Winter tents – unsupported fabric span between poles in tunnel tents

Ah. That makes more sense.  A touch lighter than Easton’s .296″.

I’ve read some threads on arrow shafts some years ago.  Would you mind sharing specifically which you use?  Save me some time over digging through all those again.  Come to think of it, this might be a good topic for an article.

Also, apologies for the thread drift here.

Roger, as you do not make/sell tents anymore, would you consider making a set of extensive instructions (maybe as a nice PDF?) that one could buy for a DIY project? I’d buy it.
It’s not that simple.
First of all, I tend towards very technical designs (because I can) to get exactly what I want. The most technical bit for the tents are the elbows for the poles:

These are machined from 1/4″ ERW SS tubing on my CNC machine (although you could make them on a manual lathe with some care), then bent to 31 degrees in a precision tube bender I made, then they have heavy heatshrink added to the middle, then the heatshrink is trimmed square in a custom jig. Not everyone can do this.

The next problem is in the sewing. Some BPL readers are experienced MYOG fanatics (ahem), while others do not even own a sewing machine. How do you write an instruction manual to cover both extremes of that spectrum? And yes, the sewing is quite technical in places. Even an Asian tent mfr working for Easton had too many problems trying to meet my QC standards – not helped by the fact that the workers in the factory could not read English instructions! They and Easton gave up.

So I am not prepared to sell my designs at this stage. Too much hassle. All I have are the fairly detailed notes I have written for myself for when I want to make another version. However, if you think you can make the elbows and are still keen, email me direct. A few enthusiasts have. For personal use only, not for production and sale.

Cheers
roger@backpackinglight.com

Hi Rene

Ah, CF arrow shafts and tent poles. Imho, they MUST use 2D wrapped tubing rather than wrapped fabric, but I am biased. The 2D wrapped tubing is made on a machine like this:

I know of one such machine, in China. It was of course custom-built.

You can make CF arrow shafts using wrapped CF fabric, but they are nowhere near as rigid. There are quite a few small mfrs doing this. You just wrap the CF fabric around a mandrel and cook it. They are OK, but just not as good.

Now, the arrow shafts I use come from a local archery shop which bought them from the factory in China in bulk, with their own brand stamped on them. I am not sure whether they still import them. That’s not much use to you. However, I think the Victory Archery VForce 400 arrows, V6 straightness, are the same stuff. They do have the same dimensions. They say ‘made in America’, but I think that refers to the fletching, not the CF blanks. That is, ‘made in America from imported components’.

Beware of other brands! One American arrow company sells what looks the same but is really pultruded glass fibre with a single coating of carbon fibre dust on the outside, for appearances. Cheap and nasty underneath, and they split full length as soon as they are bent. Yes, I bought some …

Sad to say, this 2D wrapped stuff is not cheap. Quite painful in fact – until you are at 2,000 m in a howling sub-zero snow storm.

Cheers

I have the updated 3-P version of the OPs tent.

The Helsport Lofoten Extreme Camp

https://www.helsport.no/lofoten-x-trem-camp

I have wondered myself about adding in a midpoint pole but thought it might interfere with the way that Helsport have configured and sewn the side guy

I also wondered about replacing the main pole with one of larger diameter or to double pole. Helsport do sell a larger diameter pole to suit but recommend using a double pole.

I can’t tell you how it handles wind, so far the conditions I have used it in have been very mild with winds well below 40 knots

I have wondered about the ability of this tent to handle even a moderate snow load but have no doubts about its ability to handle winds. Would adding a centre pole have much effect on wind resistance? Assuming good  CF wands to keep the weight down a bit? CF even tho Helsport recommend not using CF poles via email, Hilleberg also give the same advice

I have very serious doubts about my ability to sew a tunnel, even a short one, despite your help Roger I cannot sew Silnylon on my sewing machine

Hi Ed

I am not sure whether adding an extra full pole to that tent would be useful. To me it looks as though the fabric span is little more than a metre in the middle, with the tapered end providing a lot of the extra space. That was going off the floor plane at the RHS of the web page. But I am not sure about that, because the floor plan does not match the coloured pic of the tent. The latter shows a much shorter tapered end and a much longer main body. Something does not match. If the middle span is much over 1 m, then an extra pole might help.

