Bivy-Tent Idea

[Casey Cardwell]

Last night I made my first bivy. It was really basic, but I really enjoyed sleeping in it. It even snowed on me for a few hours and I stayed warm with only minor condensation. But I wanted to go a little bigger and fancier, so I came up with this idea.

I figured I would put a little roll-away "door" to completely seal the opening if wind was an issue. Any thoughts?

P.S. I freakin' love Goodle SketchUp. What fun!

[Peter McDonough]

Looks like it would be difficult to get into….especially in a rainstorm.

[Casey Cardwell]

>>Looks like it would be difficult to get into….especially in a rainstorm.

Yeah, the opening is short, but it's the same as what I made for the other one and it wasn't too bad. It's a little bit of squirming. How do you get into a bivy in the rain anyway? Aren't you getting wet no matter what if you don't have a tarp?

[todd]

Casey,

I don't know if I could sleep w/the top that close to my face, but your creativity is impressive!

I bet between you & the other minds here you'll have a working model soon!

Todd

[Steven Evans]

Re: Difficult entry.
I find my bivy quite tough to get into smoothly. It requires a snake like movement in order to keep things in place. I think the idea has potential, and would like to see it progress. Very interesting!

[Roger Caffin]

> I figured I would put a little roll-away "door" to completely seal the opening if wind was an issue. Any thoughts?
Condensation nightmare.

[Casey Cardwell]

Aren't bivy's condensation nightmares by design? They're completely closed, there's no airflow, you're constantly breathing moisture into it, and there's a high temperature difference b/w the inside and outside.

The only thing I can think of doing to help the problem (besides the little door and vestibule by the head, is maybe adding a vent above the face (and maybe one behind the head for a pathway for air…?). But that adds a bit more complexity. Would it help? Is it worth it?

Here are a couple pictures of a more ventilated option:

[george carr]

It seems that your bivy is becoming more of a tarptent as it evolves! How do you envision supporting the "tarp" section of the shelter. You've got a great idea, Casey, just needs easier access. Maybe some sort of velcro flap that overlaps near the ridgeline.

Just out of curiosity, if you remove the condensation from breathing from a bivy, how much would still accumulate from body heat, insensible perspiration, etc. I realize that different conditions will affect the answer, but generally what would be the outcome?

[Frank Deland]

Re difficult entry: I put my sleeping bag into the bivy first, then I get in. The required motion is a bit like putting on a pair of pants when sitting on the ground. Using a bivy when it is cold has not created condensation problems for me other than around the breathing area as pointed out above.

[Casey Cardwell]

>>It seems that your bivy is becoming more of a tarptent as it evolves!

Aint it the truth. I'm beginning to wonder how heavy this thing is going to be.

I think I can manage the tarp support with a couple trekking poles. I'll try to do a little prototyping to really see what I'm looking at.

As for condensation due to insensible perspiration…well, you got me. As far as I know, it occurs continuously and all over. I didn't include it above because I figured it could be controlled through temperature management, and that the majority of perspiration will occur where your body is already covered (by quilt, etc). So, I don't know. Is it a slow process and much less of an issue? Or with no ventilations from torso down am I still going to be sleeping in a sauna? Lol!

Cheers!

[george carr]

>>Aint it the truth. I'm beginning to wonder how heavy this thing is going to be.<<

I'm sure with the right materials it will be much closer to a bivy than a tarptent. Figure an average UL bivy falls somewhere in the 8-10 ounce range, while a HS TT Contrail is around 24.5 ounces. If your bivy is 16 ounces or less (even a tarp/bivy combo averages that much or more) you've got the best of both worlds. Can't wait to see the prototype!

[Ron Moak]

Casey,

A few more things to consider.

1) Ultralight bivys (6-12 oz. range) are designed to be used in conjunction with a separate tarp. They will provide protection from spray, condensation and wind. The will not work by themselves in a sustained downpour.

2) Bivys that are designed to be standalone in adverse conditions, such as OR or Integral Designs, tend to be as heavy or heavier than UL tents. This is because their WB fabric is much heavier than the silnylon used in most tarps or tents.

3) Using Silnylon or Spinnaker as the top of your bivy would be a condensation nightmare. Moisture comes from many sources aside from breathing.

4) You could use something like Epic as the outer shell. It's used in both tents and bivys. It's heavier than silnylon but lighter than some other fabrics. Personally while I might us it in tents, I wouldn't use it in a bivy that needed to survive significant rain. When it wets out in a tent, it can be a little annoying but survivable. In a bivy, if it wets out it'll start soaking the bag. Also it's prone to condensation.

One question that I always ask myself several times during the design process is: What will it be like in this shelter after 18 hours of sustained winds and rain? If I can come up with a satisfactory answer then generally I'm on the right track.

Hope this helps.
Ron

[Casey Cardwell]

Ron,

Yeah, I think you're right. The more I think about this design, the more I think, why don't I just use a tarp. If it's light enough, I could see it being used for light rain, fog, and windy nights on short trips…but there you are again, why not just use a tarp.

I've got a bunch of $1 fabric, so I'll go ahead and put it together, but in the end, it may be that it's a project just for the sake of having a project.

Casey

[Franco Darioli]

Ron has already spelled it out and by no means I have the experience or knowledge to add to that. One point that stands out ,to me,is this:
One question that I always ask myself several times during the design process is: What will it be like in this shelter after 18 hours of sustained winds and rain? If I can come up with a satisfactory answer then generally I'm on the right track.

That is exactly the criterion missing from a lot of DYO projects. They are amazing in theory and in the backyard but don't work in practice.
I would go nuts after 8 hours of rain inside a bivy ( without a tarp on top) , never mind 18 hours.

From a design point of view, you need some air-flow to minimize condensation. That would mean adding some mesh in the foot area , necessitating the use of more fabric, a pole and at least one guyout point. But even with that, if using silnylon it will be a rain factory, if using Epic it will wet out and eVent is difficult to get,expensive and heavier.
In the end something of the size of a Wild Oasis or in my case (bugs) a Contrail or Lunar Solo makes more sense.
Franco

[Frank Ramos]

There is no such thing as a fabric which breathes when wet but is also waterproof, and that includes goretex and epic. (Goretex and Epic breathe when partially or fully dry, but not if covered with liquid water.) So if you spend much time in a bivy when it is raining, the foot end of your sleeping quilt/bag will be soaked with condensation. Do this several nights in succession, without a chance to sun dry the quilt/bag in the interim, and you will have a severe mildew problem with down and a lesser mildew problem with synthetics. I am speaking from experience. A bivy (without tarp) is a nice idea as an emergency piece of equipment, such as mountain climbing or desert or slickrock camping where rain is a rarity and the sun soon comes out after a rain, but it is a really bad idea for extending camping in climates where several days of rain in a row is a possibility.

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