Subscribe Contribute Advertise Facebook Twitter Instagram Forums Newsletter
Tunnel Tents Tutorial and State of the Market Report - Part 2: Details and Commercial Models
Display Avatars Sort By:
Derek Goffin
(Derekoak)

Locale: North of England
"Tunnel Tents Tutorial and State of the Market Report - Part 2: Details and Commercial Models " on 04/23/2012 04:33:11 MDT Print View

As no-one else is saying it I feel I must. Josh if as a small manufacturer you made money out of playing games with the enthusiasm of your potential clients, deceiving them. I hope it was a lot or it will not have been worth it

Stuart Murphy
(stu_m) - MLife
Snide comments on 04/23/2012 05:31:41 MDT Print View

I don't thing Josh is contributing anything useful to this particular thread through what appears to be making ambiguous and disparaging comments about Roger.

Josh, if you have a point to make come out and say it.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: "Tunnel Tents Tutorial and State of the Market Report - Part 2: Details and Commercial Models " on 04/23/2012 06:42:00 MDT Print View

Hi all,
I was examining some of the engineering stuff with tunnel tents (not my usual forte.)
One of the things that seems to jump out at me is the loading on the poles.

As Roger said, the loading needs to be symetrical around the poles. In one section he wrote that the failure modes usually occured on the sides of the tent, though. And I agree that sleeves are inherantly stronger than clips for this reason.

I would submit that a tapered pole may better withstand this pressure. With Rogers poles he simply uses the same diameter arrow shafts. The taper could be approximated using two different diameter poles. One smaller size for the top 33-50% of the curve. It has low live wind loads and static loads from materials. The sides need more strength to support averything above it and takes up the brunt of the wind.

I noticed that the pole connections could be interlocked much as they are in fishing rods where curves are quite important to the perfrmance of a flyfishing rod. In a flyfishing rod, maintaing a fairly smooth arc between the butt and tip results in the best transferance of casting energy to the line hence quite a bit of effort has been expended in pole design, and joint function wich can be reused to our benefit. From the perspective of a tunnel tent (with no snow/ice load, of course.) it appers that the actual static stress on the hoop is almost all tension (Well...aproaching infinity as the angle goes to 180" with the wind) as we go to the top. Only as the tent deforms under wind loads does it pick up any other stresses. A stiffer pole on the sides should mostly prevent that... By guess and by gosh, it looks like about 1/2" at the bottom to about 3/16" at the top (given the changing slope.)

Sort'a thinking out loud...

Anyway, I would suggest you contact a couple rod manufacturors and see if such a pole is possible, and the cost of placing joints every 12-15" around the perimiter. Probably a bit lighter anyway. And, it would do away with internal guys, simplifying things, even if there was no weight savings.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: "Tunnel Tents Tutorial and State of the Market Report - Part 2: Details and Commercial Models " on 04/23/2012 16:16:27 MDT Print View

Hi James

With all respect, I think you may be over-analysing this one. My reason for saying so is that the loading on the poles varies a huge amount, depending on the weather and how the guys are set. There is no single situation.

Strong sideways wind: high sideways loading from the fabric to the poles, but properly set guys take a lot of this load. However, if the tent moves, then there is a fair bit of variation in stress at the top of the poles.

Snow loading: high sideways loading, but in the opposite direction, bulging the poles outwards and taking stress off the middle section. Here you need the horizontal internal guys.

> it appears that the actual static stress on the hoop is almost all tension
Not so. There will be high stress on the outer part of the pole, but there will be roughly equal (matching) compression on the inner part of the pole. 'Outer' means on the outside of the curve, 'inner' means on the inside of the curve. However, if you look at the failure modes of wrapped poles and pultruded poles, you find different things. Here the structure of the pole itself comes into play.

Pultruded poles split full length when bent. This is because the plastic or epoxy holding all the fibres together fails down the middle. It is actually quite weak. But it means that the compressive forces are very significant, and this translates into a high shear force on the epoxy.

Wrapped poles fail with an abrupt break at right angles, when the fibres on the very outer face fail in tension. The shear forces are handled by the 2D wrapping.

I have had poles fail at the top of the arch and half way down the sides. Yes, both positions - but under different conditions.

Hope this helps!
Cheers

Simon Gunn
(simongunn)

Locale: Sweden
Re: Tunnel Tents Tutorial and State of the Market Report - Part 2: Details and Commercial Models on 04/24/2012 02:12:48 MDT Print View

Enjoying the articles Roger, looking forward to part three as I have been procrastinating about which tunnel tent for some.

A couple of points which may need to be checked:

* I think you may have included the pegs in the weight of the Nallo 2. 2.3kg should be with all the bells and whistles.

