My Bridge Hammock System - Part 6
Next assemble the bug netting end panels by sewing the belly bands to the end panels exactly the same as for the draft stoppers. You will probably not have to snip the belly band seam allowance here as you did for the draft stoppers since the bug netting mesh is much stretchier than the draft stopper ripstop.
I did not bother to fold the seam allowance before sewing to the belly band for the bug netting. Simply sewing flat against the belly band is sufficient for the bug netting mesh.
Sew octagon patches to the middle of the belly bands for the pack clips by folding a patch in half, sandwiching the netting and sewing in place. Next sew the pack clip in place using the grosgrain as before.
Now mark the bug netting main body by drawing a straight line from the middle of the end, 1" in from the edge, at the attachment loop, to the pack clip attachment points. This will be the seam line for the end panels. This seam line is illustrated in the main body diagram above as red lines.
Next assemble the main body and end panels by sewing the bug netting end panels to each end of the main body along the 1" seam allowance lines on the triangular tops of the end panel and main body seam lines marked above.
The main body and end panels are only sewn together along the triangular top portions of the end panels.
The parabolic arcs are sewn only to the belly bands.
Mate the end of the main body to the end panel triangle by matching the seam lines, inside side to inside side. Be very careful to mate the proper sides of the end panel and the main body and the proper end panel to the proper end of the main body, do not mix head and foot end panels and head and foot ends of the main body.
Also, make very sure that the outside attachment loops remain on the outside side of the netting.
The easiest way I have found to sew the end panels to the main body is to match the two pieces and sew a small tack at the apex of the triangle to the main body at the attachment loop and then tack it again at the base of the triangle and 1/4" to 1/2" above the pack clip attachment point. Both ends of the triangle side are now ready to be sewn in place.
NOTE: It is best to use a zig zag stitch in sewing the end panels to the main body. The zig zag stitch should be placed in the seam allowance with the edge of the stitches on the seam line. This will allow the bug netting to stretch from the accessory rings to the attachment loops.
Note: The side of the triangle will probably be slightly longer than the main body distance. Fold 1 or 2 small darts in the triangle sides as you are sewing so that the ends match.
Sew from the middle down to the base of the triangle. Stop sewing where you have tacked the base of the triangle 1/4" to 1/2" above the pack clip attachment point.
Repeat for the other side of the triangle.
Note, DO NOT sew the tops of the end panels to the main body past the bottom of the triangles.
Then lay the seam allowance against the end panel and sew flat. Again only sew as far as the end panel and main body were sewn together.
The bug netting is now installed on the hammock just like the overcover and draft stoppers are installed and tensioned just like the overcover.
When installed the shock cords tensioners should be pulling the pack clips and some of the grosgrain attaching them through the accessory rings. That pulls the octagon patches up tight against the rings. The main body, the end panel and the belly band all meet at the accessory rings and seal the netting tight. The sides pull tight and the sides of the Bridge Hammock capture the sides under the hammock so that everything is sealed up tight.
You have a Bridge Hammock sealed against small critters.
The bug netting may be used in combination with the draft stoppers and/or an under quilt, e.g., a poncho liner. Here I have pictures from inside with the draft stoppers also installed.
Note: you do not have to use the draft stoppers with the bug netting. The end panels and belly bands of the bug netting keep the critters out there.
Poncho Liner as under quilt
Making special under quilts is not necessary for the Bridge Hammock.
This section and the next section will detail using commonly available and inexpensive Poncho Liners and rectangular sleeping bags as excellent under quilts.
The poncho liners I investigated on the internet are almost exactly the right size for an underquilt for my Bridge Hammock. The fabric at the head end of my hammock is 56.5" and 56" at the foot end. Almost all poncho liners I found, listed the dimensions as 56" to 60" wide. The lengths were listed at close to 80" which is a very good match for my Bridge Hammocks.
The poncho liner I bought came in at approximately 58" wide by approximately 80" long.
