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#175177 - 02/19/13 10:18 AM Is My Tarp Long Enough?
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
I'm building a tarp of SOL "Survival Blankets". The main body will be about eight feet long, but there will be a bit of an overhang on each end (I think this is called a beak, but not sure if that term applies unless it slopes downward to the ground - mine don't slope down). To get an idea of the shape I'm talking about, it should be very similar to the MSR E-Wing, only with a bit different proportions. I'd originally planned to make these overhangs at least two feet long or more on each end, making the total length 12 feet, in order to keep out more rain, but decided to make them 16" on each end in order to save some of my survival blanket for another project. However, after attaching one side of an overhang on one end, visually, it just seems very short like it's not going to keep out the rain, but I'm hoping to hear from more experienced tarp users. Is 8' plus a 16" overhang on each end, for a total length of 128" at the ridge line enough to keep out the weather?

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#175178 - 02/19/13 11:58 AM Re: Is My Tarp Long Enough? [Re: 4evrplan]
finallyME Offline
member

Registered: 09/24/07
Posts: 2710
Loc: Utah
Personally, I don't like less than 10 feet for a ridgeline. I don't know if what you have should be sufficient. Probably. I know people do a lot less. But it depends on your entire system, and how/where you pitch.
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#175180 - 02/19/13 12:14 PM Re: Is My Tarp Long Enough? [Re: finallyME]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
Originally Posted By finallyME
Personally, I don't like less than 10 feet for a ridgeline. I don't know if what you have should be sufficient. Probably. I know people do a lot less. But it depends on your entire system, and how/where you pitch.


I have juuust enough uncut material left over to make two foot beaks instead. I think I'll go back to my original 12' ridgeline idea (or very slightly less - I'll have to cut off an inch or so with tape on it to remove the smaller beak). My other project will just have to wait. If anyone's curious, I wanted to try my hand at homemaking an inflatable mattress. At least I'll have enough scraps to test out some ideas.

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#175183 - 02/19/13 12:19 PM Re: Is My Tarp Long Enough? [Re: 4evrplan]
finallyME Offline
member

Registered: 09/24/07
Posts: 2710
Loc: Utah
I just bought material to make a homemade inflatable mattress. smile
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I've taken a vow of poverty. To annoy me, send money.

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#175184 - 02/19/13 12:25 PM Re: Is My Tarp Long Enough? [Re: finallyME]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
That's really cool. Are you going to use reflective material or insulation, or will it be purely for warm weather use? I've played around with welding plastic, and I can hardly wait to make one, but I've got CCF pads, and I'll probably use a frameless pack, which I need the foam pads for. So, it's really not necessary for me to build one, just a cool fun side project. Post lot's of pictures for us.

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#175188 - 02/19/13 04:59 PM How much drop? [Re: 4evrplan]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
Here's one more quick question before I do any more cutting. I've got Ray Caffin's caternary curve calculator, but how do you determine the optimal maximum drop in the middle? I know this depends on tension, less drop for higher tension, and more drop for less tension, but I don't know how to relate this to real life typical numbers. What would be a good all-round middle of the road drop for typical tension on a 12 foot ridgeline?

And yes, I know people don't typically put cat. curves in plastic tarps, but I think it will work, and I want to try.

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#175206 - 02/20/13 11:07 AM Re: Is My Tarp Long Enough? [Re: 4evrplan]
finallyME Offline
member

Registered: 09/24/07
Posts: 2710
Loc: Utah
Originally Posted By 4evrplan
That's really cool. Are you going to use reflective material or insulation, or will it be purely for warm weather use? I've played around with welding plastic, and I can hardly wait to make one, but I've got CCF pads, and I'll probably use a frameless pack, which I need the foam pads for. So, it's really not necessary for me to build one, just a cool fun side project. Post lot's of pictures for us.


I plan to put down in it. But I am still kicking around putting some reflective material in it.
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I've taken a vow of poverty. To annoy me, send money.

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#175212 - 02/20/13 11:51 AM Re: Is My Tarp Long Enough? [Re: finallyME]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
The reflective insulation they use in house attics really needs air space to work properly. In other words, nothing should be touching the reflective side, as little as possible anyway. I gather the reflective insulation in an air mattress works the same way, so if it's stuffed with down, it may not be of as much benefit.

