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Tullochgorum
15
Dec 16, 2018
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@dandurston Been working on a similar design myself (a High Route variant with sloping vestibules), so immediately understood how smart you've been with this solution. Given your price-point and all the prototyping you've done, if I'm going for the offset design it would make sense to join this drop.
But I'm dithering between an offset mid and my own take on an A-frame. My issue is that I spend a fair bit of time camping high in exposed sites (Scotland, Scandinavia, Western Alps). I don't seek out big winds but sometimes they find you anyway. You say that you've found the X-Mid stormworthy, but I'm concerned that North American perceptions of a wind storm can be a bit different from our perceptions here in Scotland! Can you put some figures on this, in terms of mph? Using all the pegging points, what's the max wind-speed where it would remain stable and quiet? And what's the max wind speed you think it could survive without damage? Could I improve performance by adding tie-outs to the seams? And if I ever did get caught out in Armageddon, is there any way to improvise a storm pitch to minimise the risk of damage?
Andrew reckons that the HR would max out at about 40mph, which would be a bit tight for me. And there 's a YouTube video of it flapping badly in a relatively modest wind. So I'm wondering how much better the X-Mid would perform with its different geometry?
I've protyped my A-Frame and it's rock-solid at 40 mph, and I'm pretty confident it could survive 70 mph undamaged in a low storm pitch. But the X-Mid would be a lot more livable for the 99.5% of the time when you're not in big wind. I had a chat with Andrew about his HR and he said that he'd have been happy to take a lightweight version on his Alaska trek, so perhaps I'm over-thinking this. But with all your experience, I'd value your advice.
Finally, I'm currently using a TrailStar. Having fabric in your face does get old, but I've come to appreciate the openness. If the wind isn't too bad, is it possible to porch the lee door of the X-Mid without flapping, so you can still get a view in driving rain?
Sorry for such a long question, but this is a safety issue so I'm keen to get it right. And you've been incredibly generous with your responses on the thread.
By the way, Andrew reckons that this style of design would work well in DCF as it doesn't rely on stretch for a good pitch and it would stiffen the panels. But I'm not aware of anyone who's built one. It would be a bit of a scary MYOG project because of the cost, but a slightly smaller single skin version in DCF is tempting...
dandurston
4986
Dan Durston
Dec 16, 2018
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Hi Tullochgorum,
Talking about wind speeds is a tough one because of most folks aren't great judges of windspeed. Even a moderate 20 mph breeze actually seems pretty intense in the field, so a lot of folks think that's 50mph and then when they read a tent is only good to 50 mph, they get worried and think they would have wrecked it.
I'm not just saying you are doing that, just that tossing out specific numbers is hard because my estimates might be off, and even if they are accurate, other folks reading them might not sound impressed because they think they the moderate breezes they encounter regularly are faster than that.
So anyways, with that disclaimer out of the way, I think the X-Mid would easily do better than the HR for the obvious reason that it doesn't have vertical side walls. Those vertical side walls are the weak link of the HR since they catch a lot of wind, and this is compounded by the wind pushing in on this wall and making it into more of a scoop shape. I expect the HR is pretty good in the wind except for this. The side walls of the X-Mid are still somewhat steep but much less so. They are in the range of 55 - 60 degrees, versus 90 degrees which is a big difference when it comes to shedding wind. So I think it's safe to say it's quite a bit more wind capable than the HR.
Below is a diagram of the X-Mid that shows its shape along with all of the stake out points available. The direction shown for the peak guyouts is normally optimal (rather than extended them straight out the ridgeline) because it anchors the peak from that side while the longer corner seam anchors it from the other side. But you can vary this angle quite a bit to support it from whatever direction it needs it.
(Edited)
Tullochgorum
15
Dec 16, 2018
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Thanks for the detailed reply! The way you are approaching this project is going to win you a lot of fans.
Scots and Scandis who are looking to go light tend to favour the TrailStar or the DuoMid. Both solid in the wind, but with iffy livability and HUGE footprints. The general experience is that the Duplex and other Zpacks shelters are for fair weather only - too noisy and fragile in big winds. Open tarps aren't much used here in the hills - too hard-core in our conditions. But reports on the StratoSpires are pretty positive, so if you can match their performance you should have a market over here.
