Sunshine-or-thunder
11-13-2014, 15:41
Okay... Maybe I'm exaggerating a little, but I'm interested in whether it's possible to design and build a polycro tarp that can be trusted when extreme whether is expected.
This is my first post after a lot of reading and I gotta say thanks to everybody for all the great information, suggestions, and opinions about hammock camping, not to mention dozens of laughs. This place is great.
I've done a fair amount of backpack camping, but I've always been stuck on the ground and I like being comfortable, so I'm putting together a hammock camping rig and trying to learn as much as possible as quickly as possible.
Trial and error is one way to learn, but when a bunch of experts share their own trial and error experiences it makes learning a lot more efficient, so I hope somebody will have some suggestions besides telling me I'm a fool, since I already figured that out.
There's been some excellent experimental work with polycro tarps done by others and It's safe to say they've run into a lot of problems, so if I just slap something together and assume it's gonna work I'm going to end up soaking wet and miserable six hours before sunrise.
So why bother with polycro at all? Well, I'm short on money and polycro is cheap and light weight, but that's not the main reason. Wilderness ain't wilderness without rain and wind and storms, and when I can't see out of my shelter I'm missing the show, so I want to go with polycro if I can make it work.
There's only two problems. When polycro fails, it fails catastrophically, and adhesives usually don't stick to it very well, so other than the material itself and the tie outs there's no problem at all.
Considering what polycro is designed and used for, I'm not ready to rule it out. It's commonly applied to the outside of windows where it sits there for months exposed to everything winter throws at it. That's exactly what I want my tarp to do.
Looking at the customer comments on the web sites that sell the stuff, a lot of people are unhappy, but they're always complaining about the mounting tape. Either it doesn't stick well enough or it sticks too well and peels the paint off the window frame. I haven't seen anybody saying that the polycro itself shredded in a storm. Same with the stuff posted about polycro tarps. It's pretty much always the tie outs that fail. That's not to say I should ignore the possibility of the ultimate rip.
It's been mentioned, but not emphasized enough that polycro comes in different thicknesses, and the facts lead to a striking conclusion. The Ace Hardware store brand is 0.6 mils thick, the 3M stuff is 0.75 mils thick and Frost King and Duck both make a "heavy duty" version that's 1.5 mils thick.
Thing is, the thicker versions are about as easy to find as authentic hairs from Genghis Khan's mustache. Looking all over the internet, not too many places even carry the stuff and those that do list it as "out of stock." One guy is selling patio door size heavy duty stuff on Amazon for 25 bucks, which is about twice what a retailer would charge if a retailer existed.
On the internet, I could only find the heavy duty 1.5 mil stuff in the 42 by 62 inch size. I gotta conclude that essentially nobody sees a need for the thicker stuff. If thin polycro was prone to fail when it's exposed to storms all winter, people would be demanding the thicker stuff, so manufacturers would be making a lot of it and the retailers would be selling it. That obviously isn't what's happening.
Considering the consequences of a hammock tarp failure, I'd be a fool to assume it can't happen, so the design has to minimize the probability. The local Ace Hardware store ordered the thickest stuff Ace had available, 1.2 mils in a 7 by 10 foot sheet. I got two of them. More on catastrophe avoidance later.
The other problem is trustworthy tie-outs. From all the experimental projects I've read and my own kitchen table research lab, it seems the only thing that reliably sticks to polycro is Gorilla tape, with the qualification that Gorilla tape doesn't stick all that well to itself.
I learned that the engineering types got a term for this problem: "Hard to Bond Plastics," and Gorilla tape isn't the only solution as long as you've got all kinds of industrial equipment and 55 gallon drums of chemicals that aren't sold in small amounts or used for anything else. Guess I'll stick with Gorilla tape.
I accidentally conducted some relevant research. I had a crack in an out-of-the-way window pane so I slapped some Gorilla tape over the crack and forgot about it. That was five or six years ago. The tape is peeling in places, but it's mostly still holding. Contrary to what others have reported, the places where gorilla tape is stuck to another piece of gorilla tape are still holding rock solid. I don't know what caused the difference between my results and theirs. Maybe it's because I didn't bother to clean the glass first and the tape-to-tape bond is the only bond in the system that's realizing it's potential.
Anyway, I usually carry a small gold pan with me, so I'm sure in a few months I'll be able to buy anything I want. Oops, I just lost all credibility.
So how do I minimize the probability of a catastrophic failure of the polycro? Using thicker material is obvious, but there's more. Polycro is flexible, but I'm comfortable thinking of it as brittle. Like a coffee cup, it's strong, but when the force applied to it momentarily exceeds the strength of the molecular bonds that hold it together a failure occurs. The failure creates a loss of essential structural support in the material that immediately surrounds it, so the failure spreads until there ain't much structure left and I'll be trying to decide on the best option while I'm getting rained on in a storm.
