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Benchmark time for Tarp Set Up?
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Al Shaver
(Al_T.Tude) - F - M

Locale: High Sierra and CA Central Coast
Short Bus Rider on 02/21/2006 03:07:59 MST Print View

Vick,
Although I am often enlightened by your posts, Im afraid I don't posess the education or mental horsepower to visualize the situation that you describe in your last post.

If you guys decide what you think the best tarp guyline set-up is, I would like to know about it. I do like the idea of tying shock cord loops on each tie out to absorb gusts and help with slack from wet tarps.
Al

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Short Bus Rider on 02/21/2006 03:16:26 MST Print View

Al, I believe Vick is right, hence my "Bingo" comment. Vick (if he read one of my earlier posts???) understood what I meant by vector analysis and number of tie-outs determining the number of panels. I'd really like to see a finite element analysis of a tarp under loading - that would be very interesting.

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I wasn't going to get into this stuff as I'm nowhere near the engineer DrJ is - I was hoping that he'd reply. I'm going to be somewhat brief and in some nitpicky respects maybe technically inaccurate, or technically "lean" here.

Keep in mind, that as I stated earlier, I believe that the problem is even more complex and that both Vick's and my comments are mainly related to a static loading of the tarp. Dynamically loaded, the tarp will want to shift, bot the tarp and guylines are essentially, to some small degree, springs, and therefore subject to Hook's Law (F=kx). Some lines of force on the tarp's conceptual "panels" will go slack (or to zero), others will increase in tension. This dynamic loading will give DrJ's single continuous guyline approach an advantage since the lines of force can change somewhat as the tarp attempts to shift due to wind loading. Also, in DrJ's approach, since the three middle stakes are connected by, conceptually, two guylines, they don't have half the force applied to them, they have the same force (but each conceptual guyline on a stake bears half the load) - the two end stakes being an exception.

I still think as I stated in a prev. post that the number of panels doesn't really change, either statically or dynamically, since any shift results in the same number of panels but in different directions, so "straight" conceptual panels will become "diagonal" conceptual panels. I'm open to instruction here as maybe I'm forgetting something or not visualizing this properly.
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Depends upon what you mean by "best". Easiest to adjust - well,...you know the answer to that one already.

Strongest in wind - "the more's the merrier." You could end up adding so many stakes and guys (or larger, longer, better shaped stakes, and stronger guylines - either single or multi-guyline arrangment) that either the tarp fabric, or sewn seams, or the tie-down stitching is the weakest link - would depend on the tarp material and construction - not that such an arrangement is necessarily practical.

I would imagine that the conditions that exist on any given night might be better suited to one approach or the other.

Edited by pj on 02/21/2006 07:15:54 MST.

Vick Hines
(vickrhines) - F

Locale: Central Texas
Re: Short Bus Rider on 02/21/2006 07:53:56 MST Print View

OOOF! Are we getting esoteric or what? Maybe we need to model this. Naw...

Edited by vickrhines on 02/21/2006 08:05:15 MST.

Vick Hines
(vickrhines) - F

Locale: Central Texas
Re: Short Bus Rider on 02/21/2006 08:03:37 MST Print View

Al,
Yep, we're dancing a bit much on the heads of pins here. My best advice is to set up in the back yard and try things out. But don't neglect to simulate stressful conditions.

Jacks'R'Better has elastic guys already made up. Or you can make your own as simply or as whoopeedo as you like. There are lots of different ways floating in these forums. Loops tied with water knots, loops where shock cord is stitched to lengths of gutted parachute cord, in-line lengths of shock cord - tied with water knots or slipped into gutted paracord and stitched, medical tubing in loops or lengths, etc.

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Re: Short Bus Rider on 02/21/2006 08:26:42 MST Print View

Also "Naw..."

>>"...dancing on heads of pins..."
agreed, but feels more like the points to me!! Ouch!!!

Edited by pj on 02/21/2006 08:29:34 MST.

Scott Peterson
(scottalanp) - F

Locale: Northern California
Re: Re: Re: Short Bus Rider on 02/21/2006 08:56:13 MST Print View

Regarding the self tensioning lines, as made by Jacksrbetter, how are those properly used in conjunction with a treking pole? I like the concept of having the ridge guyed out with these tenioners, but it seems the rubber is right where you would loop the line before sending it to the stake. Would it be functional to use a short piece to tie the tarp to the pole, and then loop the tensioner piece to the pole as well?

