Mar 21, 2014 at 8:45 pm #1314706
I'm working on yet another Zimmerbuilt pack and I'm stumped on what to do about the compression system. This would be my primary bear can/water hauler pack that (hopefully!) will be my PCT pack for 2015.
I'm drawn to the aesthetics of the ULA Ohm style zig zag cord side compression, as well as the simplicity of it. But I wonder if that is going to be sufficient to contain the full bear can or several liters of water for my desert hikes.
The other issue is that one of the side pockets will be a tall one for my shelter…if I do the zig zag cord, that can go under the pocket; a traditions webbing strap design would have to go on top of that pocket. Maybe that's a good thing…I haven't decided.
And those of you who work with such things…if I went with the webbing straps, which direction should they go? (I'm having a heated discussion with my engineering father about this….) do they angle upwards towards the back, or downward towards the back????
Any opinions here?Mar 21, 2014 at 9:50 pm #2085116
@millonasLocale: Santa Cruz Mountains, CA
Aesthetically and economy-wise I do like the zig-zag pattern, but before I got my Kalais built I decided against it. Independent is probably much better and more versatile – you have to think of the zig-zag as like a shoe lace – there is only so much you can do to customize the compression that way – and all the best ways involve tying knots and in effect making the system work again like independent straps. Probably with a bear can a "custom" compression is more important than a for a pure "fluffy cloud" type SUL load without the huge boulder in the pack.
All I got at the moment. The angle thing is above my pay grade, though I'm thinking horizontal (no angle). Or down toward the back. Definitely not up towards the back, I'd stake my life on it….Maybe.
I can only imagine the discussions with you father. Strap angles – sounds like another of those "if there is a truck filled with birds, and the birds start flying inside the truck, does the truck get lighter?" questions. Answer, no. It weighs exactly the same.
Your father will understand. :-)Mar 21, 2014 at 10:43 pm #2085122
@skomaeLocale: northeastern US
After trying and owning an embarrassingly large number of packs I have come to the conclusion that:
– zig-zag straps are cute, but useless for real compression
– two straps on either side are a must
– straps angled up towards the back seem slightly better
Of all the packs I've owned and own, the Boreas Buttermilks does the best job of going from multi-day pack to day pack once it's shed of its base camp gear. It also compresses the easiest with partial loads. I attribute both of those features to the way the compression straps are designed and distributed on the pack.
Packs I've owned that use zig-zag compression tend to bend in weird ways with partial loads, or do not compress enough to prevent flopping around. It's also harder to compress due to compressing 2+ parts of the pack at once.
I should note that some packs like most of the Ospreys have their exterior pockets stitched with a hole on either side where the webbing strap is mounted so the user is given the choice to route it on the inside or out. This might be a solution for you.Mar 22, 2014 at 5:51 am #2085139
@abhittLocale: southern appalachians or desert SW
I agree with the webbing better than zig zag, just can't get good compression with the cords. At least two straps, three better if possible. Horizontal or slighty up to the back. Tall side pockets are a problem but you could design it as Stephen says with a slot to access/accommodate straps. Please no straps over pockets, might as well not have the pockets.
My Kalais has three and they seem to work wellMar 22, 2014 at 6:11 am #2085142
"sounds like another of those "if there is a truck filled with birds, and the birds start flying inside the truck, does the truck get lighter?" questions. Answer, no. It weighs exactly the same."
Okay, forget Jennifer's questions, explain this answer! I'm not an engineer and never understood this answer, elaborate please!Mar 22, 2014 at 7:43 am #2085152
@fluffinreach-comLocale: no. california
" Okay, forget Jennifer's questions, explain this answer! I'm not an engineer and never understood this answer, elaborate please! "
THANK YOU !
i suspect what we have here originally is an inaccurately posed question.
because : if the birds are sitting on the truck, and their little feets are pushing down on the truck, then the truck weighs what it weighs Plus the birds. so that there is the weight of the truck .. truck with it's birds. thusly : truck+birds=weight.
weight normally considered to be the amount of how hard something is pushing down. you need gravity (or close to it) to have weight in common terms. no gravity = no weight. and hence the moon-shot like term "weightless".
