Mar 21, 2020 at 9:35 pm #3637163Craig BBPL Member
Wow, quite the thread drift here from the OP question, which I don’t think anyone has really hit on the answer to.
Yes, the mechanics of this situation are extremely complex. However, I think MORE loosening of a stake in its hole by a guy line that has LESS average tension (by quite a bit) can can be explained by static vs dynamic friction, and the differences in impulse forces between the two situations. People have already mentioned these things on their own, but have not really put it all together yet.
In the lower tension situation with the tent free to flap, you will have oscillations in the fabric that lead to energy being directed down the guy line in a whip like manner. This leads to greater variation in the percentage of static load as Ryan observed, but more importantly this will result in force being applied to the stake on a very short time-scale which will have a very high impulse force. It’s likely there were higher impulse forces experienced in the lower tension scenario vs the higher tension setup. The higher the impulse force the better chance you have to overcome static friction. Think about the hammer and nail example that was described previously; you can drive a nail half way in with a 1Lb hammer, then gently place a 50Lb load on it and it will not move.
The static vs dynamic friction part comes in with respect to the ground around the stake. There is a certain amount of friction that holds the stake in the ground in the direction you drive it in, but that is not really the whole picture of what keeps a stake held in place when you start pulling on it sideways. If the ground deforms and suddenly you have a loose hole, there will be much less friction on that stake. What is keeping the ground from deforming and opening up to be a larger hole? The friction of all the particles that make up the soil/sand with respect to each other. If you start applying high impulse forces to the stake from the side, you can overcome the static friction of the ground itself and it will deform to a larger hole.
So really what you want to do is minimize those impulse forces. Clearly a tauter pitch can do this as Ryan has demonstrated, or having some sort of elasticity in the chain as many others have pointed out. Measuring the impulse forces will probably be difficult with the equipment Ryan is using. You will likely need a high-speed analog to digital converter and perhaps a specialized load cell/force gauge to see things on the millisecond (or faster) time scale. I haven’t looked, but I’m sure it’s possible though.Mar 21, 2020 at 9:46 pm #3637167Eric BlumensaadtBPL Member
@danepackerLocale: Mojave Desert
Craig, I’m guilty of thread drift as charged.
However the tent photos previous to my “drift” do shed some light on design as it obtains to distributing wind load forces. Some newer tents with pole hubs and intersection connectors do tent to spread wind load to other poles instead of one pole taking most of the load. That may be a factor when designing for wind loads in future tents.
This thread is not just about stakes but the entire wind load situation.Mar 21, 2020 at 9:50 pm #3637169Paul SBPL Member
Exped “needs” to make it fly first?
I was trying to make the point that unlike most of the pop-up tents I see these days, the Gemini is not 100% mesh. So, yes, some rain will get on it, but not as bad as some others that are all mesh.
It ain’t perfect, but I have had some wonderful trips with that tent! It is so much sturdier than the Big Agnes/MSR, etc, tents that I see, by a mile.
We also have other tents that pitch fly first, and they’re great, but we still love our Gemini II!Mar 21, 2020 at 11:38 pm #3637173
So, yes, some rain will get on it, but not as bad as some others that are all mesh.
And ‘not as bad’ is meant to be good?
Meanwhile, other tent designs do not ever let rain under the fly.
My mind boggles somewhat.
CheersMar 22, 2020 at 8:11 am #3637193Jerry AdamsBPL Member
@retiredjerryLocale: Oregon and Washington
I took a 3.5 inch wide strip of fabric. 7 feet long. Along the grain. About 0.25 ounces.
Folded over 6 times and sewed it to make a strip about 1/2 inch wide.
Sewed that to the ridge:
Red arrow points to the top of the strip.
Doesn’t seem to make any difference, but maybe the ridge isn’t as stretchy. At least it didn’t seem to hurt anything.
Now I need a trip where it’s windy to test this out.
When I was sewing it one time I accidentally captured a piece of fabric underneath. “Damn It!”. Ha, ha, ha,… Oh well, only about 1 inch of seam to rip out, and it was part of the strip, not the tent.Mar 22, 2020 at 9:39 am #3637209
I think that we can all agree that the theory behind tenstakes pulling out is prety complex. In general, situations like this are studied by Civil Engineers and they develop best practices and guidelines.
In the back of my head, I tend to believe that soil compression is nonlinear and a hiogher load will “pre-load” the soil providing a better anchor. It is difficult to really find information about soil properties.
