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  1. #1
    designer@quickdata.com's Avatar
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    Need physics lesson - bottom condensation

    So many treads I could piggyback on about this but specifically, I've read that a waterproof undercover (Silnylon) can cause condensation to form on/in the under quilt.

    My experience is that heat (warm vapor) rises. I have many experiences with frost on the TOP of my sleeping bag, inside the walls of a tent, and on the inside roof of my car when sleeping in it during one miserable "homeless" winter (I called it "adventure").

    So first - what is the temperature range I need to be concerned about? For example, is this condensation issue only a fall/winter issue within an approximate min/max temperature range?

    And within that range, does condensation really form on the bottom of an UQ that has Silnylon below it?

    At my age, taking things on/off can lead to forgetting something. Once I took a friend to the Jefferson Park Wilderness in Oregon and grabbed what I thought was a full tent. Turned out, I only had the fly and poles. But I made that into a feature instead of a bug because though not designed for it like current tents that work with just fly and poles, I was able to make a covered low arch. It kept us dry in the rain storm that night. We awoke to find small rivers of water flowing under our thermarests - but we and our bags were dry. And there was a 4 minute break in the rain. I streaked of the shelter, was able to heat exactly one cup of water to boil, add instant coffee, and hand it to my sleeping partner before the torrent began again. She learned a lot about not giving up and finding the maximum good time in a potentially bad situation. She said she will never forget the coffee.

    But I do like everything together. So I planned on keeping the HH, the UQ, and the HH undercover (for weather protection) as one unit. One FAQ said the HH undercover fits too tight for UQ use - compresses the loft. Have you found that to be true? I only see the undercover when I'm outside the hammock and then it seems to be loose enough to hold an UQ without compression. Or maybe its suspension can be adjusted?

    But then I read that because it is Silnylon I could get condensation problems - back to my original question.

    Paul

  2. #2
    designer@quickdata.com's Avatar
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    Also, I suppose I could put a barrier - thin CCF pad or thermarest between the bottom of the hammock and UC - that should shield any condensation from the UQ - right?

    All summer I was comfortable with my HH and a thermarest in the UC. Then I tried a WBBB and had a ccf in the double layer - no UC. I woke with a wet back. I thought it was some kind of convection lose as the ccf was pretty narrow. Later, I realized it could have been just sweat. I didn't think of that at first because I had never experienced it before (in the HH).

    So if condensation is an issue, would a pad between the hammock bottom and UC solve the issue? But how do I do that without sweating because of the pad barrier. Could it be I was too warm We're talking high 20's F.

    Paul

  3. #3
    DuctTape's Avatar
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    Possibly too warm, ccf is a great insulator by itself it could have made you too warm and sweating resulted. You might also be a naturally greater insensible perspirer. Or both.

  4. #4
    DuctTape's Avatar
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    But to your question about the undercover... I often will rig my poncho (not breatheable) under my hammock and don't have a problem; with UQs, pads and both. But I am also not a "sweaty sleeper" (for lack of a better term)

  5. #5
    Senior Member zukiguy's Avatar
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    Vapor Barriers

    Do a search for "vapor barrier" on the forums here. There are tons of discussions to make your head hurt even more. The gist of it is if you have something waterproof (vapor barrier) on the "warm" side of your insulation (as close to you as possible) then you'll get a minimum of condensation issues. If you have it on the "cold" side such as an underquilt protector, then you'll likely see that warm moist air radiating from your body hit the barrier and condense into a little puddle.

    I experienced the latter first hand on a trip a few years ago. I bought a brand new UQP in sil thinking I was now bulletproof and immune to the elements. The low got down into the mid 20s with a stiff breeze. I dawned most every piece of clothing I had and put the UQP over my down UQ and hopped in the sack. I woke up to a mild case of CBS and reached under my hammock to readjust the quilt. When I raked my hand inside the protector I found it to be very damp. Luckily the quilt was still pretty dry. This is when I traded out the sil model for a breathable one.

    Had I been laying on a foam pad or wearing some vapor barrier clothing I don't think this would have been an issue. Managing moisture is a little more complicated with a hammock setup but certainly doable.

  6. #6
    BillyBob58's Avatar
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    There is a current thread here some where about huge condensation inside a Spindrift sock, which is breathable! IOW, getting to the physics - vapor condenses into liquid when it reaches the dew point. The dew point can be a cold pad or a piece of breathable nylon or a car windshield or a fleece Shug style bib hanging in front of your face, or just your breath in plain air.

    And then there is sweat, a completely different deal. Overheating, maybe even in just one area of the body, = sweat.

