Catenary Ogee tarp design: thoughts?

[AnthonyVH]

Hi everyone!

I got interested in an (ultra)lightweight camping setup a little while ago and since I love DIY, I plan to try to make myself some gear. Tarp-wise, the Ogee design seems like a very nice compromise between weight and coverage, which I will be able to use in all seasons. However, I'd appreciate it if some of you pros could give me some feedback on the (very slightly) modified design I have in mind.

Below is the design, the original dimensions I got from a post by cwciwatch (link). I've also attached a PDF with the design. In case the image is not readable, the PDF is a vector, so zoom away . It's to scale by the way, so anyone interested in making one, scale it up 10x and you'll get the same size as the marked dimensions.

catenary_ogee.jpg

The next few sentences are going to be hard to follow without having at least a look at the design . Note that the apex/maximum/... (green dots in drawing) of the big catenary cut is not at the same location as the "hex" tie-out point (the one you would use with the triangles flapped up). This is not possible if a continuous catenary curve is required from the central triangular tie-out to the door tie-out. An alternative would be to split this long catenary cut into two shorter ones, however, in that case the two catenaries will not be tangential at the "hex" tie-out point. I guess that most of the time either the triangle tie-outs or the "hex" tie-outs will be used, not both at once. Are the catenary cuts as they are right now going to be a problem? Would it be better to split them up? Is this such a tiny detail that it won't matter one bit, because my first-time hemming won't be nice anyway ?

A second (even tinier) modification is to add catenary cuts to the inside of the doors (lightest blue in the design). I'm guessing this is probably a bad idea, since it will make closing the doors completely harder. Correct?

Any other ideas for possible improvement? Did I overlook another/better design for my first tarp?

Edit: Updated attached PDF to newest version.

[Mouseskowitz]

I'm interested to see how this works out for you. One thought I have is with the side pull outs. In my mind it would make more sense to just have one if they are only going to be 3' apart. That would cut down on weight especially if you're doing a poll mod. Whether it works the same way in practice as it does in my mind is different matter entirely.

[boulderv7]

I think you're correct in that adding cat cuts to the doors will make them harder to close. My OES winter tarp has cat cuts on the doors and they don't close up all the way. I believe you should try it with the remaining cat cuts and post up some feedback here. I am interested. You might be able to ask Gargoyle if he has ever done this with the cat cuts, I know he is the creator of the Ogee design. Maybe he will chime in....

[gmcttr]

...which I will be able to use in all seasons....

Nice design, but I think you'll find it a bit breezy under it for winter.

[AnthonyVH]

Thanks for the insights! Keep them coming .

I'm interested to see how this works out for you. One thought I have is with the side pull outs. In my mind it would make more sense to just have one if they are only going to be 3' apart. That would cut down on weight especially if you're doing a poll mod. Whether it works the same way in practice as it does in my mind is different matter entirely.

I've attached an updated (if you can call it that) version of the design showing central pull-out locations. I can't imagine pull-outs weighting more than a few grams though (except of course if you take 1 vs 2 poles for a pole mod into account). The reason I put on two pull-outs on each side is because the hex design over on DIY Gear Supply has them as well, spaced 3.5ft apart.

Nice design, but I think you'll find it a bit breezy under it for winter.

Is this due to the small width of the design, i.e. that it won't extend far enough below the hammock? I got the impression from pictures (e.g. this one) that it should be possible to set the tarp up extremely small, almost completely wrapping around the hammock. Do you think that will not work out too well in practice?

[WV]

It will look neat, but I question whether the cat cuts are necessary at all. Their purpose would be to keep the edges from flapping, but Gargoyle's geometry may already do that. I suggest making it first without finishing the edges, and then deciding whether to add cat cuts or just hem the straight edges. Any edges cut on the bias may stretch and flap a bit, but hemming might fix that. You could also include a piece of narrow grosgrain in the hem. I use 3/8" width to stabilize bias edges; it will work for cat cut edges, too.

[AnthonyVH]

I think you're correct in that adding cat cuts to the doors will make them harder to close. My OES winter tarp has cat cuts on the doors and they don't close up all the way. I believe you should try it with the remaining cat cuts and post up some feedback here. I am interested. You might be able to ask Gargoyle if he has ever done this with the cat cuts, I know he is the creator of the Ogee design. Maybe he will chime in....

I was thinking about this a bit more and just had an idea. The main problem (in my mind at least) with the catenary cut doors is that they don't fully close. That is, unless they are crossed over each other far enough. What if an attachment point on one of the doors was added, which could then be used to attach the other door to with a little shock cord. And as a bonus, the catenary cuts will make the whole thing look a bit more streamlined. If you happen to have your OES winter tarp at hand, would you mind checking if this is a viable idea? Or is it simply impossible to get well closed doors with a cat cut?