The liner came with braided tie offs at the corners and the middle of all sides.
Decide which ends of the poncho liner will be used for the head and foot ends. It will make a difference. You cannot swap the ends once the poncho liner has been adapted as an under quilt if your header and footer spreader bars are of unequal lengths.
If your poncho liner doesn't have tie offs at the head end corners of the poncho liner, you will have to add them. I have found braided tie offs work best for this application. You can get braided polyester or nylon tubular webbing from Hancock Fabrics in the accessory dept. It is less than 1/8" diameter. I think it is usually used as decoration.
I sewed two small loops of small diameter braided nylon cord, not the webbing above, to the corners of the liner at the foot end of the poncho liner. The cord is also available from Hancock Fabrics in the drapery department. Any small diameter cord such as guy line cord will work.
This will always be the foot end of the poncho liner when attached to the hammock.
Then I took two lengths of 1/8" diameter shock cord and used 4" cable ties, 4, to join the lengths into 2 loops, 2 cable ties per loop, through the cord loops. You could easily replace the cable ties with a sheetbend knot. The shock cord loops are approximately 2" long when pulled out straight.
Using the corner tie offs at the head end of the liner, tie the corners to the head end accessory rings.
I then took a length of guy line cord and a small Figure 9. The length of cord needed is approximately 2.5 to 3 times the distance between the foot end accessory rings.
Tie one end of the cord to the shock cord which will be on the entry/exit side of the hammock using a bowline knot. At a distance from the bowline equal to approximately 3/4 of the distance between the accessory rings, use a bight to tie an overhand knot. This gives you a loop in the cord which will used to attach the small Figure 9 to the cord.
Thread the free end of the cord through the accessory ring on the entry/exit side of the hammock and pull the loop through the ring. At this point it is most convenient to attach the small Figure 9 to the loop. Then run the cord through the opposite accessory ring, through the shock cord loop on the other corner of the liner and then back through the accessory ring, to the Figure 9.
Wrap on the Figure 9 and using the cord, pull the liner until the shock cords are just touching the accessory rings. Do NOT pull them through the accessory rings.
Wrap the Figure 9 to secure.
Run the free end to the accessory ring opposite the entry/exit side of the hammock and wrap around the ring and back to the Figure 9 and secure to the Figure 9.
Once I entered the hammock the poncho liner was snugged up tight under the hammock fabric from my head down to my knees. Since the liner was shorter than the distance from accessory ring to accessory ring, the liner tended to pull down slightly away from the hammock fabric below my knees.
This was easily solved. I sewed two more cord loops to the edge of the poncho liner 1/4 of the length from the foot end. I took a length of 1/8" diameter shock cord and formed a loop in one end through one of the new cord loops. Ran the shock cord up over the ridge line and adjusted the length to snug the liner up under the hammock. Formed a loop on the end and connected the loop to the second cord loop using a micro-carabiner. I use 4" cable ties for forming loops in shock cord. Works better for me than knots. Also, I have measured and found that the cable tie is slightly lighter after trimming excess cable tie than the extra shock cord needed for a knot.
Back into the hammock. The liner is now pulled up snug under the hammock from head to foot. The shock cord over the ridge line 1/4 from the foot end eliminated the gap under my lower legs.
Since the sides of the Bridge Hammock slant up and out, away from the center line, the sides of the poncho liner followed this tendency. I decided that I would like to have the sides of the poncho liner vertical in the middle.
Sewed two more cord loops in the middle of the liner sides, one each side. Again, using 1/8" diameter shock cord, I formed a loop in one end through a cord loop. Ran up and over the ridge line and down to the second cord loop. Found the right length, cut the shock cord and formed a second loop on the end.
Now after getting into the hammock, I simply hand the shock cord over the ridge line, pull down to the loop on the entry side and clip into the micro-carabiner already on the cord loop there.
The sides of the poncho liner are now vertical in the middle.
