Dimensions For a 3p tarp? Flat or Cat cut?

[Don Burton]

I want to make a tarp that can comfortably fit 3. 12 ft width by 10 ft length? It will be for my 3 kids to use but I want it sized for adults. I would like to make a flat tarp for ease of making and more pitching options but I’m not sure if a larger tarp will be tougher to get taut. That’s why I’m thinking a cat cut even though that’s not my first choice. Thoughts? Thanks

[James Marco]

A lot will depend on your pitch. A Lean-To pitch is not real weather proof and at a 45degree drip line can penetrate a long ways under a tarp. With the three open sides, it allows a LOT of weather to blow in. A lean-to is OK for cooking spaces, or, to have a fire in front in less windy weather or in a sheltered location.

An A-frame pitch has better weather resistance with only two openings.  But, it allows less space for sleeping, but it is better covered. Only the two ends are open and these are lower. The 45 degree drip line penetrates less

A corner Diamond pitch (one corner tied to a tree or a taller pole with three corners staked down) is fairly weather resistant but will provide even less space for people. The drip lines are all a bit longer than with an A-Frame, but turns wind better. The walls are all angles or open so it is good with a fireplace out front or a small fire under the one corner. This is good for wet weather when fire-wood is stacked near the open sides.

A Center Pole (a single pole set in the center of one of the sides) can be nearly completely enclosed.  It sort of depends on how high a pole/stick you use.  It will form a triangle inside at it’s maximum enclosed pitch, but sleeping space can be difficult. This is a great pitch in cold weather since a small fire can be maintained near the door opening. Fully enclosed means fairly dry inside.

Anyway, you can see the pattern with flat tarps. The more enclosed they are, the less room for sleeping. A larger 10×12 tarp can be configured as a fully enclosed Center Pole Pitch for one or two people or as a lean-to with room for 4, 5, 6 people.

Cat tarps are usually a single configuration. I use one for solo camping, but it is pretty much locked in. All I can do is raise and lower it.  A flat tarp allows more flexibility.

 

 

[Don Burton]

Thanks for the input James. I should’ve been more specific.

What dimensions do you think for a flat tarp when considering the primary configuration is an A frame to fit 3p? I don’t mind taking the kids out in modest weather so the A frame set up would be fine so that’s what I’m aiming for primarily. Is 12 x 10 big enough for this? For a tarp this large, is it still feasible to get a taut pitch?

[Todd Stough]

Most of the hammock tarps are close to this size and they pitch nice and tight.  Could put “doors” on one side to close up the back.   Look for winter tarp plans.

Everyone says if you use the silpoly fabric you won’t need cat cuts.

I think you could fit 3 kids and probably 3 adults laying with the ridge.

[James Marco]

Yes, a 10×12 will work for three people. And no, you don’t want any cat cuts with silnylon. Even silpoly will pitch OK without cat cuts. Just watch out for shifting winds, setting up broad side to it. Usually, I do not bother setting up a ridge line. I simply loop into a couple centered tie outs and set it up with found sticks or at least one tree. Typically, the center will stretch after four or five nights. Often after the first couple weeks of use, you will find it can actually start leaking or misting. So, plan on adding a thin coat of sealer/mineral spirits after the stretch. It will add around .2 or .3 oz/yd so for a 10×12 it would add 2-4oz of weight on top of the normal ~20oz weight of the tarp (seaming, tie outs.)  Still, a pound and a half is good weight for a 3 person shelter. I made several in the 9×9-10×12 range that work really well for car camping,as a lean-to by the fire and for back country camping as a shelter.

 

[Don Burton]

Thanks James!

Also, this may sound like a stupid question but should the ridge line always be a seam so it creates a sharp peak in the A frame configuration? This is for a flat tarp.

[James Marco]

Don, Well, several people advocate vertical seams. They say they leak less. But, I seal my seams before use. Leakage is of no concern after sealing, so this becomes a “don’t care.”

Having a two or three layer center seam can make setups stronger and easier (It acts as a visual clue laying it out for erection, and, for actual construction.) I usually use a Flat Seam (French Seam or Felled Seam) for the center. Then I do an extra roll. There are three stitches and 6 layers of fabric. This reinforces the center seam a LOT. Not so much for the fabric panels, but against stretching. This lets me use the center as a structural component and by adding the loops carefully over the seam it gains extra strength from the stitching. Adding loops does not require reinforcement pieces and the seam automatically centers; no measuring. Setting up is simply using the two center loops for an A frame. The seams are actually structural components, not weak points.

On large 9′ tarps, I use the main seam in the center.This helps with strength. Again, 45degrees out for the A-frame walls is best overall: most “people” area for interior space vs strength for pitching vs good water runoff vs least interior loss due to pitch tapering. So, for height of a 9×12 tarp, you want poles about 50-51″. I just measure about 50″ on my chest and tie one end off to a tree leaving about 2-3′ for entrance and to clear any root structure.  The other end, I often use a found stick about 2′ or so. This drops one end against wind and reduces rain infiltration. And, it works to improve overall ventilation, but overall pitch taper means this area is only used for gear storage.

For 10′ it doesn’t really work out and I would need a strip about 8-9″ wide on one end. So, the center is NOT on a seam with standard 60″ fabric. Anyway, when they are erected as A-frames, the more natural 9′ length (I believe it is actually about 9′ 6″) works best for the minimum amount of seaming. Just take two 60″ panels and stitch them together with a flat seam. Some cloth bolts are 61″-65″, some are 42-43″. The edges may not be in good shape. The metalized fabric is something less, I seem to remember, though. I was lucky getting some Purple at 65″ that actually was good out to all but an inch from each side. I actually hit 10′ with that one. Otherwise they fall at as close as possible to 10′; often 9″6′-9’10”. This edge measurement varies, but commercial people do not consider anything beyond 60″ usable. They often miss out on that extra few inches. Even their “10′” is often 9′ 10″ or something like that.

I do my tarps with the least number of seams. So, simply use two panels. I make a largish panel, first. Then roll all the edges, twice for additional strength. Use loops because grommets can become problematical. A couple interior tie outs are good to have handy. Especially near the center for other pitches. And near the 1/3 points for netting.

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