Plants invented a solution to this problem a long time ago. When a force is applied they bend and flex, distributing the shock and reducing the force of the impact. Human engineers use the same principle when they're designing airplane wings and tall buildings. Could this principle be applied to a material that seems to have zero capacity for stretch? Maybe.
The only place flexibility could be introduced to this system is in the tie outs, and there's a well established technology for tensioning guy lines to compensate for the stretch in nylon tarps. Could this technology be modified to create shock absorbers that would transform extreme momentary wind gust forces into longer duration forces with less intensity?
I'm envisioning a guy line with three tensioners of increasing strength set up in a series. The design of the tensioners would be the same, with the only difference being the number of strands of shock cord used. I've been calling them "Storm," "Hurricane," and "Apocalypse."
A rough schematic:
Tarp-----Storm-----Hurricane------Apocalypse-----Stake
I'm figuring that as each tensioner reaches maybe three quarters extension the next higher level will start to stretch, creating a dynamic response system that responds to increasing wind force with increasing levels of spring resistance.
The danger of my hammock becoming a tent stake slingshot target cannot be ignored. Using more guy lines would reduce the force on each one, which would help unless I end up inventing the slingshot machine gun.
I was also figuring on installing Apocalypse strength tensioners on the ridge line. These would be irrelevant under all but the most extreme wind conditions, when they would allow the entire tarp to move. If it comes down to it, I don't mind if the tarp slams into my hammock as long as it stays together and springs back to where it was.
A catastrophic failure of the polycro material would probably occur in fractions of a second once it started, but it has to start somewhere. It would start at a weak point. The most obvious weak point is the edge since the molecular bonds there are only supported on one side. People often hem polycro edges with the provided double sided tape, but this doesn't always hold. I've also been thinking about running a strip of gorilla tape around the edge folded over lengthwise so it would support both sides.
Since I've got two sheets of polycro, each ten by seven feet, I was planning to fasten them together with gorilla tape on both sides, giving me ten by fourteen feet to work with. I'm figuring on an overall design based on the Winter Dream. Cat cuts are an option, but I'm concerned that cutting them out might create microscopic weak points and I'm not sure that hemming cat cuts with gorilla tape would work.
For the gram weenies, I recognize that all that tape is gonna add weight and I'm okay with that. Watching a lightning storm is worth a carrying few extra ounces.
Before I start building this thing, I'd be most grateful for any comments, suggestions, and even insults.
This is my first post after a lot of reading and I gotta say thanks to everybody for all the great information, suggestions, and opinions about hammock camping, not to mention dozens of laughs. This place is great.
I've done a fair amount of backpack camping, but I've always been stuck on the ground and I like being comfortable, so I'm putting together a hammock camping rig and trying to learn as much as possible as quickly as possible.
Trial and error is one way to learn, but when a bunch of experts share their own trial and error experiences it makes learning a lot more efficient, so I hope somebody will have some suggestions besides telling me I'm a fool, since I already figured that out.
There's been some excellent experimental work with polycro tarps done by others and It's safe to say they've run into a lot of problems, so if I just slap something together and assume it's gonna work I'm going to end up soaking wet and miserable six hours before sunrise.
So why bother with polycro at all? Well, I'm short on money and polycro is cheap and light weight, but that's not the main reason. Wilderness ain't wilderness without rain and wind and storms, and when I can't see out of my shelter I'm missing the show, so I want to go with polycro if I can make it work.
There's only two problems. When polycro fails, it fails catastrophically, and adhesives usually don't stick to it very well, so other than the material itself and the tie outs there's no problem at all.
Considering what polycro is designed and used for, I'm not ready to rule it out. It's commonly applied to the outside of windows where it sits there for months exposed to everything winter throws at it. That's exactly what I want my tarp to do.
Looking at the customer comments on the web sites that sell the stuff, a lot of people are unhappy, but they're always complaining about the mounting tape. Either it doesn't stick well enough or it sticks too well and peels the paint off the window frame. I haven't seen anybody saying that the polycro itself shredded in a storm. Same with the stuff posted about polycro tarps. It's pretty much always the tie outs that fail. That's not to say I should ignore the possibility of the ultimate rip.
It's been mentioned, but not emphasized enough that polycro comes in different thicknesses, and the facts lead to a striking conclusion. The Ace Hardware store brand is 0.6 mils thick, the 3M stuff is 0.75 mils thick and Frost King and Duck both make a "heavy duty" version that's 1.5 mils thick.
Thing is, the thicker versions are about as easy to find as authentic hairs from Genghis Khan's mustache. Looking all over the internet, not too many places even carry the stuff and those that do list it as "out of stock." One guy is selling patio door size heavy duty stuff on Amazon for 25 bucks, which is about twice what a retailer would charge if a retailer existed.
