Saturday, April 12, 2008

Fly Me Up Scotty

Now it is April, and time to start thinking about a new backpacking season. Well, maybe not. A person should never quit thinking about it, but some of us haven't mastered the art of being busy little beavers all winter, and refining or remaking our gear when we have a good chance.

We (me, I, myself) get lazy and sloth around. Personally I like to nap a lot, and scratch those places Mom said not to scratch in public. Winter is good for that too, and this year hasn't been great for getting out. Not where I live. Too icy, and there has been snow in even the low hills, which is unusual. The average temperature for last month was six degrees below the same month last year, and we've had cold weather all winter.

True, this weather is pretty mild in an absolute sense. I spent my first 28 winters in North Dakota, so I've had my nose hairs frostbitten a few times. After a few years of that you don't ever lose all your winter hair again, not even in high summer, and you learn not to turn your back on winter, mild or otherwise. But still it's been a good winter to loll around and read books.

Snow pack is heavy I hear, too, from 100% to 160% of normal, depending on location. So this year will have a slow start to it. Maybe I have time to catch up.

One item I've been thinking of working on is a new fly for my hammock. I really need two, and one I've got already.

The hammock I use is the Hennessy Adventure Racer, base weight, 15 ounces (425 g). It isn't intended for backpacking, and is guaranteed for only one year, but I've used mine for about six seasons with no problems. I'm light and careful. The fly, like all by Hennessy is a diamond shape. This is fine for most conditions but not for all.

Given a cool night with a slow and steady downslope air flow, I can just lower the upslope edge of the fly and horizontally pull out the downslope side. With the hammock pitched level across the slope, I'm cozy and have a view. It's like using any other tarp.

Wind is tougher. A steady breeze coming from either the head or foot end can be defeated by pitching the fly almost closed at that end and leaving it open, funnel-like, at the other. Moisture escapes at the open end and cold wind is blocked at the other. A side wind is more like an overnight downslope flow, but harder to deal with. The fly tends to rattle if not pitched right, and usually has to be re-tensioned at least once during the night. The downslope side has to be pitched lower, too, to prevent backflow from turbulence.

Still not too bad.

Things get worse when rain falls. Now you have to worry about both wind and wet. They usually come together, if not now then later, when the night is dark. The fly has to be set up carefully to protect from falling rain, from blown rain, and from water dripping off the fly itself.

Cinch it down too close to the hammock body or attempt to wrap it against the hammock at all, and you get wet. Your sleeping bag too. Another set of issues come into play as well, because setting up the hammock and fly for sleeping may not be right for evening or morning chores.

This is especially true with the tiny fly of the Hennessy Adventure Racer. I've cooked and eaten breakfast under the hammock, and gotten dressed, but not stayed completely dry. This sounds odd, but the usable area right under the hammock is really cramped. There is just enough room for me to sit in one spot and be protected. This doesn't leave quite enough room to set up even my tiny alcohol stove and cook kit, let alone lay out my food bag and pack, or change from jammies into hiking clothes. Putting anything even six inches off to one side or the other, or out front or back gets it into the rain.

My other Hennessy hammock is an obsolete model called the Ultralight Backpacker. It weighs about twice as much. It's fine but I don't often use it. It's fly is also bigger, but not hugely, and has the same sorts of problems.

Both flies are diamond shaped as I said. The way this works out is that they have a really long axis that covers the length of the hammock (roughly 10 feet or 3 meters), and a shorter secondary axis from side to side. There are pointy ends at the head and foot, and two more points guyed out to the sides. Trying to find cover under the pointy edge of a fly is hard. There isn't much room there, so while a fly of this shape naturally fits the hammock and is easy to guy out, it isn't useful in general.

I leave the head and foot ends of the fly attached to the hammock for simplicity. At the sides I use my trekking poles for stakes. Conventional stakes are pretty much useless, but the trekking poles are great. In soft soil I can bury one 18 inches or more (0.5 m.) and it will stay put. I can put a huge amount of tension on it, and since the poles are adjustable, I can raise or lower the pitch as needed. When the weather is calm and dry but I need some protection from the overnight downslope flow of cool air, I can just let the upslope part of the fly hang with my trekking pole in one of its guy loops. The fly tensions itself while hanging straight down, and you can't get better draft protection than that.

But that still leaves me with a fly that has too many points on it. As mentioned, this is not a problem in decent weather. In fact it's an advantage because a tarp with this geometry is very frugal with fabric, and therefore light.

So the problem if any comes in really windy weather (which isn't too bad) or in wet weather (which can be). The biggest problem would come if camped in one spot for several days, or if stuck with serious rain for days on end even if changing campsites on a daily basis. Either way, with days of rain, you need some real protection.

Hammockers have found basically two solutions. One is a rectangular fly and the other is a hexagonal fly. Either one provides more coverage than the standard diamond shaped fly.

So what is a rectangular fly and how does it work?

Eh? You dumb or what? A rectangular fly is rectangular. It pitches over the hammock like a large pup tent, held in place by two attachments, one at the head of the hammock and one at the foot. As with all hammock flies, this may either be attached to the main line supporting the hammock or may have its own guy lines. Some like it one way, some like it the other way.