I like it much better this way when it is cold. Like laying at the bottom of a deep warm bathtub. The poncho liner blocks the wind from the sides and really protects the warm air built up inside. Need the draft stoppers on the ends if there is any breeze to keep the warm air trapped.
Lesson learned. Simple rectangles work really, really well for under quilts on a Bridge Hammock. Easy fit and the fit is perfect.
Thus, a poncho liner works very well as an under quilt for a Bridge Hammock.
poncho liner installed:
The white things on the edge of the poncho liner are the braided nylon cord from Hancock Fabrics that I used for the cord loops. The shock cord 1/4 of the length from the foot end of the liner can be seen also. On the top of the photo on the edge of the liner are the loops for the shock cord in the middle of the liner. The micro-carabiner can be seen on the right. It is blurry because it is out of the focal plane of the lens setting. You can see how the sides of the liner are pulled vertical in the middle by the shock cord. They are not so close that they hinder my movements in the hammock. Also, they are high enough to block any wind.
How does it perform?
I use a Wiggy's Poncho Liner. The only reason being that he is selling them for $17.50 each until his stock is depleted. That is the best price, cheap, that I could find for a good poncho liner. I found prices ranging from about $25.00 to over $50.00 for the "new technology" poncho liners. Wiggy's has a good reputation among those who don't mind his personality and a bad reputation among those who do. I don't have to live with the man, so for $17.50, I was ready to try his poncho liner. Liked it and bought a second. He emailed that the weight was 1.5 lbs. Mine weighed 39.5 oz when I received it and 39 oz after I washed it and applied ReviveX to one side. So it isn't the lightest option around, but after using it awhile, I will say that I believe it will withstand a lot of rough treatment. Very tough fabric and well made.
I have decided to use the poncho liner as an underquilt for early to late spring, summer and early to late fall. Don't know about other poncho liners and the insulation used, but the Wiggy's liner alone under my Bridge Hammock has taken me into the 30s. Don't know if it will do this consistently or if the conditions prevalent at those occasions were just right for that performance or maybe I was feeling extra warm for some reason. YMMV
I use two 3/8" Gossamer Gear pads in each hammock. I have cut 20" off the end of two. One had minor defects and so was reduced by about 40%. The defect turned out to be a discoloration on one end. That was the end I cut off. After attaching the poncho liner to the Bridge Hammocks, I lift the hammock and lay the full length pad down the center of the poncho liner. That brings the pad from my feet to the top of my shoulders. I then lay the cut down pad across the top of the first pad, forming a 'T'.
That gives me 3/4" of insulation under my torso on top of the poncho liner and the second pad warps up around my shoulders protecting my upper arms and sides. I had been thinking of using the 20" I cut off in a SPE, but decided it was better and easier to just use the remainder as I do above. Both pads are then under the hammock and they stick together and to the poncho liner like they have been glued in place, yet the hammock fabric slips on the pads quite easily. Together, the pads weigh 9.1 oz. The weight is excellent for the insulation afforded. A little more bulky than down, but since they are impervious to water, I just roll and secure outside the pack. I don't have to take the extra precautions that I do with down that increase the bulkiness and packed weight of down. In the field with down, I protect it from water with special zip lock plastic bags from Cabela's that have one-way valves on the bottom to evacuate the air. Seals out air and water, but increases the bulkiness somewhat.
When I use the overcover, I use it on the outside of the poncho liner. With the poncho liner, the overcover and the draft stoppers, our Bridge Hammocks are closed up pretty good. Nice and comfy inside and warm. For more warmth I can add the Gossamer Gear pads. When the winds are blowing and the weather is really nasty, it is nice to be swinging free, comfortable and warm in a private berth. Fancy tarps with "doors", etc. Would probably make things better, but with the overcover, draft stoppers and poncho liners, I already have a private floating tent. Just a plain tarp overhead to block rain, snow and the worst of the wind is all that we really need.
I prefer using the draft stoppers with the poncho liner or under quilts even with zero breeze or wind since they seal the ends of the hammock and keep air from spilling out the ends. More effectively traps the air in the bath tub formed.
