How to get more width for a tarp....

Or how to use narrower fabric and still gain something...

I was looking at dimensions and coverage and fabric widths and had a bit of an epiphany that while it involves more seams is also an efficient use of fabric and allows a greater effective width... Depending on the chosen dimensions the gains may be considerable. With the nominal BlackCat dimensions about 30" width per side could be achieved if you so wanted....

Here is an attached drawing showing how. Basically the parts you cut off for the taper of the hex at the ridgeline get sewn on the outer edges of the fabric. Piece 1 on the drawing, goes to the position shown. The tip (piece 2) may be used to fill the low point, again as shown. Repeat for all 4 corners...

Do the piecing then cut your curves. In my case I wanted a 14' ridgeline, and a 9' length at the 60" width fabric, but once I cat cut it my maximum effective covered width dropped from 10' to about 8'...

I LIKE BIG tarps (and I cannot lie... sorry flashing on MC Hammer :rolleyes: ), so I wanted MORE... This gives me up to 24" more on each side... I chose a middle ground where the dotted line shows the tarp cut I'm planning. This increases my coverage by about 18" on each side at the points and I get more like 12' coverage...instead of 8'.... (in the flat..)....

Anyways.... Here's the PDF of the idea....

It appears to sacrifice coverage on the ends for the extra width. Is that correct?

You can call it the "OrigamiCat".:D

Quote:

---

Originally Posted by Cannibal

It appears to sacrifice coverage on the ends for the extra width. Is that correct?

---

Not really....

If you use a "hex" design that's material you'd just throw aside as scrap. Instead you attach it to the edges... Like I mentioned with the BlackCat standard dimensions you cut off a triangle with a 34" base and a 66" height. This is material you could maybe use on another project, or to make a stuff sack, but it wasn't going on your tarp... Now it is.

There are already things that show a hex tarp has more coverage than a square for a given ridgeline length. Such as this photo by Blackbishop http://www.tothewoods.net/ImagesStay...ackCat-JRB.JPG

In my case I wanted a 14' ridgeline, but to get a reasonable angle so I'd have a taut pitch I couldn't make the sides between the tie-outs much longer than 9'. That still gives more end coverage than a square. But the length difference meant I was cutting off a triangle 30" at the base by 60" high. This way I can add them to those sides and gain most of that back, instead of wasting it.

Giving me a tarp that can either be pitched wider and flatter with more area under it, or higher and narrower with better side coverage and headroom.

Quote:

---

You can call it the "OrigamiCat".:D

---

:p I was wondering what to call it...

I get it now, thanks!

Looking forward to pics of the final project.

How much more width are you trying to gain? The BlackCat already uses material that is 60" to 66" effectively giving you a 10'X12' tarp less the cat cuts. IMO it's a pretty big tarp already. Any bigger and it just gets heavier and cumbersome to handle.

I'm limited by only having 60" fabric, but the idea would work with any width of fabric so it'd be possible to use 48" width say...

But personally mine is going to be 14' along the ridgeline and about 12' at the tie outs... Yes its larger than absolutely necessary, but 1) hate getting wet, 2) at times it'll be sheltering more than one person, 3) I want it to be absolutely bomb proof when it comes to rain...

So I'm not using all the potential gains. Just what I want to get from it... :)

I have 10 x12 tarps now and they never seem big enough.:eek:

Interesting Rapt.
How much would you loose if you had the cat cut go just above the #2 pieces? I was just thinking that would be three less seams (per side) and still give a pretty darn wide tarp.

Rapt that is a big tarp. I just finished mine and when I was done I thought it was huge already. I say go for it. It will weigh less than a pound and a half anyhow. I used the scraps from mine to make rain kilts for my wife and I. I also think putting end sheild could easily by using the scrap. I know I've seen pictures of it done.

Quote:

---

Originally Posted by Dutch

I used the scraps from mine to make rain kilts for my wife and I.

---

That is classic. What a great idea!
Is it still a 'kilt' if a lady is wearing it? :D

Quote:

---

Is it still a 'kilt' if a lady is wearing it?

---

I really call it a rain skirt around most circles. Actually I really like mine and I am trying to figure out a way to turn it into a weather shield for the end of my tarp or my bridge hammock. It should be a piece of cake since it is just a rectangle with elastic and a couple buttons. I don't usually dress in drag in the woods, but I can't hike in rain pants and the skirt, errr kilt weighs nothing and keeps my bum dry.

