Bridge Hammock Refinement
I've refined my Bridge Hammocks from what I've learned and designed prior to and during the hike.
The refinements are:
- the suspension system - a separate thread
- the undercover weather shield - a separate thread
- switch from nylon ripstop to polyester ripstop
- replacement of bar and accessory rings
I used the Corded Bridge Hammocks exclusively on the trip and I now prefer the Corded Bridge Hammocks.
- I replaced the DWR nylon ripstop with DWR polyester ripstop.
I tried an uncoated polyester ripstop. It is very light, 1.4 oz/sq yard. It will not work too well in breezy or windy conditions unless it is also hot and/or humid.
I then tried a DWR polyester ripstop that is super soft and silky. Almost as soft as the uncoated polyester ripstop and far, far more so than any nylon ripstop. It's weight comes out to 1.84 oz/square yard.
I made a couple of Bridge Hammocks using both the DWR and uncoated polyester ripstop and Spyderline and was able to test them.
When I first hung the Bridge Hammock made with the polyester, I was really surprised.
I initially set-up the new Bridge Hammock with exactly the same suspension triangle dimensions as my nylon ripstop Bridge Hammocks and hung from the same suspension and ridge line that was already in place that I had been using for the nylon ripstop Bridge Hammocks. Unhooked the nylon ripstop Bridge Hammock from the suspension and ridge line and hooked in the new Bridge Hammock.
To my initial consternation and later delight, I found that my head and feet were lower than my butt - the sure sign of an inverted banana Bridge Hammock configuration. The drop of the head and feet wasn't excessive, but definitely immediately noticed.
This initially confused me and I rechecked the suspension triangle on the new hammock. It is exactly the same as the suspension triangle on the nylon Bridges.
Then I understood what is happening. The nylon ripstop in the old Bridge Hammocks stretches, especially where the forces are greatest - the butt.
That nylon ripstop stretches a lot to accommodate the butt, hence the butt drop in hammocks.
That butt drop in a nylon Bridge hammock has consequences that are not to the occupants total benefit. In order to obtain the flat lie that the Bridge Hammock is capable of, you have to compensate for the butt drop. If you don't, you end up with the proverbial banana that the Bridge Hammock is designed to overcome.
To compensate for the butt drop in the Bridge Hammock, you do one of two things or a combination of both:
- increase the length of the ridge line - this works against you in that you need a longer tarp ridge line and hence a bigger and heavier tarp.
- decrease the length of the suspension triangle - this works against you in that a shorter suspension triangle increases the compression forces on the spreader/hiking pole and hence the need for stronger spreader/hiking poles.
Both options pull the arc out flatter which pulls the butt up, compensating for the butt drop.
I hadn't really thought about it in terms of the stretch of the nylon ripstop before.
But with the polyester ripstop, it became obvious.
So the solution is now the reverse of the two options above.
After a few minutes experimentation, I found that shortening the ridge line from 120" to 115" for the new fabric gave me nearly the same feel in the flatness that I had in the nylon ripstop.
A 5" shorter ridge line may not seem like much until you put a 10' tarp ridge line on top of it. I have also replaced the bar and accessory rings which gained me some more in shortening the ridge line. It is now down to approximately 112".
It just got better and better. !!!!
This is great, more margin under the tarp. I can leave the suspension triangle alone and retain the same compression forces on the spreader/hiking pole.
I can feel the even flatter lie with the polyester ripstop with the butt drop drastically reduced.
My Bridge Hammock body fabric weight dropped from 5.90 oz for the nylon ripstop to 4.75 oz for the DWR polyester ripstop and even less for the uncoated polyester ripstop.
- Switched from arc webbing to arc cord.
I wanted to use the same type and size rope throughout my Bridge Hammocks: my suspension, the suspension triangles, the ridge line and the arcs. Using the same kind and size of rope for all would save me time in constructing a Bridge Hammock, suspension triangle, suspension and ridge line. It would also mean that I can buy just one rope instead of 3 different kinds and/or sizes of rope.
I researched more double and single braid ropes and purchased more than I want to think about.
I recently found and obtained some 3 mm diameter dyneema cord rated at 1,200 lbsf, equal to the Spyderline in rated breaking strength. I should say that my wife's cousin found it. He got a good price and after buying the first spool, purchased 2 more. I had asked him to keep an eye out for dyneema/spectra cord during my hike. He also found guy line of the same dyneema. A little under 2 mm diameter. Great stuff. I have switched totally to the dyneema guy line. He bought a 600' spool and one for me. The price on the 3 mm dyneema came to only $0.16/ft. The least expensive rope of that kind I have seen anywhere and about half the price of the webbing. The strength, weight and price all made it the winner for my future Bridge Hammocks. I have found though that it needs to be pre-stretched to pull the braiding tight for use. I simply string it between two vertical supports and pull tight using a HitchCraft Mini Rope Tie and leave it until needed.
