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Shelters The Shelters forum is for the discussion of backpacking shelters (tents, tarps, poncho-tarps, bivy sacks,...).


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  #1  
Old 10-18-2009, 06:34 PM
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Reality Reality is offline
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Tarp Cut / Hex Design (Catenary Curve, Flat)

There's been a fair amount of discussion and general chatter regarding certain (catenary, hex) cuts of backpacking tarps over the past few years.

I've discussed my feelings on this subject in detail with a few tarp designers and avid tarp users in the past. In short, I've been a fan of the simple, flat design. I don't see any particular need for any significant cuts/curves in a tarp.

Some feel that this "cut" allows for a more taut pitch and perhaps handles the weather (wind) better. I agree more with the former. That is, a subtle* curve (correctly designed) can indeed facilitate a taut pitch. However, this is something that I've done over and over with a flat tarp. [*I've experienced slight curves in a MLD Grace tarp and perhaps even the Hilleberg Tarp 10 UL (at my outer limit of an acceptable cut range) that are effective without radical cuts.]

As for handling (or flapping in) the weather/wind/rain better. That's open for debate (though I've already come to my own well-tested conclusion - based upon effective pitching).

I believe the simple fact that the absence of fabric is (allows for) the presence of the elements/weather.

For a basic (non-scientific) illustration (see attached); I've draped an OES MacCat Deluxe (10.8' x 8.7' - not true dimensions/coverage) catenary cut tarp over a flat 10' x 10' tarp.

This is merely to show how the absence of fabric (i.e. the cut) allows the weather to penetrate areas that would not otherwise be affected sans the cuts.

One thing the cut definitely achieves is less weight. Which stands to reason: cut away the fabric, cut away the weight - or less coverage = less weight (considering the same fabric in use).

My intent is not to suggest that a catenary tarp is of no worth, but rather to add some perspective as to how it compares (IMO) to a flat tarp.

A flat tarp can be pitched very taut - even to the point of not flapping (any more than a cat tarp). To reduce weight, one need only opt for smaller sized flat tarp - eliminating a need to cut large (content/person-exposing) curves into the sides.

I feel that some of the more radical catenary cuts I've seen are not needed. Some cuts are so significant that they nearly defeat or certainly compromise the intent (keeping precipitation and/or wind out). Indeed they have long contact points (ridge/guy points) only to remove (cut away) protection from the main body (i.e. the portion providing the protection).

A 10' x 10' silnylon tarp weighs just a little more than a half-liter of water. And it meets one of the primary needs in the wilderness: shelter. Weight well-worth the function.

I prefer a large tarp - perhaps due to the type of weather it must shield me from. If I'm in good weather, I can go smaller (but it'll likely sit in my pack, since it's not needed when the weather is good).

Again, my point is that a flat tarp can be pitched nice and taut and certainly not flap any more than other designs.

Backpacking and shelter use really is a simplistic and wonderful thing. I recommend that we continually put things to the test to be sure they meet our requirements for comfort, safety, and maximum enjoyment. A tarp, like the proverbial wheel, doesn't require any radical re-invention. Sure some enhancements can be beneficial, but others may just be unnecessary. Who knows, a little extra effort (pitching practice) could save money and hone some skills.

Food for thought.

Reality

[Photos: 1) Large view: shows cat tarp coverage in comparison to square/flat tarp; 2) Closeup view: shows corner coverage. Note: These tarps are pitched overa hammock.]
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  #2  
Old 10-21-2009, 12:22 PM
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richwads richwads is offline
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I've been tarping for 30+ years and have never used a catenary cut tarp for one basic reason: Its effectiveness is based on only one way of pitching it.

Even though I have a favorite pitch (modified A-frame) that I use in the absence of tie-out points like trees or shrubs, I usually improve on the A-frame pitch by using such points.

Anyway, a taut pitch in the A-frame shape with a flat tarp is easily obtained without such tie-outs by either 1) staking the midpoints of the sides farther away from centerline than the corners or 2) adding 6" cord loops to the four corners so one or more may be slightly off the ground, allowing parallel sides while the ridge sags slightly. Actually, I leave the cord loops on the corners now because irregular ground is more easily accomodated by having multiple options at the corners.

Also, I like having two ridges to choose from with my 8x10 tarp, or no ridge at all, and wonder how "flat" a catenary cut tarp is when its ridge isn't used as one.
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  #3  
Old 10-21-2009, 12:30 PM
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Reality Reality is offline
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Quote:
Originally Posted by richwads
I've been tarping for 30+ years and have never used a catenary cut tarp for one basic reason: Its effectiveness is based on only one way of pitching it.

Yes, a "flat" tarp is very versatile in comparison. Although I have pitched a "cat" tarp in a modified A-frame too.

Thanks for your input, richwads. Feel free to share a photo of your tarp-pitch.

Reality
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  #4  
Old 10-21-2009, 05:54 PM
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FamilyGuy FamilyGuy is offline
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Wow - a picture says a thousand words!
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  #5  
Old 10-22-2009, 09:06 AM
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richwads richwads is offline
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Quote:
Originally Posted by Reality
Yes, a "flat" tarp is very versatile in comparison. Although I have pitched a "cat" tarp in a modified A-frame too.