If anyone has built a large tarp with a catenary curve before, I'd love to hear your input on how much droop (the amount of drop in the center) to give it. Getting everything lined up and taped properly is really tedious with survival blankets because there can't be any wrinkles to let in water, so I'd prefer to only cut and tape it once rather than try a small curve and see if it needs more (wash, rinse, repeat).

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#175346 - 02/26/13 09:52 AM Re: Is My Tarp Long Enough? [Re: 4evrplan]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
It's one step forward and two steps back with this project. The only time I've got to work on it is if I get up early before my family, which is hard to do because my youngest son keeps crazy hours, and any sleep I can get is precious. I've been working on it in my office before business hours, because there's space, the kids won't get into it, and I don't have to worry about waking anyone up. Anyway, I finally got one side taped up with the beaks attached on both ends and pulled out another survival blanket to use as the other side and discovered that it's significantly shorter than the first side. Like a foot shorter. Aaaargh! Well, if you ever build anything with survival blankets, do yourself a favor and pull them all out of the package first and measure and be sure of what you've got. I had to cut the first side down to match the length of the second one, and I'll have to reattach the beak on that side. This means that the main body will only be about 7.5' long instead of 8' (it was a bit over-sized before I had to cut it down), with a total ridgeline length of about 122". I don't think my gear is going to be ready for spring break like I wanted. Well, I'll just keep picking away at it, and come high water or that other thing, it'll get done sooner or later.

EDIT: 122" inches is wrong; that's if I still had 16" inch beaks on it, but I've switched to 24" beaks, so the total ridgeline length will be more like 138".


Edited by 4evrplan (02/28/13 12:20 PM)

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#175371 - 02/27/13 08:07 AM Re: Is My Tarp Long Enough? [Re: 4evrplan]
topshot Offline
member

Registered: 04/28/09
Posts: 242
Loc: Midwest
Originally Posted By 4evrplan
I had to cut the first side down to match the length of the second one, and I'll have to reattach the beak on that side. This means that the main body will only be about 7.5' long instead of 8' (it was a bit over-sized before I had to cut it down), with a total ridgeline length of about 122".
I'm curious how you are attaching these "beaks" where you can remove them easily. My experience with space blankets (LDPE) is once taped, you rip and stretch the material when trying to remove the tape. Are you using mylar blankets instead? If so, just know that if you get a puncture you could have a catastrophic failure.

An A-frame with 10' ridgeline is more than sufficient if you know how to pitch it well. Most would have the foot end (windward) lower so protection is greater. Those with a bivy get by with as small as 5x8 tarps.

BTW, the reason you don't normally put cat curves on plastic tarps is the material doesn't stretch. For silnylon and spinnaker it helps keep the pitch tauter longer but you may still need to tighten lines, esp if it rains. If you still want to go through the pain of this, a few inches should be fine for 10' ridgeline.

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#175384 - 02/27/13 12:24 PM Re: Is My Tarp Long Enough? [Re: topshot]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
You're right, there's definitely no "detaching", I'm having to cut it off, as close to the tape as possible so I lose as little of the material as possible. Luckily, I only used a 1/4" strip (on each side) to attach the beaks, so I'm only losing 1/8" of the one I have to cut off (half the width of the quarter inch strip).

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#175404 - 02/28/13 08:56 AM Re: Is My Tarp Long Enough? [Re: topshot]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
Originally Posted By topshot
...If you still want to go through the pain of this, a few inches should be fine for 10' ridgeline.


Counting the beaks, it'll be about a 11.5' ridgeline. I was thinking six inches?

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#175416 - 02/28/13 10:49 AM Re: Is My Tarp Long Enough? [Re: 4evrplan]
topshot Offline
member

Registered: 04/28/09
Posts: 242
Loc: Midwest
I'd say 4" would be plenty, but I still wouldn't waste your time doing it - taping a cat curve will be harder than sewing one and you'll receive little if any benefit.

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#175421 - 02/28/13 12:23 PM Re: Is My Tarp Long Enough? [Re: topshot]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
I thought the curve would help to pitch wrinkle-free (even before it stretches) so it performs better in the wind?

