why tents fail in the wind

[Paul McLaughlin]

A little pertinent info from a related source – tarps on houses. As a project manager/contractor/foreman/carpenter, I have seen many a tarp deployed on many a jobsite. The vast majority of them, very poorly. And the typical failure is due to loose pitch, with folds and flapping going on. These tarps are relatively fragile, and the nature of the jobsite tends to mean tarps stretched over various odd shapes. So I teach the guys who work under me on the site that if the tarp setup is such that you can’t get a tight, smooth surface, forget it. If it can flap, and if it has wrinkles, the wind will tear it apart overnight. If it is tight and smooth it can handle a lot of wind. Same thing definitely applies to tents and tarps in the backcountry – whatever shelter you are using, pitch it drum tight and it will handle more wind than it can if pitched loose.

 

[Diane “Piper” Soini]

So if pitching it drum tight can handle more wind, why are people saying that a material that doesn’t stretch, that you CAN make drum tight, is more prone to failure than a more stretchy fabric?

[Geoff Caplan]

“The two together placed in a “V” are quite a bit stronger than two individual stakes. ”

Here’s a vintage idea from that great innovator Robert Saunders. Never really caught on, but I can see some value for exposed camping with iffy ground conditions:

[Nick Gatel]

So if pitching it drum tight can handle more wind, why are people saying that a material that doesn’t stretch, that you CAN make drum tight, is more prone to failure than a more stretchy fabric?

I think (I’m a retired auto mechanic that fixes things the scientists invent and engineers design) the stretchy fabric gives a little reducing the forces on the guys and stakes, especially wind gusts. However, my experience is that stout guylines and burly stakes really reduces problems with UL shelters — IMO, many hikers use line and stakes that are too light for the application.

[Jerry Adams]

Don’t let Nick fool you with his “I’m just an auto mechanic” talk, just trying to get you to underestimate him : )

[Sam Farrington]

It’s certainly possible to rig a fan propelled marsh boat to blast a tent and find weak spots.  Kuiu has done this with videos posted on their website.  However,  the Lunar Solo has some commonalities with other tents supported by trekking poles, one being force that runs in a straight line from the top of the pole slanting diagonally to the ground.  Part of the straight line may be incorporated as a seam in the tent canopy, or all of that line may be a guyline.

In either case, all that keeps the pole vertical are the lines or seams running from peak to ground.  There is nothing else to brace the pole in its vertical or near vertical position.  When wind strikes the tent, the canopy collects the force from the wind and directs it to the stake, or stakes.  And as was pointed out, if the canopy is not taut, and creates scoops that collect the wind, the force on the stake(s) will be even greater.

So agree that somehow the canopy must be kept taut.  However, the less aerodynamic it is, and the more it presents a vertical wall to the wind, the greater will be the pulling force on the stake(s) for that reason also.  Double staking, and more secure staking will help; however, the structure has no inherent stability.

So I prefer tents with canopies that cover a framework that reduces the force on the stake(s).  The big drawback being that no matter how well designed the framework may be, it will add significantly to total tent weight.   Carbon poles reduce pole weight somewhat, but it will not approach zero as does using a trekking pole.  Nonetheless, I think that because trekking pole supported tents lack inherent stability, the weight reduction is not a good trade-off for inherent IN-stability.

Therefore, I’ve no problem with carrying a solo tent weighing around 2 lbs.  The Lunar Solo really doesn’t beat that by much, and the weight and multiplicity of stakes to keep it upright have to be considered.  So how to design an aerodynamic framework that reduces pulling force on stakes?  That is another issue; but suggest it is the issue that most deserves attention.

[James Marco]

Rene, This was from the same lawn but that doesn’t mean much. There are typically rocks and stuff buried in the ground. Like I say, not very scientific and only a quick test one day…it only took about a half hour as I remember.  I placed them in 6 different  locations, of course. In all cases, a single stake pulled loose at around 17 pounds average as I remember. It pulled through the turf and eventually bent (not permanent) around enough to slip out.

Two stakes: 1 test pulled out after around 40-45 pounds the other 2 tests didn’t pull loose at the scales max (50 pounds.)  a pretty good strain for two fingers on the scales loop.  However, they did eventually pull out (test to destruction, so to speak.)  The two stakes pulled a chunk of turf up before pulling loose.  The big difference was that large chunk of grass and loam that flipped up and not simply cut through it. (I have been using this technique for over 20 years and it has happened several times in the field, too.)