* I haven’t been able to see the Macpac Olympus model first hand like the Hilleberg’s. But from what I have seen on the web the latest model’s dimensions don’t match what you have listed. It looks wider (1350mm) and has a sloped inner at the rear which would (I expect) cut down on the usable space from the full 2200mm groundsheet length. Are you refering to an older Olympus model or are their web descriptions off?

You seem a bit sceptical of the larger tunnel designs (which are on my shopping list). Do you have any specific reasons as to why? I had noticed that the pole span of a Hilleberg Keron 4, Nallo 4 and Kaitum 3 is quite different to a Keron 3 or Nallo 2. The bigger tents are larger but don’t have the same near vertical walls of the smaller tents as the pole has a flatter curve more like a ‘pop-up’. I had seen that useable space might be less per person in these larger models but hadn’t thought that would affect performance. Any thoughts?

Roman Vazhnov
(joarr) - MLife

Locale: Russia
Helsport 3-person model on 04/24/2012 06:42:36 MDT Print View

Just for the record - there is new interesting 3-person Helsport model for 2012:
Helsport Fjellheimen Superlight 3 Camp

Jason Elsworth
(jephoto) - M

Locale: New Zealand
Anjan on 04/24/2012 15:50:29 MDT Print View

Thanks Roman. Hilleberg now have a video on the Anjan http://www.hilleberg.com/home/products/anjan/anjan3.php.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Tunnel Tents Tutorial and State of the Market Report - Part 2: Details and Commercial Models on 04/24/2012 16:27:45 MDT Print View

Hi Simon

Nallo wt: the weight of the fabric always varies, and that makes the tent wt vary. Happens to everyone, and well-known. Listed wt is without stakes.

Olympus Sitting Space: yes, typo, being fixed. It should be 200x110. The width shown is an approximation overall. The widest bit is more like 120 cm, but the ends are narrower. Let's just say the sitting space is quite adequate for two. The 135 cm is across pole feet, which is of course even wider.

Larger tunnels - probably OK in many cases. The problem is how do you get increased width without either a) increased height, or b) a flat top, or c) sloping sides. So imho the 2-man size is about optimal for stability. But if you really need a 3-man tent, then look at the Hilleberg ones. You might note however that Macpac, who REALLY do know tunnel tents and extreme weather, don't make a 3-man Olympus.

What to buy? That *really* depends on what sort of use you are planning.

Cheers
Roger Caffin

Edited by rcaffin on 04/24/2012 16:50:39 MDT.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Helsport 3-person model on 04/24/2012 16:55:29 MDT Print View

Hi Roman

I would have loved to have included the Helsport Rondane Light, but they were not interested in the USA market.

Cheers

J C
(Joomy) - M
Pre-curved carbon poles? on 05/02/2012 00:59:25 MDT Print View

Fibraplex have recently listed new pole designs, one of which is for the Hilleberg Soulo, which is advertised as having a pre-curved middle short pole. Now maybe they are using some sort of Aluminium join as you do, but it doesn't sound that way.

I've never understood why you couldn't make a CF pole around a curved metal mandrel of constant radius. You would still be able to slide the forming mandrel out.

http://www.fibraplex.com/tentpoles2B.asp

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Pre-curved carbon poles? on 05/02/2012 04:00:52 MDT Print View

Hi Jeremy

They may be using an aluminium centre section with lots of curvature.

> why you couldn't make a CF pole around a curved metal mandrel of constant radius
You could ... IF (and only IF) you could find a mandrel of absolutely CONSTANT curvature and CONSTANT cross-section - to within microns.

Cheers

Stuart Murphy
(stu_m) - MLife
Carbon on 05/02/2012 04:07:03 MDT Print View

I don't know how it's laid up etc. but from looking at bicycles it is obvious that carbon can be fashioned in all kinds of shapes including curves for forks.

The fact that nobody seems to have bothered for tent poles is probably a function of economics and market demand rather than the material/technology as such.

Is there something I'm missing here?

Cheers
Stuart

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Bent Carbon on 05/02/2012 06:23:36 MDT Print View

Yeah, you can certanly bend carbon. In fact, they could probably be made a bit lighter with a known finished radius in mind. Mostly, the material will shrink slightly when curing. This would eliminate some of the internal compression that contributes to the failure mode. So, really, the only problem would be extracting the mandrel evenly at the end...perhaps with some rollers. It might be easier to simply use a slightly larger form of heavy wax, then melting it out when you were done with the preliminary curing. Several methodes that could be used that I can think of, so, yeah, the reason it is not done must be economic.

Rakesh Malik
(Tamerlin)

Locale: Cascadia
Re: Carbon on 05/02/2012 08:35:04 MDT Print View

"I don't know how it's laid up etc. but from looking at bicycles it is obvious that carbon can be fashioned in all kinds of shapes including curves for forks. "

I had the same thought while reading this thread, because my road bike has a carbon fiber monocoque body.