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#175441 - 03/01/13 08:32 AM Re: Is My Tarp Long Enough? [Re: 4evrplan]
topshot Offline
member

Registered: 04/28/09
Posts: 242
Loc: Midwest
Originally Posted By 4evrplan
I thought the curve would help to pitch wrinkle-free (even before it stretches) so it performs better in the wind?
It's more about tautness than wrinkles though they are somewhat related given the stretchy material. I'll be curious how you can manage to tape the plastic without wrinkles! mad

I know I'd never waste my time doing it, but there's no harm in it so go for it. I could be wrong. shocked

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#175446 - 03/01/13 09:33 AM Re: Is My Tarp Long Enough? [Re: topshot]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
Originally Posted By topshot
It's more about tautness than wrinkles though they are somewhat related given the stretchy material.


I didn't mean the small wrinkles under/adjacent to the tape; I meant the long waves of loose material running more or less parallel to the ridgeline, the same thing you're calling tautness. In my mind, those are also "wrinkles", though I'll do my best to eliminate both. It definitely will be a challenge to keep out the small wrinkles. That's part of the reason I've been taking so long; I've been going slow and being very careful. I've actually been lining things up a tiny bit at a time and temporarily taping it up with office tape, which pulls off without leaving damage. Once I've got enough small pieces of office tape patched on to one side of the seam to hold it all straight, I turn the whole thing over to put the permanent tape on the other side. Then I flip it back to the first side, remove the office tape, and re-tape with the permanent tape on that side as well.

Thank you for all your advice on this topshot. Since I'm doing this all by the seat of my pants, your input has been invaluable.

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#175451 - 03/01/13 10:38 AM Re: Is My Tarp Long Enough? [Re: 4evrplan]
topshot Offline
member

Registered: 04/28/09
Posts: 242
Loc: Midwest
Originally Posted By 4evrplan
I didn't mean the small wrinkles under/adjacent to the tape; I meant the long waves of loose material running more or less parallel to the ridgeline, the same thing you're calling tautness.

I know what you were referring to. I've not had any issue with those, but I don't pitch A-frame either so maybe that's worse. I'm thinking of playing with that this summer though (7x10 for my son and I). Looking at pics of others' plastic tarps in A-frame leads me to believe that it isn't a concern.

Quote:
Thank you for all your advice on this topshot. Since I'm doing this all by the seat of my pants, your input has been invaluable.

Go ahead and push the envelope. That's how we find new discoveries. I need to snag some of that nylon sail tape David Gardner found. I wonder if that will make sewing any less gummy. smile

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#175452 - 03/01/13 10:40 AM Re: Is My Tarp Long Enough? [Re: topshot]
topshot Offline
member

Registered: 04/28/09
Posts: 242
Loc: Midwest
I guess I'd also add that it isn't a concern unless the tieouts are done poorly. If the material bunches on the corners, you're going to get some wrinkles obviously.

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#175455 - 03/01/13 12:44 PM Re: Is My Tarp Long Enough? [Re: topshot]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
My tentative plan for stake loops is based largely on what Al Geist has done.


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#175456 - 03/01/13 01:00 PM Re: Is My Tarp Long Enough? [Re: 4evrplan]
topshot Offline
member

Registered: 04/28/09
Posts: 242
Loc: Midwest
Originally Posted By 4evrplan
My tentative plan for stake loops is based largely on what Al Geist has done.
Don't recall that particular diagram from him, but it's close to what I do. I now prefer to use synthetic washers within the tape and only use shockcord on the corners. You can see pics of mine if you search BPL for polycryo tarps.

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#175457 - 03/01/13 01:55 PM Re: Is My Tarp Long Enough? [Re: 4evrplan]
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3886
Loc: Ozark Mountains in SW Missouri
I know I'm chiming in late here, but this "Outdoor Nylon Patch" is really cool stuff.

I've used it on tents and tarps I've made from plastic and it's light and very strong. Perfect for reinforcing corners and grommets, and making tie outs.

