A Simpleton's Differential Cut UQ*

[MacEntyre]

Pick any 2.

WV asked for perfection... that requires all three!

[WV]

Actually, I'm willing to dispense with "inexpensive" for the time being, but I don't think we've achieved the other two yet in a form that works over a very wide temperature range. Besides, for me "perfect" must include "no fiddle-factor".

[Shotgunred]

Simpleton? Pffft, ya right! Most excellent write up, thanks for sharing.

[MacEntyre]

Actually, I'm willing to dispense with "inexpensive" for the time being, but I don't think we've achieved the other two yet in a form that works over a very wide temperature range. Besides, for me "perfect" must include "no fiddle-factor".

I submit the Snugfit... the original differential cut UQ, if I am not mistaken.

It's got no fiddle factor... just hang it and get in.
It works over a wide temp range... I've used one from 50*F to below 0*F
It's not available, so it is infinitely expensive.

[gargoyle]

Good bump.
Grizz, a few q's.
You stated you used sil as the inner layer..
How does that perform as far as condensation is concerned.
This thread is obviously from the archives ('08) and sil has been, as of late, a no-no for breathabilty and condensation.
What say you?

[GrizzlyAdams]

Fun to get a bump! Been a long time since I wrote so much in a posting.

...
This is all most interesting. Why do you think there is CBS in the first place? I recall seeing a low-angle side photo of someone lying in a bridge hammock. and noting that the occupant's butt was clearly lower than the rest of him, so fabric stretch clearly creates a partial banana posture which would tend to make an insulating layer thinner in that crucial area. I submit that it's not just the outer shell of the underquilt that warps in two directions. The inner shell needs to be 3D, too. Griz, is that what you were referring to when you speculated about the cause of CBS not being just a need for more insulation - rather a change in the volume it's contained in as well?

yep.

Somebody should figure out a way to measure the pressures that various parts of the body exert on a hammock's fabric, notably heels, shoulders, head, and butt. Then calculate the variable densities of insulating materials or shape of containments thereof needed to compensate. I doubt that I would have the mental stamina to read such equations if they existed, so thank heavens for the experimental method of our finer researchers, who juggle materials (thanks, Shug) in search of uniform bodily warmth and comfort.
What is the perfect hammock insulating system?

I think it is possible to overthink these things, and you and me are just the kind of guys who do!

So I'm reminded of some work I did early on in the DIY bridge hammock explosion of posts working with a model to craft a suspension curve to the particulars of a person's weight distribution. You get to the foundational specifics of what's going on in a suspension bridge, go after the assumptions of uniform weight load, tinker with the equations to allow for heterogeneous weight distribution, and voila! A personalized suspension curve. I even made a couple of hammocks using that...but as far as I could tell it didn't matter

So, you're right, even with a bridge hammock it would be better to do a little tucking on the inner body so that in the region of the butt there is a little more space when the body is cinched up. I haven't taken that one on yet.

Good bump.
Grizz, a few q's.
You stated you used sil as the inner layer..
How does that perform as far as condensation is concerned.
This thread is obviously from the archives ('08) and sil has been, as of late, a no-no for breathabilty and condensation.
What say you?

So on the inner layer being sil...my next UQ after that was a bit lighter for summer as well as the warmer ends of spring and fall, and I used Cuben for the inner layer of that one (mom-90 for the outer layer). All the hanging I've down in my bridges for the last couple of years have been with non-breathable inner layer under-quilts. My motive for these has been to limit the possibility of moisture getting into the down, doesn't belong there if it can be helped, particularly if I have a weather cover as well (and I have one of those in Cuben as well, with venting on the bottom.)

In all this I've not experienced any problems with condensation that I've notices. Perhaps the fact that there's a layer of wicking nylon between me and the UQ helps. Perhaps the fact that what I wear to bed wicks also helps. I dunno, the way I do things, it's not been a problem.

As it happens I'm in the midst of making another UQ, this too has a non-breathable inner layer. Perhaps there's a "Grizz makes an UQ" video in the offing....

[MacEntyre]

All the hanging I've down in my bridges for the last couple of years have been with non-breathable inner layer under-quilts. My motive for these has been to limit the possibility of moisture getting into the down, doesn't belong there if it can be helped, particularly if I have a weather cover as well (and I have one of those in Cuben as well, with venting on the bottom.)

That's a good approach, I'm sure. On cold hangs last winter I used highly breathable fabrics, for the same reason: to keep condensation out of the down. I was amazed at how well it worked. So, I've become an insulation schizophrenic, alternately using non-breathable and breathable layers. What got my attention was the realization that there is a huge humidity differential between my skin at 85*F and the outside at -15*F. I think some of us don't make much condensation, or it goes up or out or somewhere, while others find a puddle of water in the morning.

- MacEntyre, up at 0430, tough to stay on-topic

[JerryW]

I think some of us don't make much condensation, or it goes up or out or somewhere, while others find a puddle of water in the morning.

I think that is the key statement right there! Some folks can get away with using a non-breathable inner layer and others can't. Individual experimentation needed.

Everyone is different, just like being a cold or warm sleeper.


Jerry

[Catavarie]

Perhaps there's a "Grizz makes an UQ" video in the offing....

Ooh, I'll get soda and popcorn ready. I always enjoy your gear making videos.

[gt7599a]

Grizz, thanks for the walkthrough. I'm part way through building my own and I've taken the liberty of creating a calculations page on Meteor's google doc page to ease the process for anyone else.

Users can enter their desired specifications (finished length, head width, foot width, # of baffles, baffle height & fill power) and it'll spit out a basic parts order list (yrd of cloth, oz of down, baffle material are), and measurements to cut. It also lists metric units for our non-american friends.

Feel free to add things I've forgot/haven't realized I need. (Line locks, shock cord...)

DIY Bridge Hammock Trapezoidal Underquilt Calculations Spreadsheet

-Ed