Again, not very scientific, they were all simply hooked around the stakes for mounting the scale.  Angles were rough and not really measured, about perpendicular to the stakes. Again, not very scientific.  It isn’t a spring scale. so, i didn’t worry about snapping free and throwing stakes around. I first noticed the wire pegs cutting through the lawn but leaving about 1″ or so of grass puckered around the stake as it pulled through. Two stakes pull about three times more grass up, a good chunk of turf.

The angle and placement of two stakes is much like digging two fingers in the dirt, then trying to lift the larger clump of soil out of the ground. Different from simply using one finger. I believe the additional strength comes from the weight of the soil and the overall soil compaction between the stakes, at guess. The “V” shaped spread between the two stakes means you will always hit the optimal soil compaction strength somewhere along the length of the stakes. …that is, they work together as well as individually. They help in all but loose sand.

[Geoff Caplan]

Sam:

So I prefer tents with canopies that cover a framework that reduces the force on the stake(s).  The big drawback being that no matter how well designed the framework may be, it will add significantly to total tent weight.   Carbon poles reduce pole weight somewhat, but it will not approach zero as does using a trekking pole.  Nonetheless, I think that because trekking pole supported tents lack inherent stability, the weight reduction is not a good trade-off for inherent IN-stability.

Except that all the major shelter failures I’ve actually seen in the field have been caused by breakage of bendy poles. Obviously you can design bendy pole tents to be stable enough for anything, but the weight penalty is substantial. Many lightweight bendy pole designs seem prone to failure.

While 7075 T6 aluminium trekking poles are going to take anything that nature can throw at you, so you are eliminating what I suspect is the main cause of failure in lightweight shelters.

Provided you avoid extremes like 7D sil or 15D poly and use proper seams and reinforcement, fabric isn’t a common cause of failure either.

So with a properly executed trekking pole shelter the only significant point of failure is pegging. There’s a lot of experience in this thread, and it seems that most people find this is workable in most scenarios provided you don’t skimp on anchors and lines and use a degree of skill and judgement. If you often have to camp on bedrock, well that’s a specialist requirement.

So Ryan’s explorations are focusing on the key issue for lightweight shelters – and the more we can learn the better.

It’s an odd world – we can send a probe to Pluto, but we still don’t fully understand what keeps a tent up!

[Geoff Caplan]

Brad

The Delta Anchors are an interesting concept, though I wouldn’t trust a plastic peg many places I go (they break trying to drive them in the soil). … I wonder if this could be done with aluminum or titanium?

They do them in stainless steel. Heavy and expensive, but I guess they would be bomber.

You give me an idea though. I do think the idea of a remote attachment point is interesting – one of the few worthwhile innovations in the field. I’ve tried pulling on one of their yellow plastic anchors placed in waterlogged ground, and the performance really is impressive. I wonder how well this concept would work on a lightweight aluminium stake at the GroundHog scale?

They are just 15 minutes down the road from me – I think I’ll ping them and see if they are interested in exploring this. Till now they seem to have focused on the family tent market.

If they don’t bite, I know a little engineering shop who might weld a couple of prototypes for me based on the GroundHog. Quite an interesting project.

Here’s the patent: https://patents.google.com/patent/US20010039769A1/en

The original idea was to hinge the angle, so the peg could be collapsed and nested for easier carrying. But they seem to have abandoned that as impractical:

[James Marco]

Yeah, the Delta stakes are interesting in concept, but always heavier than a simple wire stake. At a minimum, 50% to 100% heavier. Not real terrible when a standard ti shepherds hook weighs about 0.23oz each (avg, they vary.)  Perhaps a simple ti wire stake with a bend in it would supply all the advantages at the sacrifice of the hinge.  Easy to manufacture, small enough to fit into the back of a pack, and more effective at holding power.  Something like this:

 

[Jerry Adams]

Maybe make a tent stake like a staple.  Just bend it in the middle.

I use shepherd hook stakes.  Sometimes they rotate around and the guyline comes off.  If I pound it into the ground, then the hook end also goes into the ground, which prevents it from rotating.  Maybe make that hook end longer – staple.

[Diane “Piper” Soini]

Don’t let Nick fool you with his “I’m just an auto mechanic” talk, just trying to get you to underestimate him : )

I’ve figured out who/what Nick is because I stumbled upon his blog and have been reading my way through for a few days.

