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DCF X-Mid Clone


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  • #3727144
    Eric Blanche
    BPL Member

    @eblanche

    Locale: Northeast US

    Great post Stumphges! I concur with your thoughts and statements regarding “deformation” near tieouts for dcf mids. More noticeable with the lighter weight .5oz dcf as well in my experience.

     

    Maybe I am in the minority here, but what kind of life expectancy does everyone here think they should be getting from their tents/tarps?

    #3727145
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    “In my opinion, this type of construction would be stabilized with the application of ~1 inch DCF tape (typically available in thickness equivalent to 0.8 DCF) to the underside of the ridge seams. Reinforcing all the seams this way should provide dramatically improved dimensional stability with very little weight increase. Doing all the seams on a Duomid-sized shelter might add 1-2 ounces.”

    That’s sort of what I’ve done on silpoly mid

    Ridge seams are on the bias.  So they stretch a lot.  In the wind the tent flaps.

    I don’t know if there’s long term creep, I’ll have to think about that, but there’s short term stretch

    I just took a 3 inch strip of fabric.  Fold over to make a 1/2 inch wide, 6 layers, along the grain.  Sew to ridge.  Tent flaps less in the wind.  I think you could use a 1/2 inch grosgrain strip or some other stiff material.

    I haven’t had to put up my tent in months, 60 nights of backpacking.  No rain.  Next time it rains I’ll have to look at it to see if there’s long term deformation.

    #3727152
    Stumphges
    BPL Member

    @stumphges

    Thanks, Eric. I haven’t used my DCF tents long enough to gauge life expectancy. I think there are various estimates out there made by through hikers, who probably have the best visibility of this subject.

    Jerry, it was one of your earlier posts that gave me the idea of using DCF tape to stabilize ridgelines. You’d written that reinforcing the ridges with stiff material had reduced ridge deflection. I think that you could use 0.8 DCF tape (like this stuff: https://dutchwaregear.com/product/single-sided-dyneema-tape/) as a ligther option than grossgrain or similar. Expensive, but very light and stiff as hell in that orientation. Doh, I guess you’d have to first put a layer of siloxane tape on, then the DCF tape. Darn slippery sil!

    I’ve also noticed that the ridges sewn bias/bias will deflect more in a mid. I have a rectangular mid in silnylon that has the four corner ridges sewn bias/bias, and the other four seams (which in this rectangular octagon are also ridges) sewn selvedge/selvedge. Here’s a photo of the tent:

    The door seams are selvedge/selvedge and don’t stretch. The two seams orthagonal to them (in line with the orange apex guy lines) are also selvedge/selvedge. The corner seams are bias/bias. In the pitch shown, I walked all around the tent and pressed inward on the ridges with my palm, trying to similate the blunt force of the wind. The zipper seams don’t really deflect; the selvedge orientation of the fabric there, combined with the zipper fabric itself, makes for very stiff seams. The other selvedge/selvedge seams also do not deflect very much – a little, but not much.

    However, the four corner seams deflect significantly with pressure. Now, I took care to tension those ridges as much as I could without damaging the fabric, so I’m not certain how much of that deflection is actually coming from the ridge seams proper. I suspct that the bias orientation of the panel fabric adjacent to the seam is actually what is stretching – the panels are stretching along their biases towards the seams, allowing the seam itself (and the panels adjecent to the seam) to deflect inward. But the seam itself may not actually be lengthening.

    That hypothesis runs counter to yours, and it could be a combination of the two – some panel stretching, some stretching of the actual seam – at play. I would prefer that your hypothesis of seam stretching is correct, as that is more easily countered with stiff tape:)

     

    #3727159
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    we will eventually figure it out.  When we’re done with this we can move on to uniting quantum mechanics and gravity : )

    Your tent is pitched with very taut sides

    #3727166
    Stumphges
    BPL Member

    @stumphges

    Deleted due to unsecure method of sharing a video:(

    #3727188
    AG
    BPL Member

    @dlkj83jdk3883ll

    nice mid. what kind is it?

    #3727205
    Stumphges
    BPL Member

    @stumphges

    AG, it’s the “Mini2″ by a Chinese company called Knot or Knot Gear, aka Ice River, aka Aricxi – Aricxi seem to be the owner of the Knot “brand.” It’s a rectangular octagon, comparable in rectangular dimensions to the Duomid or Khufu, but with an octagonal shape rather than a true rectangle. This creates two vestibules, so like a Khufu with two vestibules and two zippers. The 20d silnylon is of decent quality and quite light, making the shelter a good weight/volume proposition despite the dual zips. I would prefer a higher quality silnylon and would pay more for it, but there’s nothing else on the market like this with two vestibules and two zips.

