Pseudo-Cat Tarp Experiment

[Cannibal]

I don't know if what i mean makes seance or if what I wrote means what i mean if you know what i mean

What's in those pineapple newtons you're eating?

[Frawg]

It probably what you said that the fabric isn't quite lined up but it could also be that when you sew a seem you might take more fabric into the seem so that one part might be shorter? I don't know if what i mean makes seance or if what I wrote means what i mean if you know what i mean

I think I understood you okay, PN. To clarify one thing, it wasn't that the fabric didn't line up -- it's that the grids are oriented in slightly different directions. I did it that way to maintain a straight line along the ends, which is probably easier to see in the second 'on the floor' picture.

No, there's really no puckering in the seam when it's not under tension. I've been pretty lucky about that with my sewing -- er, thread injection. If you look at the right (narrow) end of the 'wing' in the picture you'll see that there's no puckering to speak of on the seam.



Honestly, I don't see the ripples as a particular problem. It's just an interesting artifact of this particular design. One of the reasons I like DIY is the analytical challenge and this particular one gives me a chance to exercise my brain in ways I haven't done in a long time.

With any luck another t-storm will blow through here in 45 minutes or so. The fun continues...

[Frawg]

...oh and if you would be interested in selling one of the other tarps that you've made and don't use I would be interested.

Yeah, at some point I should probably sell some of the excess stuff I've been making to recover some of the cost of my education. I've been working mainly with the heavier 1.9 oz (or so) DWR for tarps so I wouldn't use up the 1.1 stuff I have on hand until I zero in on a solution.

Anyway, if you are seriously in need of something PM me and maybe we can work something out.

Cheers!

[Ramblinrev]

I'm going to go out on a limb here and say the puckering you have there is almost certainly a combination of two factors. 1 the seam is less elastic than the base fabric so the stress of the tension is distributed differently. In other words. Even if you were to specially cut and re-orient the triangular piece to match the bias direction of the main tarp you would still get puckering but it would affect both the main tarp and the triangle.

2 the bias differential of the triangle is what makes it stretch so nice and smooth up to the seam. The seam then interrupts the stress pattern, which combined with the change in bias direction results in the puckering of the main tarp. The way to minimize that would be to experiment with a specially cut triangle which completely and totally negates the plan of productively using the cut off from the original fabric.

In short... you may be stuck with it as a consequence of the design. But then does it really matter?



Notice the puckers along the line of the rolled hem as well as the seam of the reinforcement patch. Part of that is my own stitching but part of it is inherent in the interruptions and redistributions of the stresses by the seams and hems.

[pineapplenewton]

you could find bigger fabric and cut out the trapezoids.

[Ramblinrev]

As you tension the tarp point A is drawn toward point B. The seam, being less elastic does not transfer that stress smoothly so the main tarp puckers. The added triangle has the bias oriented so the puckering is pulled out and appears to be smooth.

Even if you were reorient the bias of the triangle you would still get some puckering on both pieces.

[Frawg]

As you tension the tarp point A is drawn toward point B. The seam, being less elastic does not transfer that stress smoothly so the main tarp puckers. The added triangle has the bias oriented so the puckering is pulled out and appears to be smooth.

Even if you were reorient the bias of the triangle you would still get some puckering on both pieces.

Rev, thanks very much for the insightful comments; I do appreciate the voice of experience! I hadn't thought about the mechanics of it as you had described it, but it makes good sense to me. I had noticed before that the wrinkles lessened considerably when I pulled point 'A' to the left.

That 'obligatory' corner photo of yours is instructive, too. I'd looked at your photos earlier, but forgot about that one. Good info.

From your previous post:

In short... you may be stuck with it as a consequence of the design. But then does it really matter?

A man after my own heart! That's my thinking. The whole point for me was to decrease flapping in the breeze, and get a better distribution of stress.

It's also an interesting analytical exercise for me. There's some similar work in the gaming community on fabric modeling, including modeling the effects of deformation by contact with other objects, e.g., how clothing deforms as a simulated person moves about. I immediately thought about tarp and hammock design as a spinoff application for the technology, but I'm not convinced it'd be worth the effort. Would still be fun to play with, though...

Cheers!

[Frawg]

We had some nice thunderstorms roll through here the past couple of days, and I just came inside from the most recent one. Again, I pitched broadside to the prevailing wind, but this time I added mid-tarp guy lines as well as some tensioners.



Despite the windward side blowing up against the hammock, everything stayed dry underneath. I enjoyed some coffee and did a sudoku again, and stayed quite dry.

Significantly, there was very little swirling to the wind although it got quite strong and gusty. The driving rain came down very heavily at times, often at a 45 degree angle. All in all, I'm pretty encouraged so far.

Next on the agenda is orienting the ends toward the wind, and closing them in.

One lesson learned - don't let the tarp rest on the ridge line; water does seep through at the point(s) of contact.

[sclittlefield]

Next on the agenda is orienting the ends toward the wind, and closing them in.

One lesson learned - don't let the tarp rest on the ridge line; water does seep through at the point(s) of contact.

Thanks for the updated reports. I'm keen on following this - seems a great way to get a super light tarp with minimal material.

Your note about the ridgeline drip is interesting, and has me rethinking how I have my tarp setup. I've got a long cord with a mini-biner on one end that wraps around the tree, then is tied to the other tree with a taut-line hitch. The tarp rides on that line and is held in position with mini-biners to the ridge tabs that slide into place with prussik knots onto the long cord. I wonder if this cord will give me drip-through? I'll keep it this way for a while to test it out.

[Frawg]

Thanks for the updated reports. I'm keen on following this - seems a great way to get a super light tarp with minimal material.

I'm now reworking my original silnylon (? Walmart 1$/yd stuff) 5x10. This time I angled back about 12" from the end instead of 8". We'll see how that works. Also gave me an excuse to make some bias tape and learn how to use the bias tape foot on the sewing machine.

Your note about the ridgeline drip is interesting, and has me rethinking how I have my tarp setup. I've got a long cord with a mini-biner on one end that wraps around the tree, then is tied to the other tree with a taut-line hitch. The tarp rides on that line and is held in position with mini-biners to the ridge tabs that slide into place with prussik knots onto the long cord. I wonder if this cord will give me drip-through? I'll keep it this way for a while to test it out.

I like that method of hanging and centering the tarp, and the possibility of using the ridge line for a clothes line, etc. Even though the seepage puts me off, the good news was that only one drop actually coalesced and fell. Not sure yet how it would progress over a period of hours.

I should be able to pitch the new old one later today and see how it does, if Mother Nature will cooperate; 70% chance of rain, but she's been finicky lately. More later...