Wow, that's some serious width. And I am someone who likes big tarps. The extra seams would add some weight though. With them being low to the ground and not overheard, I wouldn't worry about seam sealing them.

Oh and it was Sit Mix Alot, and not MC Hammer.

Quote:

---

Originally Posted by hammock engineer

Wow, that's some serious width. And I am someone who likes big tarps. The extra seams would add some weight though. With them being low to the ground and not overheard, I wouldn't worry about seam sealing them.

Oh and it was Sit Mix Alot, and not MC Hammer.

---

OOps showing my age a bit there... LOL! My bad for getting the artist mixed up.

Schrochem, It depends on the geometry you're using, but for mine or something similar about 6" of coverage. I haven't decided if its worth the hassle or not.

Quote:

---

Originally Posted by Rapt

Not really....

If you use a "hex" design that's material you'd just throw aside as scrap. Instead you attach it to the edges... Like I mentioned with the BlackCat standard dimensions you cut off a triangle with a 34" base and a 66" height. This is material you could maybe use on another project, or to make a stuff sack, but it wasn't going on your tarp... Now it is.

There are already things that show a hex tarp has more coverage than a square for a given ridgeline length. Such as this photo by Blackbishop http://www.tothewoods.net/ImagesStay...ackCat-JRB.JPG

In my case I wanted a 14' ridgeline, but to get a reasonable angle so I'd have a taut pitch I couldn't make the sides between the tie-outs much longer than 9'. That still gives more end coverage than a square. But the length difference meant I was cutting off a triangle 30" at the base by 60" high. This way I can add them to those sides and gain most of that back, instead of wasting it.

Giving me a tarp that can either be pitched wider and flatter with more area under it, or higher and narrower with better side coverage and headroom.




:p I was wondering what to call it...

---

Note that this is a Black Cat which is some 30 percent larger than a MacCat...It is very close to a 12x10 that has been reshaped to provide a wide angle hex with cat edges. It is on the order of 100 sq ft and 16-18 oz or so.... It is compared here to an 8x8 with approximately 60 sq ft of coverage for 9 oz.

The unshown relationship is that the 8x8 is a actually the same or larger than a standard Mac Cat, just a slightly different shape . And that both the 8x8 and the MacCat are 30 percent larger than a standad BULA tarp.

All three tarps discussed here provide more than adequate coverage.... The real issue is, how much extra room would you like and at what cost in $ and weight.

FWIW, while we are on this point, it is fair to note that for any given size, the traditional rectange provides more coverage, more flexibility in pitch options and frequently weight LESS that the Cat Hexes because rectangles with rolled hems eliminate the weight of the gross grain tape commonly used to edge this design. They also are normally less costly.

Further, it is worth noting that the emerging rectangular tarps with mild cat cuts , like the Speer 8x10, may be the best of both worlds. Max coverage, less weight, more versatility, taut pitch and approximately equal cost for equivalent length sizes. So if you are into max coverage, taut pitch and less weight for a given ridge length consider these emergent cat rectangles.

Pan

What do you guys think of the Gosamer tarp?

http://www.gossamergear.com/cgi-bin/...inn-Twinn.html

It looks like it might be a bit short for a hammock at 117".

Quote:

---

Originally Posted by Dutch

I really call it a rain skirt around most circles. Actually I really like mine and I am trying to figure out a way to turn it into a weather shield for the end of my tarp or my bridge hammock. It should be a piece of cake since it is just a rectangle with elastic and a couple buttons. I don't usually dress in drag in the woods, but I can't hike in rain pants and the skirt, errr kilt weighs nothing and keeps my bum dry.

---

You might try replacing the elastic with a draw string.

Pan,

Love to talk more about about "coverage". Everyone has different perspectives. From my point of view and experience with the conditions I typically camp in (down bag, windy driving rain, temperature swings, solo - as in no other people for days/weeks in any direction) And the things I've survived, but wasn't comfortable with or happy about at the time. I'm not comfortable having less than a LOT of margin when it comes to keeping dry.

A diagonal pitched square is to my mind "less" effective because your ground coverage is MUCH smaller since there are no long sides near the ground. Granted I know that this is a hammock forum, but we still walk and cook and store many things on the ground even if we sleep and sometimes sit in a hammock. I like to be able to do things when its raining, but still have someplace to get out of the rain without being in bed. A hex seems to suit this compromise by giving longer coverage for the hammock but still "longish" sides close to ground for when you're NOT in the hammock.

Oh and my hammock has an 11' ridgeline... Maybe I need to make a shorter one...

