Storm Resistance of Ultralight Shelters: Part 1, Introduction

[Addie Bedford]

Companion forum thread to:

Storm Resistance of Ultralight Shelters: Part 1, Introduction

[Rakesh Malik]

> The Akto is light when you consider it is designed to work in winter storm conditions
> reliably.

That's also why I picked up a Twin Sisters. Well, that plus it was on clearance at REI. :)

[David Ure]

"The Akto is light when you consider it is designed to work in winter storm conditions reliably."

But poorly designed for the conditions that you suggest. The tent cannot withstand very much snow load. In terms of design, the Scarp had surpassed it in every way. As such, it really isn't that 'light' for winter storm conditions.

FWIW, I have used a Duomid and an Akto in high alpine, snowy conditions. The former withstood the conditions much better and we don't have to discuss the weight differential (or price differential).

[Craig Rowland]

The Akto is not designed for heavy snow loads it is true. But it is used routinely in arctic conditions anyway by some. They have tunnel tents that are larger for slightly more weight but better snow load handling.

I've looked at the Scarp and it looks OK. I've looked at the pyramid type shelters in the past. I got turned off from them after a couple stories from people I know discussing the failures they had.

[Nick Gatel]

I think the Scarp is double-walled, mine is.

[Craig Rowland]

Yeah I confused it with another tent and edited my post.

[Sam Haraldson]

I predict the "winner" to be the Black Diamond Mega Light.

[James holden]

i look forward to the pull no punches testing to come …

it doesnt matter whether they are sacred cottage cows … or hated mainstream demons … just call the results as it is … thats all i ask of BPL

ultimately what makes it valuable for me is for BPL to test and indicate the most survivable shelters for the conditions at hand …

[Roger Caffin]

Hi Peter

> if i pre-bend my poles, in a situation where the mfg expects the rear pole to be installed
> with a ridiculous** amount of bending .. does this make the pole ultimately stronger (as i
> suspect) or weaker, considering it gets hit with equal loadings.
Not simple.
* A tighter bend does put more stress into the arch and that makes it stiffer, which is good.
* But a tighter bend leaves you with less safety margin, so it would be easier to break.
* In addition, with some poles, repeatedly bending the pole too much 'work hardens' it, which makes it more brittle, and leaves it very susceptible to abrupt failure. The Easton 7178 poles suffered from this problem, and snapped on me.

Cheers

[Roger Caffin]

Hi Michael

> This series might have me re-think using shockcord loops for my LDPE shelters.
There's shock-cord, and there's shock-cord. I used 100 mm long loops of 4.5 mm shock-cord on the down-wind end of my winter tunnel tent to apply the lengthwise tension. But I use loops of 3 mm nylon on the upwind end: I do not want that end moving!

Cheers

[Hamish McHamish]

Great article, looking forward to this line of inquiry.

Already, I can see justification for MLD's approach to using cuben. Not every Joe Blow working out of their garage is properly designing and manufacturing their cuben products.

[John Coyle]

I truly welcome this series of articles because wind worthiness, and to a lesser extent snow loading in tents has always been a pet peeve of mine.

It would be nice if tents were rated with a W factor (for wind) much like sleeping pads and air mattresses are rated with an R factor for warmth. Of course manufacturers could still fudge the rating, but places like BPL could keep them honest.

For example, I have a SMD Sil-Nylon Trekker which I bought last Fall. It seems fairly wind worthy, but I haven't had it in winds over 15 MPH, so I really don't know how it would stand up to sustained 30 MPH winds.

It's funny because a friend of mine recently bought a Hilleberg Akto and I kid him about his "over engineered heavy Swedish monstrosity" But I have to admit, with 10 stakes, and each stake attached to the tent at two points, I believe it is bombproof in the wind department. This youtube of an Akto in 80 MPH winds would back up my opinion. http://www.youtube.com/watch?v=a1iJvk6tKs4

[Stuart Murphy]

I do hope even if wind machines don't become part of the test process that video is part of the data available to readers. Survivability is one thing, live-ability quite another. Some tents flap more than others and all things being equal may be less live-able in some conditions.