If the coloured pic is right, you could add an internal pole as I suggested earlier. OK, it goes right past the mid-guy attachment. No matter. But how you handle the pole feet could be tricky, as the other poles are effectively on the outside. You don’t want the pole feet going through the groundsheet.

I do not think adding a pole would have much effect on wind resistance end on. It would help with a side-on wind though.

So Helsport and Hilleberg don’t sell CF poles – OK, so they won’t recommend them. Buy the wrong CF tubing and you can have BIG problems. The good stuff is probably more $$ than Al tubing too. But there is absolutely no doubt that good CF tubing works extremely well.

As for sewing silnylon on a sewing machine – you need to use pins and to stretch and guide the fabric at all times.

Cheers

I’ll measure it the next time it is erected and pitched properly. Eyeball I thought it was closer to 1100/1200mm last time I used it.

Helsports photos of additional tarp use are strange; I would have thought that type of use would put a lot of extra strain on the tents poles

URGENT CORRECTION re CF Poles

I just realised WHY H&H do not recommend CF poles in place of their aluminium ones:
The required curvature is tighter than CF poles can handle! ie: they may snap.

Al poles work because they are given a preliminary static curve by the mfr. You can NOT do this with CF poles.

I did try to put CF poles into a Macpac Olympus tent at their request, to replace their aluminium ones. It was not going to work: too much curvature. You could put elbows into the CF poles, but that distorts the tent fabric. Not a good idea.

Sorry about that.

Cheers

Roger,
Re: Geodesic domes using 4+
Yes, that is what I was referring to, except some of them are just two person tents.
You called them geodesic – I called them multiple crossing poles.

Re: light-weight long/narrow ‘domes’ with crossed poles
The Wilderness Equipment Darts are one approach to a smaller geodesic:
http://wildernessequipment.com.au/products.php?Category=Tents&Subcat=Tent%20Archive

They are no longer made, and were quite heavy;  but could be made lighter.  A simpler design, with just two poles that double cross, is made by KUIU, and there is a video on their site showing a boat propulsion fan being used as a wind generator.  I was impressed, especially as there are no pole sleeves, but just clips holding the poles in place.

Re:  ‘2D wrapped’ poles.
These are marketed online as filament wound. Your posts advise use of the Victories, but I have also tested the Gold Tips, and they have more break strength. Won’t go over old ground as they are spec’d on my recent OP for a clamshell tent, and on many prior posts. Some have the impression that they are stiff and won’t bend to a small radius without overstressing for 1-2 person tents. So posted pix on BPL of them easily flexed to pole hoops. They can be readily double crossed to a geodesic frame shape, or even gothic arched with one elbow per hoop to insure that they will not break due to the flexing. But I intend to use flexible plastic elbows to further insure against breakage under under heavy wind loads. Also alloy rings made by Carbon Express (At least they make SOMETHING useful), to prevent degrading at the elbow connections.

gpi or grains per inch is a measure of arrow shaft weight. I use it because it is the industry standard and on the Gold Tips is shown right on the shaft. By setting my scale to grains, and then reweighing set to grams, oz, or whatever, no calculations are need. The MyWeigh scale is one of the low priced micro scales that do this. In the clamshell tent post, I specified the Gold Tip XT Hunter 75/95 shafts at .247 oz per running foot, for the benefit of those unfamiliar with grains. The more robust of the new Easton carbon tent poles (the ‘6.3’sold by Quest and TPT) are 12 grains per inch, and work out to about 33% heavier, which I agree is not a desirable weight penalty. For comparison purposed, the Easton 344 and 340 alloy poles run from in the 14 – 16 gpi, range, so are even heavier.

Ripstop: I was being charitable-the non ripstop ‘membrane’ will start to split with just a pinhole, which in the field could be caused by branches, thorns are any number of nature’s more prickly wonders. Richard has tested and posted here that the Rockywoods .7D and the ~1oz Sea-to-Summit 15D test initially well above the HH on market tents. Note that both are ‘mini” ripstop, which may explain why they don’t leak like the ripstops you have tested. I believe that the mini-ripstop reinforcement adds to the strength of the fabric, and limits any tearing from punctures that may occur, and Richard has made similar observations. Since they are more WP than other nylon offerings, it only makes sense to have the reinforcement.