Supporting the fly by its own lines allows the hammocker to raise or lower the fly independently of the hammock. And the fly does not sag with the hammock when you get into it. On the other hand, the fly does not sag with the hammock when you get into it, which means that you can get a lot of headroom between the top of the hammock and the fly. Separate suspension is also more complicated, but then again it allows you to quickly remove the fly from the hammock and use it as a pack cover or as a separate tarp, or as a poncho. Some hammock flies are made to be used as ponchos. It's a matter of personal choice.

So then, on to hexagonal flies. Which are basically rectangular with an overhang on each end. They pretty much are the same as rectangular flies but can be a bit smaller since their shape is a closer fit to that of a hammock. Because both this kind of fly and the hammock are pointed at each end, and because the very head and foot of the hammock contain no useful space, this is a better use of fabric. Hexagonal tarps also tend to be catenary cut so they pitch better and use even less fabric. But there is no reason a rectangular fly can't also be made with a catenary cut.

Both hexagonal and rectangular flies share a significant disadvantage. They both need at least four side guy points compared to the diamond-shaped fly's two. I'm not sure how I'd handle this, unless I start carrying four trekking poles instead of two. But I've sewn on some extra tieouts to my existing flies, and added line, and maybe I could do this on a new fly. Just stretch out the line and tie off to trees, shrubs, or fallen wood. This could be a bit dicier in rough weather, and I might need to carry a pair of long stakes, since rough weather would be the whole reason for using a non-diamond tarp.

Materials is another question.

The flies I have are both from Hennessy, and the quality of the fabric is first rate. It is silnylon, silicone-treated nylon. This weighs roughly 1.4 ounces (40 g.) per square yard. Another possibility might be Cuben fiber fabric. It is much lighter (something like one third the weight) but is horrifically expensive (in the neighborhood of $30 a linear yard).

At least for experimentation, three mil poly film should be OK. This might even stand up to a season's backpacking, but might have to be replaced yearly, at least. This is polyethylene sheeting (heavyweight painter's plastic dropcloth). Normally you can get this in clear and black. It is maybe twice the weight of silnylon fabric but much cheaper. Silnylon is around $12 a yard, or roughly half that if you can find "seconds", fabric with cosmetic blemishes.

I've briefly tried an eight by 10 foot (2.4 by 3 m.) three mil poly tarp for camping on the ground. Mine weighs about 25 ounces (709 g.), which isn't bad, and the coverage of a tarp this size is fantastic. I got the idea from one of Ray Jardine's books. He said that three mil plastic could stand up to a whole season's use, and it may. I don't know how that translates to use as a hammock fly, but it may work.

Cost, as I've noted, varies. The plastic sheeting is by far the cheapest, and is the heaviest. Things usually work out this way.

Esthetics are another matter. If they matter.

Hey. One thing I found out while trying the plastic tarp was that it was really cool to look up at the sky through my tarp at night. There would be no privacy during the day, but that is also true if you use Cuben fiber fabric. And there would be no protection from sun, if you camped on one spot for more than a night. Once again, it all depends.

I've never used Cuben, but the silnylon I've got in the two commercially-made flies is great. A little crinkly, but that isn't an issue when the fly is guyed out. The only real issue with those is getting one that is the right color, and you have to take what comes with the hammock. If you buy your own fabric your color choices are still limited, but at least you have some choice.

I've figured that if I choose a larger diamond-shaped tarp, an eight by eight foot (2.4 by 2.4 m.) one might work just fine. This would give a diagonal length of about 11.3 feet (3.4 m.), more than enough to handle the hammock's length.

If my choice is to go either rectangular or hexagonal, I thought I'd try avoiding a longitudinal center seam. I get skittish thinking about having a seam running the full length of my hammock fly, directly above me. In a hammock you can't just roll away from a leak.

The idea (and I think it will work) is to make the tarp from three pieces of fabric. Silnylon is 60 inches (1.5 m.) wide, so that would cover me, and I would use that for the center section, lengthwise. To flesh out the width, I'd sew another piece on each side. During rain, the two seams would be off to the sides, and any leakage would either run down the under side of the tarp or drip straight onto the ground beside the hammock.

I could design this to be either "flat" or catenary cut. A catenary is a hyperbolic curve. Hold a string between your hands, but not tight, and the pull of gravity on the string forms a catenary curve. Catenary curves are like pre-stretched fabric so it's easier to get a taut pitch, but they're fussier to make.

If I used poly film I'd just cut it down to the size needed, no seams or sewing required, but making guy points would be a bit harder.

An eight by eight diamond would be the smallest and lightest option but would also have the least coverage, which is what I'm really after here. A more rectangular fly would contain more material and also offer more coverage with more weight.

Luckily for me, there are commercial options to eyeball (though I prefer to make my own stuff), and several hammock-oriented web sites, like "Just Jeff's Hiking Page", so I can get ideas from what other people have already tried, and also see pictures.

As with most things, this will take a little more thinking and fussing. Backpacking season is still a few weeks off, so I once again have a bit of a grace period.


References:

Just Jeff's Hiking Page: How Do I Stay Dry in a Hammock?

MacCat Tarps.

Jacks 'R' Better, LLC.

Speer Hammocks.

Hennessy Hammock.

Oware. And again.

Mountain Laurel Designs.

Silnylon.

Cuben fiber at Quest Outfitters.

Cuben Fiber/Wikipedia.


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