The weight works out to 0.055 oz/ft (both as specified by the maker and as weighed on my scale), which is the lightest I have found so far. Lighter than the Spyderline at 0.071 oz/ft. The 1/2" tubular polyester webbing at 0.17 oz/ft is 3.1 times as heavy.
It is coated instead of the polyester sheath of the Spyderline.
I had originally used the steel bar and accessory rings to transfer the force from the arc webbing to the rope of the suspension. Thus, the original reason for the bar and accessory rings became invalid. Joining two ropes does not require the rings. I now join the suspension triangle rope to the arc rope using a simple double sheet bend with overhand safety knots.
So I decided to eliminate the bar and accessory rings.
Eliminating bar and accessory rings left two problems:
- how to secure the spreader/hiking poles to the suspension triangle, and
- what to use to replace the accessory rings for attaching under quilts, undercovers, over covers, bug netting, etc. to the Bridge Hammock.
The second problem was actually the easiest to solve. I simply inserted a 1/2" ID steel ring in the double sheet bend when tying the knot. On new Bridge Hammocks I will simply lash the ring to the suspension triangle cord where it exits the fabric. Instant accessory attachment device. Since the 1/2" ID ring only needs to support the weight of any under quilts, it is more than sufficient. The small ring is very light, 0.05 oz each. I was thinking of using plastic rings thinking they may be even lighter, but the steel rings are so light that the plastic really couldn't have saved much weight. Also, steel is much more durable.
On to problem #1.
Tried several methods for the carbide tips and I settled on a pouch made from Strapworks 1.5" wide seatbelt webbing. I Use a 7" length, sewed in a loop with a 1" overlap. I lay flat with overlap on top, fold in half with overlap inside and sewed the edges closed. I didn't sew the edges completely closed, but left a small opening at the tops for cord to fit through. I then thread the suspension triangle cord through one opening and through the other opening I thread another short length of cord. I secure the second cord to the suspension triangle cord with 2 half hitches with overhand stopper knots. The pouch is used for the hiking pole carbide tip.
For the handle end, I use a 1" length of 1/2" diameter UHMW polyethylene rod, drilled and tapped on the axis for the 1/4" x 20 camera mount screw. I then simply screw this on the camera mount stud on the handle end. I laid the rod on the suspension cord. I attached a short length of cord to the suspension triangle cord with 2 half hitches, looped over the polyethylene rod and secured again to the suspension triangle cord with another 2 half hitches. I secured the half hitches with overhand safety knots. Both polyethylene fittings together weigh 6 grams, 0.2 oz.
A webbing pouch weighs 0.15 oz. The short lengths of cord used weigh approximately 0.10 oz. So 0.60 oz for both pouches, both polyethylene fittings and all of the attachment cords.
Replacing the stainless steel bar and accessory rings also brought the spreader bars closer to the fabric. This has two benefits:
- It reduced the header spreader bar length to approximately 39". This wasn't planned or done deliberately, just a consequence of replacing the steel rings with the webbing pouches. This reduced the compression forces and since the spreader/hiking poles are closer to the fabric, my perceived shoulder room is the same.
- shortened the arc length from spreader/hiking pole to spreader/hiking pole. This means that without the rings, I can also shorten the ridge line
The polyester ripstop and ring replacement has brought my ridge line length down to 112" inches from the 120" inches needed previously.
I discovered that in my endeavors to give myself more options in the arc support material (rope instead or webbing) and to improve on the nylon ripstop, that I have reduced the weight of the hammock body with each successive iteration of my endeavors.
I pulled out the old Bridge Hammocks and weighed them. I weighed all of the successive models in the same configuration (well almost - the earliest has the bar and accessory rings). I have used the identical pattern in cutting the hammock body fabric, pretty much the Australian design. I haven't felt any great need to innovate on that.
- Bridge Hammock body, with the end edges bound with nylon bias tape,
- the Bridge Hammock pillow installed,
- suspension triangle, all triangles of equal size,
- 4 1/2" ID steel accessory rings,
- web pockets for carbide tips and polyethylene rod and cord loops for handle ends
I have not included the draft stoppers in this comparison since they are the same for all versions, are add-ons to the Bridge Hammock as I make one and are swapped from Bridge Hammock to Bridge Hammock. Nor have I included the suspension line and ridge line as it is the same for all versions and again swapped between them. It is shorter by 8" for the polyester ripstop versions. This keeps the parts more interchangeable.
