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newsTreeHugger 1P Mark-1 tarp deep catenary cut
On June 5, 2021, I posted instructions for a glued tarp, straight-cut, that weighs only 178g:
https://bkhome.org/light/treehugger-1p-tarp-weighs-only-178g.html
After that, I speculated about a catenary-cut on the ridgeline, to
try and get rid of looseness of the fabric along the ridgeline:
https://bkhome.org/news/202106/catenary-cut-for-tarp-ridgeline.html
...and cut a minimal catenary curve along the ridgeline.
However, the fabric along the ridgeline was still very floppy, so
decided to experiment with a much more aggressive catenary cut.
To this end, I thought about what the curve shape should look like.
It seemed to me that the curve of a boat mooring line looks "good", as
calculated here:
http://abc-moorings.weebly.com/catenary-calculator.html
I can't say that this is the mathematically best shape for the
deep-cut ridgeline, but it intuitively looks "right". I downloaded the
spreadsheet file, and gzipped it, uploaded here:
Catenary-Mooring-Line-Shape-Tool.xlsx.gz
Here is a table that I got from that spreadsheet:
...you enter "77" for the "d" parameter, and "205" for the "X"
parameter. "X" is whatever the actual horizontal distance is, as shown
in the sketch. Transfer the table to the fabric, gives the green line.
This will be done on both pieces of fabric (the first can be used as a
template to mark out the second), and when the two ridgelines are
brought together, to be glued, there will be an overlap of 2.5cm, and it
is necessary to mark a line on the fabric that will be underneath the
overlap.
The ridgelines are now curved, and have to be pulled straight, so as
to be glued. I did that by placing them overlapped and held down at each
end with concrete blocks:
...so, in theory, I can run adhesive along the underneath fabric, and
the top piece should just about flop back into the correct overlap position. The
main problem with this plan, is couldn't lift the fabric at the ends,
because of the blocks, so had to start further in. But that is OK, glued
the ends afterward.
In the above photo you can see newspaper underneath. One layer of
newspaper, with cling-wrap over that. The cling-wrap is important,
because silicone adhesive does not stick to it. When I ran the seam
roller over the overlap, a tiny bit of sealant bleeded out underneath,
which is OK -- it will simply be flattened by the roller and won't stick
to the cling-wrap.
I have posted about this before, but reiterating here, this is the roller I use:
https://www.bunnings.com.au/uni-pro-30mm-seam-roller_p1662302
Glueing worked reasonably well. I used the 25.4x25.4x1.6mm spreader tool that I discussed in an earlier post:
https://bkhome.org/news/202106/refinements-to-glueing-tarp.html
...that worked really well. Using the applicator gun, ejected the
silicone adhesive in a zig-zag pattern, fairly generously as the
spreader tool will catch any excess glue -- it just piles up inside.
Here is the ridgeline after glueing, with one side pulled out flat, so you can see the curve:
...and as you can see in the photo, the tie-out webbing has been sewn
on. It is best to wait several days after glueing, before sewing, to
avoid gunking up the sewing machine. Here is close-up of the short end:
And here is close-up of the high end:
In the original straight-cut ridgeline, I experimented with "sockets"
to hold the carbon-fibre poles. What I have done as shown above is very
simple, just silicone end-caps glued to the webbing. These, 7.7cm ID:
https://www.aliexpress.com/item/1005001609758449.html
I have experimented with this, and found it to be very strong.
Silicone adhesive bonds to the silicone end-caps very strongly -- so
strong, that it can't be separated. The weak point is the bond with the
webbing -- I used the applicator gun pressed firmly onto the webbing and
forced silicone adhesive as much into the webbing fibres as possible.
Then used my finger (wearing disposable gloves) to press the adhesive
firmly to try and force it into the fibres even more.
The end-cap is glued right on top of where the webbing loop is sewn together, so it is, I think, a pretty strong end-result.
I have mentioned in an earlier post, reiterating here, I now use a
mini-applicator gun, that takes 150g tubes of silicone sealant:
https://www.bunnings.com.au/monarch-mini-compact-caulking-gun_p1662108
...I find this easier to wield while glueing hems and ridgeline, and
also, unlike the full-size gun, the flow stops immediately I take my
fingers off the lever -- I like that very precise control.
The black webbing is this, nylon 12mm wide, and 1mm thick:
https://www.aliexpress.com/item/4000126877988.html
The blue webbing at the high end is for when want to erect the tarp
in "tree hugger" mode, tied around a tree trunk. That is much lighter,
nylon 10mm wide, 0.5mm thick:
https://www.aliexpress.com/item/1005001666741572.html
Oh, and that cord-tensioner on the black webbing is from here:
https://www.aliexpress.com/item/1005002198346631.html
Here is the final weight of the Mark-1 deep-cut tarp: 183g (6.46oz)
Photo erected:
...yes, very good, the sides are fairly taut.
Of course, you do lose head-height, but it still looks OK. When erected in "tree
hugger" mode, I will be sitting at the very end, leaning against the
tree trunk (or wall inside a shelter), so my head will be at the highest point of the tarp. And yes, there will need to be
rain protection to make that feasible, will get onto that stage of
construction soon.