I’m glad you to hear about your experience with nylon’s demonstrated strength in the field. It makes me more confident about building an all 7D canopy. There is some worry about how the 7D will fare in the areas around doors where gear, pets, people, etc. are constantly in contact with the material. Hence, the incremental approach mentioned earlier. The last paragraph of your post suggests that we tend to agree.

Hi Sam

Yes, that is what I was referring to, except some of them are just two person tents.
We may have to agree to disagree here. Two person ‘domes’ with just 2 poles are not geodesics in my book. More like pop-ups to me. A true geodesic is square (or even octagonal) with 4+ poles and is typically 7 – 8 foot square. When there are only 2 poles along the length, the strength is just not there in my experience.

On the Darts – again we will have to agree to disagree. The Dart2s are just pop-ups in my book. The poles are too few and too long. I do not take much notice of any mfr claims. (And Ian Maley, the original owner of WE, is well aware of my opinions too. But he had to exist in the commercial world of clumsy novices.)

2D-wrapped and filament wound – yes, the same thing I believe. The tight winding is what gives them the strength.

This illustrates the winding layers.

Gold Tip vs Victory: the problems with most arrow vendors is that they use obscure measurement unit AND they don’t mention the underlying technology. ‘Archers do not need to know …’ But the Gold Tips are I THINK also ‘filament wound’. One should ask them first, or get a broken sample for dissection.

In this photo of a broken pole you can see the layers at the right hand end of the break. (The owner ‘leaned’ on the pole by mistake.)

I have done some double-tongue tear tests on classic ripstop silnylon and the ripstop threads had zero effect. The silnylon load spreading overrode the ripstop threads completely. I find the idea that a non ripstop ‘membrane’ will start to split with just a pinhole somewhat inconceivable in silnylon. There is just no ‘membrane’ in a classic silnylon, although there IS with a PU coating. What might happen with PU-coated fabrics I am not sure. (Proper double-coated silnylon is better described as a nylon fabric reinforced sheet of silicone polymer.)

It’s all good fun! Until kids or dogs jump on it…

Cheers

OK, thread drift my fault for venturing briefly into ‘geodesic’ designs on a tunnel tent thread. It was due to my bias against tunnels for use in solo tents and the desire for more vestibule space in a solo tent that will accommodate pets and gear storage and still have space for cooking and meals when wind and/or rainstorms hit hard. Still believe that less complex geodesic designs can be built that offer more in every way than the mids, wedge-domes, A-frames, hoop & strut, tadpoles, and dare I say tunnels that haven’t changed much in decades. None of what I’ve seen under 3 lbs are anything I’d want to be caught inside during serious storms with winds like those shown in Tipi’s Walter’s video, not to mention driving rain that will polish one off if left soaked and unsheltered.

A few years ago, a group of hardy youngsters attempted a 160 mile winter trek of a N/S trail called the Cohos Trail in northern NH. They intended to take a short detour up Mount Washington along the way; but there are a number a challenging heights further north on the way to the Canadian border. Fortunately for them, the trail does cross several highways, and passes hunting camps. There was a an ex special forces guy who lived up there for over a year before the wardens were finally able to catch him. But both he and the youngsters were able to do it only by resorting to other folk’s properties for shelter. Otherwise, IMO they would have perished from hypothermia. The trekkers had tents, but nothing that would protect them from freezing rain and some of the highest winds on earth. Even for less than severe winter conditions, we need better tents.

So I’ve put a proposal out there that I’d be comfortable with, so long as there can be resort to a more protected area to pitch when things get really nasty, although it is a clamshell, not a geodesic. Will keep working on it. Meanwhile, Roger is probably right about tunnels built to a low weight and well-guyed being the best option out there. Even though his tents give me a burning desire to double-cross a pair of hoops or two in order to add more stability.