I keep a piece in my backpacking "repair kit".
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#175458 - 03/01/13 02:17 PM Re: Is My Tarp Long Enough? [Re: billstephenson]
topshot Offline
member

Registered: 04/28/09
Posts: 242
Loc: Midwest
Originally Posted By billstephenson
I know I'm chiming in late here, but this "Outdoor Nylon Patch" is really cool stuff.
I've not seen that in my store though it claims it is there. Is it in camping, sewing or hardware area? How much is the 8"x8" sheet? I suspect it would be thicker than the sail repair tape.

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#175459 - 03/01/13 03:07 PM Re: Is My Tarp Long Enough? [Re: topshot]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
Originally Posted By topshot
Originally Posted By 4evrplan
My tentative plan for stake loops is based largely on what Al Geist has done.
Don't recall that particular diagram from him, but it's close to what I do. I now prefer to use synthetic washers within the tape and only use shockcord on the corners. You can see pics of mine if you search BPL for polycryo tarps.


The diagram is mine, but it's very similar to the way Mr. Geist did it on his "18oz. two man shelter". The main difference is that he had a 1/2" loop (1" before folding) and put the stakes directly through the tape loop, twisting them 90 degrees to put them into the ground. I plan to use a 1/4" loop and put a small elastic loop through the tape loop, then the stake will go through the elastic loop instead of the tape loop. The loops should be short enough that I can pitch very close to the ground, but I won't have to twist the loops like Al.

Regarding the polycryo tarp thread, I've seen it. Visually, I like the tape loops better, and Al made a good point about the soft tape loops packing better than a tarp with hard objects attached. Incidentally, polycryo looks like a fantastic material for this purpose, but I chose metalized LDPE instead to help with thermal and condensation management. I'm building the tarp in such a way that I can pitch with the reflective side out in hot weather, and supposedly, vapor won't condense on the reflective surface.

EDIT: Of course, I know that condensation could still be an issue when the reflective side is out, but should be a real boon when it's pitched reflective side in.


Edited by 4evrplan (03/01/13 03:11 PM)

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#175460 - 03/01/13 03:40 PM Re: Is My Tarp Long Enough? [Re: 4evrplan]
topshot Offline
member

Registered: 04/28/09
Posts: 242
Loc: Midwest
Originally Posted By 4evrplan
I plan to use a 1/4" loop and put a small elastic loop through the tape loop, then the stake will go through the elastic loop instead of the tape loop. The loops should be short enough that I can pitch very close to the ground, but I won't have to twist the loops like Al.

FWIW, I didn't find the twisting to be an issue. I did my LDPE tarp that way. 1/4" wide may be a bit thin though, depending on what tape are you using. Using a thicker cord should help.

Quote:
Visually, I like the tape loops better, and Al made a good point about the soft tape loops packing better than a tarp with hard objects attached.

I haven't found that to be an issue at all. I have always left my triptease guylines attached and had mesh with a zipper, too. May not have been as neat a roll as without those but worked perfectly fine. I also think the washers inside the tape loops look more elegant (and they will last longer). smile

Quote:
Incidentally, polycryo looks like a fantastic material for this purpose, but I chose metalized LDPE instead to help with thermal and condensation management. I'm building the tarp in such a way that I can pitch with the reflective side out in hot weather, and supposedly, vapor won't condense on the reflective surface.

I doubt it would condense on the top anyway, but people are only concerned if it condenses on the occupant side. I haven't gotten to test it much yet, but polycryo may ward off condensation as well. At first I thought it wouldn't but then I put my metalized LDPE next to my polycryo for 2 nights and they seemed pretty similar. The only reason I'd consider reflective side out would be during high sun (may be a bit cooler) or to signal aircraft.

Let us know how all your tests turn out.

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#175464 - 03/01/13 04:25 PM Re: Is My Tarp Long Enough? [Re: topshot]
4evrplan Offline
member

Registered: 01/16/13
Posts: 640
Loc: Nacogdoches, TX, USA
Even though I mentioned putting the shiny side out and condensation in the same breath, they were separate thoughts, only related because they both have to do with the reflective surface. I realized after I posted that sentence, it could be construed that I'm trying to prevent condensation on the outside (which of course, wouldn't matter), which is why I edited my post (see above).

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