Actually, the weight is a little bit higher than it could have been. I
cut the ridgeline open twice, going from a straight-cut, to a slight
catenary curve, then a deep-cut curve. This resulted in a mess at the
ends of the ridgeline and had to glue extra layers of reinforcing fabric
to rejoin the ends of the ridgeline. Even so, 183g is pretty good.
Next instalment coming soon!
Tags: light
Ultralight wood-burning stove for hiking
Years ago, I bought a few different metholated-spirits-burning
stoves, aiming for extreme light weight. I was reminded of this today,
reading this post:
http://bushwalk.com/forum/viewtopic.php?f=53&t=36046
...forum member 'crollsurf' has a really light setup, stove and windshield:
https://www.ebay.com.au/itm/324185702933
https://www.ebay.com.au/itm/144062317171
...total 42g. But may also need a metal disk under the stove, to insulate from the ground. And of course a small pot.
I also have this kind of gear. Of course, meths has to be carried,
lets say a 100ml bottle for a multi-day hike. So, at least another 100g,
and the bottle has to be carried such that it doesn't leak.
lately, I have been exploring the option of a wood-burning stove. It
certainly does appeal -- just using fuel from the forest floor, no need
to carry fuel. Even in the most arid wilderness, there are going to be
leaves and twigs lying around on the ground.
These little wood-burning stoves are in a grey area, in places where
open fires are banned. Here in Western Australia, many hiking trails
allow fires within designated fire-pits, and in some places even on open
ground, but usually only over Autumn - Winter - Spring. In the hot dry
season, only a gas or meths stove may be allowed.
It is an interesting question, whether any tiny wood stove could have
its combustible material so constrained as to be considered equivalent
to a gas or meths stove.
Anyway, here is a comparison of many of the choices:
https://www.youtube.com/watch?v=ajPCW41YWOU
...some fantastic wood stoves!
But, are any of those suitable for the ultralight hiker? Like, under 100g? Yes, he reviews one, the Emberlit Fireant:
https://emberlit.com/products/fireant-titanium-multifuel-ultralight-backpacking-stove
...weighs 85g (3oz).
There are plenty of others like this on Aliexpress, Amazon and eBay,
but not this light. If you want to research what is out there, go to
these sites and search for "wood stove folding ultralight" ...or similar
words... cast the net a bit wider: "wood stove hiking".
The Emberlit Fireant can also hold a meths burner.
Thinking about burning wood, it is not really constrained. You would
insert twigs in the side, so there is always the possibility of burning
wood to fall outside of the stove body.
The Emberlit is fascinating, but I have ordered a different kind of
wood-burning stove, that weighs 100g (and much cheaper). It is also
titanium and folds flat for easy carrying. Will post a report after it
arrives and have tested it.
EDIT:
Here is another interesting comparison of wood-burning stoves for hiking:
https://www.youtube.com/watch?v=P28PK5m4Gjw
And if you would like to see something really creative, here is a no-drill gasifier tomato-juice-can wood stove:
https://www.youtube.com/watch?v=8he7txE6uLw
EDIT 2021-0630:
I received an email from ally, with links to very light stoves. For an
alcohol-fuel stove, you can't get any lighter than this spill-proof
stove and folding frame:
https://speedsterstoves.co.uk/20ml-spill-proof-mehs/alcohol-burner.html
https://speedsterstoves.co.uk/utralight-mini-pot-stand-for-cups-mugs.html
...8g plus 4g, great for making a quick coffee on the trail!
He also posted a link to a tiny ultralight titanium wood-burning stove, Firebox Nano, 4oz (113g):
https://www.fireboxstove.com/folding-firebox?product_id=337
...including its case, weight is 6oz.
Tags: light
Refinements to glueing tarp
Continuing TreeHugger 1P Mark-2 project, previous post:
https://bkhome.org/news/202106/treehugger-1p-tarp-mark-2.html
Some issues have been identified, and solutions...
Glueing reinforcements
I have glued on the tie-out reinforcements, and it has, in some of
them, been unsatisfactory. These reinforcements are at the tie-out
points, where webbing is to be sewed on, to spread the tension. They are just pieces of the same fabric
glued onto the tarp.
The procedure is to spread silicone adhesive on a reinforcement,
using the fingers, then lift it up and place it onto the appropriate
place on the tarp. Getting it to lay nice and flat, and in the right
place, no ridges and no bubbles, is a challenge.
There is a video on YouTube where a guy shows how to do this, that I
have linked to in an earlier blog post. However, I have concluded that
his method is not suitable for me. Where is that video? Ah, here:
https://www.youtube.com/watch?v=Ec8YhQffRj8
He might have got away with it using heavier fabric, however, 10D
silnylon is incredibly stretchy. Using the fingers to smooth out the
piece of reinforcing, and push out bubbles, stretches it -- and here is
the thing -- the underneath fabric does not stretch, or will stretch
less. So, after attempting to smooth the piece of reinforcing, ridges
can form in the underneath tarp. You might then battle to stretch the
tarp to remove those ridges.
