The Star Tarp

[funbun]

Here's an idea I'm kicking around for my next tarp:

It's a hex tarp, but instead of a cat cuts it's diagonal cuts. How do you guys think this would work compared to a cat cut hex tarp? Would wind flap still be an issue even with the diagonal cuts? Concept drawing in on my blog: http://biketour.blogspot.com/

[Arkwater]

I think that would focus all the edge stress to one point. Would be easy to rip at that point. IMO.

[funbun]

Hmm, yeah.

[Coffee]

I have to agree with Arkwater on this. The cat cut is pretty easy if you take your time.

[funbun]

Okay, cat cut it is.

[lvleph]

If you have $1/yd material there is no reason not to try. The first thing I thought looking at it was, "why not cat cut?" But then I realized it is simpler.

[attroll]

I think that would focus all the edge stress to one point. Would be easy to rip at that point. IMO.

I thought of this idea a while back and mentioned it to Blackbishop351 and he said the exact same thing. He thought it would put stress to the areas where the angles are and it would cause a stress point an easy rip point.

[blackbishop351]

Basically what you're doing there is taking a first-order linear approximation to the curve. I think this is problematic at best.

Turning one long edge into two slightly shorter ones will still leave you with straight edges which are long enough to be subject to the same sag problems that the single edge had in the first place. If you were to use a second- or third- order approximation (basically divide the edge into four or eight "V's" instead of just one) it would probably work OK, but that would most likely be more work than just using the cat curve itself.

I also agree with Arkwater about the stress issue. By using a smooth curve, the stress is evenly distributed along the edge and the only foci occur at the corners - where you've got reinforcements. By using the "V", you're basically creating an artificial (inverted) corner, but without reinforcing it. It might also cause stress problems at the ridgeline, and would likely not produce a tight pitch.