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  1. #1

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    Lightbulb DIY Double Layer Hammock Idea

    Ok, I've just spent the last 2 hours scanning through search results to see if anyone has talked about this...

    A double-layer, cinch-end hammock: the top layer being 1.1oz ripstop nylon and the bottom being 1.3oz silnylon.

    I'm aware of the concern that the waterproof layer might leave me swimming, so the thought is to create a gap of 2 inches between the layers. The question is what might be the best way to achieve this gap. If you're talking about fairly rigid material, making the bottom layer 2" bigger on all sides should effectively drop the layer down by 2". But what about with flexible material? The layers would be sewn together on the ends and along the middle of the sides for 1/3 of the length.

    The plan is to be able to slip a DIY Insultex pad (4 layers in a 1.1oz RSN shell) between the layers. I anticipate that there will be little-to-no draft, seeing as the water/wind proof qualities of the silnylon will be combined with no open edges. (I expect the access points on the side would naturally be pulled closed) The weight of the pad would help structure the gap and create a "dead air" space that should enhance the overall insulative value of the system.

    So, some specific questions for feedback from folks:

    1. Would I end up wet, even if the only thing touching me is the upper layer?

    2. Would 2" be too much of a gap? not enough?

    3. I'm having trouble wrapping my mind around what the effective gap would be created by adding 2" of material to all sides when the material is hung and lies in a arc. I know the gap would be lost on the sides (and that's OK), but what would the gap look like on the bottom (assuming the pad is in place)?

    4. Would darts be the best way to even spread out the extra material of the lower layer?

    Comments? Thoughts? Questions?

    Mucho Gracias!

    ** on second thought, maybe this should have gone in the "DIY" forum. Can it be moved there? **
    Last edited by mrmike65; 11-17-2011 at 22:32. Reason: second thought on forum catagory

  2. #2
    Senior Member hippofeet's Avatar
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    My DIY is coated nylon. I have overnighted in it without swimming. I think the bug net allows enough airflow. I messed around with something like what you are referring to. My inside layer (polyester) stretched at a different rate than my outside shell ( dwr nylon ripstop) and caused a rip at a line of stitch near the peak. For the pad I had a sleeping bag with the zippers off and cut to a long diamond shape.
    I would worry about darts bearing load, but maybe you coul do it so they didn't.
    An emergency of my own making...is still an emergency.

  3. #3

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    So, I wonder if untreated 1.1oz Ripstop Nylon would stretch differently from 1.3oz silnylon? To my understanding, they are essentially the same threadweight. My thought is that the upper layer would be the weight-bearing part. The lower layer is really only providing a pocket to hold the insulation and acting as wind/water barrier.

  4. #4
    Senior Member hippofeet's Avatar
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    I had the same plan, thinking the polyester inner would stretch less than outer. I freely admit I didn't spend much time figuring out how to get the bottom layer loose. Think my problem was just a bad stitch placement, and probably lack of planning. Get some other projects out of the way I would try again.
    An emergency of my own making...is still an emergency.

  5. #5
    Redoleary's Avatar
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    From a structural stand point what you have is a 1.1oz single layer hammock. It probably won't take long for that layer to stretch until it contacts the second layer and now your insulative air gap its gone, to include compressing the layers of IX, which enjoys greater efficiency from air gaps as well. IX is essentially windproof anyway, especially when there's 4 layers of it. So you could do a 1.9 oz breathable nylon as the layer you're going to lay on (hoping for less stretch) and a 1.1 oz outer layer to hold your IX. Just thinking out loud.
    Good luck,
    RED

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  6. #6

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    Great response, Redoleary! It gives me more fuel to brainburn. That's what I love about this forum.

    I wonder how much 1.10z RSN stretches. My first hammock was made of it and I could detect only a little stretching on the initial break-in. After that, it seemed stable. That was why I had made the gap 2", since my insulation layer be less than an inch. I guess that was what I had in mind with the question of the 2" gap not being enough.

    I'm not sure I want to go up to 1.9oz, as I'm really trying to be a "gram weenie" with this whole setup. Perhaps 1.3 might serve if I find that the 1.1 does stretch too much. In the end, practical testing will prove this out.

    Thanks!

  7. #7
    gargoyle's Avatar
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    Compressing IX defeats its insulative quality. Since your IX is already in a semi-uq form ("4 layers sandwiched between ripstop"), why not just use that as a uq? Add a suspension system of shockcord and hang it under the hammock.

    Essentially, a underquilt is a second layer. But its construction/suspension system avoids the structural issues you speak of.

    Whats your weight? That will have a lot to do with what fabric will perform best.

    You'll need to dart the individual layers of IX to get the optimum performance, as well as the top and bottom layer of fabric that covers the IX. Each layer being a smidge bigger than the previous. There are several threads dealing with that.
    But you need to allow the layers to gap or open, once you slide it into the
    2nd layer you kinda defeat the darting.

    Trying to keep the IX quilt in place in between the two layer hammock will be problematic also. It needs a suspension system or something to hold it in place (velcro, ties, snaps?) Without a way to hold the quilt in place, everytime you move, the quilt can/will move and bunch up. Pads are firm enough to somewhat decrease this movement effect in the pocket.

    My opinion, build a breathable hammock and suspend your quilt below on its individual suspension.

    As far as condensation goes..theres probably a reason most of the major manufacturers use breathable materials as hammock fabric. Use your judgement on that.

  8. #8
    Senior Member Just Jeff's Avatar
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    You have to dart the material both length and width to create the space between them. But Redoleary is right - 1.1 oz will stretch...which is fine unless you're trying to maintain a gap between the two layers.

    I made a 1.1 oz sil hammock and slept in it without swimming...but weather conditions play a big role in that. I think I'd hate it in warm humid weather, but for fall/winter in a relatively dry climate it works fine.

    A couple insulated hammock experiments here might give you some ideas.
    http://www.tothewoods.net/HomemadeGear.html
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  9. #9
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    I noticed that when you were attempting to make the calculations for the underside, you said, "If you're talking about fairly rigid material, making the bottom layer 2" bigger on all sides should effectively drop the layer down by 2"."

    I have not done the calculations, but I am not sure that 4 inches in each dimension is enough to make the space you wanted to make. The geometric problem is one of arc and you actually need to calculate the arc length, which is a bit more complex than if the hammock lays along a circular radius. It is easier to calculate a circular radius than a parabolic one and most hammocks seem to hang parabolically.

    Furthermore, the stretch factors complicate this mathematically.

    This is easily a sophisticated calculus III problem with this sort of multidimensionality.

  10. #10

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    @ Gargoyle: Thank you for the info on working with Insultex and your opinion. The pad of Insultex that I plan to use will actually be a vest of my design. It occured to me that if a vest (being a front & a back) could reach from waist to top of shoulder, then if it were laid flat, it should be long enough to reach from top of head to near knee. I have devised a way to do so and assure that it will lie 6" wider on each side. BY my calculations, this is as big as any 3/4 length sleeping pad sold. Hopefully, I will have a vest that looks like a vest and acts as a sleeping pad.

    @ Just Jeff: Thank you for your input. I wonder though, will the 1.1oz RSN stop stretching at some point, or will it stretch until it falls apart. If it will stop before it fails, I wonder if the amount of stretch can be predetermined.

    @ nicholas.mauriello: LOL! them's a lot of big words there, fella! But I catch your drift, and thank you for your input, as well. Since I last took Geometry in 7th grade and have never taken Calculus III, I can only focus on the opinion that 4" may not be enough and keep that in mind as I press forward.

    Again, than you all for your interest. I'll be sure to post info and pics when I complete this project.

    Cheers!

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