One factor though, in support of his method, he is using Gear Aid
Seam Grip seam sealer. In his case, the surface is PU, but for
silicone surface, as for silnylon, Gear Aid have "Silnet", also known as
"Seam Grip + Sil", which is a thinned silicone adhesive. Seam sealer,
being thinned, is quite runny -- it is designed to seep into the sewn
threads.
Silnet is far more runny that
straight silicone adhesive from the tube, that you buy in a hardware
store. The runny seam sealer has much less "grip" between the
two surfaces, so you are more easily able to push the reinforcing around
after placing it on the tarp.
Note, I have experimented with that Silnet. You buy it from camping
stores, it is for seam-sealing tents. It is very runny. Also, it is much
less "sticky". I found when folding the hem, that it was somewhat
reluctant to stay down. The straight silicone, you fold the hem, and
that's it, it is stuck.
So, using straight silicone adhesive and pushing the reinforcing
around with the fingers, what you end up with is a weirdly distorted
reinforcing.
Extra notes about the video:
Do not use bare fingers, as he has done in the video. Exposure to harsh chemicals may not have an immediate effect, but in the long term the body will react.
Also, I think the way that he has spread the seam sealer is inefficient -- dribble beads over the entire surface first, in roughly parallel lines, then simple sweeps with side of a finger can spread it.
Also, with care, the piece of reinforcing can be laid pretty much in the correct place, without all the wrinkles requiring to be pushed out as he has done.
He used a soldering iron and comments that it cauterizes the edge so won't fray -- however, as the reinforcing is glued to the tarp, there won't be any fraying -- besides, ripstop doesn't fray. Cauterizing will cause lots of little melted lumps -- notice, later in the video he trims some of them off. OK to cut out the circles with scissors.
I used this finger method on a few of the reinforcing pieces, then
remembered that with Mark-1 I only used the fingers a little bit, then
used the Uni-Pro seam roller. See photo of the seam roller here:
https://bkhome.org/news/202105/tarp-glueing-hems-and-ridgeline.html
Yes, this is the way to do it. Hopefully, lay the piece of
reinforcing down accurately, so you don't have to pull it around, then
run over with the seam roller.
So, some of the reinforcing tie-out points look good, some look crappy.
Spreading adhesive
I posted about a problem with spreading the adhesive for hems and
ridgeline. A dribble of adhesive along the line to be joined, then use
side of a finger to spread it. But of course the adhesive will spread
out, and the problem I had was the chalk mark getting erased. I posted
about this problem, with a suggested workaround to draw arrows:
https://bkhome.org/news/202106/treehugger-1p-tarp-mark-2.html
However, today I devised another solution. Bought 16x16x1.5mm
aluminium channel from Bunnings, cut it at 45 degrees, and very
carefully filed the tip so that (hopefully) a thin film of adhesive will
be spread, only 13mm wide:
 |
 |
I filed so that an extremely thin film of adhesive will slide
through. The channel is held with the index finger pressing lightly so
that the sloped end slides over the fabric, following the marked chalk
line, the sides keep the adhesive from spreading out. Adhesive still
needs to be dribbled down the line-to-be-joined beforehand.
Length is non-critical, I cut off 14cm of channel, which fits nicely
in the hand. Cut at 45 degrees because my hacksaw-jig thingy only does
22.5, 45, or 90 degrees. Perhaps a steeper angle would be even better.
A little bit of experimenting, and it works well. The great thing
about this is two-fold. Firstly, the chalk line is still there, so can
see where to fold the hem, or overlap the ridgeline. Secondly, no glue
is wasted.
That second point is very important. I have found when constructing
Mark-1 and Mark-2, that the glue can very quickly become a significant
part of the weight of the tarp. I would even say, that if you apply it
liberally, you could even double the weight of the tarp-sans-glue.
A little thought about the weight compared to sewn tents. They need
seam-sealer, such as Silnet, and you can very easily use up a 50g tube
on one tent. My glued tent does not need seam-sealing, except where the
tie-outs are sewed on, and the amount of glue used could be similar to,
or less, than that used to seam-seal a sewn tent. As long as there is no
excessive glue applied.
The 16x16x1.5mm (13mm inside width) channel is OK for the hems. For
the ridgeline, need wider channel, but the biggest that Bunnings sell is
20x20x1.5mm (so 17mm inside width). Actually, the 3cm overlap that I
have done so far for the ridgeline, is probably more than needed. Will
think about that. Might shop around, see if can find slightly bigger
channel.
Chalk marking
I have posted about using a fabric marking pencil. Still not happy
about it. It is some kind of "chalk", but is too hard, and I have to
press harder on the fabric than I would like.
What I am using now is a chalk bar, designed for use on fabric:
...I bought the second one, because the first is out of stock at my
local Spotlight. The inbuilt "sharpener" is a joke -- just use a blade,
or any sharp edge.
I also bought some chalk from the kid's section in Kmart, but found
it to be unsuitable -- too crumbly. It tends to come off in chunks
rather than a nice line on the fabric. Maybe it is just the cheap brand
-- "Anko", which is Kmart's own brand.
