Updated - New silnylon tarp build thread with a few questions

[latriper]

The background: I hang an eleven foot DIY channel end gathered hammock. Also, the vast majority of my hangs will be of the car camping variety so a few ounces heaver is not a deal breaker.
Good coverage that can be pitched tight are my goals.

I settled on this design
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and 1.1 oz sil nylon for the material

I usually see this type of tarp cut into a hex pattern but I would like to keep the length 144 inches. According to the catsplat calculator, for a 62 inch width with a 1 inch per foot sag, would need a 5 inch cut in. For the length (144in) I would need a 12 in cut in. Does that sound about right?

The main question is this. Once I have my two sides cut out, should I join them with flat felled seam then hem the sides or hem the sides first and then join the two pieces? In my head, I see problems each way. If I FF seam first then roll hem the permiter, I think I will have a problem when I get to the ridge line, like there won't be any material to roll. If I go the opposite route it seems the rolled hem will cause problems with the FF seam. I do not plan to add gross grain to the perimeter, just the rolled hem.

I thought I would try to do this right so I made a template out of foam poster board for my cat cuts

Materials for the template
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Long curve generated.

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I plan to update this post as I go along. Hope someone can benefit from it in some way and I look forward to any help on the rolled hem/FF seam question. Thanks everybody!

[jolunder]

I would sew the ridge first. In my experience (which is limited to one tarp) the flat felled seam ain't in the way very much when hemming the perimeter.
Cheers Jo

[xxl_hanger]

I usually see this type of tarp cut into a hex pattern but I would like to keep the length 144 inches. According to the catsplat calculator, for a 62 inch width with a 1 inch per foot sag, would need a 5 inch cut in. For the length (144in) I would need a 12 in cut in. Does that sound about right?

I would cut the tarp a little different. I think the distance between your tie outs is too long. I would perhaps also have a rl of 144", but my distance between the tie outs would be not more than about 100". I would try to have doors for rainy and windy weather. With such a tarp you can realise almost the same tarp dimension which you have in mind - if you use the doors straight and not closed.

In Blackbishop351's "The BlackCatTarp" Tutorial is stated:

Somewhere between 1" per foot and 1.5" inches per foot should be plenty, but exactly how much is a personal preference - and there's a tradeoff. The more cut-in you use, the tighter the tarp should pitch. More cut-in also means less coverage, though. You want a good balance of both.

The main question is this. Once I have my two sides cut out, should I join them with flat felled seam then hem the sides or hem the sides first and then join the two pieces?

I would first hem all sides, but it depends how you join the two pieces together. A flat felled seam has to be sealed. This is the reason why I would make it different:

https://www.hammockforums.net/forum/...-Seam-Question

[The LumberJack]

I have a WB SuperFly and It has lots of tie outs, a pair of doors on each end, two tie downs on either side, and one tie out in the center on either side to make a gable shape, one thing I wish they would put on the SF is a tie down on either side directly in the center, because when it gets really windy, it can be hard to rig the tarp tight enough. maybe there is a reason for not doing so, but I think it would be a great idea to try out.

[Bubba]

I would do the ridgeline first. I think its good to work from the middle to the outside. Also, if you are going keep the rectangular shape I would do a double cat cut along the sides so as to have a tie out in the middle as The Lumberjack mentioned. I think its a long distance to only have only two tie outs.

[Redoleary]

I would definitely sew the ridgeline first, and 12" is IMHO a little deep for the cat cut. To echo the others I would put a mid point tie out along the side as well. A good rule of thumb for cat cut depths (calculators aside) is 4-6% of the length so the deepest I would make it for a 144 length is 8.5-ish inches, and even that seems excessive, not to mention you'll end up even deeper after you roll the hem. If it were me, I'd put a tie out at the mid point (72") and cut a 3" cat then roll the hem. That's just my opinion.

[Monkeyboy42]

I second what most people are saying. With a few modifications you could have a much more versatile tarp. I did this drawing for a tarp I'm considering building:

https://www.hammockforums.net/forum/...hmentid=101193

After drawing it I discovered the bullfrog tarp which is very similar.

[Boston]

Your catenary curves are WAY too deep. You really don't need much. I'd start with 3" on the long edge and 1" on the short. You can always remove more material later if you think you need to.

For heming: roll hem 3 sides of each panel first. Then sew the ridgeline.

[latriper]

Thanks everybody for the feedback. I think I will pattern the new tarp after one I made a year ago. This was a DIY waterproofing attempt that worked pretty well but noticed some leaks after 3 days of pretty continuos rain. I like the idea of doors but think I will save that for the next tarp and add the extra foot of material when I order.
Any feedback on this design? All of the sides are cat cut using the string method to gauge the cat cuts and it is a 144" ridge line. This tarp also has a gross grain ridge line seam and that is one place I did not notice a leak. I did not seam seal this ridge line. I believe if I go the gross grain seam it would be best to roll hem the edges first then do the ridge line. I can't remember how I did it last time but looking at it closely, I don't think I did it that way and it looks a little shabby at that spot. Let me know what you think and thanks again for all of the feed back!!

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[hangNyak]

This might help. DIY Blackcat tarp Also, forget the string. A piece of 1/4 round moulding works great. Hold at your two points and bend in the center. You're going to get a much neater measurement than trying to trace a silly string. Just get someone to help hold it.