It will look neat, but I question whether the cat cuts are necessary at all. Their purpose would be to keep the edges from flapping, but Gargoyle's geometry may already do that. I suggest making it first without finishing the edges, and then deciding whether to add cat cuts or just hem the straight edges. Any edges cut on the bias may stretch and flap a bit, but hemming might fix that. You could also include a piece of narrow grosgrain in the hem. I use 3/8" width to stabilize bias edges; it will work for cat cut edges, too.

Yes, I figure that the easiest way of making this is to first sew on the triangles and only then do the cuts, so it should be easy to test it without the catenary cuts first. I'm trying to keep weight down as much as possible as well though (well, within budget & usability limits ofc), and the cuts seem an easy way of shaving off some weight. Plus they definitely won't make flapping worse .

When you talk about reinforcing with grosgrain, do you mean to put the grosgrain inside the hem? So far, I've only seem people stitch it to the outside, which certainly gives a professional look. On the other hand, I have not seen any posts about problems due to not using grosgrain. Adding an edge with 3/4" grosgrain would, depending on the exact design, add between 2-3oz of weight (17-23% of the finished weight), so I'm currently leaning in favor not to use it.

PS: Attached is an updated PDF which now also lists circumferences for all three designs. This makes it easier to figure out finished weight, e.g. "how much extra weight will adding grosgrain add?". Also, now tilted 90 degrees for your increased viewing pleasure .

[boulderv7]

If you happen to have your OES winter tarp at hand, would you mind checking if this is a viable idea? Or is it simply impossible to get well closed doors with a cat cut?

If you have a shallow cat cut it will not be a problem. I have crossed my doors and I added snaps to them as well. It doesn't hang as nice looking with the doors snapped shut, you kind of have to pull them together to snap them and it leads to a funny shaped tarp. It works though. If you add a way to attach one door to the other, I don't see why it wouldn't work.

[Mouseskowitz]

I can't imagine pull-outs weighting more than a few grams though (except of course if you take 1 vs 2 poles for a pole mod into account). The reason I put on two pull-outs on each side is because the hex design over on DIY Gear Supply has them as well, spaced 3.5ft apart.

Now that I look I see what you're talking about with the DIY one, although the winter tarp has them 56" apart if I did my math right. All that to say, personally I'd get the tarp hung and then see where the pull outs would work best. My impression of pull outs is that they function to move the slack in the center of the side panel away from you to provide more usable room. If this is the case, I'm not sure how much slack will be available other than very near the widest point. I also noticed that your distance from the end to the pull out should be 4' not 5' if you want a 3' distance in the middle. For the added weight aspect, are you considering the weight of the extra lines or just the pull outs them selves? If you are willing to go through the trouble of extra cat cuts to save 5g I would think it might be a big deal. If the plan is to use a single tie out, I'm wondering if it would be better to move it further down the side? My thought is that you might get more effect down the length of the tarp that way (think out instead of up).

[AnthonyVH]

If you have a shallow cat cut it will not be a problem. I have crossed my doors and I added snaps to them as well. It doesn't hang as nice looking with the doors snapped shut, you kind of have to pull them together to snap them and it leads to a funny shaped tarp. It works though. If you add a way to attach one door to the other, I don't see why it wouldn't work.

Great! Thanks for the info.

Now that I look I see what you're talking about with the DIY one, although the winter tarp has them 56" apart if I did my math right. All that to say, personally I'd get the tarp hung and then see where the pull outs would work best. My impression of pull outs is that they function to move the slack in the center of the side panel away from you to provide more usable room. If this is the case, I'm not sure how much slack will be available other than very near the widest point. I also noticed that your distance from the end to the pull out should be 4' not 5' if you want a 3' distance in the middle. For the added weight aspect, are you considering the weight of the extra lines or just the pull outs them selves? If you are willing to go through the trouble of extra cat cuts to save 5g I would think it might be a big deal. If the plan is to use a single tie out, I'm wondering if it would be better to move it further down the side? My thought is that you might get more effect down the length of the tarp that way (think out instead of up).

I did not take any lines into account, and am doing the cat cuts mostly for better tensioning of the tarp (i.e. those small cat cuts are not done to save 5g). I was checking the distance between pull-outs on some other DIY tarps and they are pretty much all further apart than the ones in my design. So I'll definitely follow your suggestion and first try out some options before sewing on the final pull-outs!

Nice catch btw! PDF with fixed dimension is attached.