3/4 UQ questions

[Youngblood]

There are darts on the inside shell but those particular darts are a result of compound differential curves which could have been achieved without darts on the inside shell if I had chosen to put two darts on the outside shell for every one of those darts on the inside shell. If I understand what you are asking, the inside shell is taut and smooth, like the exaggerated differential curve on the sketches I posted as opposed to a reverse differential curve. Your draft stoppers you talked about on one of your underquilts are kind of like a reverse differential curve. Reverse differential curves are good for filling in gaps and are used in the hoods of some sleeping bags.

The "negative curve" can still leave an air pocket with the SnugFit but the full width suspension system helps minimize that and it isn't very noticeable. If the suspension system doesn't pull along the center area of the underquilt, that "negative curve" will be more problematic, particularly if you lay a certain way. I used a net hammock to easily test for that for gathered end hammocks when I was testing the suspension system. When I was testing asymmetrical hammocks I just had to feel around with someone laying in the hammock and it seemed to work fine on them also.

[Youngblood]

Brandon,

When you are using loose fill insulation compared to sheet insulation there are some fundamental differences in what you can do where shaping is concerned. In some ways it is like comparing apples to oranges. They are both fruits... but you can't make orange juice with apples and you can't make apple sauce with oranges.

[hangnout]

ever notice the "negative curve" in a loaded hammock, basically under the knees, the hammock fabric tends to curve upward from the horizontal plane rather than downward like everywhere else. seems like it can curve upward by a couple inches, and can extend quite a ways up toward the suspension. does the snug fit still leave an air pocket under that spot or does it loft inward to fill the void? i felt like this was always the hardest spot to fit the uq to.

Don't you think this is the advantage to the 1/2 UQ? I think it is very easy to get a 1/2 UQ to fit without air pockets and let the pad take care of the legs. Wonder when someone will start selling them?

[warbonnetguy]

Don't you think this is the advantage to the 1/2 UQ? I think it is very easy to get a 1/2 UQ to fit without air pockets and let the pad take care of the legs. Wonder when someone will start selling them?

yes, that along with overall reduced weight (even with a sit pad).

[warbonnetguy]

Brandon,

When you are using loose fill insulation compared to sheet insulation there are some fundamental differences in what you can do where shaping is concerned. In some ways it is like comparing apples to oranges. They are both fruits... but you can't make orange juice with apples and you can't make apple sauce with oranges.

oh, i'm sure, i'm looking forward to making the down version.

[warbonnetguy]

When I was testing asymmetrical hammocks I just had to feel around with someone laying in the hammock and it seemed to work fine on them also.

tell me about it, my fiancee is getting so tired of being my test subject.

[Youngblood]

Don't you think this is the advantage to the 1/2 UQ? I think it is very easy to get a 1/2 UQ to fit without air pockets and let the pad take care of the legs. Wonder when someone will start selling them?

There are all kinds of combinations available to help stay warm over a variety of conditions and it is wise to consider all of those. I have used 3/4 ccf pads in a SPE and used the 10x20 inch pad that I use in my GoLite Breeze backpack in the footpocket on my sleeping bag. That is a very light, inexpensive, and flexible setup for moderate conditions.

Using ccf pads with breathable underquilts extends the range of breathable underquilts dramatically. The ccf pad is also a vapor barrier. A vapor barrier by itself extends the range of a breathable underquilt so you get quite a 'push' when you add a ccf pad that brings its on insulation to the mix along with its vapor barrier.

There are a lot of variables with all of this-- cost, weight, bulk, flexibility, comfort, reliability, easy of setup, durability etc.

[Take-a-knee]

You guys have convinced me to shorten my JRB Nest. I plan to remove two baffles from the slit end. That way, I can tighten up the UQ by moving the velcro if need be without leaving the hammock. I will also be able to mate half of the hennessy slit velcro with the Nest installed. I can use the down from the two baffles to overstuff the torso section. It'll be warmer and weigh less.

[Schneiderlein]

There is some magic to differential shaping for an underquilt application. When you talk about differential shaping on a curve, or radius, you can have several classes of differential shaping. Most of us are familiar with an exact differential on a radius as shown in the first attached sketch. But there are some interesting properties one can obtain with various types of differential shaping. I have tried to demonstrate some of those that I could define in the second sketch. The SnugFit uses exaggerated differential shaping to allow it to be held snug against the underside of a hammock with minimum sensitivity to compression caused by that contact. That differential shaping is achieved fundamentally by curved baffles along the length of the underquilt and by radially spacing them along the width of the underquilt. To better fit in the crucial tush area and to get more uniform insulation, there are compound curves along both the length and the width as well as variable thickness in the baffles. All this calls for darts to make all that fit together. It gets rather complicated, but that is the general jest of the shaping.

Of course shaping is just part of it, because you still need to hold it up against the bottom of the hammock along as much of the surface as you can. That is where the full width suspension system comes into play.

Thanks, Youngblood. The idea of exaggerated differential shaping as you call it had not occurred to me. I will try that.

The problem of designing darts in a quilt to give it a certain shape is extremely complex, and I cannot quite wrap my head around it.

I now have this crazy idea that I want to make a 3/4 length underquilt with exaggerated differential shaping and varying width so I would have 45" of width in the torso section and 24" at the foot and head end. I was thinking I could use six fabric panels that are shaped roughly like an elongated old west coffin to accomplish that.

But trying to imagine the shape of the quilt makes my head explode. Anyway, I'm off to New Mexico to do something easier for the rest of the week, rocket science.

[warbonnetguy]

darts aren't so hard to understand. basically if the shells are different sizes, they will not fit together, there will be extra length on the larger one. the darts make it so the edge of the larger shell will fit onto the edge of the smaller one, they take up the slack.