A wind/snow rating should also take into account whether the structure can function in the conditions for a protracted period (a tent surviving a storm for an hour is different from it being routinely able to withstand such conditions without damage).

Another important factor is pitching/striking camp in those conditions (when a tent is at its weakest and seriously at risk of bent poles etc) as per the person that posted about Hilleberg's testing, so there should be video of that too.

Come on BPL, buy a wind machine… you know you want to.

[Adam Kilpatrick]

"There's shock-cord, and there's shock-cord. I used 100 mm long loops of 4.5 mm shock-cord on the down-wind end of my winter tunnel tent to apply the lengthwise tension. But I use loops of 3 mm nylon on the upwind end: I do not want that end moving!"

I've done something similar with my trailstar, putting shockcord loops about that big on three of the main corners that go into the wind, the other two I've got guyline on. It works well. I'll do it in the future with other tents and tarps. Having that bit of gust resistance is valuable in protecting your stake outs.

:-)

[Diplomatic Mike]

I use shock-cord on mid-panel tie-outs, but not on main guying points. Especially not the ones into the wind!
I also use it on the tie-outs of bivvys made from UL materials.

[Kevin @ Seek Outside]

It has it's advantages, as it tightens a panel over time, so it can keep the tent pitched tighter. The key, is to find shockcord of the appropriate tension for your tent, and to pull it tight or extremely near tight, so there is little give , but much more take. IMO it really works better on non seam tie outs, as seam tie outs have the stretch limited anyway.

Snowloads are extremely difficult to mimic, as almost every snow is different. I live in an area where we get substantial (250 + inches some years) snow, and I test a lot of single pole tents and tipi's to determine failure.

Yesterday and last night it snowed, but it was the type of snow that started wet, so without maintaining it , it would stay on the canopy. I let the snow accumulate over night, then measured the carbon fiber center pole deflection (very minimal), brushed the snow off the tent, then put the snow in containers and weighed it , to get an idea what weight was on the canopy. The weight on the canopy from the snow, was close to 120 lbs accumulated on the canopy, in fact probably more if I take residual ice into account.

The best way to minimize snow load on center pole mid / tipi type structure is to have a place for the snow to go, like a trench if snow camping, or a short sod skirt style mini wall

[Roger Caffin]

Hi Kevin

> The weight on the canopy from the snow, was close to 120 lbs accumulated on the canopy,
That is interesting. We would love to hear more about the weights of snow found on the tents. Photos would be nice. I am not aware of this data being available from anywhere else.

Cheers

[Jason Elsworth]

A quick google search turned up quite a few places that hire out wind machines. Not sure how useful it would be, but it would be fun to watch.

My old Terra Nova Voyager tent got its front pole badly bent (tent stayed up) in a storm many years ago. I wrote to Tera Nova about it and they explained that they had tested it in a wind tunnel up to a certain level and were rather surprised about what had happened. I guess they had never been to Wellington. They did send me a free replacement pole and the tent still gets used as a loaner.

[Kevin @ Seek Outside]

Hi Roger,

It was very add hoc, since rarely do the conditions line up that snow sticks to a canopy so well, but in this case it did. The measurements were not what I would call terribly scientific, but I made do with what was available at the moment. I brushed the snow off on to the ground, then shoveled it into a rolling plastic trash can, however, not all of it would fit in the can. I estimate about 80 % of the snow fit in the trash can. The trash can would not roll and I knew it had to be around 100 lbs, so I carried it in and put it on the scale in the garage. It was 120 including can, which I will weigh itself when I remove the snow. I'm waiting for the snow to melt in the can to see how much water was in there. The center pole had minimal deflection, perhaps 1/4 " or so. To be clear, by BPL standards this is a big shelter thus so much snow. The shelter was about 6'8" tall and covers over 100 sq feet of ground space. There are a lot of ways to find fault with the methods, which I agree were add hoc, but it is a starting point. If I considered myself to be off by a 40 % it is still a significant amount of snow weight.