EDIT:
Bought 25.4x25.4x1.2mm, 0.45m long, "Connect It" rectangular aluminium
extrusion from Bunnings. So that is about 23mm inside width. Cut it at
45 degrees. Here it is:
Not yet tested. I think that it would be
necessary to dispense the adhesive in a zig-zag pattern along the line
to be joined, to optimize even spreading.
Tags: light
TreeHugger 1P tarp Mark-2
Complete instructions for Mark-1 tarp are here:
https://bkhome.org/light/treehugger-1p-tarp-weighs-only-178g.html
Mark-1 was a learning experience, and hopefully Mark-2 will be pretty much what I want as the final product.
The original concept was to have a 25mm carbon fibre spreader-bar
just above head-height, to give more head room. I was a bit nervous
about how that would complicate the design and how the sides would hang,
so Mark-1 does not have the spreader-bar.
With Mark-2, decided to "go for it" and construct as per the original
concept, even though haven't quite figured out some details for
affixing the spreader-bar.
This time, I am using 10D silnylon purchased via Aliexpress, from Rex Outdoors:
https://www.aliexpress.com/item/32625219053.html
Rex Outdoors only ships by China Post, which is very slow. Not sure,
think that it took about 2 months to reach my doorstep in Australia.
Construction proceeded as per the Mark-1, this time with slightly different dimensions:
4.8 metres of fabric is required, and the 2 pieces can be cutout efficiently like this:
So, had 2 pieces, and together they weigh 133g. It will be very
interesting to calculate the weight of the fabric in grams per square
metre. From SolveSpace, the bottom-left angle is 87.3 degrees and
top-right is 74.96 degrees, on the top image above. Then can calculate
the area:
https://keisan.casio.com/exec/system/1322718508
Gives the 2 pieces 4.08 metre squared, which calculates to 32.6gsm.
Very interesting! The photo on the Rex Outdoor page states 28gsm, then further down they have 30gsm.
I really do need a reference weight to test the accuracy of my digital scale. It is only a cheap one from Kmart.
Note, I suspect that the manufacturer and vendor are just stretching
the truth a little bit, by including the border of the fabric in the
area calculation. Only suspect, not verified! There is roughly 1 inch
along both sides of the fabric that are not silicone-impregnated, thus
lighter. That's why, in the photo below, you can see the ridgeline of
the first piece placed about 1 inch from edge of the fabric, because
that is going to be cut off.
Marking out this fabric has proved to be even more of a challenge
than the previous fabric used in the Mark-1 tarp. This stuff is very
translucent. Here is a photo showing the first cutout laid on the fabric
to use as a template to mark-out the second piece:
For Mark-1, I used these fabric-marking pencils:
However, with this green fabric it is difficult to see the line. With
Mark-1, I was pressing the pencil a bit too firmly onto the fabric and I
was worried that it might be damaging the delicate fabric.
I have experimented with other markers. On the forums, the Sharpie
metallic silver permanent marker pen is highly recommended. However, I
think that it is unsuitable for a couple of reasons.
Firstly, it remains highly visible through the translucent fabric.
Secondly, it may compromise the silicone glueing -- I have no idea how
well the silicone adhesive will stick to it.
I also tried chalk, but when ran a bead of adhesive along with the
finger, while glueing a hem, it also erased the chalk line. So I could
not see where to fold the hem over to, and had to estimate it visually ,
which was not satisfactory.
Actually, I did use the Sharpie pen to mark-out the two pieces, as the marked line was outside where cut with the scissors.
WARNING: At first, I bought Anko brand metallic marker pens from Kmart, as the Sharpie brand was out of stock. This is Kmart's own brand. Useless, they kept on blocking up. Initially, after some effort, they did flow OK for awhile, but they rapidly degenerated, and after a few uses they were unusable. Later, I bought Sharpie metallic pens from Woolworths, a set of three including silver -- they work great!
Note, the Sharpie pens I bought are fine-point, which are OK, but apparently there are ultra-fine available, which would be even better I reckon (Woolworths only stock the fine point).
For the hems, I went back to the Semco pencils. To make the line more
visible, needed something dark underneath. This was the only dark
fabric I had available:
...the photo shows a length of wood being used as a ruler for the marker pencil. I took care to press the pencil lightly.
Running a bead of adhesive along with the finger does still partly
erase the marked line, but enough remained for me to just make out where
to fold the hem.
EDIT 2021-06-22:
Hmmm, no, not so good. Sometimes the marked line is completely gone. As had pressed lightly with the
pencil, it gets erased when spread the adhesive with the finger. I
think that it is chalk-based, and the particles get swept away.
Struggled through with the hems, but when got to the ridgeline, tried this...
I don't need a continuous line, just
periodic visual cues showing where the other piece of fabric is to be
pulled onto overlap the underneath piece. To achieve this, I drew
arrows, about every 6 inches:
Yes, this works. Even if the tip of the arrow
gets swept away, I can still see where it is pointing to. In the photo,
you can see the other piece of fabric at the bottom, the edge of which
has to be pulled up to the marked line. Overlap is 3cm.
EDIT 2021-07-25:
For the record, appending this extra note about marking-out and glueing.