Theh second thing that comes to mind is the engineering concept of teh Goodman diagram. With respect to fasteners like bolts, higher pre-loads under cyclic loading not fatigue as fast as those under lower loading and that the longer the bolt the better. I believe that this is one of the reasons that old car cylinder heads preferred long bolts. Spitballing here a bit.Mar 22, 2020 at 11:32 am #3637225Craig BBPL Member
There are several analogies I can think of for this situation in addition to the hammer/nail example;
- pneumatic impact drivers for wheel lug nuts
- electric impact drivers for screws
- hammer drills for drilling into concrete
If you’ve ever tried to drive a long wood screw in with a regular cordless drill, then tried to do the same thing with an impact driver, you know what I’m talking about. It’s almost like magic how well these tools work. They all rely on high impulse forces that overcome high static friction. The length of the impulse force is short, so you need many repetitions to make any progress on moving whatever you’re trying to drive.
I think it’s a pretty similar situation though; flapping tent panels making many hammer-like blows on the tent stake causing the earth around it to slowly move and loosen.Mar 22, 2020 at 12:24 pm #3637232
I agree that impulse/impact loads are very effective at breaking loose certain items. What is confounding about the OP was that the two conditions were a low pre-load and a high pre-load. Assuming that the the inputs were similar, the stake with the low pre-load demonstrated more “wiggle”.Mar 23, 2020 at 12:39 am #3637312
Re: “The alternative, for pole carriers, would be a hybrid trekking-pole/bendy-pole design like the original TrekkerTent Edge 1.” Geoff, the owner of Trekkertent posted about his trekking pole design on BPL a number of years ago. Would dig it out if there were time.
Re: “Endless waffle.” Available at the Pancake House? From watching guitar demo clips for my bro, got used to putting the cursor arrow on the bottom line, and fast forwarding to when the guy finally stops talking and starts playing. Bro finally found his dream guitar. Thank goodness.
Re: “EXPED needs to put the pole sleeves on the FLY”
This is also in line with Roger’s thinking, oft expressed.
Drifted a bit from this with the link to the Kuiu tent that used external clips, instead of sleeves. The video of the tent under the blast of the propeller on a swamp boat is worth looking at. Perhaps I differ about the need for pole sleeves vs clips partly because I have a dome that uses pole clips, and find it pitches much more quickly than any tent I’ve had with sleeves, and is more rigid and stable despite the use of clips.
The other big issue with pole sleeves is whether they need to be attached to the outer fly. Suggest an approach, not thinking in terms of inners and outers; but rather, mixing them a bit.
Notwithstanding its weight, the Gemini tent, with its pole sleeves on the inner, is said to be quite stable. Ditto for the Terra Nova Solar 2, well reviewed for use as a winter tent; although arches instead of hoops would shed snow better and prevent pooling. I think that the stability of the Gemini and similar tents is not related to the pole sleeve location; but rather, to the two pole crossing design. It was tents like the Gemini that attracted me to the double-cross designs in the first place. However, I also learned from looking at a tent EMS once marketed that a tent like the Gemini could be very unstable and a disaster in the wind if poorly designed.
The inner/outer canopy that is pitched first can consist of the vestibules, attached to a breathable solid but water resistant inner, and produce a structure that is both flexible and rigid. So it is very hard for me to see the need to place pole attachment sleeves on the fly. If the fly is securely attached over a stable and solid inner, with ample overlap over a portion of the vestibules, I don’t envisage the wind distortion in the fly that Roger sees.
It is a great advantage to use pole clips, and a seamless fly over them that can easily be installed, removed or replaced when available fabrics get lighter, stronger and reasonably priced. Am not going to chuck these advantages for an outer that is adorned with many seams and pole sleeves, because I think that one rigid structure is enough. Have never been happy with inners clipped inside outers, and that feeling may be why the industry has stuck with supporting the inners and attaching a fly on top. They don’t want to change, and devotees of hanging inners don’t want to either. There are good arguments on both sides. The solution may be hybrid construction that combines the best of both approaches.Mar 23, 2020 at 1:15 am #3637316
I don’t envisage the wind distortion in the fly that Roger sees.
hard for me to see the need to place pole attachment sleeves on the fly.
If the poles can slide relative to the fly, you can get this effect under high winds.
a seamless fly over them that can easily be installed, removed or replaced
No such thing, unless your tent is flat. There will be seams!
may be why the industry has stuck with supporting the inners and attaching a fly on top.
They are catering to a large market, but one which does not go up in the mountains. They go to music festivals and so on, like this one. Yeah, they are all tents in the air.
This is part of a sequence I rather like: a music festival in the UK which was hit by a sudden squall.
The guy in front of the tunnel tent is supposed to have emerged after the damage and asked ‘what happened?’. The people in the tunnel tent were eating and did not notice the storm.