- DWR nylon ripstop, 1/2" tubular polyester webbing on arcs, Spyderline suspension triangles, stainless steel bar and accessory rings: 16.25 oz
- DWR nylon ripstop, Spyderline on arcs and suspension triangles, stainless steel bar and accessory rings: 14.35 oz
- DWR nylon ripstop, Spyderline on arcs and suspension triangles, web pockets: 10.05 oz
- polyester ripstop, Spyderline on arcs and suspension triangles, web pockets: 8.95 oz
- uncoated polyester ripstop, 3 mm dyneema on arcs and suspension triangle, web pockets: 7.15 oz
Not counting the last hammock, the basic Bridge Hammock weight has been cut to 55% of the original, a 45% weight reduction. A happy by-product I like and can happily and easily live with. The last hammock brings the weight down to 44% of the original.
Materials and Weights: (Note: Bridge Hammock includes the suspension triangle. Suspension includes the suspension line, ridge line, 2 hang knot and stopper knot pairs, 2 tree huggers, and 1 Camp Nano Wire Carabiner)
- Bridge Hammock with DWR polyester ripstop and Spyderline
- Bridge Hammock: 8.95 oz
- Suspension: 4.80 oz
- Subtotal: 13.75 oz
- Bug netting: 7.45 oz
- Subtotal: 21.20 oz
- Draft stoppers: 2.65 oz
- Overcover: 5.65 oz
- Subtotal: 29.50 oz
- Tarp, 10'x9.5': 18.35 oz
- Total: 47.85 oz
- Bridge Hammock with uncoated polyester ripstop and 3 mm coated Dyneema
- Bridge Hammock: 7.15 oz
- Suspension: 4.80 oz
- Subtotal: 11.95 oz
- Bug netting: 7.45 oz
- Subtotal: 19.40 oz
- Draft stoppers: 2.65 oz
- Overcover: 5.65 oz
- Subtotal: 27.70 oz
- Tarp, 10'x9.5': 18.35 oz
- Total: 46.05 oz
Without the overcover, the last option is strictly a summer season hammock, but for that use it is excellent and, at 19 oz an easy carry. The uncoated polyester ripstop doesn't stop the wind. You can almost see right through it. In summer conditions, I'll be taking the uncoated polyester ripstop and using the Dri Ducks poncho as a weather/bug shield since it can be used as a wind break and support for the Gossamer Gear pads. With the Dri Ducks weather shield and Gossamer Gear pads, I'm good to moderate summer night temperatures.
The first 2 options give me a four season Bridge Hammock for less than 2 lbs, not counting the top/bottom insulation or the spreader/hiking poles. The hiking poles I use irregardless, so counting their weight in the Bridge Hammock would be counting it twice. The top/bottom insulation varies widely depending on what is being used - quilts, pads, poncho liner, Dri Ducks weather shield.
The 3 mm dyneema doesn't save much in weight over the Spyderline, but a lot in cost and convenience since it is used for all cord needs.
I have calculated that I could cut the weight of the bug netting from 7.45 oz to between 3.5 oz to 4 oz by reducing the height and running from the corners of the Bridge Hammock instead of the ridge line. But that would drastically reduce the room inside the hammock under the bug netting. It's like hitting your head on the top bunk bed whenever you sit up in bed. That gets old quickly. I like the room better. It's nice to be able to actually sit upright to get at the gear loft over my feet, move around in the hammock and just plain look around. Also, the ample head room eases entry/exit, making it very simple. I can enter/exit in almost the same fashion as without the bug netting and the bug netting snaps back into place automatically. Then simply tighten the netting ridge line. No fuss, no bother. Reverse to exit. Same with the overcover. I found with the Hennessey ULBA that I really do not like something inches from my face while trying to sleep, read, watch the stars or view the scenery. And when the bugs drive you under the netting long before time to sleep, the extra room is really nice to have.
Reducing the weight was a happy by-product for me and not one of my goals.
I have not included a stuff sack in the above weights. I no longer use a stuff sack for my Bridge Hammocks. When I take the Bridge Hammock down I simply fold in half lengthwise and hold the four corners in one hand with the hammock hanging down. I then fold the hammock up in halves, holding each fold in the top hand holding the four corners. I continue this until everything is about the width of my hand or a little longer. I then wrap the suspension triangle cords around the bundle created. Finally tucking the end of the cords under the wraps. This creates a bundle for the hammock not much larger than my hand. The uncoated polyester ripstop Bridge Hammock makes the smallest such bundle. My Bridge Hammocks use approximately 1.9 square yards of fabric for the body of the hammock as compared to 5 square yards for the Hennessy ULBA.
If the bug netting or overcover is installed, I simply unhook from the ridge line and drop it into the hammock before folding the hammock. The bug netting or overcover is then neatly packed with the hammock.
The folded and wrapped bundle can then be placed in my pack in any convenient place. Since it isn't compressed, it fits nearly anywhere in my pack. I can also drop the bundle in a silnyl sack and tie to the outside of my pack and not worry about room in the pack.
I have always packed quilts, top and bottom, separately and continue to do so. Takes me longer, but I feel more secure having them stuffed into separate dry sacks.