I am now using a chalk bar (purchased at Spotlight) to do the line
marking, and aluminium channel to spread the adhesive. This spreads
without wiping out the marked line, so the above suggestion to use
arrows is not required. This technique with aluminium channel spreader
is described in a later blog post:
https://bkhome.org/news/202106/refinements-to-glueing-tarp.html
...an extra note to add, is now overlapping the
ridgeline by only 20mm, and for that using a spreader made from
20x20x1.5mm aluminium channel.
Tags: light
Sewing neophyte slowly learning
What has plagued my sewing so far, is thread getting caught up in
the bobbin area, and a rats nest of threads on the underside of the
fabric.
Today I watched a couple of videos that have resulted in significant improvement:
Singer 4411 Heavy Duty 12 Tension Test:
https://www.youtube.com/watch?v=AfDNGOug7bY
https://www.youtube.com/watch?v=qojD8LuHm2k
Following the instructions, I found that the tension setting is the
culprit. I had it set just above "4". Changing it to just below "4" did
the trick.
Incidentally, I am now using Guterman Extra Strong thread from Spotlight:
No particular reason for changing from the lighter thread, except that it looks good.
And as before, a sharp/microtex 80/12 needle:
Another problem occurs when do a back-stitch at end of a line of
sewing. The Singer 4411 has a lever, press that and then the foot lever,
and sewing will go back. It is normal practice to do this at start and
end of a line, however for me it results in messed up threads on the
underneath of the fabric.
The hint I got from watching the videos, is, when get to end of a
line, wind the wheel at right-side of sewing machine counter-clockwise,
until the needle is up and the metal part comes up out of the top of the
sewing machine, to it's highest level. That completes a sewing cycle.
Then hold down the reverse-lever and sew backwards.
Not quite sure about that last paragraph, have to experiment some more.
EDIT 2021-06-15:
I have gone back to using standard Guterman thread from Spotlight, which
is, I think, called "sew all" thread in some other stores.
Reason is, I cannot stop thread bunching
underneath the fabric when sewing webbing onto the fabric. I messed
around with tension setting, tried both walking foot and standard foot,
to no avail.
Back on the "sew all" thread, with tension
setting just on "4", it is working reasonably well. Still not perfect,
sometimes get small loops at start of a line of sewing, and when
reversing. But much better than the mess I was getting with the "extra
strong" thread.
One of the things that annoys me about
Spotlight, is they often give inadequate specifications. See the above
link. I determined from reading elsewhere what kind of thread it
actually is.
EDIT 2021-06-16:
I mentioned above about finishing sewing with the lever sticking above the sewing machine. This video shows what I mean:
"Singer 4411 Heavy Duty 20 Take Up Lever in the Highest Position"
https://www.youtube.com/watch?v=bpa7uJBCbnw
...she calls it the "takeup lever".
She advises to do it at the end of a line, before lifting the foot and removing the fabric.
But see in that video, she got to end of line,
held down the backstitch lever momentarily and did a quick back-stitch.
Didn't bother with getting that takeup-lever at max height.
So I still have the problem of some looping
underneath the fabric when back-stitch. Forum member williwaw has
suggested that I might need to adjust the bobbin tension. Will read up
on that.
EDIT 2021-06-16:
Hey, she -- her name is Sara -- does have a video explicitly on back-stitching:
"Singer 4411 Heavy Duty 16 Reverse"
https://www.youtube.com/watch?v=q9U68lwkUuw
Interesting, she sews in reverse at the
beginning. And does it real fast, like she doesn't even take her foot
off the floor pedal.
Tags: light
Catenary cut for tarp ridgeline
After constructing the TH1P tarp Mark-1 and erecting in my lounge
room, then eye-balling it, I realised that it would be better if the
ridgeline is joined in a catenary-cut. Previous post, showing photos
erected in lounge room:
https://bkhome.org/news/202106/bottom-tie-outs-and-tarp-completed.html
It is not apparent from those photos, but the fabric either side of
the ridgeline is loose, not taut. even though I pulled the cords fairly
firmly at each end. The problem is, the ridgeline is never going to be a
straight line, no matter how firmly you attempt to tie each end. It
will sag.
This photo shows the sag in a straight-cut ridgeline. OK, it is a bit
exaggerated, because the ends have not been pulled firmly, but the
shadow does show you the effect of the sag:
This sloppiness can be mitigated by having extra tie-outs on the
sides of the tarp, but I would prefer not to have more stakes to hammer
in.
There is a fix for this problem, to join the ridgeline in a curved
shape, so when erected, the fabric either side of the ridgeline will be
taut. This photo shows a tent which has such a curve:
...you can see, a reasonably firm tension applied each end, the ridgeline has a sag, but the fabric each side is taut.
My apologies to whoever posted the above photos, for not acknowledging you. I downloaded them and don't recall the URLs. Ah ha, found one URL, but he also has "borrowed" the photo from somewhere else.
The curve shape is known as a "catenary". The Wikipedia defines a catenary as:
A catenary is the curve that an idealized hanging chain or cable assumes under its own weight when supported only at its ends.
So, it would be good to join the two halves of the tarp so that the
ridgeline has this natural hanging shape. As I have already created a
straight ridgeline, I decided to modify it to be a catenary.
