So I have a new Tent plan for 2021…input welcome

[Kevin Buggie]

Either way, Shires responses make it clear to me that I’ve purchased my last Tarptent…

[Bonzo]

Okay, I can follow that math; thank you for mapping it out so clearly!  I have a follow-up question:

1) An inward movement would shorten both of the yellow lines in the diagram by a differential amount; since the force on the stake is being calculated by the difference in those lines, the further the staking point is moved inwards the less any leverage can apply to it…right up to the point where the stake is at the fulcrum, the yellow lines become synonymous with the strut, and the multiplication of force has to be zero.  Naturally, it seems rather counterintuitive to do this in a real-world situation, but that possible zero-force-from-deflection staking location demonstrates that as the staking location moves away from the fulcrum, the force that can be applied to the stake rises…but only until the point at which the two yellow lines in your diagram have the most difference in length: that point should then be the worst possible stake location for the forces depicted.  After that worst-possible point is passed, the force on the stake should drop again, although it could never reach zero when moving away from the fulcrum.  That said, it seems that there are a variety of less-than-perfectly-bad points to locate the stake, but only one worst-possible location in terms of the force that the top of the strut can apply to the stake when being pushed inwards.  Is my understanding correct, here?

I actually have a few other follow-up questions that I haven’t fully worded in my head, yet, but they center on another factor: possible movement, given various lengths of guylines, various staking arrangements, and various aspects of how the tent itself pulls on the struts.  I need to work through a few other things before I go there, though.

Thanks again for your work on these diagrams.

[Dan @ Durston Gear]

I think you’re largely correct there. The distance our strut moves stays at 4.9″ in this 20 degree deflection scenario but as you move the stake inward (e.g. 4″ instead of 8″) the distance the stake is being pried decreases so leverage increases. Instead of 204% at 8″ (4.9″/2.4″), you might have 400% at 4″ (4.9″ / 1.2″).

The leverage rises exponentially as the stake approaches the pivot point. If you staked it 0.5″ away our yellow cord distance would increase by only ~0.1″ for 4900% leverage.

If you stake it right at the pivot point your leverage is infinite or really “undefined” in mathematical terms (4.9″ / 0″). In this scenario there would be infinite leverage except the distance you are trying to pry the stake is zero, so you end up with nothing happening to the stake. The stake is not resisting the movement of the strut at all, so the stake won’t pry out but the strut will be completely floppy.

So the worst theoretical staking position (if our goal is to have it not rip out) is infinitely close to the pivot point without actually being there. That puts infinite leverage on it, but practically what would happen is that it would just pry out a tiny tiny bit and then your strut would be floppy. Or the cord would just stretch a little to allow the strut to be floppy.

[David U]

My solution is to use rocks to hold the stakes down.

How is that for engineering?

😜

[Dan @ Durston Gear]

Pretty good :)

[Dan @ Durston Gear]

What would be really cool is to use struts in a way that reverses the leverage so instead of 200% you might have 50% to make the stakes twice as hard to rip out. Maybe I should toss a patent in for that :)

[Bonzo]

Hmm…gonna have to spend a bit more time thinking this one through; I see where I’m not understanding things, but I’m having trouble putting it into words.  I guess the best way to express it is as a question of relevance.  Let’s say that there’s 4900% leverage on something, but it can only move by .01″ or whatever that distance ended up being: at what point does the force multiplier cease being relevant because there’s simply not enough potential for force to be transmitted through the system for anything to happen?

Also: how much force does it actually take to make that theoretical 4.9″ movement that you diagramed out, given an 8″ – or 12″, 0r 24″, or whatever-length – staking distance from the fulcrum?

[Dave @ Oware]

Dan said

“You point out these struts improve wind performance by reducing the panel size but omit mention of how the struts make the stakes much more likely to rip out. Staked out like this, the struts are major net negative for stormworthyness. If we look to other companies who use struts and build tents for serious storm performance – such as Hilleberg – we see them staking it out much further from the body and in line with where the canopy would have extended to without the struts. Their pitching instructions specifically note to maximize the length of these linessince that maximizes wind performance, but of course that eliminates the footprint advantage:”

Many time the footprint issue is about having room for the tent body (and occupants) but having guy lines extended outside that is not a problem. Even on ledges on cliff faces, guy outs can be redirected (over an edge and down the cliff) to function well. People routinely set up large tarps that cover nearby bushes as well as people when pressed for space too.

 

 

[Dave @ Oware]

Here is how staking for an extreme load is done. Thousands of pounds. Big Stakes.