Roger, is this about a comment you made in a recent post about loving to argue about tents.

a burning desire to double-cross a pair of hoops or two in order to add more stability.
Ah, but I suspect you would be DECREASING the stability that way. You see, the poles in a tunnel are very short, going straight across the tent. If you cross them, you will inevitably be making them longer, and longer is weaker.
Apart from that, there is no real engineering reason to think that poles are any stronger for being ‘crossed’. They are NOT joined rigidly at the crossing. I suspect a lot of marketing spin here.

loving to argue about tents.
Highly likely! :)
Gear in general, in fact.

Cheers

Roger,
Was talking about the crossed poles on those geodesics/multiple crosspole tents we discussed earlier, such as:
http://www.crux.us.com/product/x2-storm

https://www.nemoequipment.com/product/chogori/

https://www.terra-nova.co.uk/tents-and-spares/all-tents/voyager-tent/

Those are just three of the many examples of such tents designed for two persons. Of course they are all quite heavy. To adapt them for BPL would involve reducing the number of poles, using carbon poles, lighter fabric, etc. If these multiple crosspole designs are less stable than basic tunnels, wonder why there are so many on the market intended for 4 season use, and why they appear so often in tent colonies in the Everest region. The use of a self-supporting cross-pole framework as the base of a tent, creates IMO a tent that is at least as stable as a tunnel, if not moreso, and more spacious inside. Even the bodies of humans and animals are designed along these lines. Were I designed like a tunnel tent, with no framework and my bones separated and held together only by large sheets of tissue, I wouldn’t be still walking around today. The challenge is to design the framework to provide the greatest strength for a weight that is acceptable to BPL fans. That’s why I included the Terra Nova tent above as it is in the 4 lb range and might be more amenable to a weight reduction to less than 3 lbs. The Terra Nova Solar 2 was also a double cross two pole 4 season tents, but with a side entry, which I like even better for access and use of space.

So yes, I guess we will have to agree to disagree on this point.  But only with greatest respect for your designs and guidance over the years.

An observation about that TerraNova Voyager design from my experience in wet snow. Don’t

That flat top surface collects a huge amount of snow and tends to flatten the tent. Luckily it wasn’t my tent, it was a loaner to see if I liked it; obviously I did not. I call the other tents hybrids and for my usage they are superior in high winds combined with heavy snow loads but they are much heavier. My old FairyDown Plateau weighs over 5 kilos. I add guylines to each point where poles cross if I expect really strong winds

Hi Sam

All very interesting. My comments for general readership:

I am not sure you could replace the Al poles with CF poles, even with the slight elbow in one of the tents. The Al poles are precurved to handle the amount of curvature needed: you can’t do that with CF tubes.

If you tried to reduce the number of poles you would end up with a classic pop-up in most cases.

As for the tent colonies at Everest Base camp etc: I think most of those are 4-man geodes. The tents sometimes used on the South Col – they last for a night or two in summer, then they die. The climbers rarely bring them back down. Even the Trekking companies use cheap 4-man domes: I have slept in some.

Are these crossed-pole designs as stable as a full tunnel? Probably not imho. No engineering reasons why they would be any better, and engineering reasons why they would be worse (longer poles). Ease of pitching suffers due to tricky longer poles too. As for the mfr claims of 4-season – well, they would, wouldn’t they? And anyone can pitch a tent in mid-winter in fine weather.

My admittedly biased opinions.

Now, to details.

Crux X2 Storm: not yet available, weighs 2.95 kg (heavy). I know Crux as a brand: they are not bad. Yes, this comes close to being a ‘geodesic’ in some ways. Lots of guy rope attachment points too. Ease of pitching is at present unknown: it may be a little difficult in high wind as you have to get most of the poles in place before the tent is stable enough to avoid breakage.

Their use of clips and broken lengths of sleeves could make the tent very hard to pitch in bad weather. You would have to steer the poles into every sleeve section right in the middle of the tent, possibly with elbows. Try doing that in a storm when verging on hypothermia. Why did they do it this way? I have NO idea.

Nemo Chogori: their claim of ‘ first big innovation in mountaineering tents in decades’ does not sit well with me! Pure marketing BS spin, that lot, which makes them very suspect imho. It is little different from quite a number of other similar tents, and at 3.8 kg rather heavy. Nothing new.