So as usual it's all about tradeoffs - storm-worthiness for the occasional extremes vs livability the rest of the time. The big drawback I can see with the X-Mid is than unlike a tarp like the TrailStar or my A-frame design you can't really hunker it down into a survival storm-pitch. Though maybe I could mod it with some tie-outs farther up the walls? As a last resort, I guess I could always just wrap myself in the fly - at least I'd survive without shredding the shelter...
The point you make about the resale value is a good one - I'm pretty sure that this will become a cult classic. I agree with your reasoning that this is a better way to handle the transverse ridge. Simpler, lighter and easier to pack and pitch than the Strato (provided it handles the wind as well), more storm-worthy and with better vestibules than the HR (at the expense of a slightly larger footprint), and I just don't understand the thinking behind the Yama...
dandurston
4986
Dan Durston
Dec 16, 2018
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At the risk of too much conjecture, I find the X-Mid really similar to the DuoMid in high winds. I've owned three different DuoMids (and also a Locus Gear Khufu) so I'm quite familiar with the performance of those. Comparatively the X-Mid does have steeper walls, but it also has two advantages:
1) It has peak guylines, which really help since you're taking the load off the fabric and spreading it over more stake points.
2) The panels are smaller since they are going up to two shorter (~46") peaks rather than one taller (~54") peak, so you don't have as much area on any one panel to scoop and catch wind.
Compared to the StratoSpire, the X-Mid peak guylines can be easily oriented to support the long side if you end up in the unfortunate position of being broadside to a strong wind, whereas the SS guylines don't really work to orient over to here. The other thing with the StratoSpire in strong winds is that the weakest link is the long sides and all of the wind force in this area is loaded onto the pitch lock corner. So you have a ton of surface area on one stake, and then the Pitch Lock corner typically applies a leverage effect onto the stake (hard to explain but I could create a diagram). I've never heard of anyone talking about this. Depending on how you have the pitch lock cords setup, you typically create a force multiplier onto this stake so it rips out easier than it should (this is hard to explain, maybe I should make a diagram). I've used the SS a lot in strong winds (when I hiked the PCT in 2014 it was always super windy in SoCal - I gave up on wearing a hat).
As you say, it is about tradeoffs, ultimately shallow wall slopes are going to shed wind better but then you end up with either a lack of headroom or a really large footprint. So I think the X-Mid is a well rounded design that will serve most folks well, but users with extreme needs may want to look elsewhere.
You're points about a "survival mode" are interesting. A small portion of customers like yourself are experts in this niche and would be thoughtful enough to potentially use something like this if the occasion arose, but I suspect even if I had a good "survival mode" most folks wouldn't think to use it.
With that said, I suspect there might be a good way to do this. I think you could use the peak lines to pin the whole thing to the ground. So stake the four corners (and maybe some extra points around the base), but then instead of erecting the poles, omit these and instead pull the peak guyouts out roughly opposite of the normal direction, so the peaks are pulled down to the ground and taut. This way the non-erected peaks wouldn't flap in the wind like a non-erected DuoMid. So basically this would be a tarp pinned to the ground. Hardly a spacious lounge, but better than a burrito. I think this would work but I haven't tried it. Here's a poor diagram:
(Edited)
dandurston
4986
Dan Durston
Dec 16, 2018
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Actually I'll go a step further and make a diagram showing the potential for leverage problems with struts around the base of a tent because I think is real problem in the field. I've owned a number of TarpTent's and for a long time I've wondered why it is usually the PitchLoc corners that rip out first in a storm.
Anytime you have a strut around the base of any shelter, it can create a leverage effect on a stake depending on the angles and distances. In the diagram below, the black line is a strut and then imagine we are pulling up on the end with an arrow. If you have the stake positioned at the end of the end of the strut (below left) then every inch you lift on the strut it also attempting to lift the stake by 1", so you have a 1:1 ratio and no force multiplication (or extra leverage).
(Edited)
Tullochgorum
15
Dec 18, 2018
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Many thanks for all your thoughts - it's fun to find someone who's even more of a shelter geek than I am!
On the wind performance vs the DuoMid, your six panels must help compared with the basic 4 sided mids. On the other hand, to achieve the greater headroom two of the panels are inverted, widening towards the top. Given the ground effect, fabric at the top will catch the wind more, which will probably offset the advantage of the smaller panels somewhat. And I can't see how you could add a practical mid-panel tie out to support them (at least without using a lifter). I suspect that you've achieved the max wind performance possible with this geometry - the additional head-room will inevitably add more wind-catching fabric high up. I think you're right that for most users in most conditions this will be a good tradeoff, and your impressive order figures suggest that a lot of people agree.