Firstly, I need a formula for calculating the points along the catenary. Fortunately, 'XTrekker' has done it:
https://www.hammockforums.net/forum/showthread.php/85208-Catenary-Parabola-Curve-Calculator
...you can run the formula online, or download the Excel spreadsheet -- which runs great in LibreOffice.
I have uploaded the Excel spreadsheet here.
Note, XTrekker's formula is for both ends of the tarp to be at the
same height. My tarp is lower at the foot-end, but I don't think it
matters if the cut is not to an exact catenary mathematical formula.
Back in an early post of these tarp construction instructions, I gave
the dimensions of each side of the tarp, and the ridgeline was 222.2cm.
After folding the hems, the final ridgeline length on my tarp is
215cm.
But the big question, how much "sag" to put into that formula? After a
bit of reading other people's experiences of a minimal catenary, I
chose 4cm. Tabulating the results from the spreadsheet:
| Distance | Offset "b" |
| 0 (centre) |
4.0 |
| 25.0 |
3.8 |
| 35.5 |
3.6 |
| 43.5 |
3.4 |
| 50.0 |
3.2 |
| 55.5 |
3.0 |
| 61.0 |
2.8 |
| 65.5 |
2.6 |
| 70.0 |
2.4 |
| 75.0 |
2.2 |
| 78.0 |
2.0 |
| 81.0 |
1.8 |
| 85.0 |
1.6 |
| 88.0 |
1.4 |
| 91.0 |
1.2 |
| 94.0 |
1.0 |
| 97.0 |
0.8 |
| 99.5 |
0.6 |
| 102.5 |
0.4 |
| 105.0 |
0.2 |
| 107 (end) |
0 |
I have modified my tarp, by cutting along the ridgeline, then re-glueing.
For someone constructing the tarp from scratch and wanting the
catenary curve on the ridgeline, I would like to theorize on a couple of
ways it can be done. Let's call them "method-1" and "method-2"....
Method-1: variable overlap
This
sketch explains theoretically how I think it could be done:
The top sketch shows the two tarp ridgelines placed together, and the
red dashed line is the pencilled catenary shape. There has to be some
overlap at the ends, named "a", and in the centre there will be an
overlap of "a" + "b", where "b" is from the above table.
One thing that I think you will need to be careful about, is not just
to pull #2 side up to the pencil line, as the ridgeline will be
slightly wonky. #1 and #2 edges need to be pulled equally. I think that a
way to achieve a nice non-wonky join, is to do what I suggest in the
bottom sketch.
I have indicated a sequence, 1, 2, 3, but you might find it better to
do 2 first. That is, anchor each end firmly with weights, then pull the
two edges so that they overlap and follow the pencil line. Then put in
pins to hold the overlap in place.
Then step-3, glue. Tarp #2 will be sitting on top of #1, and you can
glue it down. Usual procedure: dribble a line of silicone adhesive, then
run your finger along to spread it, then press down. The only thing to
be concerned about is that the spread of glue as you run your finger
down, reaches the edge, so edge #2 is glued down all the way along.
Take out the pins, leave overnight. Next day, flip over and glue the
other edge. It is then wise to leave for several days, to fully
cure.
Method-1 is wasteful of fabric and glue, and the tarp will be
unnecessarily heavy, as the "b" value gets bigger. Plus, I am not sure
how the ridgeline will hang with a large centre overlap.
I came up with that 4cm sag figure from reading forum posts, but
those people were using method-2. So, "b" should be doubled for
method-1, but 8cm fabric overlap is, I think, not the way to go. I am
describing method-1 in this blog post, for consideration if you only
want a tiny sag value.
The alternative is the traditional way, cut a catenary shape on the
ridgeline edges of both tarps, and then join them with a constant overlap the
entire length. This is Method-2...
Method-2: Catenary cut
Another sketch to show this:
With this method, you mark catenary lines on both edges, then cut.
This is shown by the pink dashed lines. If you used a "b" value of 4cm,
as per the above table, then you are going to get twice the catenary
effect than for method-1.
To glue the two sides, I think that you could still use the pins. So you
would pull side #2 over side #1, pull each end and put weights, then
pin, then glue.
Leave overnight, then flip over and glue the other edge.
I used method-2 on my tarp, and used pins. To make it easier to
insert the pins, I hung the two tarp-sides near vertically, using a
plank. The plank is dressed pine, 184x19x2400mm. Use a large crocodile
clip at one end, to hold the two pieces of tarp together, with 3cm
overlap, onto the end of the board. At the bottom end, you could use
another crocodile clip to hold the tarp pieces together, again 3cm
overlap.
Haven't got a photo of that, but it should be easy enough to visualize. That made it very easy to insert the pins.
I then laid it horizontal and glued. I left the pins in, but that is
OK, next day flipped the tarp over and glued the other flap.
I had removed the tie-outs at each end of the tarp. Need to
reconstruct those, then will take a photo of the erected tarp, and will
update the tarp construction details here:
https://bkhome.org/news/202105/tarp-glueing-hems-and-ridgeline.html
This time, will use some heavier-duty webbing for the ridgeline tie-outs.