We used that method in Scouts for anchors on rope bridges and such.

This can be replicated using ultralight stakes, cord and as mentioned, my favorite , BFR, (big friendly rocks).

 

[Dan @ Durston Gear]

“Many time the footprint issue is about having room for the tent body (and occupants) but having guy lines extended outside that is not a problem….People routinely set up large tarps that cover nearby bushes as well as people when pressed for space too.”
Fair enough. The footprint situation is very site specific.  Long guylines are usually not an issue since you can almost always find someway to extend them. Shorter guylines like those from struts need to be at a specific angle and they are often designed to only have a bit of adjustment in the distance, so they usually work but not always. And the canopy itself might work as it covers bushes etc, but is the least flexible.

“I guess the best way to express it is as a question of relevance…at what point does the force multiplier cease being relevant….how much force does it actually take to make that theoretical 4.9″?
The leverage is approximately the same regardless of the magnitude of the movement. If we deflected the strut by 5 degrees instead of 20 degrees, we’d get about the same leverage since both distances would be proportionally reduced (perhaps 1.2″ / 0.6″ which is still 200%).

Regarding relevance, stakes do pull out in storms so the tents stress on stakes is a real consideration. If a certain geometry results in 2x the stress, that can be a meaningful difference. What’s not meaningful is extreme stake positions. If you stake it out 24″ instead of 8″ that’s a nice reduction in stress (200% -> 116%) and practical to do, whereas if you staked it way further yet (e.g. 20 feet) you’d get a much smaller benefit (perhaps 116% -> 105%) which is impractical and with diminishing returns.

The same goes at the other extreme. Once you get to >400% leverage you’re putting a pretty extreme load on the stake where the strut is going to rip out the stake or the strut will floppy because 0.5″ of stretch in the cord is 2″ of movement on the strut. So stake positions closer than 4″ to a strut are also largely impractical.

What’s relevant here is how you adjust it within that potentially practical range. In a sheltered site with footprint constraints a 4″ distance might make sense. Whereas in an open exposed site with a storm rolling in, that would have a high likelihood of ripping out whereas opting for 24″ would dramatically reduce the strain on the stakes so there is much better chance you’re not running around in the dark trying to put them back in. Similarly when you find yourself camped on unexpectedly soft soil – lengthen those lines and improve your odds.

[Bonzo]

It makes more sense, now that I’ve had a bit of time to sit down and work on The Maths…and yes, when we get to the real world, there are a lot more variables involved than just a simple angle on a line and what it does to the surrounding parts of the system (and I struggle with even those simple parts).  If nothing else, this discussion shows why there’s a lot that goes into a tent design.  It also shows why a few extra stakes and a few yards of cordage can make all the difference in the world.

[David Franzen]

Maybe pulley (as in block and tackle) is a better analogy

[Iago Vazquez]

I do not own any tents with struts so I have no real world experience on the matter. Physics and math are not my strength. My understanding at the moment from this discussion and others, which could be incorrect, tells me that struts are a great advantage when considering a shelter with a smaller size while maintaining “practically” the same usable interior volume for a given design.

When wild camping, I often find  limited sites with elements around the perimeter that impede an ideal pitch; be it rocks, roots or vegetation. I simply do not want fabric flapping in the wind rubbing against these obstacles for fear of damage. Having a shelter with almost equivalent usable volume but reduced footprint and/or reduced fly dimensions seems preferable to me. As was said previously by Bonzo & David,  I am not so worried about what happens to the guyline cordage. As I set my guylines, I will identify friction points and use a stronger or more slippery line. I will perhaps run two lines if the risk seems high. Check on them as the opportunity presents itself and go from there. I may perhaps anchor those lines to those perimeter obstacles without worrying about fabric damage.

If I understand the issue of leverage presented around struts, it seems that all that is needed is simply making sure that the cordage at the struts is long enough to reduce the negative forces. As a user, having long enough cordage for the conditions one camps in seems to go along with any other modifications we make when we acquire a shelter. Based on our needs, we add cordage to the provided guyline points, we choose appropriate stake designs for the conditions and soil one will encounter, we consider the need for different footprint options, etc.  We camp in different locations and face different situations. Some people may camp in areas with plenty of shelter from wind for whom guylines and stakes may not be as critical to a good night sleep… They perhaps can set up a shelter right out of the box and have it work for them. That is not me. Outside of car camping, I use very few of the 6″ V stakes provided with many shelters. All my shelters have had guylines added. And how many threads at BPL on footprints? I typically choose to use one.