The Biased OneMar 23, 2020 at 3:46 pm #3637383Eric BlumensaadtBPL Member
@danepackerLocale: Mojave Desert
What I see in the photos of “failed tents” is a lack of guying, perhaps because there were no guy points on the flys.
I’ve also seen on some Hilleberg tents that the pole sleeves were large enough to accommodate an extra pole for rigidity. I can just barely put two poles in the main sleeve of my Tarotent Moment DW. Thus I will use guy lines and do without that extra sleeve pole, relying on my DIY under-the-fly crossing pole to supplement the hoop pole.
Again, the subject of tents and high winds is about poles and guys as much as stakes.Mar 23, 2020 at 6:38 pm #3637413
Yes, but the single most important factor is design.
CheersMar 23, 2020 at 7:35 pm #3637415StumphgesBPL Member
Here is the stress test video Sam mentioned of the Kiui dome with external pole clips: https://www.youtube.com/watch?v=8hEX5R761XcMar 23, 2020 at 10:29 pm #3637454
Stumphges, yes that is the video. Thought I’d posted the link earlier on this thread, but maybe not, so thanks. BTW, it is spelled Kuiu. It is an island off the coast of southern Alaska, but Google won’t tell me the origin of the word, which probably comes from the people who were native to the area.
“I don’t envisage the wind distortion in the fly that Roger sees.”
No, not like any Big Agnes tent. I can’t go into the differences yet again, because I’ve been timed out by the debate moderators. No applause, please.
“If the poles can slide relative to the fly, you can get this effect under high winds.”
That is why a structurally sound frame is necessary under the fly. Then the poles won’t slide, and the fly over them won’t slide if securely attached.
“No such thing,” as a seamless fly. OK, will put some seams on, but it will just add weight. All right, all right, was thinking to put some seams at the ridge, and at the juncture of the fly and fly extensions. Just to make construction easier. Recall that the canopy in the original prototype posted on BPL and linked umpty times, had only the ridge seam. The dome shape is created by the greater expansion of silnylon on the bias.
“They are catering to a large market, but one which does not go up in the mountains. They go to music festivals and so on, like this one. Yeah, they are all tents in the air.”
Surely you know that many makers of what you call “pop-ups” cater to backpackers.
“The people in the tunnel tent were eating and did not notice the storm.”
Agree that we must not discriminate against the hearing impaired, or any other minority.
Will leave it at that. Hope you are doing fine. Alas, we are not.Mar 23, 2020 at 10:50 pm #3637457
because I’ve been timed out by the debate moderators
Wicked lie! Scurrilous fabrication!
I am sure lots of readers are being entertained.
That is why a structurally sound frame is necessary under the fly
I will certainly go along with that, although when you can’t put guy ropes on the poles that can be tricky in a high wind.
we must not discriminate against the hearing impaired
BTW, while I did watch the video, I note that they pitched the tent in dead calm, before they switched the blower on. I would like to see them get the tent up with the blower already going full bore. The results might be a bit different.
Just make the tent!
CheersMar 24, 2020 at 1:09 pm #3637548
Tent design, guylines, tent stakes, soil conditions, yeah it is all complex system. Let’s assume that we all convert to tunnel tents. Looking at these last few pictures though, it you had to pick one of these elements to fail, wouldn’t you want it to be the tent stake? Yes, the tent losing the suport and collapsing over you is bad, I get it. Isn’t having a pole snap or the fabric tear worse? Just thinking out loud here.Mar 24, 2020 at 2:51 pm #3637576
Thing is, when you talk about something failing, that usually means that the weather has become a bit extreme. It is no longer a matter of comfort; rather it can be a matter of survival.
Now, points of failure. I can speak to tunnel tents as I have had most experience with them.
The very last things you want to fail are the two windward corner anchors. If they go the whole tent can easily be lost. If they hold, then the tent and its occupants survive. The two downwind anchors are the next in importance, but they are not likely to fail.
I have had guy ropes fail in a storm – in ‘When Things Go Wrong’ here on BPL I mention that we lost about 6 out of 8 side guys (Spectra) due to fretting or abrasion overnight. The guy ropes were coated in ice to about 20 mm thickness: they looked unreal. Fortunately I had pitched the tent end on into the wind, and all four corner anchors were holding well.
Yes, I have had poles break. Most unfortunate. They were Easton’s new and still experimental 7178 alloy (since withdrawn), and they had a brittle fracture at the peak. I had to do a repair in the field.
That is three layers of sardine can wrapped tightly and secured with nylon cord and patching tape. It lasted.