On the internet, I could only find the heavy duty 1.5 mil stuff in the 42 by 62 inch size. I gotta conclude that essentially nobody sees a need for the thicker stuff. If thin polycro was prone to fail when it's exposed to storms all winter, people would be demanding the thicker stuff, so manufacturers would be making a lot of it and the retailers would be selling it. That obviously isn't what's happening.
Considering the consequences of a hammock tarp failure, I'd be a fool to assume it can't happen, so the design has to minimize the probability. The local Ace Hardware store ordered the thickest stuff Ace had available, 1.2 mils in a 7 by 10 foot sheet. I got two of them. More on catastrophe avoidance later.
The other problem is trustworthy tie-outs. From all the experimental projects I've read and my own kitchen table research lab, it seems the only thing that reliably sticks to polycro is Gorilla tape, with the qualification that Gorilla tape doesn't stick all that well to itself.
I learned that the engineering types got a term for this problem: "Hard to Bond Plastics," and Gorilla tape isn't the only solution as long as you've got all kinds of industrial equipment and 55 gallon drums of chemicals that aren't sold in small amounts or used for anything else. Guess I'll stick with Gorilla tape.
I accidentally conducted some relevant research. I had a crack in an out-of-the-way window pane so I slapped some Gorilla tape over the crack and forgot about it. That was five or six years ago. The tape is peeling in places, but it's mostly still holding. Contrary to what others have reported, the places where gorilla tape is stuck to another piece of gorilla tape are still holding rock solid. I don't know what caused the difference between my results and theirs. Maybe it's because I didn't bother to clean the glass first and the tape-to-tape bond is the only bond in the system that's realizing it's potential.
Anyway, I usually carry a small gold pan with me, so I'm sure in a few months I'll be able to buy anything I want. Oops, I just lost all credibility.
So how do I minimize the probability of a catastrophic failure of the polycro? Using thicker material is obvious, but there's more. Polycro is flexible, but I'm comfortable thinking of it as brittle. Like a coffee cup, it's strong, but when the force applied to it momentarily exceeds the strength of the molecular bonds that hold it together a failure occurs. The failure creates a loss of essential structural support in the material that immediately surrounds it, so the failure spreads until there ain't much structure left and I'll be trying to decide on the best option while I'm getting rained on in a storm.
Plants invented a solution to this problem a long time ago. When a force is applied they bend and flex, distributing the shock and reducing the force of the impact. Human engineers use the same principle when they're designing airplane wings and tall buildings. Could this principle be applied to a material that seems to have zero capacity for stretch? Maybe.
The only place flexibility could be introduced to this system is in the tie outs, and there's a well established technology for tensioning guy lines to compensate for the stretch in nylon tarps. Could this technology be modified to create shock absorbers that would transform extreme momentary wind gust forces into longer duration forces with less intensity?
I'm envisioning a guy line with three tensioners of increasing strength set up in a series. The design of the tensioners would be the same, with the only difference being the number of strands of shock cord used. I've been calling them "Storm," "Hurricane," and "Apocalypse."
A rough schematic:
Tarp-----Storm-----Hurricane------Apocalypse-----Stake
I'm figuring that as each tensioner reaches maybe three quarters extension the next higher level will start to stretch, creating a dynamic response system that responds to increasing wind force with increasing levels of spring resistance.
The danger of my hammock becoming a tent stake slingshot target cannot be ignored. Using more guy lines would reduce the force on each one, which would help unless I end up inventing the slingshot machine gun.
I was also figuring on installing Apocalypse strength tensioners on the ridge line. These would be irrelevant under all but the most extreme wind conditions, when they would allow the entire tarp to move. If it comes down to it, I don't mind if the tarp slams into my hammock as long as it stays together and springs back to where it was.
A catastrophic failure of the polycro material would probably occur in fractions of a second once it started, but it has to start somewhere. It would start at a weak point. The most obvious weak point is the edge since the molecular bonds there are only supported on one side. People often hem polycro edges with the provided double sided tape, but this doesn't always hold. I've also been thinking about running a strip of gorilla tape around the edge folded over lengthwise so it would support both sides.
Since I've got two sheets of polycro, each ten by seven feet, I was planning to fasten them together with gorilla tape on both sides, giving me ten by fourteen feet to work with. I'm figuring on an overall design based on the Winter Dream. Cat cuts are an option, but I'm concerned that cutting them out might create microscopic weak points and I'm not sure that hemming cat cuts with gorilla tape would work.
For the gram weenies, I recognize that all that tape is gonna add weight and I'm okay with that. Watching a lightning storm is worth a carrying few extra ounces.
Before I start building this thing, I'd be most grateful for any comments, suggestions, and even insults.