IMO, the best thing to help mid / tipi style structures in big snow is pitched up a bit with a bit of a sidewall so it can get off the structure.

Photo's are below:

After clearing

[Roger Caffin]

Hi Kevin

> The measurements were not what I would call terribly scientific,
Some data is better than no data at all. :-)

Cheers

[Kevin @ Seek Outside]

I agree some data is a starting point at least.

I think one of the interesting things that will be found, is that what is good for wind is not always good for snow. For instance, a slightly extreme cat cut, that is overly tight is best for wind, but with snow these cuts have a tendency to create a concave structure, which impedes natural snow removal. For snow, you are better of having a bit of a convex shape. With a single pole this can not easily be accomplished without guylines and some vectoring, even if over a stick in a couple spots. This lets the snow move of the canopy much easier.

[Paul McLaughlin]

A simplistic way of looking at it is that wind resistance is mostly about tautness, while snow loading requires steepness as well. And convexity definitely helps, part of the reason why tunnels and domes are so prevalent for deep winter use.

[Mike Cecot-Scherer]

Hi Ryan,
I like your article. Good careful work. As a tent maker of some experience, I'd like to offer three hopes I have for your work:
1) That you can demonstrate that most tent fabrics in use are too strong – making our shelters heavier and probably more expensive. (I base this on interviews with roughly a half dozen manufacturer's repair departments where the answer to the question, "Have you ever seen a returned tent where the cause was that the fabric was not strong enough (other than extreme UV damage)?" Their answer is ALWAYS: "No, never.")
2) That the sagging problems of nylon, caused by its expansion with moisture, will be finally exposed as the root cause of many users' problems with their tents.
3) That between 1&2, above, the use of recyclable polyester fabrics is embraced by our industry and the use of silicone impregnation treatments is stopped because they prevent any possible recycling of the fabrics.
Best regards,
Mike Cecot-Scherer
http://www.inklinginc.com

[Roger Caffin]

Hi Mike

> the use of recyclable polyester fabrics is embraced by our industry and the use of silicone
> impregnation treatments is stopped because they prevent any possible recycling of the fabrics.

Sorry, but I have to disagree strongly with all points.
* Polyester does not stretch like nylon, and cannot absorb shock loading the way nylon can.
* Silicone inpregnation increases the strength of nylon fabric. The alternative, PU coating, decreases the strength.
* With respect, worrying about recycling the fabric from a tent is a waste of time when a 100 kph gale hits you. If I want to recycle one of my tents, I will do so myself, by reusing the fabric myself.

> the sagging problems of nylon, caused by its expansion with moisture,
It sticks in my mind that the sagging is actually caused by cooling. Yes, nylon fabric has a negative thermal coefficient of expansion. Btw, the same aplies to nylon guy ropes. I have actually measured that myself.

Cheers

[Stuart Murphy]

Polyester vs nylon stretch… Surely you can compensate by using shock cord on peg and guy points? The fabric can't suck too much given it's in use in a number of serious expedition tents (eg. including some Macpac domes). I don't think Macpac even goes to the trouble of using shockcord (though perhaps they should?).

Polyester has other advantages too (potentially more reliably waterproof, better UV resistance and virtually no issues with temperature/humidity making the tent 'slacken', so no need to readjust to get a taut pitch). I'm not convinced one way or the other as to which material is "best". Quality examples of both seem viable. Hell, even Hilleberg (which seems to be the holy grail on these forums as far as quality goes) was using it a couple years back (not sure if they still do).

Perhaps Ryan's tests will shed some more light on this interesting subject…

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