Please critique my Pyramid design

[David Chenault]

My wife and I just got back from a rainy trip on the Beartooth Plateau with a friend, and the conditions made us see the need for a new shelter that better suits Montana conditions. (As opposed to our Firstlight, or the small tarps I've been used to using in the southwest.)

We're tossing around designs for making a Pyramid tarp. It would be useable for 2-4 people in all seasons, from mosquitos in early summer to mid-winter ski touring. It would be light of course, but more importantly would be 100% bombproof.

I'm thinking 1.9 oz Silnylon (from Seattle Fabrics). I've used it for packs and clothing, and it works very well. It comes in 60" yards, thus making an overall bottom length of 112" (with two-panel sides and generous seam allowances) convenient. I'm also thinking an overall height of 72" would work well.

My questions are several:

-What seam style would be most effective for the main seams?

-Should the 10-12" of mosquito netting be placed right along the bottom, or sewn a bit higher along the sides?

-I'm thinking that eight tie points are necessary along the bottom (corners and mid points). How necessary are mid point guy points (a la MLD)?

Any other thoughts are also very welcome.

[brian blair]

I have a Sierra Designs Origami you can borrow if ya'll need some time in a Mid to figure out what you want and don't want.

B

[Tim Marshall]

Why 1.9 vs 1.1? The 1.9 from seattle is only coated on 1 side, not impregnated like 1.1sil. I wouldn't think that a 1.1sil with 1.9reinforcements would be too weak for you.

Also, you will want the midpoint tie-outs, but you may also want tie-outs on more than just the ground perimeter, you may want some 1/2 way up the mid to give more stabilization in higher winds (and more interior space)

I would go with 10' square if you want to use it with 4ppl. (only a few more inches, and with 1.1 you normally get wider than 60")

-Tim

[Jim Colten]

re: 1.9oz SilNylon … not all nylon thread is created equal. The 1.3oz stuff was created for parachute and hot air balloon use and is the best. I don't know about the 1.9oz stuff but Seattle's product catalog says it has a tear strength of 16-18 lbs vs 15 lbs for the 1.3oz stuff. Not much gain for the weight penalty (keep in mind that it is 1.9oz before adding the coating whereas the 1.3oz stuff is 1.1oz before coating). Also, the 1.3oz is silicone impregnated vs silicon coated for the 1.9oz stuff so the uncoated side will probably absorb more moisture (weight) than impregnated fabric.

re: guyout points. Definitely use 8 stake points on a shelter that size. And I'd include guyout loops 1/3 of the way up all eight seams … negligible weight penalty for the option to stabilize the thing in a storm.

re: bug netting. I don't have an opinion about attaching it at the edge vs part way up the wall but be prepared to repair damaged netting after every use in snow (snow in ski-able quantities anyway).

edit: Tim suggested you may want some 1/2 way up the mid to give more stabilization in higher winds (and more interior space) … we could compromise, 1/2 way up the corner seams and and somewhat lower on the center seam of each panel (draw a line from the corner to half way up the opposite corner seam and put the guyout where it crosses the center seam). That divides the panel into three equal sized areas.

[David Chenault]

B, thanks for the offer. I've spent enough nights in a Megamid to know that I like the concept, just want it a bit bigger.

Tim, the fabric point makes total sense. And I could get the fabric from Thru Hiker instead.

I like everyone's thoughts on the guy point placement.

The damage to the netting on ski trips makes sense as well. Perhaps leaving the netting off is best, as all compromises seem too complex (ie velcroing the netting on and off).

Cheers folks.

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