Sleeping bag as under quilt
My neighbor was disposing of an old sleeping bag. Being the frugal person that I am, alright cheap, I asked if I could have the bag. I figured that if it wasn't any good, I could then continue it's travels to the trash.
Well, other than being old, it is in very good shape. It is down. Down can last a long time. I have a king size down comforter with 9 lbs of down that I use in the winter on my bed. It is currently approximately 40 years old and still like new.
The bag is Sears brand - no temperature rating listed.
The down feels to be in good condition. I have had down bags and down and feather bags. I can feel no feathers in this bag, so I'm pretty sure it is all down, maybe duck down instead of goose although my experience with Sears in the past argues for goose down. Measured the loft: varies from 3.5" to 4". So it should be good to some fairly low temperatures.
The bag tag specifies the following - Yes he was even careful enough to retain those cloth flaps they sew on everything:
The loft is pretty even across the whole bag. I can find no low spots or thin spots. It is baffled, offset baffles, and not sewn through. It is somewhat of a rectangular bag, wider at the head end and tapering down narrower at the feet.
The zipper lets me open it up quilt style. There is a draw cord for closing in the head end. Simple shoestring. I will have to replace that with some guy line cord for better durability and put a cord lock on each end to keep it from getting pulled through.
Opened up as a quilt, it measures 64" wide at the head end, 42" wide at the feet and 80" long. That matches the dimensions specified on the manufacturers tag.
Great! I think this thing will work well as either a top quilt inside or as an under quilt. As a top quilt I could zip the bottom and a little up the side to form a foot box.
The 64" at the head end is actually much wider than needed there. The fabric at the head end of my Bridge Hammock is 56.5" so there will be plenty of coverage for the upper body.
Now I get to really test how easy it is to adapt a somewhat rectangular sleeping bag as an under quilt for my Bridge Hammock. I have already easily adapted rectangular poncho liners. So I have some experience.
The rest of this description is being written in real time as I adapt the bag.
All done. Took about 15 to 30 minutes. I used about 20" of braided nylon cord from Hancock Fabrics. Cut into 4 equal lengths. Overhand stopper knots on the ends. Sewn on the bag as loops in 4 places.
The two loops on the foot end are sewn on the corners, on the inside of the zipper, where the lining and zipper meet, slightly on the stronger zipper material. There is a down filled draft tube on one side of the bag. I sewed the loop at the inside junction of the tube with the lining and still through the zipper material.
foot end cord loop just inside draft tube:
On the head end, I sewed the loops 28.25" apart to match the 56.5" fabric width of my Bridge Hammock. The loops are centered on the end of the bag and sewn at the inside seam of the draw cord channel.
head end cord loop on draw cord channel seam:
Note: it is simpler to bar tack the cord loops using a zipper foot.
I attached both ends of the sleeping bag to the hammock in the same manner I attach the foot end of my poncho liner. So, if you have already read that portion of this write-up, you can skip a few paragraphs. The only difference is that since the sleeping bag is narrower than the poncho liner, the sides will not reach as high on the sides of the hammock. For this reason, I have not used the shock cord loops at the corners as I did for the poncho liner.
I used two lengths of BPL guy line cord (BPL guy line cord simply because I had 2 pieces about the right lengths) and 2 small Figure 9s. Tied the end of one length of guy line cord to a loop on the head end and the other length to a loop on the foot end. Used a simple bowline knot to make small loops. Used the loops that will be on the entry/exit side of the hammock.
Measured off a distance form the bowline approximately 3/4 of the distance between accessory rings and tied an overhand knot using a bight. This gives a loop for attaching the small Figure 9.
I attached the head end to the hammock first because I want the head end loops tight against the accessory rings which would ensure the best coverage under the hammock for the torso.