I'll carry weight if I have to, to acheive that., I'd prefer not to, so things like Cuben seem appealing to let me go big AND still be light.

I'll dig into squares (and rectangles) vs hexes and do some overlays...

Having spent some time thinking, and doing some math, I can state that a hex of a set area gives better "effective" coverage than a rectangle of the same area, provided the material from cutting the end angles is used to extend the width.

In doing the math I made some assumptions. 1)The ridgeline length is the same in both cases, for example if a 14' ridgeline is required and fabric is 60" wide for a maximum rectangular area of 14 x10' 2) the hex would be 14' ridgeline with an approximately 12.5' width and 8' parallel to the ground on the sides, (actually this shortchanges the hex by about 1.8%, but as we'll see its still better. 2) The ridgeline pitch height is the same in both cases. 3) The low sides are pitched the same vertical distance from the ground.

For example... Assume a 5' ridgeline pitch height and the low sides are 1' off the ground (Not too unreasonable I think for a windy rainy pitch.)

The covered area of the 14 x 10 rectangle is: using Pythagoras to get 3' per side 6*14= 84 sq ft. Not bad and you probably won't rub against the tarp sides with the hammock with such a steep pitch....

BUT using the hex as described above and Pythagoras the width is 4.8' per side. The area is 8*9.6 (for the long sides) + 3*9.6 (for the hex points at each end) = 105.6 sq ft Clearly better with the tapered ends giving less coverage where the hammock is higher off the ground. Not to mention the greater width ensuring that its very unlikely the hammock will touch the tarp.

As a side note a 10' x10' square is clearly less in area (about 30%) but pitched diagonally has pretty close a 14' ridgeline. At a diagonal, the above pitch gives the following: 5.75' per side of coverage distance or an area of
11.5*7 = 80.5 sq ft. This is clearly less than both the above, but not a lot less considering the difference in weight for 100 sq ft vs 140 sq ft of fabric. The only thing is without any "long side" near the ground there is much less lateral coverage with windblown rain.

Convenience in pitching, flexibility, tautness, etc, are less easily compared since they have a large subjective content. But I think that its likely that a rectangle 14 x10 will require at least as many tie outs as the hex to remain taut. The square saves a couple of tie outs...

All in all I think I'll stick with the hex...

Quote:

---

Originally Posted by Rapt

Having spent some time thinking, and doing some math, I can state that a hex of a set area gives better "effective" coverage than a rectangle of the same area, provided the material from cutting the end angles is used to extend the width.

In doing the math I made some assumptions. 1)The ridgeline length is the same in both cases, for example if a 14' ridgeline is required and fabric is 60" wide for a maximum rectangular area of 14 x10' 2) the hex would be 14' ridgeline with an approximately 12.5' width and 8' parallel to the ground on the sides, (actually this shortchanges the hex by about 1.8%, but as we'll see its still better. 2) The ridgeline pitch height is the same in both cases. 3) The low sides are pitched the same vertical distance from the ground.

For example... Assume a 5' ridgeline pitch height and the low sides are 1' off the ground (Not too unreasonable I think for a windy rainy pitch.)

The covered area of the 14 x 10 rectangle is: using Pythagoras to get 3' per side 6*14= 84 sq ft. Not bad and you probably won't rub against the tarp sides with the hammock with such a steep pitch....

BUT using the hex as described above and Pythagoras the width is 4.8' per side. The area is 8*9.6 (for the long sides) + 3*9.6 (for the hex points at each end) = 105.6 sq ft Clearly better with the tapered ends giving less coverage where the hammock is higher off the ground. Not to mention the greater width ensuring that its very unlikely the hammock will touch the tarp.

As a side note a 10' x10' square is clearly less in area (about 30%) but pitched diagonally has pretty close a 14' ridgeline. At a diagonal, the above pitch gives the following: 5.75' per side of coverage distance or an area of
11.5*7 = 80.5 sq ft. This is clearly less than both the above, but not a lot less considering the difference in weight for 100 sq ft vs 140 sq ft of fabric. The only thing is without any "long side" near the ground there is much less lateral coverage with windblown rain.

Convenience in pitching, flexibility, tautness, etc, are less easily compared since they have a large subjective content. But I think that its likely that a rectangle 14 x10 will require at least as many tie outs as the hex to remain taut. The square saves a couple of tie outs...

All in all I think I'll stick with the hex...