Vick Hines
(vickrhines) - F

Locale: Central Texas
Re: Re: Re: Re: Short Bus Rider on 02/21/2006 15:12:36 MST Print View

Depends entirely on how your pole is made and how you generally attach your tarp to it. Some poles have a hole or strap you can put the line through. Some folks tie on with a clove hitch. The shock cord might have to be placed beyond that. One way: envision a continuous line with a length of shock cord tied somewhere in the middle so a loop forms in the line that is pulled out straight when the shock cord is fully extended. This is most easily done with water knots. 8 inches of 3/8" shock cord is a good weight for ridge lines. But there is less benefit from putting shock cord on the ridge line than putting it on the side pullouts.

Scott Peterson
(scottalanp) - F

Locale: Northern California
Re: Re: Re: Re: Re: Short Bus Rider on 02/21/2006 16:20:23 MST Print View

Back to the a-frame tarp set up. I will use rather standard leki 3 piece treking poles. From what you state, it seems I probably should not worry too much about self tensioning the ridge. (I want to try and keep the setup as effecient as possible). When you say place them on the side pullouts, are you referring to the four corners? So optimally I would attach shock chord to the triptease line? Are there any instructions on this site that might show how best to do that?

Thanks!

Vick Hines
(vickrhines) - F

Locale: Central Texas
Re: elastic lines Short Bus Rider on 02/21/2006 18:26:20 MST Print View

Yes, the 4 corners and intermediate points on the sides (1 or 2, depending on make or tarp. Let me see if I can post a pic or two in addition to this:



bungee loop with gutted parachute cord girth hitched to a tyvek poncho/tarp

Edited by vickrhines on 02/22/2006 08:11:21 MST.

Mike Storesund
(mikes) - F
Re: Re: elastic lines Short Bus Rider on 02/26/2006 16:13:47 MST Print View

Vick,
Thanks for the picture. I has seen many different diameter sizes of elastic line at local fabric stores. From other pictures I have seen, it looks like most are using 1/8" diameter cord. That just doesn't look strong enough to me, but then the 1/4" diameter looks too thick.
Any input or ideas?

Vick Hines
(vickrhines) - F

Locale: Central Texas
Re: Re: Re: elastic lines Short Bus Rider on 02/26/2006 20:17:17 MST Print View

1/8 inch is about right. I think you can find 3/16 and 3/32. Do a break test to satisfy yourself about strength. I think you will find that even the small round cord used in garments is plenty strong.

One product that will NOT be strong enough is beading elastic - a very small round cord. I don't know the size, but it is almost thread-like. It will certainly break.

You need a cord that has enough resistance that you won't stretch it fully during set up. Some stretch should remain in the line so it can absorb wind shock. The small cord has to be doubled to achieve the right amount of resistance - as in the loop shown in the photo in an earlier post.

Edited by vickrhines on 02/26/2006 20:18:47 MST.

Peter McDonough
(crazypete) - F

Locale: Above the Divided Line
Wind Shock on 02/26/2006 20:54:45 MST Print View

I'm confused about this wind shock belief. If a load is being applied to a sting, then that is the load applied to that string. If an elastic is used as part of the string, then the load applied is still the same. I guess the only thing that might be a factor is impact force(I think thats what its called), or the duration of time over which the force is applied. With the bungee, the impact force would be applied over a greater period of time and that might save the tarp panel. However, for the amount of force required to tear the tarp panel, the bungee is already going to be stretched to its maximum, and most probably won't do one any good in protecting the tarp. It might help with the tension after a night of rain(I just tension it really tight), or protect from clumsy campers, but I think the hassle outweights the benefits.

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Wind Shock on 02/27/2006 04:01:08 MST Print View

Peter, You are correct, impact loading and the resultant "surge" effect is reduced by the self-tensioners (note that is what JrB properly calls them, i.e. self-tensioners, not load absorbers or some such thing). You're also correct, Newton's Second Law of Motion (F=ma) applies here to extend the time that the load is applied over. Acceleration is a change in velocity and instead of going from zero to whatever, essentially, instantly, it accelerates over a very short period of time instead of instantly, and also a much greater relative distance is involved, obviously, in the acceleration, hence time to accelerate. So, the change in velocity from one moment in time to the next is reduced by the self-tensioners' ability to elongate to a greater extent than the other components in the system (guylines, tieouts, tarp). The whole spring constant of the system changes and its response to dynamic loading due to the inclusion of the self-tensioners in the system. This, IMHO, is a minor/minimal benefit of the self-tensioners given the sizes of the loads the "fully extended" system could be "seeing"/experiencing. However, without performing either a carefully controlled experimental analysis with either load cells or strain gauges, or a mathematical analysis on an accurate model, no one can really say how much of a benefit this feature might be in this regard. Lastly, you're right again, self-tensioning to reduce sag and the resultant flapping is the primary benefit of this system.