Mega-tarp sun shade - help!

[Flannelfoot]

Hi guys

I'm trying to work out a design for a big tarp sun shade. We plan to plonk it in the middle of a field in France and it will serve as a airy & shaded dining area, chill-out spot, bushcraft work space, etc. We (my girlfriend and I) are building a house on the land and will be living on site in a couple of large canvas tents.

Here's the prelimary design so far:

Over the top of the ridge line i'm going to throw a polycotton canvas tarp (600gsm) which we're making ourselves - dimensions (6x9m) and, with lots of brass grommets, guy and stake the hell out of it! The tarp will weigh about 30kg give or take.

Before I pull the trigger on an expensive used industrial sewing machine and a big roll of fabric, can anyone see anything wrong/potentially hazardous in the design. We'll be monitoring the weather forecasts closely with respect to the building work going on anyway, so if any violent weather is ahead we can take the tarp down.


Any comments or criticisms really appreciated. Cheers!

 

[rik_uk3]

I'd look at rigging a parachute, easier all round.

 

[Hammock_man]

If you think of a 30kg plus hammock i.e. 2 people in one .... would that setup support the weight? While 9metres of ridge line means you must be flying one heck of a sail ...err tarp! with it well pegged out I would trust it.

 

[mountainm]

Buy a big bell Tent and leave the sides open.

 

[British Red]

If that is expected to be there a long time, I would put a LOT more support on those fence posts. Those spikes are not deep enough (IMO) to support 3m of above ground height. In addition, the tarp, when pegged out, will exert significant lateral (sideways) force on the posts in high wind. I don't believe a 50cm pegged guy line will stop that - it'll just tear free in a good wind. Think how big and strong and deep the butress roots are on a tree.

For me, sink the post to a depth of half the above ground height. If you want 3m above ground, then have 1.5m below ground. Notch the post and set a fencing foot (90 degree bar that prevents the post tipping sideways) into the base of the post (you will have to dig a trench as well as a hole). Then concrete the posts in. Ideally I would set up 45 degree bracing struts to both posts between them to 2/3 of the above ground height of the post. The part of the bracing post in the ground should be butted up against another 90 degree foot (stob) to stop it pushing through the ground when force is aplied. Better yet, bury a big rock or paving slab on edge as a "thrusting plate" against the free end of the bracing strut. I would add similar bracing struts to both sides of the post.

Now I do understand that you may not want the 45 degree bracing struts inside the tarp. So in that case, I would set a short post in a large block of concrete (1m deep) directly in line with the two posts on the outside at both ends and strain to that using wire rope and turn buckles. I would have 45 degree bracing struts on both sides of both posts regardless. If you are canny and do this right, you can lash the tarp down to the "A-frame" when you have built in a blow.

Lastly I would orient the open end of the A frame to the prevailing wind to prevent the sail effect somewhat and to provide a breeze.

Can draw pictures if it helps?

Red

 

[calgarychef]

I'd make it like a yurt without sides, no center post to worry about and strong as anything. You could use a parachute for the cover if you wanted. Whatever you do I wouldn't buy a sewing machine for one project. I built an 18' yurt and it was way cheaper actually to get the tarp company to do the sewing I needed.

 

[Hugo]

I'd go with Rick on this one, buy a parachute for under £60.00 delivered as it would do the job you want it to do, all you will need to add is a central pole.
Plenty of people on here use a chute at bushcraft meets me included, I find them a great piece of kit.

 

[ged]

I think Rick and Red are both right. Your design for the post supports isn't going to take the forces, and anyway I don't think you need to design something that exerts huge forces on anything for lightweight the job it's intended to do.

If you really want to do somethig like that talk to the marquee rental people, they always have scrap sheets available which might have gone a bit mouldy, or have a small hole, making them no use for a garden party at the manor but still perfectly useable. I've bought sheets anywhere between 6m by 3m and 10m by 6m for under twenty quid. They already have all the eyelets in them that you'll need and you can even join them together using the eyelets. The odd small hole in a sheet won't bother you, you can patch it with duct tape. These things are heavy, mind.

 

[mountainm]

Buy 2 gazeebo's.
http://www.amazon.co.uk/dp/B002DSYJ...de=asn&creative=22206&creativeASIN=B002DSYJHM

or this is really cheap
http://www.amazon.co.uk/Gazebo-Marq..._1_2?s=outdoors&ie=UTF8&qid=1339498666&sr=1-2

It has bad reviews - but for the price - you could re-inforce/replace where needed

 

[Graveworm]

Everyone on here has far more experience than me in building such things but I am pretty good at the maths and the net force on those poles is towards the centre of your tarp and will it will have a lot of leverage at the base if they are 3.6m tall; wind will only add to that. Wood is strongest in compression so it's best to try and reduce the torsional forces. You may want to consider adding a third well anchored supporting guy on each post in the opposite direction to the force ie about 30 degrees to the line of the main 9m line. It would be a trip hazard but would make the whole thing more stable, I would have thought, and put the force straight down.