    As to your 1st line you say:
    I've read that a waterproof undercover (Silnylon) can cause condensation to form on/in the under quilt.
    If the Sil-nylon is cold, as it will probably be if it is on the outside of your insulation, and your body vapor manages to travel down ward and hits it, you will have abundant condensation if all the conditions are right. And sometimes they will be. I have done it myself and ended up with a soaked HH OCF pad and sleeping bag both on the footend . So a suggestion is to keep all VBs- or at least the 1st VB your body vapor encounters, on the warm side of all insulation. Keep them warm. And if you over heat with too much insulation and sweat, console yourself with the idea that at least all that sweat is next to your skin rather than soaked up into your down insulation.

    What UC are you using? Are you referring to the HHSS sil-nylon UC?
    For I consider that the sufferings of this present time are not worthy to be compared with the glory that is to be revealed to us....that the creation itself also will be set free from its slavery to corruption into the freedom of the glory of the children of God. For we know that the whole creation groans and suffers the pains of childbirth together until now.
    Romans 8:18,21-22

  7. #7
    designer@quickdata.com's Avatar
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    Yes, it is the HH Silnylon UC that matches the stand up (slit) entry. I also have some 2QZQ UC's in Silnylon I haven't tried yet for a WBBB and WBRR. In the case of the WB, my UQ's will be synthetic from AHE. I'm using a Nest (JRB) for the HH Survivor.

    I am new to Hanging from spring/summer of this year. I found it so much more comfortable than the ground. But my gear was entry level HH Expedition and mild weather, no wind and little rain. I was using a ThermaRest with the HH UC instead of the ocf included with the super shelter. Worked great. No condensation because summer temps.

    I was ready to expand the temp range a bit with UQ's but the temps here just dropped to near single digits - outside the range of all but my sleeping bag.

    I usually make a snow shelter and imagined making kind of a snow wall around the hammock for wind blockage - cutting snow blocks is easy if you have a snow saw and compact the quarry first.

    I've toyed with the idea of leaving the 3/4 thermarest at home, but I just can't assume I'll always have trees. This summer, a situation came up at BlackBerry Point, BC where I had to use the hammock as a bivi bag. So I'll most likely always have some kind of pad with me.

    I was already to try things out - until it got so cold. Need to wait till it warms up to the 30's again.

    The other problem is getting the "snug" right. It would be easy if I could get someone my approximate size inside the hammock while I tinker with the suspension. I guess it is more important they are my approximate weight rather than height - or maybe anyone just to load the hammock suspension.

    I suppose I can just lie in the WB's unzipped and reach underneath with my hand to fell the fit. the HH Survivor I was using - slit opening - would be more difficult.

    I just thought that because heat rises, the vapor issues "below" would be minimal as the vapor - even that from the bottom area - would be wafting upwards rather than down to the bottom of the UC. But I can see that if I am warm on one side (my side) of the UC, then that heat is also making its way (unless stopped by a barrier; pad, etc.) to the other side of the UC where it meets the cold.

    Past experience was that it turns to a thin layer of frost that can be brushed off. The "water" issue it there - but minimal concern, especially with synthetic fill (but the Nest is down). I am not going for long "through-hike" treks - just a couple of days. So maybe a little wetness on the outside - rather than perfectly dry - is okay

  8. #8
    BillyBob58's Avatar
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    Quote Originally Posted by designer@quickdata.com View Post
    Yes, it is the HH Silnylon UC that matches the stand up (slit) entry. I also have some 2QZQ UC's in Silnylon I haven't tried yet for a WBBB and WBRR. In the case of the WB, my UQ's will be synthetic from AHE. I'm using a Nest (JRB) for the HH Survivor.

    I am new to Hanging from spring/summer of this year. I found it so much more comfortable than the ground. But my gear was entry level HH Expedition and mild weather, no wind and little rain. I was using a ThermaRest with the HH UC instead of the ocf included with the super shelter. Worked great. No condensation because summer temps.

    I was ready to expand the temp range a bit with UQ's but the temps here just dropped to near single digits - outside the range of all but my sleeping bag.

    I usually make a snow shelter and imagined making kind of a snow wall around the hammock for wind blockage - cutting snow blocks is easy if you have a snow saw and compact the quarry first.

    I've toyed with the idea of leaving the 3/4 thermarest at home, but I just can't assume I'll always have trees. This summer, a situation came up at BlackBerry Point, BC where I had to use the hammock as a bivi bag. So I'll most likely always have some kind of pad with me.

    I was already to try things out - until it got so cold. Need to wait till it warms up to the 30's again.

    The other problem is getting the "snug" right. It would be easy if I could get someone my approximate size inside the hammock while I tinker with the suspension. I guess it is more important they are my approximate weight rather than height - or maybe anyone just to load the hammock suspension.