I’m not an auto mechanic or a mechanic or engineer of any kind (maybe I have some slight software engineering skills, though). My personal experience has been that the stakes are more important than the fabric, unless there are serious problems in the construction of the tent. The stakes and lines are a more controllable variable than the fabric, too, unless you have unlimited money or sewing skills. I have often replaced too-thin lines with thicker ones. Some of the best line I have found is the kind use for draperies. It is strong and handles abrasion and it is thick enough to untangle and untie when your fingers are a little numb or you aren’t wearing your glasses.

The best lightweight minimalist stakes are the ones I posted a picture of the other day. The front tine comes down so far that when pushed all the way in it’s like a staple. Those hold very well for the kind of stake they are. On the PCT I would sometimes use two shepherd hooks in the weaker corners of my set-up hoping that two would be better than one. Maybe, maybe not. A giant rock on top usually negated any pure testing of the efficacy. Since I only have two of these good shepherd hooks, I have purchased some of the small groundhogs. They’re about equal in efficacy, maybe a little better.

Of larger stakes, the bigger groundhogs and large aluminum hooks work well. As do very long, large nail-type stakes, as long as you can modify them so the little aluminum hat on the top doesn’t come off.

For the whole PCT I carried the minimalist crappy shepherd hook ones that came with my tent, but I found a large Y shaped, a small X shaped and a large aluminum hook on the trail. After much experience, the perfect combo was to put the hook in the back, the Y shaped one in the front and the shepherd hooks in the corners, sometimes two shepherd hooks in each corner. Rocks on top of the front and back stakes and on top of whichever corners seemed weak.

If the wind is really that bad, don’t set up the tent at all. Either sleep out or use the tent like a giant bivy (and prepare for a bad night) or find a cave or boulder with an overhang.

[Jerry Adams]

I am an engineer.  I have family members that are engineers.  I have worked with many engineers.  I have noticed how annoying engineers can be authoritatively telling everyone everything about everything.  Even when they don’t actually know : )

No one answered your question.

If the tent flaps and then is held by a tent stake

If it is elastically connected, then the load on the stake will be over a longer time, so the amount of instantaneous load is less, so the stake is less likely to pull out

If the tent is rigidly connected to the stake, all the load is applied over a shorter time, so the instantaneous load is much higher, stake more likely to be pulled out

For example, if you tie a rigid cord to something, and then pull on the other end, at the point all the slack is taken out there’s a sudden load.

If you use an elastic cord, at the point all the slack is taken out, there is a much smaller load.

[Diane “Piper” Soini]

Ha ha Jerry I grew up with your family as my parents and my friends’ parents. Good lord engineers are annoying.

So, elastic lines then? Just the corners? Just the front and back? Just the front?

[Eric Blumensaadt]

My experience with steady 40 mph winds and gusts to 65 mph (Weather Service stats for the time) is more stakes and guys are great.

I tested both my TT Moment DW and TT Scarp 2 at the time. Setting up was tough but doable in about 5 minutes for the Moment and 8 minutes for the Scarp 2.

Both tents had a guy line on each side of the main hoop and one at each end tied to the mid-fly guy loop. BOTH TENTS HAD 4 FLY HEM STAKE LOOPS UTILIZED. This latter stake-down was as important as the guy lines. In particular they prevented the flys from flapping.

The stakes were 8″ MSR Ground hogs, some were the newer “twisted” type. I saw no difference between them. The tents were set up on the open (no trees or structures near) grass lawn of a park about 50 yards from my home.

I also has one crossing pole on the Moment DW and 2 X-ing poles on the Scarp 2 with all running under the flys. These poles may not have been necessary but certainly didn’t hurt in maintaining a tight fly.

[Eric Blumensaadt]

My experience with steady 40 mph winds and gusts to 65 mph (Weather Service stats for the time) is more stakes and guys are great.

I tested both my TT Moment DW and TT Scarp 2 at the time. Setting up was tough but doable in about 5 minutes for the Moment and 8 minutes for the Scarp 2.

Both tents had a guy line on each side of the main hoop and one at each end tied to the mid-fly guy loop. BOTH TENTS HAD 4 FLY HEM STAKE LOOPS UTILIZED. This latter stake-down was as important as the guy lines. In particular they prevented the flys from flapping.

The stakes were 8″ MSR Ground hogs, some were the newer “twisted” type. I saw no difference between them. The tents were set up on the open (no trees or structures near) grass lawn of a park about 50 yards from my home.

I also has one crossing pole on the Moment DW and 2 X-ing poles on the Scarp 2 with all running under the flys. These poles may not have been necessary but certainly didn’t hurt in maintaining a tight fly.