 

[Hammock_man]

Having reread the opening post, I still feel this is a temp set up / fair weather area, which can be brought down in foul weather? Is not concreateing in the posts / digging a 2M hole a bit over the top.

If its to be long term / foul weather than yes a total rethink is in order.

 

[Flannelfoot]

This is why I love this forum! Thanks for the comments. Sourcing a longer 4x4 post and sinking it seems the way to go for for peace of mind in the A-frame design. The extra guy line on each post wouldn't hurt either. Plenty of lime concrete will be mixing away on the site so that's no problem.

Today I heard from a company today who suggested ditching the heavy 600gm2 polycotton in favour of a much lighter, cheaper mesh specifically designed for blocking the sun (well, 98% of it). He said the open nature of the stuff will reduce windage too. Sounds good. Never intended it to provide rain protection so polycotton is actually unnecessary, the more I think about it.

Now it's between the mesh fabric and a used parachute canopy (a great idea by the way, thanks- just checked out Wayland's post on the subject).
I'm also toying with the idea of putting our main living tent under the canopy/shade too - it would make things a lot more comfortable in the heat.
PLUS it's only £60!
As we only have a band of trees around the perimeter of the field, i'm not sure how I would suspend the canopy. Or, if anyone has a link to a design with a central pole, that would be great to see too.

Here's a few photos of the land:

 

[British Red]

Flannelfoot

There is a superb book on the subject of fencing (which may come in handy on your land - it has on ours) which covers how to put up and brace fenceposts, string wire, make your own post and rail, which woods rot at what speed etc.

http://www.amazon.co.uk/Fencing-Pra...=sr_1_3?s=books&ie=UTF8&qid=1339535498&sr=1-3

Not cheap - but if you have to do much in the way of erecting fences, poles etc. its worth its weight in gold

Red

 

[Scots_Charles_River]

Red's right, you need a lot more below ground. My rotoray dryer line has a block 30cm sqr and 50cm deep. For a 3m pole, I would 50cm deep, and 45cm sqr.

 

[ged]

...As we only have a band of trees around the perimeter of the field, i'm not sure how I would suspend the canopy. Or, if anyone has a link to a design with a central pole, that would be great to see too.

I'd probably spread the 'chute out on the ground, get a 6m scaffold pole (preferably aluminium) with a turning block fastened to the top end, run a loop of cord from the block to the bottom of the pole, stand the pole upright in the hole in the middle of the 'chute and then guy it upright with six guys. Tie the 'chute to the loop and haul it up to the top, guy the chute wherever it felt right and then relax with a cuppa. Let me know if you'd like me to sketch something.

Here's a few photos of the land:

Looks like a fantastic spot!

 

[AussieVic]

We regularly set up a big tarp 9m x 6m (or the little 5m x 6m).

We always look for 2 suitable trees, or one tree and a post with 2 or 3 guys if all else fails !

One of the main problems will be sagging, so a centre pole (or two) is a good idea. These should be higher than your intended end posts. You can either put a grommet in the fabric, or use a (not sure what they are called) “cup” on a collapsible camping pole; the “cup” will spread the weight of the fabric on the pole and stop it pushing a hole through. The pole can be secured at the top to the ridge line with shock cord, and a small hole dug at the bottom should stop it kicking out.

The other “issue” is the sides. To get best use of the underside of the tarp, you will need poles along the side too, these can be lightweight collapsible type camping poles; each with a guy (or two if necessary). You can either put 3 or 4 poles along each side to lift the entire length up, or just one or two towards the centre, so the ends of the tarp will flop down.

One nice thing about the adjustable camping poles on the sides is that you can raise or lower them to provide a sunscreen when the sun is low (morning and evening). You can also lower one side to keep out (reduce) rain or wind or for privacy.

 

[rik_uk3]

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This is how I set up a chute these days, will take a fair bit of wind too. You could sleep eight in there or like me just use it for cooking and getting warm near the woodburner, or staying cool in the warmer weather. Ignore the little tarp on the top I use a 7x5m one now to waterproof the canopy.

 

[Tony]

Yeah, that's a good job Rik, plenty of room inside, we've done that with a huge chute before, massive space inside, takes quite a bit of setting up though


I was thinking about this tarp issue, could you just put one big pole in the ground and the take a diagonal down from that or put it over the pole (you would need a rounded end of some sort) you could teepee it or have all the edges off the ground just by pegging the edges out....

 

[greensurfingbear]

Today I heard from a company today who suggested ditching the heavy 600gm2 polycotton in favour of a much lighter, cheaper mesh specifically designed for blocking the sun (well, 98% of it). He said the open nature of the stuff will reduce windage too. Sounds good. Never intended it to provide rain protection so polycotton is actually unnecessary, the more I think about it.

If the mesh is the same as what we used when I was in chile it will work great as a sun shade. Let the breeze though when the wind did blow and created nice shaded areas for the obligatory siesta

Guess its a matter of price

Reds advice is spot on regarding depths of posts. It's easy to think a post is in far enough and then learn after a few days that its leaning under the strain! Cough cough not that I learnt that through experience cough cough.




Orric

 

[frangsdudu]

I'd look at rigging a parachute, easier all round.