    I suppose I can just lie in the WB's unzipped and reach underneath with my hand to fell the fit. the HH Survivor I was using - slit opening - would be more difficult.

    I just thought that because heat rises, the vapor issues "below" would be minimal as the vapor - even that from the bottom area - would be wafting upwards rather than down to the bottom of the UC. But I can see that if I am warm on one side (my side) of the UC, then that heat is also making its way (unless stopped by a barrier; pad, etc.) to the other side of the UC where it meets the cold.

    Past experience was that it turns to a thin layer of frost that can be brushed off. The "water" issue it there - but minimal concern, especially with synthetic fill (but the Nest is down). I am not going for long "through-hike" treks - just a couple of days. So maybe a little wetness on the outside - rather than perfectly dry - is okay
    Very interesting post, DQD. For one thing because you have used a Thermarest inside the HH UC, that is pretty rare. And I agree with you that it seems that most vapor would drift upwards, but still enogh folks have had enough condensation down below that it is def something to be watched out for.

    Have you ever tried your HH OCF pad with a space blanket on top? And with some of your extra fleece or puffy insulation - either what ever extra you might have that you are not going to sleep in or extra you have brought along just to be put in the UC or a combination of the two? This can do wonders. You probably already know that one person here, kwpapke, used such an approach to be warm and dry at minus 27 with an augmented HHSS. Of course he added quite a bit of down, a summer bag I believe for one thing. But just adding something like a thick fleece jacket and a down vest can add a lot of warmth. Plus, if they still make them, there are the HH OCF kidney and torso pads, a bunch of extra thickness for just a few oz, concentrated right where you need it most. Plus, one thing that has not been tested much: 2 full length HH OCF pads.

    And at least give some thought to VB clothing to really do away with condensation issues, except of course possible condensation from your exhaled breath, which needs to be vented.
    For I consider that the sufferings of this present time are not worthy to be compared with the glory that is to be revealed to us....that the creation itself also will be set free from its slavery to corruption into the freedom of the glory of the children of God. For we know that the whole creation groans and suffers the pains of childbirth together until now.
    Romans 8:18,21-22

  9. #9
    OutandBack's Avatar
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    Hi Paul,
    I am in the camp of everything below the tarp need to be breathable.
    That said condensation from sweat and breath is still an issue you need to deal with.

    Heck I would get frost on my wbbb bug netting from my breath overnite sans tarp.
    One can't get more breathable than that.



    Things I have done to reduce condensation/frost:
    Larger tarp so I could raise it higher and still have good wind protection.
    Doors on one end usually setup with doors into the wind.
    I still get frost on the underside but the tarp is high enough I don't bump it when sitting up to make morning coffee.

    I only use net less hammocks in temps of 20F or below.

    I sleep with a thin balacava and hooded down jacket. This allows me to keep my head out from under the TQ preventing my breath from collecting in the TQ.

    I know you've spent some money on syl UQP HHSS but to make them work you have to go all the way with vapor barriers or you will just end up wet and cold. For me it's just not worth the gamble.

    hth
    O&B
    May your mileage in the backcountry exceed your post count.

  10. #10
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    I do not have experience with an UQ but I can speak a little to the physics. The phenomenon you are referring to with rising warm vapor is convection. It is the reason the moisture in your breath condenses on the underside of your tarp. The force that causes convection is the result of the slightly greater weight to volume of the cold air to the warm air. I am sure you are aware of this but my point is that it is a relatively weak force that is temperature driven (not moisture driven) and is easily disrupted by friction, such as the air moving through a fabric experiences. Convection can only happen if there is cooler air readily available to displace the warm air which will not be the case within your insulation system where trapped air has already been warmed by radiating body heat. Warm moist air next to the skin on your back will still tend to be displaced by cooler air in the upward direction but likey not fast enough to make up for the diffusion outward towards less moist air. That all depends on your weather conditions of course - temp, rh, wind. Anyway, the moisture in the trapped air will tend to move in the direction of lower concentration which for your back is going to be directly through the UQ.
    I understand 2QZQ makes a ripstop UQ protector to allow moisture to escape the shelter, but by the time the moisture reaches the protector whether it be sil or ripstop it has already passed through your UQ, most likely meeting the dew point before it arrived at the protector. I'm not saying you can't see any benefit from the breathable protector as it does let moisture that your down didn't absorb escape, but in my opinion the best solution is a close to skin vapor barrier as has been suggested.
    I can't help with recommendations for specific conditions as my experience is lacking but that is hopefully some helpful explanation of the physics.

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