EDIT: TH1P tarp mark-1 with catenary-cut
I cut along the ridgeline, cut the catenary curves, re-glued, sewed
new webbing tie-outs. Unfortunately, all this messing around has
resulted in a lot more glue and some extra reinforcing bumping the
weight from 178g to 218g, a jump of 40g. That is unnecessary extra
weight, would have been less if had done the catenary-cut from the
start.
Here is a photo:
I am really not convinced that the catenary-cut is worth the effort.
Yes, it does take up some of the slackness along the ridgeline. The
tautness will also have an advantage when wind hits the side of the
tarp, it will more readily flow over the tarp, instead of trying to push
it over. Some people cut even deeper catenary, but then they are going
to be loosing more height inside.
A straight-cut is probably preferable if you want to erect the tarp in other ways, not just as a V ridgeline.
For the tie-outs on the ridgeline, I have gone for a thicker webbing. This, 12mm wide by about 1mm thick:
https://www.aliexpress.com/item/4000126877988.html
...it is only available in black.
Tags: light
Bottom tie-outs and tarp completed
Here is the previous post, in this "TreeHugger 1P tarp Mark-1" project, making the ridgeline tie-outs:
https://bkhome.org/news/202105/tarp-ridgeline-tie-outs.html
Today I sewed on the tie-outs along the hems. That is, the four corners and the middle of the sides.
I used the same webbing as before, nylon, just 10mm wide and 0.5mm thick:
https://www.aliexpress.com/item/1005001666741572.html
Cut these pieces, 16mm long, folded over about 35mm and sewn, with
rubber o-rings, and one of them has a hook. The one with the hook is
folded over a bit more so that the hook is the same distance from the
tarp as the o-rings:
The length of this webbing is a matter of personal preference, how
high you want the tarp hem off the ground, and of course longer webbing
will make the tarp wider when erected.
Note, when I cut the nylon webbing, I also use a flame to cauterize the ends. Important, otherwise the ends can unravel.
The o-rings are silicone rubber, 25mm OD, 4mm thick. They feel strong
enough, however for future projects I intend to use o-rings made with
EPDM rubber, as it is stronger than silicone rubber. Note also that EPDM
is UV resistant. A cheaper rubber is NBR, and this is not UV resistant.
This is what I have on order, 25mm OD, 4mm thick:
https://www.aliexpress.com/item/1005001631629585.html
The plastic hook in the above photo is a bit bigger than I wanted, so
I ordered a smaller size. These are 3.6cm overall length, just what is
needed:
https://www.amazon.com.au/gp/product/B08P14TWG1
They arrived after the initial writing of this blog post, and I
swapped for the smaller hook. The EPDM o-rings also arrived, but will
keep the silicone rubber ones on the tie-outs -- the EPDM ones can be
for mark-2 tarp.
Sewed the tie-outs on, with my newbie wonky sewing, and erected the tent in my lounge room:
The wooden frame is my "dressmaker's dummy", to make it easier to construct the inner-tent while inside the house.
The tie-out with the hook is front-right, as the tarp is intended to
become a step-in and step-out tent, with zipper entry to the inner tent
on the side.
Those o-rings are intended to go over stakes, and in the case of the
hook, it will hook onto an o-ring. That is a detail that will become
apparent when the inner components of the tent are constructed. For now,
we only have the "stage 1" of the tarp, but still, you can see how the
hook can be unhooked from the o-ring and folded over the ridgeline:
Actually, even at this stage, the side flap is useful. If the
high-end was tied to a tree trunk, the pole not used, the side flap is a
convenient way to get in and out.
Here is a rear view:
Now for the really interesting bit, what this tarp weighs. Wait for it...
Weight of tarp: 178g
Or, in Imperial measurements, 6.3 ounces. That is good.
What is planned next, is baffles for front and maybe on the low-end.
The baffles are intended to facilitate exact spacing for the stakes, and
to hold the o-rings firmly at ground-level -- so they will be less
likely to be pulled up when wind blows on the tarp.
Planned erection procedure is you would stake out the tarp, with 4
stakes, then tie up the ends, with or without poles. I plan to use this
without a high-end pole, as then the high-end ridgeline tie-out can be
pulled up and tied to a tree, no need to have tension adjusters on the
ground-level stake tie-outs. Of course, if you have a trekking pole, the
length can be adjusted, so again, no tensioners required at the stake
tie-outs.
The same principle holds for the low-end, but I will probably use the
pole, as it might be difficult to locate a branch to tie to. Well,
could use a stick, maybe with v-notch to run the cord over.
The front and rear baffles will also offer rain protection, and will have openings for ventilation.
These are future plans, but the tarp as constructed so far is quite
useful. I cannot tell you how sturdy it is in windy conditions, as so
far it hasn't been out of the house.
