Good looking work there, WRR!
Originally Posted by WetRivrRat
I'm actually shooting for the complete opposite of this theory - I've fiddled with the HHSS enough now to notice that it's built in such a manor that it actually becomes load bearing under my weight (210#) in my ExUL. So, I've actually had to take the template shown above apart and add several inches of fabric to address this issue.
It would seem to me that the ideal in this scenario would to be to actually have an air void, as the presence of the non-breathable fabric would create a vapor barrier. Also, giving it an air void would allow the condensation to occur on the inner layer of the outer barrier. Furthermore, it seems to me that having the air void would help to insulate any sort of UQ that is in place.
Maybe this is ignorance, and it should actually be tightly fitted, but it just seems too 'right' to have a void. Mainly if for just the simple factor that nearly all insulation is rated based on it's ability to maintain resistance to heat transfer. While in general, 'air' isn't the greatest insulator, at least when trapped between two layers of a container it would absorb certain amounts of heat radiated off of a person and with one layer being non-porous it would seem to make sense that this would resist the loss of the radiant heat, thus minimizing the convective heat loss at a point of lapse that would equal the point of increase of ambient temp in the air void due to both convective/radiant heat loss. Thus, an inherit R-Value due to the trapped air void.
Again, this is totally just my understanding, and I'd like those more intelligent in these matters to chime in and help us all out.
I guess where I'm going with that is this: For some reason or another I recollect that 'air' has an R-Value of '5' per inch of thickness. That being the case, the HHSS UC with my weight produces 0 inches of thickness of trapped air, therefore providing an R-Value of '0'. Furthermore, being that it is acting as a load bearing support, I KNOW that it is against my body, so any breeze that hits it is going to effect convective cooling against the area of the UC exposed to the breeze, thereby effecting conductive cooling of my body against the area of the hammock/UC that it is exposed to. Even worse than that, is that any radiant heat is probably lost as well due to the lack of void between the 'condensation' layer.
If I alter the DIY UC to have at least one inch of void between the hammock and the wind then I cut the convective-to-conductive cooling down to a minimum, and I implement a heat transfer resistance value of 5, which only serves to enhance any R-Value provided by whatever sort of Under Quilt I choose to implement depending on the season. Plus, I also implement a void that separates my body from the condensation layer - which is always a good thing if you already sweat like a beast...
but this just may be the beer talking...
Keep in mind that even with a gap there, keeping the sil-nylon from contacting your hammock and keeping you from feeling all of the wind, it is only sil-nylon. If not backed up with some insulation, that wind can still push that sil-nylon past the gap and against your hammock, I suspect. Oh, and totally disrupting that "dead air space" built up in your UC. At least it seems to me it could. But I have never really tested it, so you test it for us!
The "load bearing" aspect helps support the HH pad, and any added insulation, holding it just barely snug against my back and butt and even legs for the most part. ( as with most UQs, there is a falling away to the left side of my legs when I lay on the diagonal. I have minimized this by using a shock cord mod to help lift in that area)
The "load bearing" or elastic tension serves to hold the HHSS pad and space blanket on top of it snug against your back, Just snug enough for no cold gaps. But not snug enough to compress the OCF pad significantly. It also serves to hold other insulation placed in the UC up against the pad, although it is enough pressure in some spots to significantly compress 800+ down. Any gaps = cold. Unless you manage to fill the gaps with puffy loft. In which case there is once again no gap.
If you have no tension or "load bearing, how are you going to keep the pad/SB ( if you are using them? ) snug against your back? The pad has a harness, but I don't think that is enough to do the job. ( not trying to discourage your plan, just thinking out loud about possible challenges )
If you have a gap allowing any condensation to not come in contact with the insulation or your back, then what is going to support the insulation in order to keep it snug against your back? Well, maybe a separate UQ suspension? I don't get any condensation using the system as designed though some folks do. The UC tension holds the pad/space blanket against my back, in theory keeping the SB warm and in theory preventing condensation against it's warm surface. ( condensation tending to occur against cold surfaces, not warm) And in theory serving as a vapor barrier to keep insensible perspiration ( vapor ) from traveling through the insulation and condensing against the cold UC. This theory has always worked perfectly for me, but not for every one.
I will be interested to see what you figure out works!