For those of us who want the freedom to camp high in exposed and windy places, it would be a calculated risk - it may be better to sacrifice the livability of the X-Mid for something that can handle really big winds in case we get caught out. And there the issue of noise in more moderate wind. At my stage of life I'm a basket case if I can't get my sleep, and the High Route really does flap:
https://youtu.be/JFDUNwbxST0?t=712
How much better is the X-Mid, do you think?
Your suggestion for a survival storm pitch looks like it might work. You could always use some cord to gather up any excess fabric on the inside, I guess. With the TrailStar, the pitch of last resort is to peg down all sides like a limpet, slide under the edge and put a minimal pole in the middle, to help control condensation. I think the central pole might help out with the X-Mid as well.
The issue of handling big wind with a trekking pole ultralight is an interesting one, as you're so restricted compared to conventional bendy-pole geometries like the tunnel and geodesic. I've started a couple of mega threads on BPL where we mined the history of shelters looking for solutions.
The most common approach seems to be the 4 sided single-pole mid. Easy to pitch. Can take big weather without damage. Easy to add a top vent. But difficult to achieve a thru-draft. Big panels which can be flappy, and need lots of pegs for support. Horrible living space in smaller versions, with doors that overhang the living area so no views in bad weather, fabric in your face when lying down, and doesn't play well with bug netting.
Then you can start to add more panels, like the TrailStar, the hex mids and tipis. Should be quieter in the wind, but harder to pitch, and they need lots of pegs. I can tell you that pitching the TrailStar on a difficult, uneven site in the dark and driving rain after a long day on the trail is not the funnest experience. And still have the disadvantages of any small mid.
Personally, for lightweight alpine use I'm more drawn to an A-frame front-loader. Designed right, this can take huge winds. For example Kifaru claim that their ParaTarp and SuperTarp are rock-solid in 70mph Alaskan storms, and can take a decent load of snow. Customer reviews confirm this. You sacrifice some ease of entry, and some views if you batten down the foot end. But in return you get an efficient footprint, plenty space for a solo walker, potential for a thru-draft, lots of space above the head and feet, a sheltered, adaptable vestibule, easy to rig insect netting, a quick, easy pitch in good weather (my design uses 5 structural pegs), fly first pitch in bad weather, with the option to add lots of additional support when it blows up. Experience with flat tarps suggests to me that for big winds you really do need lots of pegs to spread the load, especially with a 20D fabric. So the ideal is a design that can handle most weather with a few solid pegs, but which can be hardened with a number of 1g ti crooks to prevent flapping when it blows up.
I used the A-frame a lot as a kid in the 60s and 70s and like it a lot, especially solo where the space works better. It almost died when bendy poles came in, but there's a revival in the ultralight world because it works well with trekking poles. But like you with the offset ridge, I think there's scope for refinement, especially when storm worthiness is the priority. I might even show my design to Massdrop if it works, but it's more specialised than the X-Mid so probably wouldn't excite them.
As you say, one approach to improving the space and footprint of mid designs is the Pitch-loc. Intuitively I never quite trusted this idea, but you really nailed the physics with your analysis of the resulting leverage. And you're right - they do normally show it with a very short guy:
dandurston
4986
Dan Durston
Dec 18, 2018
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You've definitely put some good thought into this, and I generally agree with what you're saying. There are design considerations here that are hard to navigate because trade-offs unavoidably exist. As you say, with more headroom comes more wind drag, all else being equal.
I always think it's funny when designers say they "made no compromises" as if that is possible. There's always compromises: lighter or stronger fabric? more headroom or better windshedding? Steep walls to shed snow or shallow walls to shed wind? Etc. I think the best thing you can do is start with a smart design so there aren't more compromises than necessary, and then have a clear goal in mind when you're making those compromises so you get an end product that is coherent. With the X-Mid I was trying to make a very capable, well rounded shelter and I think I consistently made choices that achieved that. I avoided certain choices that would have been lighter but limited the shelter (e.g. eliminating the peak guyouts, or the vents, or using #3 zippers) but also didn't attempt to design the tent for extreme scenarios, as that would have increased the weight and created other downsides like less living space. So I think it's super capable but surely not as capable as a tent designed specifically for these extremes.