One thing I do NOT like is the use of a few external pole clips rather than proper pole sleeves. In general pole clips are used like this to cut down the cost of mfr; they subtract from stability because the poles can now wobble all over the place, and the use of clips like this makes pitching in bad weather much harder (despite their claim). The tent tends to collapse in a high wind when you have only half the clips in place, possibly damaging the poles.

I note from their drawings that you have to sardine the sleepers to get 3 people in the 3-man version: the floor space is just not that big. Roomy 2-man tent I guess. I wonder whether you can even get 3 conventional rectangular air mats on the floor?

The bit which really makes me wonder about whether there was ANY experienced technical input to the design is the provision of wide sod cloths around the vestibule but not at the windward end. That seems so utterly pointless. Unless you intend to pitch the tent with the door INTO the wind… Not a credible design.

Terra Nova Voyager: a tent for mild weather. The poles are attached to the inner tent by clips, so the bucket groundsheet will fill up with rain while you are trying to keep the inner upright and throw the fly over the top. They do state inner pitch first. I see they talk about pole sleeves on the Voyager, but the sleeves (if they exist) are still only clipped at a few points. Rather a tight fit for 2 people I think. At least they admit it is only ‘semi-geodesic’.

It does seem that when you open the door up vertical rain will fall directly on the groundsheet. If true, this could be a slight problem for your down gear.

—-
For those who have not (yet) read our tunnel tent series:
The windward end of a true tunnel tent is first pegged out very solidly, into the wind (so it can’t blow away!). Then all poles are inserted into the sleeves sewn to the fly while the tent lies flat on the ground. You CAN do this all by yourself in a howling storm (been there a few times …). Then you pull the downwind end of the tent so the whole lot pops up (bad phrase there!) in one swift move and you rapidly peg down the lee end, with tension. Done like this the tent is immediately stable if oriented into the wind. Add guy ropes to taste.

Cheers

That flat top surface collects a huge amount of snow and tends to flatten the tent.
Yeah, thought it might.

Cheers

Here are some basics on geodesic dome architecture:

Yeah, geodesics are very strong. Perhaps one of the strongest known structures. They are based on a single spherical shell, then modified or broken down into manageable straight-line components. I spent 11 years working with these structures back in my early days as a carpenter/framer. (The various companies still exist today producing domes for mostly large scale industrial storage of water sensitive chemicals. A typical road salt dome is a good example. Rather than a complete copy of a geodesic dome, one of our engineers (a Canadian) came up with combining several “triangles” of the geodesic dome architecture into a trapezoidal segments: 2 base segments and a common segment.) Highly efficient, modular (my end of things), shelters. Anything from 72′ to 150′ clear span structures much like an igloo, just bloody huge all made from 2×6 and plywood.

There is really no need for a fully enclosing ring, except at the base. It is more of an natural occurrence of the multiple triangles of the overall design. It derives strength from both tension and compression. As such, it distributes wind loading/snow loading very efficiently across the entire structure, meaning no one member actually carries the entire load. This is more of a dynamic engineering than static engineering or one of the big differences between Greek and Roman architecture. From microscopic Fullerenes (or “bucky balls”) to large scale sports domes, the more or less natural engineering still applies. They are strong. Most failures are from designs that do not incorporate enough stiffness into the overall structure, but that is another discussion.

One of the axioms is that the overall framing, without any skin (plastic, plywood, concrete, etc) is strong by itself. With a nod to gravity, upper sections are often a bit finer, or wall thickness is a bit thinner, but again, mostly for gravity.

Overall, though, I agree with Roger. Even with small 1,2,3, and 4 person tents, it becomes quite difficult to build geodesic domes. You really don’t see any weight advantage over a more traditional design until you start factoring in weight per person at about 4-6 people. There are simply too many poles. And the poles are of differing lengths making the overall construction a non-trivial task. Even the simplest “geodesic” like shape devolves into of a series of three identical poles in a “teepee” like arrangement. Obviously, I could question whether this was even a geodesic dome, though it started as one before the simplification process. (Further simplification of the structure simply gives you a single pole tetrahedron. One of the links above had the evolution of the geodesic dome in it.) Compared with a true geodesic, these are less space efficient and less strong, but a LOT lighter to carry and a LOT simpler to put up.

