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Joseph Williams
(deadogdancing) - F

Locale: SW England
minimum tarp size for bivvy-less camping on 03/01/2008 11:05:34 MST Print View

It's time to bite the bullet and make another tarp!

It'll be flat, multi-pitch job, made of silnylon, and my hope is to use it with a down bag and without a bivvy. So the question is, what's the smallest I can get away with and still retain full weather protection?

At the moment I'm thinking 7x9. What do you folks reckon?

R Alsborg
(FastWalker) - MLife

Locale: Southwest
Re: minimum tarp size for bivvy-less camping on 03/01/2008 11:18:13 MST Print View

7 x 9 sounds right

J W
(jhaura) - F

Locale: www.Trailability.com
Re: minimum tarp size for bivvy-less camping on 03/01/2008 11:38:40 MST Print View

Ditto, 7x9, but maybe taper the tail to 5 or 6 feet. Still flat for multi-pitch, but save an ounce.

Dan Whalley
(thedanwhalley) - F

Locale: peakdistrict natonial park, UK
Re: minimum tarp size for bivvy-less camping on 03/01/2008 12:14:27 MST Print View

yer i would recon a taper towards the rear to! this would work great!

Edited by thedanwhalley on 03/01/2008 12:15:06 MST.

Tim Marshall
(MarshLaw303) - MLife

Locale: Minnesota
Re: minimum tarp size for bivvy-less camping on 03/01/2008 14:20:50 MST Print View

I've slept fine under a 5x9 w/o bivy in a storm. But to keep the weather out the pitch has to be pretty low (i was using and A-frame)and is a big sacrifice to interior living space.

Mike Hinsley
(ArchNemesis)

Locale: England, UK
minimum tarp size for bivvy-less camping on 03/01/2008 15:51:19 MST Print View

I've used a 5ft x 8ft but it had to be pitched very very low - earthworm friendly.

7ft x 9ft is more practical. I've used this in stormy condititions with a 2ft-tall pitch and it's been fine.

It's well worth considering shaped tarps - say taper at the back to 5ft. You save a chunk of weight without any real down-side.

I've move towards a single-skin tent. It weigh's less than a 7x9 tarp and is more storm-worthy.

Ron D
(dillonr) - MLife

Locale: Colorado
Re: minimum tarp size for bivvy-less camping on 03/01/2008 16:33:45 MST Print View

Mike - What tent are your using that weighs less than a 7x9 tarp?

Tim Marshall
(MarshLaw303) - MLife

Locale: Minnesota
Re: Re: minimum tarp size for bivvy-less camping on 03/02/2008 15:12:26 MST Print View

You could do a 9ft tarp that is 6ft at head and 4ft at foot for the same 3 yards as a 5x9, it will give a little more room where you need it and allow for more head room.

David Wills
(willspower3) - F
Re: Re: Re: minimum tarp size for bivvy-less camping on 03/02/2008 15:52:48 MST Print View

9x4x6 would be great but if you want it rectangular, 6x9 or 6x10.

Joseph Williams
(deadogdancing) - F

Locale: SW England
thanks for the input! on 03/02/2008 23:40:54 MST Print View

Many thanks for the input guys. I like many I have spent time under a 5x8 without a bivvy in a storm, and it can be weather worthy, but not comfortable! I'll take on the suggestions to base it on a 7x9 but taper it, and do some pattern drawing based on that. I also take from David's suggestions that the length is actually the key factor in getting reliable full coverage.

Mike Hinsley
(ArchNemesis)

Locale: England, UK
minimum tarp size for bivy-less camping on 03/03/2008 01:04:26 MST Print View

Ronald,

it's DIY. It broadly looks like DIY Ultralight tent.

It's basically a tapered tarp with doors on each end. The tapering and the doors use no more fabric than a 7x9 tarp and of course gives good weather resistance.

I've recently tweaked it to add a dome on the front and change the back to be a beak. This increased the weight by 2oz but that weight was regained by using shorter internal rather than external poles.

It's always worth remembering with Tarps that they do not have magic powers. They do however tend to use less and lighter fabric than a conventional store-bought tent. That's all.

For example, I found that of that 9ft length I needed at least 1ft to give rain resistance to give some weather resistance at each end and yet if I put a beak on the tail end it would use less than 1ft of fabric and so was lighter. My 8ft tarp relied on this fact to save weight and width.