As you say, the Atko is amazing in high winds but it also weighs 46oz and has quite a bit less headroom (36" vs 43" peak height). So the Atko would be the right choice for someone that needs that capability, but it would be a suboptimal choice for someone who doesn't.
Anyways, I'm just rambling on here. The point I'm trying to make is that I think the X-Mid is quite capable for it is, and I think it's nice well rounded shelter that's going to hold up pretty well in almost any circumstance, but certainly there are extreme scenarios where a more specialized shelter would be the right call.
On the topic of the X-Mid vs single pole mids, indeed the X-Mid has more area up high as a product of the increased headroom. However most of this is exposed along the long side of the shelter, so the area is similar on the short side. If you look at the end of X-Mid (photo below) it doesn't actually have much more area than a single pole mid. The slope is steeper but the wall is a bit shorter ( 46" vs about 54"). Plus the X-Mid has the peak guyout which is lacking in single pole mids. So ) I think this is at least as good in the wind when pitched with the short side into the wind. The peak guyout is beefy to since it's bartacked through 210D material that is connected right to the pole.
Tullochgorum
15
Dec 18, 2018
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You're certainly on point when you say that ultralight design is all about making the right tradeoffs to achieve a coherent solution to a specific goal.
And I think you've nailed it with this design for the typical North American scenario. For the weight, I can't think of a solution that would give better ease of entry, views, venting, ease of pitching, efficient footprint, generous vestibules with safe cooking and drip protection, and decent performance in moderate foul weather. It really does look a well rounded design, with no obvious drawbacks given its target niche. To go any lighter, you've going to have to give up a lot of livability and/or move up to a much higher price point.
Then it's all about understanding the materials and getting the detail right. And you've clearly obsessed over that, with the excellent cut, reinforcements and guying. I suspect we've both been reading the same threads on BPL - it really is a priceless source for this kind of detail...
With ultralight A-frames, two of the main players have taken the North American approach of the short fly (Yama and HMG). So that's a non-starter for northern Europe, for reasons we agree on.
There's some nice touches in the Yama, and people say that the build quality is miraculous, but there's just too much I couldn't live with for my application .
I'm not surprised that you didn't get on with the Echo - to me it looks like a case study in making the wrong compromises and ending up with an incoherent solution. It tries to do everything, and ends up doing nothing very well. The removable beak looks like a dogs dinner - I really wouldn't like to erect that in a wind. It also looks flappy and failure-prone. And all for what - to give you the option to save a handful of grams and go out with a beakless shaped tarp that's too small for any serious application? In bad weather you want a bombproof tail into the wind, but they've left it open with very little overhang, relying on the inner for protection. Again, this is going to be draughty, flappy, and you're vulnerable to driven rain, dust and spindrift. And the dimensions are odd - I suspect that it's more to do with economising on fabric than with functionality. When I contacted them about performance in the wind they were evasive - I don't think it would do well. But it looks cool, so that's all right then. It seems that there are people who are prepared to pay $600 for this, but I really can't see why.
The BD Beta Light/ MSR Twin Sisters "double mid" design is a brilliant concept and great in the wind. Skurka took one to Iceland, which says a lot. But you've still got the mid problem of poles in the living space and awkward vestibules, so it's not an efficient footprint and doesn't play well with bug nets. I played around with dimensions that would move the poles farther apart and give a better living space but it doesn't work - it's a concept with its own inexorable logic.
The TT Protrail is a decent effort, but not really designed for wind, with it's rather odd blunt-nosed vestibule and unsupported side panels. I'm not really a fan of the all-in-one single wall solutions - I prefer a tarp so you can vary the pitch and choose a groundsheet, bivy or nest to match the conditions. The double wall concept of the X-Mid scores well here.
And finally, Kifaru nearly get it right with their ParaTarp and SuperTarp. The wind performance is there, and I like the radical simplicity of the design. But the dimensions are very odd - the ParaTarp is is so small you have to sleep on one side of the poles, and the SuperTarp is HUGE. They have mucked up the detachable vestibule IMHO, and they use a horribly saggy form of nylon. With the new silpolys, we really shouldn't have to put up with this kind of thing:
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