Tags: light
Tarp ridgeline tie-outs
Continuing the "Mark 1" tarp construction project, this is the previous post:
https://bkhome.org/news/202105/constructing-short-pole-for-tarp.html
So far, the tarp has been constructed by glueing, no sewing, but now,
I have sewed the webbing onto each end of the ridgeline. The webbing I
used is this:
https://www.aliexpress.com/item/1005001666741572.html
With a cord tensioner:
https://www.aliexpress.com/item/1005002198346631.html
I am going for lightest possible weight, but uncertain if have taken
it too far with this webbing. It is nylon, 10mm wide and only 0.5mm
thick. Apart from nylon having limited UV resistance, it is very thin.
Might be better described as ribbon, than webbing, but it seems strong
enough. If it breaks, I suppose can sew on something else later.
I have a Singer 4411 sewing machine. Set it to zig-zag stitching,
width "1" and length "3". Using standard Guterman polyester thread from
Spotlight -- I think this is known as "sew all" thread at some stores --
Spotlight also have "extra strong" but didn't use that. Set the tension
to just above "4". Using a walking foot.
One more thing, used a sharp needle, size 80/12:
...apparently, the standard needle that comes with the sewing
machine, has a slightly rounded point, designed to push-aside threads,
which is (apparently) not the best for sewing ripstop.
The reason to stitch zig-zag is that polyester thread is far less
stretchy than nylon. This means that a straight thread may break when
the tarp ridgeline is pulled very tight. At least, that is advice I got
off the Internet.
The original plan was to sew a nylon washer underneath, for the
support-pole to slot into. I did that, but it doesn't look sufficiently
robust:
Scrap that idea. The carbon-fibre pole has a rubber end-cap, so there
is some spread, but what is needed is something to keep the pole in
place. I want the pole to be right under the webbing.
Found a length of 25mm nylon webbing, cut two pieces, clamped them together, then used a soldering iron to make a hole:
Good, created a hole into which the pole end-cap can be inserted,
with side-walls high enough to keep the pole in place. Then glued it to
the tarp:
Looks good. Could have gone even further, with 3 layers of webbing.
Note, glued a tiny piece of ripstop underneath, so the pole is not rubbing directly on the webbing.
Note, if that sewing looks a bit wonky, it is. I'm a sewing newby,
was experimenting with different zig-zag widths etc., while doing it.
Yes, did try on some scrap fabric first, but still had to play with
settings while doing the actual job.
Will do the same for the other end. Then will do the tie-outs on the
bottom of the tarp. A bit of delay there, as ordered plastic hooks, that
go onto end of webbing or cord, and they haven't arrived.
Some other items ordered from Aliexpress also haven't arrived. Then I
made a discovery. Although I had chosen "Aliexpress Standard Shipping"
when ordering, these non-arrived items were shipped by China Post --
which is considerably slower to Australia. The vendors took the extra
money that I paid, and then posted by the cheapest means.
I have complained to two of them, asking for a refund of the
difference. Anyway, I found another vendor of those plastic hooks on
Amazon, placed an order.
EDIT 2021-05-31:
The above picture is for the ridgeline at the low-end of the tarp. The
high-end is a different story, as the walls form an acute angle. The
"cup" that will hold the pole will have to be as narrow as possible. I
oriented along the ridgeline and also trimmed the width a bit with
scissors:
...it is 4 layers, 3 of them form the "socket" into which the pole will be inserted.
Still concerned that this is too wide. Maybe also too fragile. Anyway, will see how it performs when in use.
Though, I don't intend to use a pole at the high-end, so the
fragility might just be an academic issue. Most interested in erecting
it in "tree hugger" mode.
Ideally, want the "socket" to be no wider then the webbing. An idea
is a plastic screw-on top off something -- like the screw-top on a tube
of toothpaste, but it would have to be wider. Then drill tiny holes in
the base, so that it can be sewed onto the tarp. Or even glued to the
webbing with epoxy resign. Maybe will do that for tarp "Mark 2"!
EDIT 2021-05-31:
Thinking about it some more, a narrow "socket" for the high-end could be achieved by these silicone end-caps:
https://www.aliexpress.com/item/1005001609758449.html
I already have some with 7.7mm ID, 11mm OD,
which would be just right. As they are silicone, they can be bonded
strongly to the webbing. A bit of reinforcing around the end-cap could
enhance the bond integrity. Maybe even some epoxy resin in the bottom,
to spread the force. Just making a note of this alternative, a
possibility for the "Mark 2" tarp.
EDIT 2021-05-31:
Hey, why not? I cut the 7.7mm ID silicone end-cap a bit shorter, and glued it into the hole previously created:
Now, just insert the metal pointy-end of my
carbon-fibre pole (or a trekking pole), and we are good to go. The
ridgeline width is still a concern, but we shall see once it is up and
in use. The CF pole I am referring to, is this one, purchased awhile ago
(125cm, 5-segment):
https://www.aliexpress.com/item/32918962406.html
Actually, I have two CF poles, see report here, but the other one is not suitable for this tarp, as shorter:
https://bkhome.org/news/202103/two-cf-straight-tent-poles-compared.html
EDIT 2021-07-04:
I am now favouring a simpler method for the "sockets" in which the poles
are inserted. Just glue the silicone end-cap onto the webbing. That's
it, nothing else. See details here:
https://bkhome.org/news/202107/treehugger-1p-mark-1-tarp-deep-catenary-cut.html
Tags: light