Entering into the discussion of Hoop Tents vs Dome tents. You are basically looking at the very top panel of a Geodesic architecture substituting tension for increased load on the supporting members. This is not technically a geodesic though. You really want the intersection of 5 poles for that. The sleeve designs allow a greater load on each pole. They are more or less continuously supported under snow loads. Increased bending pressure is transferred outward increasing tension, so there are limits… But, you loose the overall stability of dynamic or wind loading. Without extra guy lines, either will flatten much quicker than a true geodesic. It depends on the strength of the poles. The shorter lengths of the Hoop tents will probably hold up better, though. They are stronger because they have less length. Of course this does not consider the fabric used.

Anyway, a 5 pole into a equidistant hub would be a “geodesic.” Note that no perimeter is needed because you can use the floor fabric for tension. And, you relieve the requirement for having different pole lengths and a “tension/compression” hub. But, the top hub becomes a rather critical component. You would not need to stay with a geodesic, though, and, could easily transform this into a corbel with a small 6-8″ flat spot in the center.

The first real geodesic we built:

When I say ‘we’, it was actually the whole Club. 1966.

Not really what I would call ‘geodesic’ as it had only 4 poles, but going into a metal central hub as James describes, but it worked fine.

The tent at the front, pitched Wales in UK, ~1970. I made it. It endured a LOT for a number of years. It could NOT have handled the weather without the central hub.

Cheers

“Nemo Chogori: their claim of ‘ first big innovation in mountaineering tents in decades’ does not sit well with me!’

I had a look at that, I can’t work it out either.

It’s an exoskeleton integral pitch design :

but I don’t see what is new about it.

For example the Eureka Exo something or rather is like that too :

Hi Franco

In this game today (like most any other game today!), one has to develop a really good strong BS filter for the torrent of marketing spin the cretins shower upon us. So one has to dismiss at least half of whatever is written on any web page, if not more. Filtering it out is something I HOPE BPL can do for its subscribers, but it seems to be a bit of a full-time job.

I get an email from a marketing company every day or two, wanting BPL to endorse whatever crap they are currently pushing or to ‘swap’ links. I kid you not. Fortunately, the Plonk reflex is well-honed. I don’t reply. Some of them come back 6 – 8 times before they give up!

Cheers

Hi Roger & all:
Think I’ll stick to the term ‘multiple crosspole tent,’ as a small one is obviously not a geodesic, however broadly defined. The word, ‘multiple’ is there only to signify that there are two or more places where the poles cross, not just one crossing as is so common on the simplest domes.

Agree with Roger that pole sleeves are best for a number of reasons, and that would be my only choice for a multiple crosspole tent. Also agree with Edward that using hooped poles, there will be too much horizontal surface on top of a double crosspole, and that is the reason why I always use elbows so the poles form a gothic arch that produces steeper tent walls than a hoop. There is also the possibility of placing a short ridge pole between the peaks, but with only three feet between the peaks, that may be overkill.  At the risk of boring long term regulars at BPL, the mock-up I posted in 2011 is something like what I actually have in mind: https://backpackinglight.com/forums/topic/45631/

IMO, a frame such as this will present a stable surface under wind loads; something that the proprietor of Trekker Tent also expressed in his BPL posts to result from crossing poles in an X shape.  The self-supporting design adds to that, as it reduces force directed at the ground stakes.

As Roger suggested back in 2011, the challenge is how to design the double-cross with pole sleeves, not clips or other types of attachment.  (Note that the elbows on a gothic arch not only eliminate pooling overhead; but also allow shorter 6 foot poles to be inserted and attached to the elbows at the peaks, making handling and insertion of the poles much easier)

Not as arduous as searching for the Holy Grail, but it has been a long process at arriving at a solution.  The double-cross design depends on using the bias stretch of fabric to create the convex wall surfaces out of ordinary rectangular flies, so pole sleeves cannot be just sewn on, as the seam would eliminate the bias stretch. However, a zig-zag stitch would not, particularly if the pole sleeve is short, and if it is the higher denier inner, not the outer fly, to which the sleeve is being sewn.  As it happens, even with a gothic arch, the poles are more curved (parabolic) near the peaks, and are almost straight where they approach the ground, as may be visible in the photos in the 2011 post.  So the pole sleeves need to run only from the elbows at the peaks down to the pole crossings, leaving the poles unsleeved below.  I suppose clips might be nice below the crossing points, but am not sure they are worth the trouble.