Going back to real world of struts and the issue of reduced leverage… As I said, I have never owned a tent with struts, but I am definitely interested. I have at times had my fly land on top of a root or a rock. This resulted in an imperfect pitch with a less aerodynamic, floppy fly and the fly fabric rubbing the rock or root. But if the shelter were set back a few inches because of struts, I could perhaps secure my guyline to that rock or root, or secure the stake behind them, possibly increasing the strength of that anchor point regardless of any abstract diagrams about leverage.

I may very well be missing something, but it seems to me that struts are a very positive design feature for those of us that often find marginal campsites. The only negatives seem to be losing some low height “storage” space and that one must understand the need for longer guylines when expecting strong winds. For me these negatives are an easy compromise when considering the reduced size of the shelter for the locations I camp in. Of course, those who camp in wide open spaces and have no trouble finding large enough sites probably see no real benefit to a shelter with struts and the negatives would perhaps lead them to prefer a different design. Every shelter has pros and cons, and I strongly feel that experience is what tells us what best works for us as individuals for the conditions that we more often encounter.

[Dan @ Durston Gear]

All of that is generally correct, but note that struts are only a “great advantage” if the tent there is low angled and would otherwise have a lot of excess footprint/low fabric. It’s really making up for what would otherwise be a weakness is the core geometry. If that weakness exists to a great enough extent, then struts can be an improvement.

To illustrate, the Black Diamond Mega Light is a one pole pyramid which has relatively shallow wall slopes. Given that this low area around the perimeter isn’t that usable. Struts on the four corners might a nice improvement to trim the footprint and maybe save weight.

But then Black Diamond also sells their Beta Light which uses two trekking poles instead of one.  The dual poles steepen the walls to accomplish something similar to what struts would (since the pole is basically a giant strut) except the advantage is that if you’re carrying the pole anyways, then you’re not adding any additional structural components. The Beta Light geometry solves the same issue while being lighter and no struts to pack.

So arguably a Mega Light with struts would be an improvement over the Mega Light, but the Beta Light is better yet in terms of providing the most useable volume for the footprint at the least weight. It wouldn’t make sense to add corner struts to the Beta Light because there is so little that could be trimmed off.

[Bonzo]

Great explanations, there, Dan and Iago; thanks for providing them.  Now, I need to go back to Henry’s points and work my way through them.  I feel like the disagreement wasn’t really focused on the same points, so it would be good to understand the rationale of both sides.

Then I want someone to design me a tent that has all of the nice features of the X-Mid2 and the Stratospire 2, except that it has a bit more room for my bulky sleep system and extra-big-ass vestibules for my dog!  I know it can be done!!

[Dan @ Durston Gear]

“I feel like the disagreement wasn’t really focused on the same points, so it would be good to understand the rationale of both sides.”
I agree there was a difference in focus, as I was talking about struts in general whereas I think he was thinking specifically about the applications where he uses them. So I’m thinking about all possible applications of struts when making a statement like “whether they save a substantial amount of footprint area depends on the wall slope“. Then Henry would say that’s wrong because whenever he uses them they do save a substantial amount in footprint.

Other stuff is puzzling though because the leverage effect is clear and even acknowledged by TT’s own employees.

[Iago Vazquez]

I never used a Beta Light. No idea of how easy or hard it is to pitch. Not sure either how fair the comparison is as the MegaLight with struts could perhaps squeeze 4 cozy people but I am not sure that one could fit 4 under the Beta Light… I seem to read the Beta Light is a palace for 2 and a squeeze for 3?

But if I were buying a Beta Light or a hypothetical one-pole mid with struts, I would be more inclined to purchase the latter. Perhaps it is more personal familiarity with one pole mids. My thought process being that in any significant wind, say over 15 or 20 mph, I feel like I would be able to pitch a 2 or 3 person one pole mid but the Beta Light seems like it could become rather complicated. How easy would it be for 2 people?

Of course, the depending on the actual one pole mid with struts, it could be taller than the Beta Light with its own set of advantages and disadvantages…

Wondering why there is no one pole mids with struts… Pity I can’t sew…

[Dan @ Durston Gear]

I don’t mean to say the Mega Light and Beta Light are exactly comparable (e.g. same size). I’m just referring the basic geometry to show there are ways to steepen the walls besides using struts, such as manipulating the geometry, number of poles, and location of the poles. There are trade offs with all of this where the optimal solution will vary for each person. If you’re worried about wind resistance and want a lower volume shelter, then maybe trading some headroom for less exposure to the wind is ideal. Or maybe something in between like making the second pole shorter.