---

you want I should see if Sister Mary Augustine is around to check your figures? ;)

Grizz

If you're wrong she'll rap your knuckles with a ruler.

Sure... I think I did it right... But most of it was in my head so I may have missed something, or doubled when I should have halved or vice versa...:D

Sister Mary Augustine says that if the hex truly has 8' parallel to the ground with a 14' ridgeline, then the width of the side has to be 70/11 feet, which makes the tarp width on the ground closer to 4.95' on one side rather than 4.8'. She thought that was enough to go after you with her ruler, but I pointed out that these days she needs a passport to get back into the USA, and so I think I dissuaded her.

But I got to thinking that since not all "covered space" is created equal (your metric of coverage is bird's eye---straight down) what is really wanted here is a utility function that, for a given tarp, ascribes a "coverage" value to every point in the x-y plane. For example, the value could be the fraction of all rays in the positive z dimension with that point as the origin, which intercept the tarp. This is motivated by the idea of rain coming down. But then not all rays are equal in terms of threat, so the rays that are more likely to correspond to rain would be given more weight. Then to get the utility coverage you'd sum the coverage value over all points in the x-y plane.

There's a simpler way I'm sure. If any ideas come to me that can be easily conveyed (unlike the babble above) I'll jot 'em down.

Grizz

Quote:

---

Originally Posted by Take-a-knee

What do you guys think of the Gosamer tarp?

http://www.gossamergear.com/cgi-bin/...inn-Twinn.html

It looks like it might be a bit short for a hammock at 117".

---

For the shorter hammocks HH BULA size, ENO , Travel pod, Byers and Claytor exped and mosquito it should be fine... taper on the foot end just means a little less side coverage, probably no big deal... little pricy though

Pan

Yes, I pointed out that the hex was merely close and slightly short on area rather than exact. (To simplify the math as 6.25 is easier to use than 70/11.) I felt safe doing that as I knew it would give me a conservative result.

And yes I understand the thinking that not all covered space is equal, the closer and edge is to the ground the less wind penetration. That said, if you assume a fixed angle of rainfall being driven by a wind, this isn't that hard to calculate. I suspect that we'll find the resulting superiority of one shape over another is still basically the same, at least as long as the ridgeline is perpendicular to the wind direction.

I haven't yet worked through the ridgeline parallel to the wind direction case but my suspicion is that it'll come out the same as well, since any loss of coverage at one end will be matched by an equivalent gain at the other.

Most interesting might be to work out coverage if we assume a given rain angle and a wind that shifts a full 360 degrees. (I'd calculate one side with a perpendicular situation and one with a parallel and then take it off twice as a reasonable estimate.)

Quote:

---

Originally Posted by Rapt

Yes, I pointed out that the hex was merely close and slightly short on area rather than exact. (To simplify the math as 6.25 is easier to use than 70/11.) I felt safe doing that as I knew it would give me a conservative result.

And yes I understand the thinking that not all covered space is equal, the closer and edge is to the ground the less wind penetration. That said, if you assume a fixed angle of rainfall being driven by a wind, this isn't that hard to calculate. I suspect that we'll find the resulting superiority of one shape over another is still basically the same, at least as long as the ridgeline is perpendicular to the wind direction.

I haven't yet worked through the ridgeline parallel to the wind direction case but my suspicion is that it'll come out the same as well, since any loss of coverage at one end will be matched by an equivalent gain at the other.

Most interesting might be to work out coverage if we assume a given rain angle and a wind that shifts a full 360 degrees. (I'd calculate one side with a perpendicular situation and one with a parallel and then take it off twice as a reasonable estimate.)

---

Devil's advocate here. If the rain is coming in at the angle normal to the tarp surface, then I think your coverage area is just exactly that---area, which would be the same for the rectangle or hex, right? If the rain comes in at an angle that is not normal to the tarp surface, but is orthogonal to the ridgeline, then the spread of the tarp is going to make a difference, but the only difference will be for points that are very close to the edge. Seems a small effect overall.

I just know there's a way of doing this with rotation matrices (to describe point of view) and matrix-matrix (or maybe matrix-vector) multiplications....this is just computer graphics calculations....but I got real work to do, play time will have to wait :(

Grizz

In thinking about rain pounding on tarps at normal angles and the like, I realized that to get the coverage from rain falling straight down, you just multiply the tarp area by the sin of the angle formed by the side of the tarp, and the vertical. Does not matter what shape the tarp is, so long as the whole side is at that angle. In fact, so long as the rain is coming in orthogonal to the ridgeline, a similar calculation works, but you need to break it up into two parts to account for the two sides of the tarp. But the transformation in both cases is a matter of multiplying the given area by the sin of an angle.