BTW, since that test I had to buy a new fly and hoop pole for my Moment DW as the originals BLEW AWAY from my patio picnic table in a windstorm!  Anyway the new Moment DW fly is lower and has TWO pole sleeve guy points on each side and the hoop pole is heavier duty. All this means better ability to handle high winds.

[Jerry Adams]

Make all lines elastic?  Especially the corners?  I don’t know

That is one opinion, that elastic lines are good, an explanation that makes sense

Another justification for elastic lines I’ve heard is when the nylon gets wet and stretches a little, the elastic line will take up the slack and the tent panels will remain tight.  Polyester or DCF fabric is another solution for that.

Another solution is to have the panels really tight so they shed wind better.  In this case, maybe there’s never a condition where the panel is loose, then puts a large load on stake when the slack is taken up so no need for elastic lines?

I am open minded, this is a good discussion.  I get ideas out of discussions like this that I can try out and see what works for me, the conditions I set my tent up in.  There are no “right” or “wrong” answers…

That article from a ways back said that the stake should be angled away from the tent so that load on it will tend to push it further into the ground.  If the stake is angled towards the tent the stake tends to pull out of the ground.  That’s pretty useful in my opinion.

My big problem with stakes is the ground I sleep on is usually rocky so it’s hard to get a stake completely into the ground.  Even if I start out with the stake angled away from the tent, as I pound it into the ground it will hit a rock, then it will find a different angle into the ground that avoids the rock, but ends up with the stake angled vertical or towards the tent a little.  Thus, rocks on top of the stake to keep it from pulling out.

 

[Erica R]

I have never bothered with line loks. Do they hold better than a taught-line hitch?

[Todd T]

I don’t think you want anything “elastic.”  You want JUST A LITTLE give to avoid the extreme load spike Jerry was engineersplaing.  :-)  Too much give and the panels move too much, the tent’s shape changes, flapping increases, etc.  That’s why I think silnylon has an advantage over DCF–there’s a little stretch under load, but barely.

Disclaimer:  Engineer by training, but work in research.

[Jerry Adams]

I use taught-line hitch a lot.  With thin dyneema line they occasionally come undone.  Right now, somewhere out there is a short length.  I have violated leave no trace.  On the other hand I’ve picked up 100x as much stuff that others have left.

Another thing with the taught-line is it slips so the loop goes to nothing, becomes part of the taught-line hitch.  A very mild pain to undo.

I’ve used line-locs.  They work.  Sort of arbitrary whether to use instead of a taught-line in my opinion

For the corners on a pyramid, I really like to cinch those down.  I use 1/4″ nylon webbing and ladder loc.

[Geoff Caplan]

Eric

My experience with steady 40 mph winds and gusts to 65 mph … is more stakes and guys are great.

Three cheers for that! A lifetime of dealing with Scottish conditions has taught me that pegging everything that moves to the deck is the absolute key when the weather is bad and the placements sketchy. It’s simple arithmetic really – the more pegs, the more the load is spread.

I suspect that most US shelters are designed for use below the treeline and they simply don’t offer enough pegging points for my kind of usage. Plus there is an undercurrent in the lightweight world that if you carry more than 6 Ti toothpicks you’re a wimp with no moral backbone. You might get away with that in a West Coast summer, but there are lots of places where that kind of approach could bite you on the butt.

Most of my experience is in A-Frames, and when it gets nasty there’s a huge difference in performance between rigging a side panel like this, which at best will be flappy in the wind:

Or like this, which will happily shrug off north of 60mph:

And as someone said above there’s also a big difference between a single ridgeline guy and a double guy like this:

Ok – it’s a bit of extra line and a few extra pegs. But you only need to use it when the weather turns, and which point you’ll be very glad you have the option! And you can happily keep on trail when the toothpick fans are holed up in their motels…

[James Marco]

Yeah Jerry is spot on about wind hammer. Tod is also correct. It only takes a bit of elasticity to minimize wind hammer. Tight spectra line with a tight DCF tent is a recipe for disaster under heavy wind/gusty conditions. Nylon/poly has a lot better stretch than DCF and will ease the shock of a flap in the tent. Nylon only has more stretch when it is wet. Again, I just use a hair tie doubled over. Pull it till it is tight. It still has a lot of elasticity left that only shows as shock absorption, maybe a 1/4″ more of shock absorption, but it is NOT impact shock. Impact shock is more like a hammer blow. The high impact force is a product of momentum, not so much weight alone. The flapping is almost a whip of the fabric that resembles an actual sound barrier breaking whip tip. It has a severe impact on stakes but can be alleviated by some sort of shock control…mostly because it has little mass. It falls off rapidly even though it has a high impact force.

