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Hammock Camping Re: Oh Boy, Cold Wars II, winding up!

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  • Risk
    David, Good morning. I think you are right and wrong about wind and foam. There is no doubt that wind blowing across closed cell foam that is something like
    Message 1 of 57 , Sep 7, 2003
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      Good morning. I think you are right and wrong about wind and foam.
      There is no doubt that wind blowing across closed cell foam that is
      something like .25-.5 in thick will quickly cool your skin. However,
      the physics of the materials does not allow the air molecules in that
      wind to penetrate the foam.

      I looked into closed cell and regular latex foam rubber when I was
      building kayaks more. An engineer friend that runs one of the
      mattress production companies helped me out on the science. Closed
      cell foam is built of very many small gas filled spheres, tightly
      melted against each other. The air molecules in the foam are basicly
      stuck there and have been there since the foam was built. This is
      very different from the air cells of the foam in a mattress, most of
      which do have connection with the outside air. By the way, closed cell
      foam is much more expensive to make than foam rubber.

      My experience with thin pads is that whenever wind is blowing the skin
      on my back cools and it may even feel like the wind is coming through
      the pad... But it is not. I have proved that by creating an air
      tight chamber out of closed cell foam. Even under pressure, air does
      not get through the closed cell.

      What really happens, as I understand it, is this: If I lay directly
      on the foam, heat from my back warms the first layer bubbles in the
      foam. THis is mostly due to conduction of heat directly, but there is
      a little radiatiant heat loss as well. That layer of bubbles conducts
      and radiates heat to the next 1/16 inch or so of foam bubbles. Inside
      each bubble, there is a little convection current (an internal wind in
      the bubble) in which the warm air rises and is replaced by the cool
      air from the other side of the bubble. The structure of the rubber
      concucts heat reasonably well, but the air does not conduct heat well,
      almost all the heat that makes it across each air space is from
      convection in the bubble. This process is carried out layer after
      layer away from my body -- as long as the air outside the foam and my
      hammock is cooler than my skin.

      What is happening from the outside is that heat is lost to the
      environment. The rate at which heat is lost depends on a number of
      factors... Mostly, the air on the outer surface of the hammock, which
      has been warmed by my body, through all those layers of bubbles,
      drifts away and is replaced by colder air, which is more efficient at
      collecting more of my precious heat. If the air is blowing by the
      hammock, more heat is absorbed from the surface. In effect, the
      temperature down 1/16 in the foam and 2/16 and so on, is colder. It
      ends up being colder against my skin, and more of my heat is lost to
      that first layer of bubbles on the inside.

      If the goal is to keep body heat in, then anything which makes that
      effective distance from the outside air to the skin bigger is good.
      It is also good to make the distance full of lots of small chambers,
      instead of large chambers. (Heat travels across large chambers by
      convection almost as well as it travels across small chambers) This
      is the reason that an old fashioned air mattress (no foam inside) is a
      pretty poor insulator even if it is an inch or more thick. It is only
      one chamber thick. This is the reason that the Garlington insulator
      is improved a lot when the spaces are filled with some material which
      breaks up the space into a lot of little spaces. (newspaper,
      styrafoam peanuts, leaves, crinkled space blanket).

      Another small aside: It is important to keep that cold outside air
      from getting inbetween any layers of the insulation. If wind is
      blowing and inflates a Garlington Insulator by getting between the
      hammock and the insulator, all the effect of the insulation is
      temporarially lost. I learned this one windy snowy night when the GI
      kept getting blown downwind like a sail.

      Your idea of a tent like chamber beneath the hammock has a lot of
      merit in that it can keep cold air from blowing across the hammock.
      However, it has the problem that it can be a large volume. To be
      effective as insulation, my body will need to begin to warm the air
      inside that large bubble and the ground beneath.

      I look forward to your experiments this winter. I enjoy the give and
      take on this group. I look forward to continued discussion.