Edited by ArchNemesis on 03/03/2008 01:08:12 MST.

Joseph Williams
(deadogdancing) - F

Locale: SW England
back to the drawing board on 03/03/2008 13:29:00 MST Print View

mike, your post has just blown open my debate about my next shelter project again...Ron Bell surprised me by bringing out exactly the shelter I had designed in my head as a solution to the bivvy-less camping problem:

http://www.mountainlaureldesigns.com/shop/product_info.php?cPath=35&products_id=76&osCsid=32d8dc46397d0f257a2661b9ac6e33ab

I've been shuffling back and forth between the idea of making a smaller, shaped shelter, or a largish flat tarp, or compromising on a beaked tarp Ray Way/Jay Ham stylee- as well as weather protection I'm keen to have quite a bit of headroom for comfort and sanity- I clearly need to think more about this!

How much interior room does your tarp-with-doors have?

Mike Hinsley
(ArchNemesis)

Locale: England, UK
minimum tarp size for bivvy-less camping on 03/03/2008 15:21:56 MST Print View

Josepth,

broadly there is about 1-1.5ft of free space between the front doors and the top of your head (my groundsheet is 6ft7 long and 3ft wide tapering to 1.5ft) . There is about 6 dry inches down each side of the groudsheet where you lie. Internal height at the front is about 3ft when pitched normally.

[I tried something like the MLD design last year. The plans and pics are here and found it to be too small for happy-camping during a very wet week even if it did keep the rain off and was light]

Basically there is enough space for a pack+stuff and a stove and that's all.

When the weather is fine I can tie back front and/or back doors to produce a normal tarp again.

The best way to think of it is that when weather is fine you use it like a tarp and if things look a bit rough you shut the doors.

I sat down a few years back and worked out all the math for tarps and beaks and various variation including things like driving rain at different angles.

Simple flat doors and panels do the job with minimal fabric use. Point tapers on tarps tend to use more fabric even if they are more aerodynamic.

I've changed the design recently to turn the front into a dome (by adding a triangle extension between the two doors and a point at the rear (two equilateral triangles). This has increased the tent weight by 2oz but allowed me to use poles that are 2oz lighter and double the usable porch space.

What I often tend to do is peg out any design ideas in the garden using tent poles and long lengths of string. This can give me an idea of usable space and panel angles and things without spending money. If your neighbors see you then just tell them it's the latest in stealth camping technology ;-)

It's well worth calculating the surface area of the fabric for anything you design before you start cutting cloth. In that way it is then easy to work out how it all compares.

Most designs can be broken down into triangles and rectangles which is then simple high-school math to work wtih.

Edited by ArchNemesis on 03/03/2008 15:44:13 MST.

Vick Hines
(vickrhines) - F

Locale: Central Texas
Re: minimum tarp size for bivvy-less camping on 03/03/2008 19:02:48 MST Print View

7 x 9 sounds good if you plan to keep a simple rectangular tarp.

With large beaks, you can use a shorter ridge line. Imagine a 7 foot ridge, 9 foot sides and 1.5 foot beaks. Sketch it out and you will see what I mean.

If you want to get more radical, consider a 5 foot ridge with 8 or 9 foot sides and a pyramid (two triangles joined) at the rear and a long beak over the open front.

Shortening the ridge can reduce the yardage and weight - but will reduce the versatility and ventillation of a flat tarp.

Take this to its logical extreme and you get something like a Gatewood cape tent.

Joseph Williams
(deadogdancing) - F

Locale: SW England
a decision and a subsidiary question! on 03/04/2008 14:58:44 MST Print View

Thanks very much for your input folks- I have decided to make a 7X9 flat tarp, simply because I am at the beginning of my sewing appreniceship, and I would like to continue my apprenticeship in tarp craft-I've really enjoyed what I've done so far and would like to take it further.

I think the points about adding beaks and doors are very valid, and need exploring further when my sewing skills are up to more. If my experience with tents is anything to go by, I find shelters where the highest point is in the middle the most comfortable- think MSR Hubba. Translated into simple ultralight form, this makes me think of a small half pyramid, with doors that could be rolled away in fair weather. I think I will look in this direction if I start a shaped shelter project.