Ran the cord attached to a head end loop through a head end accessory ring, pulled the cord until the loop pulled through the accessory ring, then attached the small Figure 9 to the loop, then across to the opposite head end accessory ring, through the other loop on the head end of the bag and back through the second accessory ring. The cord is now stretched across the head end of the hammock from accessory ring to accessory ring.
Wrapped the Figure 9, then simply used the Figure 9 to pull the cord and the bag up snug to the accessory rings and secured by wrapping the Figure 9.
Repeated on the foot end of the hammock and bag.
I pulled the cord on the foot end until the bag just barely started to lift the fabric of the hammock. Stopped there so that when I got into the hammock I wouldn't be squashing the bag and compressing the down.
On the foot end, the bag corners are approximately 4" to 6" from the accessory rings and slightly below.
Both ends of the bag are now snugged up against the Bridge Hammock with the middle snug to the underside of the hammock.
Got in the hammock. The bag totally enfolds me from head to toe. The bag comes up the sides, slanting out and insulating the sides very well.
I could immediately feel the warmth building from my head to my feet. The body heat builds pretty rapidly.
With a top quilt inside the hammock, the two would meet at the sides and completely cover me and provide excellent insulation. I can also attach shock cord in the middle and over the ridge line in the same manner as for my poncho liner. That would pull the sides up closer and make mating with the inside top quilt even better.
See below for use with the overcover.
Checked the bottom of the bag and under the butt for any down compression.
If left as is, the side of the sleeping bag on the entry/exit side of the hammock gets pulled down when entering/exit the hammock, thus pulling the foot corner on that side of bag further from the accessory ring. As a result the side of the sleeping bag on the opposite side rides higher. This doesn't affect performance as far as I can tell, but it does kind of nag at my sense of order. Both sides should stay even. Accomplishing this turns out to be surprisingly easy: make sure that you have enough cord left after wrapping the Figure 9 on the foot end and run back to the accessory ring on the side of the hammock opposite the entry/exit side. Wrap the cord twice around the ring and back to the Figure 9 and secure. That keeps the entry/exit side of the sleeping bag from pulling away from the accessory ring and hence pulling the opposite side further up. Both sides stay even. Simple and works great and satisfies my innate sense of order and I can now go to sleep easier without staring at uneven sides.
Sleeping bag on Bridge Hammock:
Sleeping bag on Bridge Hammock:
Head end of Bridge Hammock (with Prototype draft stopper):
Foot end of Bridge Hammock (with Prototype draft stopper):
The ONLY modifications to the sleeping bag: four cord loops sewn onto the bag. Two more if I add them for using the shock cord over the ridge line in the middle. As of the time I wrote this, I probably won't do this, but that could always change.
Time to adapt the sleeping bag: approximately 15 to 30 minutes to cut and sew the 4 cord loops plus another 2 or 3 minutes to position the overhand loops for the Figure 9s.
Took down and re-installed a few times. Later in the afternoon, repeated installing and taking down a few times. It takes approximately 1 or 2 minutes to thread the cords through the accessory rings and loops and snug the bag to the hammock. Maybe 3 or 4 minutes or even 6 minutes when fingers are cold and stiff.
No fancy adjusting, either the first time or thereafter: simply snug the cord loops on the head end up to the accessory rings and secure the cord with the Figure 9 and pull the foot end cord to snug the bag up to the bottom of the hammock and again secure with the Figure 9.
Super Simple. And lots and lots of insulation.
The ONLY additional materials:
I now have a down under quilt that fits my Bridge Hammock perfectly. It was made for this use. I couldn't have designed and made an under quilt to fit a regular hammock this well. I know - I have tried. It fit a regular hammock, sort of, well almost, nearly, but a simple rectangular bag fits my Bridge Hammock perfectly with a LOT less time, and money and no frustration. Heck the sewing required could easily be done by hand, no sewing machine in a lot less time than 1 hr.
Total: $12.62 for BPL guy line cord or $7.58 for MLD dacron cord and $4.34 for Mason Line.