 

It doesn’t really matter which side the elastic hair tie is placed. The movement under load should be somewhat lower than the actual line, but that little bit left shouldn’t really effect a tent set-up.

 

 

[Roger Caffin]

Ryan’s chart at the start of this thread brings some real measured data to the discussion, but I question whether it has been fully understood. So herewith my 2c.

I suggest that you can get a better understanding of what is going on if you think in terms of energy transfer – a nice phrase but one which needs some explanation. When a tent panel is taut and not moving in the wind, very little energy is being transferred to the poles and the pegs. There is a static loading which everything can handle, not much more than what you would have in still air.

But when the panel is not taut, it flaps. When the fabric flaps it absorbs energy from the wind and transfers that energy to the poles and pegs, and this energy appears as spikes in the forces: compare Ryan’s red and blue plots. Once the flapping starts, the forces get a lot higher, and bad things start to happen.

Now consider a peg in the ground. The difference between the soil and (say) a block of concrete is that concrete does not deform, but soil can. Once the peg starts to wiggle a bit in response to peaking forces, the soil starts to move a bit and the peg steadily gets looser and looser. The steady-state doesn’t matter any more: it’s the peaks in force or energy that are doing the damage. Those peaks are due to the flapping. Of course, root-bound soil (trees or alpine grasses) has a lot more strength than soft soil or sand.

Anyhow, this is why having some elasticity in the tent fabric matters: suitably tensioned fabric (with enough poles) does not flap, even if it stretches a little. Without that elasticity, you get flapping. Nylon fabric is good here of course, but even DCF could be made to work if you could keep tension in the material at all times. Just using the design from a nylon tarp with DCF is not enough. I think you might need more guy ropes with DCF to get enough tension everywhere.

This is also why I have strong bungee cord at the downwind corners of my tunnels: to prevent the fabric from ever flapping. This works even when the nylon fabric stretches a little bit, provided the bungee cord loops are made and used correctly. But never put any bungee at the windward corners! Movement at the windward end can slacken off the fabric and let it flap. I have a video (made by the sales mgr at Easton) showing what happens when the windward end can move: quite disturbing stuff! The cord loops at the windward ends on my tunnels are very short 3 mm nylon.

My 2c.
Cheers

[Franco Darioli]

I posted this before but given the various comments on how and why I thought of posting it again.

It was a very windy day with small branches falling off the trees on the school grounds opposite to our place.

In between the sustained wind there were some nasty bursts and that is when I took the two photos.

The tent was set up taut so that it looked as in the TT product pages when not under heavy wind loads but this is what the wind did to it

adding the rear strut and guying out that as well as the front pole and side tie outs, under the same load it looked like this

BTW, at the time I took those shots just to see how the mods worked on it .

most likely I was using the Easton 8″ stakes. 4 on the first photo, 8 on the second

note that I dropped the rear end as well as added a ridge to it by using the extra strut.

 

[Ryan Jordan]

This discussion has me thinking a lot about DCF vs. silnylon in ultralight tents.

I’ve used and tested the following in high winds and storms:

* DCF vs silnylon MLD Trailstar
* DCF vs silnylon TT Notch Li
* DCF vs silnylon Locus Gear Khufu

My thoughts are that I’m pretty sure I’d rather have a silnylon version of these tents for high winds, because you can really crank down the tension on the stakes and guylines and create an incredibly tight shelter.

The possible exception is the Khufu – but this has simpler geometry and much less fabric, so the whole thing stays pretty stable, and can be pitched very taut, in DCF.

The MLD Trailstar could be cranked down to guyline tension forces of 30 pounds, but not without some pretty serious crinkling of the DCF fabrics, because the panels of the DCF Trailstar I had weren’t quite perfect enough (cut and sew) for that much DCF fabric.

The Notch Li is extremely well built and has very tight panel tolerances, but the weak point is the door closure, so cranking down the tension on the Notch Li requires some geometric manipulation so you aren’t putting too much stress on the door closure mechanisms.

I still own and use a silnylon Trailstar, silnylon Notch Li, and the DCF Khufu. They are all quite good in high winds, with the Khufu and Trailstar having an edge there.

These are three shelters that I’m wind-testing now with the guyline load sensors that generated the graph at the beginning of this thread. Also playing with a standard tarp and the Djedi as controls, since the former is not so stable and the latter is very stable.

I suppose I should throw a Caffin tent and maybe a Soulo into the mix as well :)

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