As with the clamshell design recently proposed, the approach would be to sleeve the poles to the inner (as is common with US designs) so that an outer fly would be close to seamless, and could fully expand on the fabric bias to the  shape shown in the 2011 post.  However, the vestibules, needing no inner walls, would be attached directly to the inner, and would avoid the need for a large awkward fly as used on many US tents, and shown in videos posted by Roger of people chasing their tent flies over hill and dale in high winds..  As with the clamshell, the fly of course would have to lap over the vestibules considerably to insure that rain etc. does not enter  between the inner and outer.  Seems like a lot of extra fabric for the overlap, but having done the math, the weight  penalty is very little with a 7-15 D fabric.  The fly attachments at the peaks and ground corners, coupled with corded attachments running out to the vestibule stake points, would keep the fly solidly attached in high winds, IMO.  One additional advantage of the double-cross is that the greater cant of the poles compared to the clamshell creates more space under the dome.

Some will say that putting up a tent with the inner exposed to the elements will not produce a dry pitch in the rain.  However, a good DWR treatment is sufficient to protect an inner for the brief pitching time before a small fly is fully attached and tightened down.

Noted Roger’s comments about the over touting of tent designs that may in fact weaken, rather than enhance performance.  This may not be deliberate.  While Roger refers more than once to engineering, the designers may not be engineers at all, just people playing around with designs on paper or screen, and putting out what looks good, or to be accurate, getting people in Asia to put them out.  The guy from Sierra Design who haunted these forums for a while typified this.

There are so many engineering issues that come up with a tent, and all must be considered.  To take one, Roger noted that many multiple crosspole designs do not secure the poles together at the crossings.  Do the poles need to be held together tightly at the crossings, or will loosely do.  Not being an engineer, I find that music wire models provide pretty good guidance with such issues.

Roger, that is a super geodesic hut!  Nothing like that on our Cohos Trail in NH, although there was a nearby chain of yurts once, but only a few remain now and they are accessible by vehicle for maintenance, etc.  We have some pretty nice lean-tos though.

Oh, it is a great hut, and we had enormous fun building it (almost) on top of the mountain over many work parties. Had to take all sort of stuff up the mountain to it for the building:

including step ladders.

BUT – a caution for the unwary. Guess what happened the first winter when everyone on a Club snow trip all piled in?

Huge condensation from our wet gear on the UNinsulated aluminium roof! Water dripping everywhere! Some rather innovative sleeping arrangements were created, and we got the wood stove going fairly strongly too. Next summer we had to line the hut with good plywood very carefully.

Strangely enough, condensation still happens inside some tents.

Cheers

Sam, Crossing poles without interference is rather trivial for two poles. Sew one sleeve inside and one sleeve outside on the fly. The fly has two surfaces, yes? Unless the few thousands of an inch will bother your design somehow, that will work. Careful design can insure all of poles to be treated that way, provided you limit the number of poles at each intersections to two. I have not been keeping track of all your posts, maybe somebody else suggested this.

Franco, neither tent is a true geodesic, as you say. The Nemo has a largish parallelogram on the roof around the roof vent for example. This induces a lot of movement with their clips. However, with rather confining sleeves, you can actually apply the tension of the horizontal members to the fabric…there should be no compression across the horizontals. The design is actually sound but the implementation (clips) is poor allowing too much movement.

Roger, nice geodesic. Yeah, I can see condensation being pretty bad.