I have never had the fabric fail. Frankly, I don’t think good silnylon would just fail. It would need to be damaged by something else.
Looking at the structure as a whole, a tunnel is probably the safest and easiest to pitch and strike in any storm. There’s a tutorial in our series on Tunnel Tents here on BPL. It takes about the same time in fine weather or in a storm.
CheersMar 24, 2020 at 4:24 pm #3637602
OK, tent systems shouldn’t fail and tunnel tents are the best. That being said, if a component is going to fail, wouldn’t it be best if it was the stake pulling out?Mar 24, 2020 at 7:41 pm #3637639
wouldn’t it be best if it was the stake pulling out?
That question is too vague to be answered with a single yes/no.
AS I said above, a good tunnel tent pitched end-on to the wind can lose its side guys or tent pegs without too much hassle. I did notice on that trip around 5 am that the poles were vibrating a bit, and that was so unexpected that I got out of the tent to see why. Maybe I should make that I crawled out of the tent, because standing up was not a good idea in that wind. The real hassle was that, without the guy ropes, I could no longer find the tent pegs under the snow! We did come back a year later and searched, but the snow melting had migrated them.
On another trip we did have to help support a very early 2-pole tunnel against a serious buffeting wind from the side one time. In that case the guy ropes were OK: the problem was the huge fabric span between the poles. That was far too big. I had misjudged the likely direction of the wind when pitching in calm weather.
But if an end peg at the windward end of a tunnel is lost, everything goes to hell in a handbasket. You absolutely do NOT want that to happen.
So the only answer I can give is that it all depends on WHICH peg is lost.
CheersMar 24, 2020 at 11:00 pm #3637667
Great pix, Roger. Love the one of the Big Agnes with the huge rocks all around, but collapsed because the framework inside has failed.Mar 25, 2020 at 8:12 am #3637704StumphgesBPL Member
Sam, sorry I hadn’t noticed that you’d already posted the Kuiu Mountain Star video.
Sam, Roger, apologies, but what is wrong with external poles with clipped to the fly? The tent in the video performs far better than most “pop ups” would in 65 mph winds. It also offers dry setup and entry. As far as domes go, it appears to maybe be best in weight class. Sure, it’s still going to be hard to set up in high winds, but that’s about the only thing wrong with it that I can see.Mar 25, 2020 at 2:58 pm #3637749
what is wrong with external poles with clipped to the fly?
Well, poles attached to the fly are infinitely better than poles not attached to the fly: that is obvious from the photos.
Clips vs sleeve: here you get into finer shades of grey.
With a sleeve the fabric is fully supported all along the pole, and in a storm that is excellent. Clips only attach the fly to the pole in a few places, so the fly can wobble around quite a bit more, and (worse) the clips make for a point loading which can threaten the strength of the fabric. Also with a sleeve the guy rope attachments are much better.
Please remember that I am a bit biased, having been through more bad weather in the mountains than I want to think about. And yes, I have tried one or two of the ‘lesser’ tents over the years.
CheersMar 27, 2020 at 1:48 am #3637999
Re: “… what is wrong with external poles with clipped to the fly?”
Recall some older threads where there was considerable concern about the external poles creating snow and possibly wind fences. But agree with Roger that for a tunnel, where external pole sleeves, and narrow ones at that, work best; then that is probably the best design because it limits the amount of mischief the wind can create.
However, tents with a framework with at least two pole crossings don’t lend themselves to the external pole sleeves. Too much fuss pitching in high winds, for one thing. That’s why we see the clips to get the tent up quickly. But I think the tent should be designed so the clips are used to support the inner structure, so a smaller fly can attach quickly over the top and present a smooth surface to the wind. The attachment and guying of the fly is of course crucial to keep it taut in high winds. And the inner structure must not fail, as Roger’s photos show.
Recall an old thread of a clipped tent in Japan being pitched. It was a conventional two pole wedge dome with only one pole crossing at the top. Roger criticized it for all the usual reasons, but with the clips it went up in nothing flat on a very windy mountain top.
So there are trade-offs with all tent designs, including tunnels. But should advise that after racking the brain for years, may have finally come up with a good way to get the side guys through the fly and attached to the pole clips at the pole crossing points. It can be done without any fiddle factor, after the tent is completely up and fly fully attached. But will say no more until the tent is done, as there will undoubtedly be many changes and rivers to cross before then.Mar 27, 2020 at 3:28 am #3638004
a good way to get the side guys through the fly and attached to the pole clips at the pole crossing points
It can be done all right, with only a small fiddle factor. Rather rare in the field though. I don’t know why.
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