I have been thinking a lot about portaledge suspension design and want to discuss some aspects of it.
Asymmetric hang
In his book Higher education Andy K describes a way of hanging a ledge asymmetric, and I've always wondered, is this possible, or is it Big Wall Theory!? In my world a portaledge have to hang symmetric if you hang it from one point and want the bed to be horizontal, you can never get the bed horizontal in a asymmetric setup, unless you support it from more than one point, for example short side against a corner. Can someone explain how that asymmetric hang can work from just one point?
The 6th suspension point
I'm a big fan of 4 point suspension and have been thinking about the use of a middle outside suspension point on a portaledge without spreader bar. The only use for this suspension point I can think of is to hang your stove from.
The meaning with this strap must be to keep the outside tube as horizontal as possible when it flex down by your weight. To achieve this you have to tighten this strap, and then you also force the outside tube inwards, making it to flex more inwards than it will do without this suspension point. It works if you have spreader bar on your portaledge, but without it you also can omit the 6th strap, unless you don't need it to hang your stove from...
Length of suspension
John Middendorf have been very generous with information about how to design a portaledge, but one aspect I have not seen so much about is the sizing of the suspension; how high above the bed should the connection point be?
If it is to low you get to small space inside the fly and you get high force on the suspension. If it is to high you add size and weight of fly and suspension, and perhaps also make it more complicated to set up, or is there more aspects? Is it the design of the fly, or rather width of fabric, that states the size of suspension?
And a question @John Middendorf
I have used sailcloth for the bed on my portaledge and this gives a pretty flat bed. It also gives pretty high forces on the tubes, which made me think of placing warp and weft in an angle to the tubes, which should give a less flat bed, and also less force on the tubes. When you made calculation for the tubes on the D4 portaledge, how did you think about the stretch in the bed fabric? You give very detailed advice about tube size related to bed size, but does this not depend on how flat the bed is, or did you make other assumptions?
/Olle