now, for us earthbound people, living as we do at the bottom of an ocean of air, if the birds take off and fly around inside the truck, or if the truck has open windows, or even if the birds are/were sitting in the back of a pickup, and are now flying all Around the truck (but not touching it), once the birds take off and are no longer pushing down (remember their little feets) on our truck. with flying birds, the truck will indeed weigh less if one is using the common and correct use of the term "weight".
but … if what the original question meant to use was the was the word "mass", then that's a related, but different thing. because the mass of our truck+birds is the same regardless of if the birds are sitting, or flying, or even near the truck, their combined Mass will not change, nor will it change in the vacuum of orbital space, nor even if the entire lot is partially buoyant in our atmosphere.
much like managerial stupidity, mass is fairly durable stuff in the blue collar world. i assure you, that if peter attempted altering the mass of random objects within the sacramento city limits, if would almost immediately attract the attention of the Authorities. at any rate, being as it's california, no doubt i'd need a permit.
v.Mar 22, 2014 at 8:30 am #2085173
@skomaeLocale: northeastern US
Ah, but we are forgetting that to stay aloft the birds are actually displacing their weight in air by flapping their wings the air must move somewhere, and naturally the truck bed is there to absorb some of that energy. Must take this into account when we consider the force with which the truck is exerting in the ground, which is our typical definition of "weight."Mar 22, 2014 at 9:00 am #2085182
In order to get lift, the birds must exert force. This force must be significant enough to offset the effects of gravity thereby replacing the effects of gravity with the same pull / push. If you stand on a scale and push off, the scale needle will show your weight temporarily with you in the air. If you were able to hoover over the scale with the force necessary to lift you, that force would be pushing down on the scale, reading your bodyweight as a constant even though you would not be standing on the scale.
Newton and all that.Mar 22, 2014 at 9:01 am #2085183
Oh – this all falls apart if the truck 'box' is open, however.Mar 22, 2014 at 9:36 am #2085190
Daryl and DarylParticipant
@lyrad1Locale: Pacific Northwest, USA, Earth
Perhaps a drone owner would like to experiment with this?
How does the scale read with:
(1) drone on scale
(2) drone flying above scale in open environment
(3) drone flying above scale in sealed box (with clear lid for observation)Mar 22, 2014 at 10:49 am #2085212
And it is awesome.
I saw the force of the air displacement will NOT be the same "weight," because the air is a gas and can disperse without increasing overall air pressure inside the truck (unless the truck was a vacuum, in which case the birds would decidedly not be flying, but rather dead).
The feet of the birds are going to be greater PSI than the air displacement, so no, the truck will weigh less if the birds are flying.
Now, if you are in an elevator and it falls uncontrolled to the ground, and you jump very high right at the moment of impact, will you be able to survive the fall?Mar 22, 2014 at 11:19 am #2085218
@pitsyLocale: Central Texas
Reminds me of a customer I had at the hardware store. Brought back a window unit air-conditioner that he claimed made his room hotter. Upon questioning, it turned out his room was windowless and he had simply placed the unit on top of a cabinet. it took a while to explain that one to him; not sure if he believed me.Mar 22, 2014 at 11:28 am #2085219
@millonasLocale: Santa Cruz Mountains, CA
I go away for five minute and you kids have gone off on a tangent. Don't look at me! I blame Doug, aka the usual suspect.
Let me just say that the physics is moderately simple (application of Newton's 3rd law), but the "paradox" comes (as it often does in such things) from neglecting things that can not be neglected. Hint: the original apocryphal story is about a bird shipper who wants to want to save weight fees when his truck is weighed. So in this simplified case the bird are flying inside the enclosed truck. Things are a but more complicated if the van is open in various ways. As a homework assignment explain why.
However, this gives me a chance to direct you to possibly the most hilarious episode of myth-busters ever, where they investigate this "paradox" experimentally. In particular their attempts at gadgets to get the birds to fly inside the "van" are a hoot – think dangerous ceiling fan.