Thanks for your input, richwads. Feel free to share a photo of your tarp-pitch.

This is how the last pitch ended up. The low rear of the modified A-frame helps roof drainage and reduces the wind/splash factor at the foot. The cord loops on the front grommets help to tension the entrance both forward and down, and makes the actual stake location less critical, i.e. if there's a rock or root at my first choice, moving the stake an inch or so still keeps the tarp taut. If rain starts coming in the front, it's easy to narrow and lower the front pitch, even "closing the door" somewhat by use of a cord through the front side 1/4 point grommets.



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  #6  
Old 10-22-2009, 10:43 AM
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Reality Reality is offline
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Thanks for the photos, richwads. That's certainly an A-frame pitch that has been modified.

However, many understand "modified A-frame" to refer to one side of the tarp being lifted up.

Reality
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  #7  
Old 10-22-2009, 10:53 AM
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richwads richwads is offline
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Quote:
Originally Posted by Reality
. . . many understand "modified A-frame" to refer to one side of the tarp being lifted up.

Reality

Aaahhh . . . good to get the terminology right - and here I've been calling that a "shed" pitch . . .

The shed (oops - modified A-frame) was my favorite pitch with a 7x9 tarp for many years, but the advent of silnylon has me taking advantage of the better coverage of a "pup tent".

I wish I could post photos of years of various pitches, but this is the first season I've had a digital camera .
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  #8  
Old 10-22-2009, 11:00 AM
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Reality Reality is offline
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No worries on the terminology. It's good to know that you've been able to get good coverage and versatility from your flat tarps.

Reality
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  #9  
Old 02-26-2012, 08:07 PM
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The following is somewhat redundant in this thread, but it's been a while since I've discussed this here.

Recently, a friend shared a comment with me that he read regarding tarp size (cut) and ample protection from the elements.

The gist of the comment was that if a tarp user was "skilled" [enough], s/he could get by with a small tarp (i.e. keep self and gear dry). My initial response was a respectful chuckle, that I quickly squelched when it became clear it was meant to be taken seriously.

Certainly, one might be able to pitch the tarp out of the worst of the rain, scrunch up, or simply experience well-behaved precip (i.e. straight down). However, there's more to be said on this matter - to keep the uninformed from adopting advice that could lead to a wet mess. [Fair-weather campers or those just using a tarp for 'sap and crap' may disregard the following. ]

I've been saying for years that the novel/trendy cuts and curves are primarily to save weight. Seems obvious, but apparently not to all. Granted, certain "cuts" may help some who are having troubles obtaining a taut pitch with standard tarps, but it's my opinion that these cuts and curves are merely a means to trim away ounces or grams (and/or to be competitive). [This is not unlike the logic applied to slim and tapered sleeping bags.]

Now, before I'm misunderstood, I'm not suggesting that these designs are wrong. I can appreciate some slight, precision curves that are intelligently engineered to improve the pitch (e.g. CubicTwinn Tarp, Hilleberg Tarp 10 UL).

But I'm not going to overlook a very fundamental absolute regarding tarp size: Less Fabric = Less Coverage.

I hold lightweight backpacking principles close in mind and apply them, but not to the point that the purpose or functional integrity of an item is defeated. An exaggerated example, to make a point, is that I will not punch holes in my water container to remove (plastic) material to save weight [Likewise, a diamond cut (shaped) umbrella isn't as efficient as the traditional design.]

I have tarps with "cuts and curves," but I just make sure that the tarp is large enough that they don't come into play - meaning that a full/adequate rectangle/square of coverage still remains.

I'm not sure what type of weather these "skilled" 'tiny-tarpers' are camping in, but I do know that torrents of rain can blow from many directions - in which even the most gifted contortionist would be drenched without adequate coverage.

Some small, dramatically cut tarps may look good when crunching the ounces in a spreadsheet or when viewing on some guru's gear list, but quite different in a sustained windy, rainstorm. [I can just see the exceptions popping into some minds now. "I was in 'Hurricane Bubba' and I stayed dry under my bandana..." So, let's just get it out of the way: there are exceptions.]

My advice for the apprentice, skilled, or anyone else is to use the right tool for the job - in this case, suitable (smart) protection from the elements. This has less to do with individual skill and more to do with science (mother nature) and even common sense.

The informed/experienced tarp camper will be quick to warn that there's more to tarp coverage than an aerial view may reveal. Rain blows in from any direction - even towards those open areas that were exposed by fabric removal (from the side-ends of some tarps). [See attached images at top of this thread.]

Here's a test for the unconvinced: Walk around in the pouring rain one time with only a kippah on your head and another time with a Seattle Sombrero (or similar) on your head. Then compare the results.

Reality
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  #10  
Old 02-27-2012, 04:24 AM
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Ralph Ralph is offline
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I have made, carried and used square, 21-connecter flat tarps for many years because they are light, compact, relatively inexpensive and have many ways to pitch. Cutting a catenary curve makes more sense for a one-way-pitch tent than for the more flexible tarp although modern usuage blurs the distinction between those two.
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