The theoretical weight efficiency for domes doesn’t kick in until there is a relatively large tent/structure. Basically, the larger you make it the more efficient the dome. For geodesics and small backpacking tents, there is too much weight and too much complexity for setting them up. It is similar to using a value of 1 in all the equations.
Example:
The area of a semisphere is: A = 2π square(r)
The volume of a semisphere is: V = (2/3) π cube(r)
In any approximation it is easy to see that the CUBE will grow quicker than the SQUARE. Yet the loading (strength) of any structure is approximated by the surface Area needed, not the Volume. If we substitute a unit of 1 (think 1 meter) for the radius, the powers go away.so:
A= 2π * 1= 6.28
V= 2/3π * 1 = 2.1
Doing the same calculations with a 2 (think 2 meters):
A= 2π * 4= 25.13
V= 2/3π * 8= 16.76
Doing the same calculations with a 3:
A= 2π * 9= 56.55
V= 2/3π * 27= 56.55
Or the crossover point between A and V meaning minimum weight and maximum volume occurs at right around 3 meters for domes. However, a 6 meter tent is on the very large side.

Doing the same calculation with 10 meters for radius gives us:
A= 2π * 100= 628.31
V= 2/3π * 1000 = 2094.40

Clearly, it is viable for larger structures, ie, low A means low weight in structural components making up the shell and large V means a lot of space. But, for small structures(small radius’ in the usable range,) the overall strength/loading per unit volume is too high. This is for ANY dome type.

Of course, playing with numbers can do a lot, if you use feet instead of meters, it starts looking a bit better, but domes still have large structural weight for the size till you reach about 8′ feet in diameter. Usually, there are better ways to hit lower weights for smaller sizes. Stretching a dome into a hoop tent or tunnel, for example. Using treking pole supported structures like a Duplex or Plexamid. And so on. Generally speaking, the smaller something is, the stronger it is.

James,
A pole sleeve by definition has to be wide enough to make threading poles through it an easy task. In that width, there is a lot of room for pole movement in the wind – not a good thing because in addition to being annoying, it stresses the structure, including the poles.
For what I have in mind, as outlined in my last post, there appears to be a simple solution, and that is to join the sleeves on just the inside where they come together and the poles cross. This should hold the poles snugly together. But what about the friction where they rub together? Another issue than can be readily resolved, but must be addressed.
Only raised this issue to illustrate all the details involved in hardening a tent for use in high winds etc. Just the number of differences Roger found with some of my assertions illustrates that there are a lot of not so obvious issues about which folks can reasonably disagree, yet which must be resolved in order to produce the best possible tent. As this thread shows, just adding a center pole to a tunnel can become quite a complex issue. And I’ll leave it there, as this is a thread about that, not many of the things I expressed. Enough already, unless one is a fan of severe thread drift, which believe it or not, I’m not. Like Roger, I enjoy discussing these issues, and benefit greatly from doing so, and thus get carried away some times.

A pole sleeve by definition has to be wide enough to make threading poles through it an easy task. In that width, there is a lot of room for pole movement in the wind
I agree with Sam that the pole sleeve has to be wide enough for easy insertion of the pole. From the notes I wrote for Easton when they were trying to get an Asian factory to make my tents:
The pole sleeves have a 12 mm seam allowance on each side, a 25 mm tube width on each side, and a 12 mm wrap around the tent pole. This makes the pole sleeve strip 86 mm wide.

The key point here is that the pole sleeve on my tents is either 20 mm wide or 25 mm wide. I use 20 mm and have no trouble, but I made the sleeve 25 mm wide for commercial sales. I would not use that width myself.

Now, just how much room is there for pole movement in a 20 or 25 mm sleeve?

[GR5, central France, pitching the tent]
Well, not a lot in my humble opinion. Can you see these poles moving around, even in a storm?

My 2c.
Cheers

Yes, I understand about threading a rod through a hole. But this is a LOT less movement, as Roger points out, than clip & loop arrangements. Anyway, we have had this discussion in the past, though I don’t remember which thread, offhand.

The point was that on a dome loading (especially the geodesic styles) you can skip the horizontal members (all the force of the tension component is taken up by the fabric. leaving the simplified parallelogram arrangement Franco posted for the Nemo. This also has the simultaneous effect of tensioning the fly fabric against dynamic and static loads (wind & snow loads.)

Their implementation is flawed in the sense that clips/loops allow too much movement. But a sleeve would not allow the same amount of movement. One flat sleeve inside for one pole and one flat sleeve outside for a second pole avoids the complication of crossing poles at the joints.The only place that would be trouble would be with the sewing at the crossover point. Perhaps a bit of bonding tape or glue?