It's probably economics. Carbon fiber bike frames are quite a bit more expensive than steel and aluminum, and even titanium frames, and I'm sure that manufacturing cost accounts for a significant part of the difference.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Carbon on 05/02/2012 16:14:30 MDT Print View

Curved parts of bicycle frames and especially forks - given their price, I think a lost-wax process is likely. OK - a lost wax process is the only way I can possibly imagine!
Any parts which are straight and tapered can be done on a steel mandrel of course.

Cheers

J C
(Joomy) - M
Mandrel materials on 05/02/2012 20:08:04 MDT Print View

I can think of a few different ways you could remove a curved mandrel. Wax or polymer that you could melt out as suggested already; some sort of inflatable tube; a material that has a sufficiently different coefficient of thermal expansion from carbon, (perhaps aluminium?) that could be heated and then cooled (or just cooled). Basically anything that can be made even just a little bit smaller so it'll slide out.

The more I think about it the more I think an inflatable bladder would work well. At high enough pressure it would be solid enough to form around and then you could just deflate it and remove it.

Edited by Joomy on 05/02/2012 22:46:50 MDT.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Mandrel materials on 05/03/2012 04:25:34 MDT Print View

Hi Jeremy

> I think an inflatable bladder would work well
Well, yes, but what do you make the bladder out of, so it does not burst and it holds its size at the very high pressures needed? Sounds a bit like Unobtanium to me, but I am very open to suggestions.

Chilling aluminium down to -40 C might work. Wonder what that does to the CF and the plastic or epoxy?

Cheers

Tim Hawthorne
(tim_hawthorne) - M

Locale: Southwest
Tunnel tent survey and tutorial mini-reviews on 05/04/2012 16:50:17 MDT Print View

The author expresses concern about the Stephenson Tent having only one rear stake. We have two tents, 2R for high cold climbs and the 2X for light backpacks. Both have side window ventilation. The 2X weighs just over 2 lbs.

Our Stephenson Tents have been used more than a hundred times over the past 30 years on many of the highest mountains and never had a pullout of the rear stake. It is a case of using the right stake for the job. Even with two stakes, if one comes out a tent will not be stable.



Normally, we use an eight inch tubular aluminum stake. It holds well in everything but rock and snow. On high altitiude climbs in snow, we often use an ice axe. On Aconcagua we used nothing but large rocks (over 70 lbs.) for the entire two week trip. We have experieinced winds up to 85 mph and snow storms up to 6 inches in our Stephenson tents without difficulties.



During many base camp discussions, others have expressed that they had heard that the Stephenson does not have enough guy-outs, stake down points, it doesn't offer enough ventilation, etc. All these comments have seemingly come from those who have never used a Stephenson tent.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Tunnel tent survey and tutorial mini-reviews on 05/04/2012 20:08:56 MDT Print View

Hi Tim

Your comments are welcome. Yes, 70 lb rocks and ice axes are a bit beyond what I was using for the rear stake, and yes, they would work fine.

I remain concerned about the quality of the sewing, as illustrated, the lack of any real vestibule for cooking and gear, and what was for us a distinct lack of 'living space'. The last is of course a personal preference.

Cheers

Tim Hawthorne
(tim_hawthorne) - M

Locale: Southwest
Stephenson Warmlite Tent on 05/04/2012 21:49:15 MDT Print View

Clearly you have a good understanding of tents. I hope no one takes my comments as critism of other tents discussed in the article. I can only speak of tents that I have used.

I was concerned about the sewing of the Stephenson tent as well when I first bought my 2R which was in the 70s. I have always tried my best to treat ultralight weight gear with great caution, and I never have had any seam failures with either tent in more than 30 years of hard use. My son also uses a 2X with no seam problems.

Regarding, a vestibule, we were always able to cook in the front part of the tent that Stephenson refers to as an attached vestibule. When weather was better, we cooked just outside the entrance or with the door clipped open. On miserable nights we risked cooking inside with the door closed. Cooking inside is always a risk. People have lost their tent in seconds due to fire. Check out the Wilcox disaster on Denali in 1967.

Room is another issue. The square footages of floor area for the Stephenson tents are higher than most tents on the market. We often slept three in the 2R when weight was a major issue (about 1 lb. per person). The 2X tends to get damper on the inside due to condensation than the double layer 2R so we always limited it to one or two people so we did not touch the sides.

The 2X tent is a bit lighter than the 2R because it does not have the liner. Also,on the 2X I use the smaller 3/8" main pole instead of the 5/8 " pole (saves about 3 oz.), a shorter version of the tent (saves a couple more oz), 2 titanium stakes in front and one 8" in the rear (another oz), and no stuff sack (two more oz). All in all for a tent that is so light and can withstand severe weather, I really like the Stephenson.