    On the other hand, the silnylon on this tent is higher quality than a larger, true octagon tent we’ve been using for family trips for three years, and that tent has done really well for us. But if I could get the above tent in the 20d sil MLD uses I would be all over and pay good money for it. And if I were to make a mid with DCF myself, I would copy this design.

    In addition to the two vestibules, it is my opinion that this type of octagonal mid performs better in wind than a true rectangle. The footprint and cross-sections are larger, but the octagonal shape tensions into an elliptical cone that seems to spill the wind better. The cat cut hems look goofy, and prevent a winter-worthy seal with the ground, but they make it easier to pitch with very taut panels; one can focus on ridge and panel tension, since the tension on the hems does not need to be perfect.

    The overall shape is similar to the MYOG mid described in one of my favorite BPL forum posts, here: https://backpackinglight.com/forums/topic/mid-set-up-issues-got-advice/page/2/#post-3443441

    Despite the B-grade silnylon, I rate the fly highly enough that I just bought a Locus Gear Khufu Full Mesh inner for it, which cost nearly three times as much as the fly! (The Khufu inner is 15 cm wider and about 5 ounces lighter, but the inner that comes with the fly at the link above is actually excellent quality with tough 40d floor, and has two zips, though it’s only ~120 cm wide.)

    To get back toward topic, I feel that this design offers something of the function of a two-pole mid like the X-Mid, namely dual zips and vestibules, but with better wind performance. The downside is that you still can’t get the dry entry of the X-Mid with this type of fly if used by two people. The footprint might be a little larger than an X-Mid, too, not sure, although the cat cut hem allows for some maneuvering in relation to rocks and stuff in the camp site, so the footprint is functionally a bit smaller.

    #3727206
    Stumphges
    BPL Member

    @stumphges

    Jerry, I have a nice video of the wind playing on that tent (the images I’ve posted in this thread are actually stills from that video) but I can’t find an anonimized way to post video online.

    So below is another still from that video, showing a ~30 mph gust pressing into the near corner seam. I’d purposely pitched the mid broadside to the wind to study this bias-stretch corner issue, so the wind is having its way with that corner seam.

    To my eyes, it looks like the seam is hanging in there, but the panel fabric adjacent to the seam is stretching on the bias and deflecting quite a bit.

    I mentioned above that I also have a larger, truly octagonal tent by the same company. I have not observed this seam behavior with that tent, and I think this is the reason why: I think that radially symmetrial mids are very easy to tension such that the stretch is “pulled-out” of the bias. One reason I think this is because that larger, true octagon mid, does not sag in the cold and wet. This smaller, rectangular octagon does sag, despite being made with higher quality silnylon with more silicone coating applied to it. And I believe the lack of sag is due to the bias stretch being tensioned out of the panels, so when the fabric expands when cold and wet there is little movement possible in the fabric, or it’s almost been over-tensioned on the bias. This also means that when the wind hits the bias/bias ridgelines, all the stretch has been taken out of the panels already, and so the panels don’t deflect as they do in the photo above.

    If this is so, I would predict that a truly octagonal mid in DCF would tend to deform at the corners over time, because that shape so naturally loads the panels along their biases (i.e. orthagonal to the Dyneema filament orientation, with respect to DCF). So maybe not a great idea to build an octagonal tipi out of DCF. But this rectangular octagon does not seem to naturally load the panel biases as much, so the above design might be dimensionally stable if made with DCF, and the panel stiffness of DCF might better prevent the type of deflection seen in the photo above. So maybe I should make one of these with 0.8 DCF.

    #3727284
    Stumphges
    BPL Member

    @stumphges

    A follow up to the posts above about the Knot Min2 pyramid tent pictured. I compared its silnylon fabric to several other silnylons and I think it has too much bias stretch to make a truly great tent. Compared to the 30d silnylon used by Locus Gear, for example, the 20d Knot stuff has probably 3 times as much bias stretch. I think the design is great, price is great, and it’s a good way to try out a pyramid tent without breaking the bank, but I would not recommend this tent for expedition use, the fabric just isn’t stiff enough.

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