Lesson learned: You do NOT need a costly, specially designed underquilt for the Bridge Hammock.
If you have an old or not so old rectangular, or nearly rectangular, sleeping bag, you have a perfectly good underquilt for the Bridge Hammock.
Alternatively you can buy a reactangular bag. I searched the internet via Google for down sleeping bags. It seems that the mummy style is all the rage now. I guess it makes sense, but I doubt that a mummy style will fit as an under quilt nearly as well or very well at all. Don't know, maybe somebody will try.
For goose down reactangular bags, Campmore is selling reactangular goose down sleeping bags:
Any of the above bags will serve very, very well as under quilts for a Bridge Hammock. Due to the dimensions, 2 and 4 would actually be better. And cheaper too. A Bridge Hammock down under quilt rated to 0 deg F at only $170, that is a bargain when compared to anything else on the market.
I found over 15 synthetic sleeping bags at Campmor with prices ranging from $139.97 down to $39.99. All with a rating of 20 deg F and lower, much lower. All would make good underquilts for a Bridge Hammock. Sportsmans Guide is another good source for rectangular sleeping bags at good prices.
And since the bag has not really been altered, it can be used when necessary quite simply for what it was designed for, a ground based sleeping bag. If I had to go to ground, with the Gossamer Gear pads and the rectangular sleeping bag, I'd be able to quite easily.
Plenty of options for attractively priced under quilts at reasonable weights and very low ratings.
But if you can find an old, serviceable rectangular down bag, then you can get a great under quilt for the Bridge Hammock for very little money. Try some of the thrift stores. People are getting rid of their old bags and buying the new mummy bags so that they can sleep on the ground. Maybe ebay has them also. Buy their castoffs and laugh all the way home or, better yet, to the campsite. Do so now before more people switch to hammocks and the Bridge Hammock in particular.
So - make your own Bridge Hammock and get a great underquilt for a lot less money and a lot less work.
A down sleeping bag will probably be heavier than a down quilt made with 1.1 oz ripstop, but then if you have to go to ground for whatever reason you're covered, literally. The sleeping bag is made of material that is a lot more durable and sheds water better and is thus heavier. 1.1 oz ripstop can be shredded pretty easily by trees and bushes a and rocks, etc. Even if you don't have to go to ground, using more durable material can be more important depending on where you hike, e.g., bushwacking. I don't like trails and stay as far away from them as possible, except for animal trails.
Now if only my neighbor has another old Sears reactangular, down sleeping bag he doesn't want. Hmmmmm .....
So Judge the conditions and take what is appropriate.
Overcover with sleeping bag or poncho Liner
I hang the overcover outside of the sleeping bag or poncho liner as underquilts. When the clothes lines is pulled tight, the overcover pulls the sides of the sleeping bag or poncho liner in towards the center of the hammock and more vertical and the sleeping bag or poncho liner pull the overcover nice and tight and making everything nice and cozy and very, very warm. The shock cords are run under the sleeping bag or poncho liner. I have not had to vary the adjustment on the shock cords doing this.
The shock cords do not compress the sleeping bag down noticeably.
First the shock cords are only 3/32" diameter and don't exert a lot of force on the underside and second the shell of the sleeping bag is good quality nylon meant for outdoors use, read stiffer than 1.1 oz ripstop.
The combination of the poncho liner or sleeping bag, the overcover and draft stoppers makes for a very tight and very warm sleeping compartment. Like your own private berth on a ship or train.
I liked the Hennessy supershelter and overcover combination. I could get pretty low with the Supershelter with the Gossamer Gear pads on top of the Hennessy OCF pad. The Bridge Hammock with the Poncho Liner and Gossamer Gear pads or the sleeping bag can get much lower than I could with the Hennessy and Supershelter. I don't even dare to think how low the Bridge Hammock with a top quilt and the sleeping bag, Gossamer Gear pads, overcover and draft stoppers can go. I don't think I want to pack into that kind of country anyway. I'd probably freeze hanging the hammock.