Daryl, they in fact tried your drone idea first! But where is the fun in that. Since they are the most-coolest arch-geeks on the planet they just would not stop until they tested with actual live birds. :-)
Daniel, I thought for a second you were gong to say he had it backward in the window, in which case it really would have been a heater. LOL
Jennifer, your elevator scenario reminds me of my favorite "existentialist" joke, a guy is parashooting and is deciding to wait for the right moment to pull the cord. He waits and waits until he is 10 feet from the ground. At which point he say something like "nevermind, I can jump from here".
I hope to be able to say that on my death bed!Mar 22, 2014 at 11:49 am #2085224
That was a great episode, which showed that the weight stayed the same.
Sorry Jen. Your premise only works if the truck door is open. Newton was right.
As far as the elevator question, are we in the Matrix when this occurs?
Oh, and I like standard horizontal compression.Mar 22, 2014 at 11:51 am #2085225
@todd1960Locale: Coastal Southern California
I have many packs, including the Kalais. The straps on the Kalais work great. Threaded cords do not compress well. Go for the straps like the Kalais….Mar 22, 2014 at 4:22 pm #2085263
Never use them. The sleeping bag just gets more room.Mar 22, 2014 at 6:23 pm #2085279
@dwambaughLocale: Pacific Northwest
Jennifer wrote, "The other issue is that one of the side pockets will be a tall one for my shelter…if I do the zig zag cord, that can go under the pocket; a traditions webbing strap design would have to go on top of that pocket. Maybe that's a good thing…I haven't decided."
You could still do straps under the pocket, adding some for a tail and an exit hole a la Osprey. The narrow webbing straps on the Osprey Exos worked fine for me and you get to use smaller hardware too. I think that is a good compromise between wider webbing and small cord.
I agree with Ken that you can allow your insulation to fill in for excess space. Straps can help stabilize stuff that tends to bounce like water and bear cans. Note Golite's trick of using hooks and loops at the bottom to reduce volume.Mar 22, 2014 at 6:34 pm #2085283
I too have yet to ever really compress a pack, other than by rolling the top down tighter.
I removed the compression cords from my Ohm even. Just dont compress the sleeping bag, or maybe put CCF pad inside to when theres room. When the foods gone, well, the pack doesnt have anything heavy in it, its just a soft pillow on the back.
Admittedly, have never tried to use my pack as daypack full of water bottles or such.
I guess I dont see it as anything worth really worrying about. I do prefer the horizontal side straps though if carrying tent poles in side pocket, for obvious reason.Mar 22, 2014 at 7:19 pm #2085294
Dave…the truck door wouldn't have to be open…there is plenty of ventilation and it is not a vacuum ;)
As for the compression question…you guys have brought up a big reason why I ask the question. Since this pack will be a tad bigger to accommodate a heavy bear can and large water loads, it IS the heavy, bulky stuff I'm trying to contain. I'm in no way worried about my quilt, shelter or clothes….they'll be fine.
And of course, the closer the weight is to your back the less force there is for you to manage, so a deeper pack will actually require more work than a shallower one. So when dealing with that bulky, fully loaded can, or maybe 6 liters of water, I wondered if I I could get away with the obviously inferior compression system of the zig zag cord…or if I did need to go ahead and do the actual straps.Mar 22, 2014 at 7:30 pm #2085296
So why exactly do you want to compress a pack full of live birds ?Mar 22, 2014 at 7:34 pm #2085298
C'mon Franco, there I'll be, on the JMT with my most perfect pencil, trying to walk, and that darned pack full of birds will be flopping all over the place! I mean, how in the world am I supposed to hike with all that racket back there?Mar 22, 2014 at 7:35 pm #2085300
"I mean, how in the world am I supposed to hike with all that racket back there?"
Dehydrate them first, of course….Mar 22, 2014 at 8:41 pm #2085309
If you hike in Colorado you can have terns and marijuana in your pack.
That is so you don't leave terns unstoned.Mar 22, 2014 at 9:41 pm #2085321
@pitsyLocale: Central Texas
Perhaps we could fashion you a bindle-stick or a carrying yoke to supplement your existing pack.
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