few feet will be in the ability of a 250W motor ... Sinclair C5's have/had a 250W 12V motor and as I'm a big fan and owner (I hold the unofficial record for single-day solo mileage at a bit over 100) I have spare Sinclair motors kicking around and the relays to turn them on and off. 3 minutes will enough to fill the butt toooo the required level, 10 days will only see half an hour total useage of the battery, less than a sixth of its capacity so recharging isn't really required if I arrange to take it out occasionally in normal use and put it on the big charger at home, All this boils down into a need for a timer circuit that will turn on a 12V relay for a few minutes a day with a ball-thingy switch that is a single-shot reset if I want to be posh...... This is now a pretty simple engineering task, kit that I already have and sixty quids worth of bund tanks.....I'm now happy that it's acheivable, and as a QA engineer I don't like being pinned down to making definitive statements like that unless I'm certain I've got plenty of overhead in my estimation process and well constrained and tightly defined aims :D

chrisc

[Deb P]

Chris.......good luck mate!
You seem to have it all sorted out in theory, lets hope it all works in practice! ;D