Possible light weight botton insulaton

[barchetta]

I'm considering making something and i'm wondering if anyone can tell me if i'm wasting my time.

So i want to take some fabric (i'm thinking heavier and water proof) and make an under cover for my hammock. If my hammock is 60 inches wide i'm thinking about going 70-80 wide for my under cover. I'll attach it with mitten hooks to my ridgeline and have drawstring channels on both ends. I was thinking about having 4 velcro strips along both sides of the hammock for attaching to the sides. This would create a nice pocket of air under the hammock.

My thinking is that i'll end up with something sort of like the Clark Hammocks have where there is an air gap on the bottom of the hammock to trap in body heat.

Will this be worth my time or am I just wasting time and material?

Thanks for any help/advice,
John

[Boston]

It'll keep you warmer, but not warm, if that makes sense.

A large pocket of air still allows for convective currents, which is the primary source of heat loss in a hammock. How warm it keeps you will depend on how much heat you generate, and how quickly it can be removed from the pocket.

What temp are you trying to use this type of system to keep warm in?

[barchetta]

It'll keep you warmer, but not warm, if that makes sense.

A large pocket of air still allows for convective currents, which is the primary source of heat loss in a hammock. How warm it keeps you will depend on how much heat you generate, and how quickly it can be removed from the pocket.

What temp are you trying to use this type of system to keep warm in?

Well i think that the Clark Jungle claiming you can get down to 32F is pretty much BS.

That being said i would think that i could get down to whatever they are good for plus a little because of the heavier material. Didn't really have a certain temp in mind, just trying to make my hammocking a little more comfy and lighter at the same time.

[OutandBack]

A summer 3/4 down UQ = ?? in weight
Heavy material 60" wide x ? long, clips, velcro = ?? in weight

It really doesn't sound very light. I would be cold at 65F
IMO dead air space to conserve heat is highly overrated, YMMV

[Boston]

A summer 3/4 down UQ = ?? in weight
Heavy material 60" wide x ? long, clips, velcro = ?? in weight

It really doesn't sound very light. I would be cold at 65F
IMO dead air space to conserve heat is highly overrated, YMMV

For the record, the only way you stay warm is "dead air space". That's what down, primaloft, climashield, fiberglass, fleece, etc..all create. Because air is a GREAT thermal insulator. In engineering terms it has very small thermal conductivity.

However, the convection coefficient is very high. If you have air that can move, it will pull heat from a surface. The purpose of insulation is to make TINY TINY pockets if air, that can't create convective currents within them.

I think I remember that the efficiency of heat transfer for convection vs conduction is in the order of 100:1. It's a huge difference.

The problem with what you're proposing is that with-in your pocket, you'll still allow a convective current to develop. And the greater the temperature difference between you and the outside air, the stronger that convective current will be.

I wouldn't trust it to get me lower than 65* or so, if that. I believe Clarks claim of 32*F is with the pockets filled with something to insulate you, not just an air space.

[barchetta]

For the record, the only way you stay warm is "dead air space". That's what down, primaloft, climashield, fiberglass, fleece, etc..all create. Because air is a GREAT thermal insulator. In engineering terms it has very small thermal conductivity.

However, the convection coefficient is very high. If you have air that can move, it will pull heat from a surface. The purpose of insulation is to make TINY TINY pockets if air, that can't create convective currents within them.

I think I remember that the efficiency of heat transfer for convection vs conduction is in the order of 100:1. It's a huge difference.

The problem with what you're proposing is that with-in your pocket, you'll still allow a convective current to develop. And the greater the temperature difference between you and the outside air, the stronger that convective current will be.

I wouldn't trust it to get me lower than 65* or so, if that. I believe Clarks claim of 32*F is with the pockets filled with something to insulate you, not just an air space.

That makes a lot of sense, especially about the Clarks.

Thanks for the info. I'll save the material for another project.

[FLRider]

Above 50* F, I use a poncho with a crumpled-up space blanket in it as under insulation. The space blanket does nothing more'n keep breezes from moving through the undercover, but that alone adds an additional ~10* F to my comfort zone. The poncho has the same width as the hammock, with shock cord at both ends to help close it up.

Total extra carried weight for this over my normal rain gear? 3 oz. It also acts as a weather shield for blowing rain, allowing me to use a tiny asym tarp.

I would rate this for a normal person's comfort (I'm an human space heater) down to ~55* F. I'm comfy at 50*, and I've survived 41* (wearing nothing but a pair of boxer shorts and using a poncho liner as a top quilt).

Note, though, that if you're in an high-humidity area (as I was on my FHT thru), you may feel a little colder than otherwise. This isn't breathable at all, and condensation (or sweat) won't pass through, making for a damp night under such conditions.

So, yes, it's doable, but isn't suitable for real cold. Summertime (or ten months out of the year in FL), it works.