      --- In hammockcamping@yahoogroups.com, "o123david" <o123david@y...> wrote:
      > Some ideas and responses. I hope they help.
      > 1. Cold wind DOES blow through closed cell foam. I have felt it.
      > Closed cell foam is just one more form of insulation where, to the
      > extent that cold air blows into it, it loses its ability to
      > insulate. This is both my experience and what is predicted by
      > Newton's Law of Cooling.
      > In other words, closed cell foam does not protect you from more than
      > a little bit of wind.
      > 2. Thank you for pointing out a serious mistake that I made.
      > While it is true that convection results in stagnant air being less
      > that a perfect insulator, it is not true that that this prevents
      > stagnant air from providing any insulation. If obviously does. It is
      > definitely warmer in a two layer tent. Stagnant air definitely
      > provides what can be a significant amount of insulation.
      > In other words, if you have a windproof material surrounding the
      > hammock and hold it away from the hammock you will be warmer than if
      > you let the windproof material blow up against the hammock. And if
      > you connect this to a tarp above and a floor below (or just bring it
      > down to the ground) you will be warmer still. This can easily be
      > done using a diamond-shaped tarp, the two stakes already used to
      > hold the tarp down, and a cord at each end going around the bottom
      > of each tree. Condensation could be controlled with a couple of
      > vents at the bottom to let in dry cool air and a couple of vents
      > at the top to let out warm moist air, as Stephenson has done with his
      > Warmlite tents. Since this is very similar to his tents it is clear
      > that it would work. Netting protecting each vent would eliminate the
      > need for add netting over the hammock. The entrance could be through
      > the floor held up by velcro since any other design would probably
      > result in accidents and damage to the tent. It appears that this
      > would work very well with a Peapod or a thicker bag filled with down.
      > I don't like this idea because it is unnecessarily heavy and
      > complicated.
      > But it isn't that heavy and it might be a good idea.
      > I spent a lot of time while thruhiking the AT last year ('02)
      > thinking up this design. It would be nice if somebody would try it.
      > Maybe it is a mistake to include the hammock as one layer of a two
      > layer tent and it would be best to build the tent as a two layer
      > tent.
      > Whatever, if you try it, please post a message on this list so I can
      > hear about how it works (or doesn't work).
      > 3. One other idea. This would make it so you wouldn't need a separate
      > barrier to block the wind.
      > You could construct the hammock from three parallel pieces of
      > material going lengthwise. The two outer pieces of material would be
      > windproof, such as the 1.9 oz ripstop which is then silicon
      > impregnated. The inner piece would be breathable, such as uncoated
      > 1.9 oz ripstop. It would be interesting to see if this is both
      > sufficiently windproof and provides sufficient fresh air to prevent
      > condensation. --David
    • Thomas Peltier
      Looks very nice. _____ From: Chet Clocksin [mailto:cclocksin@buckeye-express.com] Sent: Friday, September 12, 2003 5:55 AM To: hammockcamping@yahoogroups.com I
      Message 57 of 57 , Sep 12, 2003
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        Looks very nice.



        From: Chet Clocksin [mailto:cclocksin@...]
        Sent: Friday, September 12, 2003 5:55 AM
        To: hammockcamping@yahoogroups.com


        I just posted another photo in "chet's home made" folder (I also deleted a few) Take a look at the last photo in the folder. A dog could be very cozy in there, and provide some additional heat. This set-up should also be a true storm proof set-up simply by closing the "doors" at the bottom.



        -----Original Message-----
        From: chcoa [mailto:jdeben@...]
        Sent: Friday, September 12, 2003 2:25 AM
        To: hammockcamping@yahoogroups.com
        Subject: Hammock Camping Oh Boy, Cold Wars II, Doggie heater

        The ground in more what I was thinking for several reasons, material
        strength, warmth, etc.. but you are right they could hang a little
        too.  My only concern with this idea is that in the night if for some
        weird reason the hammock malfunctioned and I fell on her.  I wouldn't
        want to do that of course!  ACK!

        jamie in az

        --- In hammockcamping@yahoogroups.com, "Ray Garlington"
        <rgarling@y...> wrote:

        > This is a really good idea.  An open-bottom cone could be staked to
        > the ground with a side entry hole for the dog.  He would have a
        > house separate from your sleeping quarters & he could contribute
        > heat.  Much better than tenting with a wet dog!
        > If the dog was 'hammock trained', you could have a closed-bottom
        > with a side entry for the dog.  He would then be suspended above
        > ground.

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