This means that the farther out the tarp is staked (given a fixed height pitch), the more coverage you get.

Which means that an isosceles triangle whose area is the same as the 14x10 rectangle or hex with same area will have larger coverage.

Which led me to wonder why the triangle in your example came up short---and it is because a 10x10 tarp has less area than a 10x14 tarp. Which you knew, the point was to choose among tarps with common 14' ridgelines, not necessarily tarps with common surface area.

To complete the thought, given your figures, the length of the tarp from ridge to corner is 10', giving 127 sq ft of coverage. A tarp that large, with that shape---which maximizes coverage of a certain type---accentuate the point that not all coverage is created equal.

Grizz

Grizz you lost me (which is easy to do :D).

But

Quote:

---

Originally Posted by GrizzlyAdams

.....Does not matter what shape the tarp is, so long as the whole side is at that angle. ....

This means that the farther out the tarp is staked (given a fixed height pitch), the more coverage you get.

Which means that an isosceles triangle whose area is the same as the 14x10 rectangle or hex with same area will have larger coverage.

---

If the shape doesn't matter, how does that triangle give larger coverage?

Quote:

---

Originally Posted by TiredFeet

Grizz you lost me (which is easy to do :D).

But



If the shape doesn't matter, how does that triangle give larger coverage?

---

With the height pitch fixed (say at 4 ft) and the width pitch (of the furthest point) fixed, then it doesn't matter what the shape is. The whole surface is at the same angle. If that angle was zero (sides hanging flat) then there is no coverage. If that angle was 90 degrees (of course it can't be) then the covered area is just the area of the side, no matter what shape. The same is true whatever that angle is. In geometric terms you'd say that the coverage is the "projection" of the area onto the plane. (Quick, call your mother and thrill her with your big new words :) ).

Here's another way to look at it. Think of the surface of the tarp as being the assemblage of many many tiny squares. If you can figure out how much coverage you get from one tiny square, then you get the total coverage by adding up the coverages from all the tiny squares because they are the same. So if every tiny square is at the same angle with respect to the ground, and you get the total coverage by adding up the coverages of all the tiny squares, then any way you shuffle those squares around will give you the same answer, provided that each is at the same angle. That's why shape doesn't matter for a fixed pitch.

So why should angle matter? If you imagine looking straight down at a tiny square and imagine how much of the ground is covered from view as a function of the angle, you see nothing is covered when the angle is zero, and as much as possible is covered when the angle is 90 degrees. The closer the angle is to 90, the more is covered.

So coverage is driven by this angle, and for a fixed tarp height pitch the angle is determined by how far out you can pitch the sides of the tarp. Of the three (rectangle, hex, triangle), the farthest pitch is the triangle, so it has the angle closest to 90 degrees, and the largest coverage (as defined above).

here ends the reading of the First Lesson
Grizz

Man I sold my freaking graphing calculator when I was done with college, this stuff is giving me a headache. I'm gonna go play sodoku it's less complicated!

I think this thread needs pictures... oh wait... That'd mean I'm probably the one to make them...:eek:

Anyways, I think I understand what you're saying Grizz, and if you're saying what I think then I agree... While its possible with matrices, I was thinking more in line with your follow up post. To my mind the fairly simple trig is the way to go. However we can't neglect the effect of the drip line on the leeward side acting to reduce the "covered" area for that half... With winds orthogonal to the ridgeline.... So its not actually the whole area... However its still in the same proportions as the projected areas.

Quote:

---

Originally Posted by pure_mahem

Man I sold my freaking graphing calculator when I was done with college, this stuff is giving me a headache. I'm gonna go play sodoku it's less complicated!

---

You are new here, and maybe haven't explored the site well enough to know that this sort of thing does happen. As a reminder, I've attached a screen-dump of the page with the required-by-law alert. ;)

Grizz

pure mahem- Be glad they are doing the math-work; it could be your butt hitting the ground if the engineers of the world all went hiking.

Besides, you'll get used to it. If your really lucky and study hard enough, some if it starts to make sense. :eek: That's how I know it's time to get off the website and go hiking. :D

Grizz, my son has math homework tonight I was going to help him with but now my brain is mush, can I post his questions for you... :D

And I thought my 10X10 Hex was big!

this thread has forced me to take an extra dose of my Adult ADHD med:D