My Bridge Hammock specifications
I am listing below the specifications obtained for the finished Bridge Hammock, i.e., "as built" specifications.
There are at least three methods for deciding which "sides" of the hammock are "ends" and which are "sides". The three methods on which I finally settled are (in no particular order):
All three methods are easy to visualize and use and, for regular hammocks, all three methods yield identical results.
However, some hammocks are "odd" and you will not get identical results from all three methods.
For example, for the Hennessy hammocks, the occupant doesn't lay on the line from tree to tree, but rather on a diagonal. For the large Safari model, this diagonal lay can be very pronounced, as much as 45 to 50 degrees or greater in my Safari clone. So since the head and feet are not pointing at the whipped ends of the hammock, it may be confusing to use The Occupant method.
For a Mayan hammock in which the user lays even more on the diagonal and in fact is usually laying perpendicular to the line from tree to tree, the Occupant method is at total odds with the other two methods.
Other hammocks exist for which the three methods do not agree. The "Bat Hammock" is one for which all three methods do not even seem to apply.
Since for the Bridge Hammock, the webbing in the arc cuts acts as the whipping, the Structure method is at odds with the Orientation and Occupant methods which agree.
Previously, for various reasons, I have used the structure method exclusively and consistently. Most people seemed to disagree, but were kind enough to tolerate this. I gravitated to the structure method naturally since I was initially drawn to the structure of the Bridge Hammock and couldn't understand why people didn't see what I saw. I have finally realized after analyzing the situation and defining the three methods above, that most people view hammocks from the Occupant and Orientation viewpoint, which is at odds with what I saw. Thus, in this article I have switched to the Occupant and Orientation methods for defining the hammocks "ends" and "sides".
However, for the structural ridge line, I retain the structure method and I explain why below.
Most people define the sag of a hammock as the angle made by the hammock fabric at the whipping with the horizontal. This angle and, hence the sag, is set by the distance from whipping to whipping.
In the Bridge Hammock, a structural ridge line doesn't run from whipping to whipping and thus does not set the "sag" of the hammock. The "sag" is set independently by the two spreader bars which do set the whipping to whipping distances.
Instead, for the Bridge Hammock, the structural ridge line sets what I term the "flatness" of the hammock to differentiate it from the sag.
Note that, as Dave Womble pointed out in the Yahoo hammock group, that "flatness" as used here does not refer to flatness as for a mattress. Rather flatness is referring to the more or less straight line that can be achieved from the shoulders to the hips to the feet. This "flatness" also removes the forces present in the banana shape of a regular hammock that are forcing the knees to bend in an unnatural manner.
Spreader Bar Compression Forces
I have put this section at the end because it is really not necessary to understand the forces involved to rig the suspension. I have included it here simply for those inclined to know and as a reference for those desiring to compute the forces so as to choose a spreader bar with sufficient strength.
For the Bridge Hammock we must consider at least 2 planes:
The suspension line plane also contains the attachment point of the hammock end webbing and the forces exerted by the end webbing.
The forces exerted on the spreader bar by the hammock are through the end webbing.
The following figure, #1, illustrates the vertical plane looking at the hammock buckle, ridge line, suspension lines and spreader bar.
The next figure, #2, illustrates the suspension line plane.
The next figure, #3, illustrates the forces in the vertical plane at the apex of the suspension lines, i.e., at the suspension.
From figure 1, we have: sine(delta) = d/h
From figure 2, we have: cosine(beta) = S/2L
From figure 2, we have: h = (S/2) * tan(beta)
Note: h can also be computed from the ridge line length and the distance between the spreader bars. I have found that it is more convenient and accurate to measure d instead.
From figure 3, we have: Lf = W/(2 *sin(delta)) = Wh/2d
The next figure, #4, illustrates the forces on the spreader bar due to the suspension lines:
Last edited by TeeDee; 12-10-2007 at 14:28.. Reason: fix missing picture problem