Mike, thanks for your feedback on your prototype- it's really good to have the benefit of your experience there- it's something I might have tried myself- if I do I'll make it taller!

So here's a question to do with flat tarps- would you guys pitch a rectangular tarp with a lenghthwise centre seam in a half pyramid configuration, or would the stress across the centre seam be too much? If you reckon it'll be ok, I'll make sure there's a tie out in the middle of each long side (total three). If not, I'll put two tie outs on each long side instead of three.

all the best,
Joe

Mike Hinsley
(ArchNemesis)

Locale: England, UK
minimum tarp size for bivvy-less camping on 03/05/2008 01:40:32 MST Print View

Joe,

to actually sew a 9' seam well is tricky. I still struggle to do it and the result is a little lack of tension in places.

The felled seam will be pretty tough whatever you do.

If you are using RipStop fabric then for a first tarp you could consider putting the seam in the other direction - sewing two 4.5x7 lengths together. 4.5 is the width of a typical roll of fabric and will reduce the size of the seam you need to do and give you a ridgeline that will be taught even if the flappiness moves elsewhere...

There are plenty of Sewing 101's out there but even so its always worth practicing with the actual fabric you are goihg to use.

I tend not to use pins (but I've done this quite a bit now) but its gonna be worth you using a few and pinning within the seam allowance for the first seam - these will be pinholes that never see daylight.

The other thing that's gonna be worth practicing is keeping the fabric undder tension as you sew. It helps to avoid wrinkles. For the first seam I hold either side of the fabric as far as I can reach along the seam-line. This creates fabric tension and helps me to sew a straight line (with no or very few pins).

For felling the seam I tend to hold the fabric flat and under tension either side of the needle.

Think of your first one as a training exercise. If at the end of the day it works then it's a success.

You can always sew extra bits onto it or chop it around at a later date.

Edited by ArchNemesis on 03/05/2008 01:55:50 MST.

Tim Marshall
(MarshLaw303) - MLife

Locale: Minnesota
French Seam on 03/05/2008 14:46:25 MST Print View

On my most recent tarp i used a French seam for the ridge line. I was able to get a much better seam than my previous flat felled attempts. When sewing the "tube" down i sewed through all the layers with the tube being on bottom, this helped me get a much smoother seam than when i have done frenches with the tube on top.

Mike Hinsley
(ArchNemesis)

Locale: England, UK
minimum tarp size for bivvy-less camping on 03/05/2008 15:15:54 MST Print View

Do you mean something like this?

or this (two operations)


1.
---!--------------
---!--------------

2.
---------------!---\
--!--!/
--!--!------------------

This is quite strong, easier to get the tension right.

It doesn't render in a proportional font.

Edited by ArchNemesis on 03/05/2008 15:18:11 MST.

Tim Marshall
(MarshLaw303) - MLife

Locale: Minnesota
Re: minimum tarp size for bivvy-less camping on 03/05/2008 15:35:19 MST Print View

This is what i mean
http://www.thru-hiker.com/workshop.asp?subcat=11&cid=16
but i top stich it with the tube on the bottom. With silnylon you can see through it and can always see the tension but it is out of your way and you can just pull apart the 2 layers of fabric and don't have to worry about the tube because it is being held in place

Robert Strickland
(robstr) - F

Locale: Central Texas
6x9 Tarp plan with catenary ridge line. on 03/06/2008 21:54:49 MST Print View

Here is a plan for a 6x9 foot tarp with an optional catenary cut ridge line.
Catenary cut 6x9 foot tarp plan
This can be cut from 3 yds of 64" width silnylon. Besides the cut out for the catenary ridge, the only scraps left are two right triangles 6x21 inches. I have almost finished a tent based on this plan with screen ends and bottom.
This catenary curve ridgeline has a 2 1/2 inch sag. The measurements are symmetrical about the center 2.5 inch one. Your diagonal measurement might differ from mine if you have to lose a bit of fabric to square the ends. Whatever it comes out to, divide it by 10 and mark off 10 equal segments. I multipled the meaurements by 25.4 to convert to mm and used a millimeter ruler:
24, 42, 54, 61, 63.5, 61, 53, 42, 24 mm.
To connect the dots, I used a metal ruler on edge, bent it to follow the curve and then traced a section of the curve with a fabric marking pencil.

Robert

Edited by robstr on 03/06/2008 23:48:17 MST.