The Beta Light is quite simple to pitch because you stake the base and then the poles are located inside the base, so you can just insert them and extend until taut (like a one pole mid).  The six sided shape does complicate staking the base a bit but the base shape is another topic. There are two pole shelters that are still rectangular like a single pole mid, where the setup is very similar.

The Aeon is about as close as it gets to a 1 pole mid with struts.

[Dave @ Oware]

“Wondering why there is no one pole mids with struts… Pity I can’t sew…”

Some pyramids are made with side walls but guy out in the same way as those without. There are usually additional points at the bottom hem to stake too.  A slight weight savings in fabric but may take more stakes and cord.  The first mid’s I made (1985) all had 1′ sidewalls and were 8 ft tall to fit 6 people. Luxurious to hang out and to change clothes in. Eliminated the side walls eventually as customers decided they were harder to set up, especially being floorless. Some heavy car camping tents will have 4 short poles for the corners. You have probably seen movies set in the desert or Camelot with tall, side walls held up with “struts” or poles. Often they also have a large front canopy.

The beauty of a mid is how quick they can be set up. Four stakes in, pole up and your out of the weather. SAR can even set one a floorless one up over a prone victim. If you use really good anchors, they can hold up in extreme winds.

[Roger Caffin]

Eliminated the side walls eventually as customers decided they were harder to set up, especially being floorless.
Or were they being clueless?

Cheers

[Iago Vazquez]

Again, I do not know anything about tent design and my geometry is long forgotten. I had to ask my math teacher wife for help with this… A question about the very hypothetical one pole mid with struts for backpacking… If one takes the common square mid size of 9’x9’x6′ (LxWxH) and puts 12″ struts at the corners, one ends up with a 90″x90″x72″ mid. So we lost 1.5′ in length and width while maintaining the height, snow shedding profile it seems. How practical or marketable such a tent would be I wonder?

Probably not at all since no one has done it… Some random thoughts that could be totally inaccurate… So feel free to correct my impressions… :)

0–I wonder about the number of struts needed for such a size shelter. Would 4 at the corners be enough? Would additional ones at the center of each panel add anything significant to the performance of the shelter?

1–In snow pitched low to the ground now there is a foot of height before snow piles up on the fly affecting the pitch.

2–A low end ventilation system could be added to the non door walls at the center of each fly panel while maining the majority of the perimeter low to the ground giving the option to open or close as needed. With the 12″ of height created by the struts the vents could be rather large which could allow for good ventilation paired with top vents? I haven’t figured out exactly how this would work… Just thinking…

3–In rain, if having 4 sleepers in 4 regular pads, the fly would probably have to be low to the ground to avoid back splashing? With 45″ on each side of the pole, there is not much room to raise the fly… Perhaps 2 or 3 of the low vents described under #3 could be open to aid in ventilation… Perphaps to avoid backsplash a second layer of fabric could be added to these low vents and act as a liner that would redirect rain back out.

4–In wind, would the 12″ struts and the “vertical” walls they create be an issue?

As I was putting this together, I could not help think of the TT Hogback and their pitchlocks… Different tent, but similar footprint and no middle pole. No clue how tall those pitchlock struts are…

[Iago Vazquez]

I have seen those tents in films and photographs as you say David, but they all look much larger than even the typical 12’x12′ hunting/backpacking mids/teepees.

Wondering what was hard about pitching the 8′ mids with the 1′ vertical wall… Again, never played with such a design…

[Bonzo]

Other stuff is puzzling though because the leverage effect is clear and even acknowledged by TT’s own employees.

I’m kind of new to these tents so I’ll have to look that up and see what I find.  Regardless, I do think you guys were just at odds on the terminology being used, and the application thereof.

Unrelated question: is there an upper size limit to tents like the X-Mid and Stratospire?  Is there some sort of point at which they just can’t structurally work, and is that why we don’t see a “3” version of any of them?

[BlackHatGuy]

“0–I wonder about the number of struts needed for such a size shelter. Would 4 at the corners be enough? Would additional ones at the center of each panel add anything significant to the performance of the shelter?”

I know nothing about tent design, so I’m sure there’s an obvious answer to my question: Why couldn’t you just sew, on the outside, a tieout point or whatever they’re called at the same spot the top of a strut on the inside would be? Guyout each of those points, guyout the bottom straight down to form your walls. Only pole is the center pole. Workable? Not really workable?

[Roger Caffin]

‘Workable’, until you get a good wind. Then you have:

And I am sure many will have seen other photos of similar collapses at the edges, like this..

Cheers

[Author]

Posts