[pct-l] packs: comfort vs weight: Why packs work, Part 2

[reynolds@iLAN.com (Reynolds, WT)]

>From Part 1 it should be apparant that the centerline of the body at the
pelvis is in the center [actually slightly in front of center] of the
pelvis. However, you may be suprised to know that the centerline of the body
at the head is well behind the head and the centerline at the shoulders and
upper back is actually behind the back. To see this observe a person walking
from the side. You will see that most people don't walk in a straight
upright stance. They STOOP to some extent, meaning that their head and upper
body is carried forward of the pelvis. Ok, did you ever wonder why a person
can't easily carry a 50 pound pack but can gain 50 pounds and walk around
easily? [Note: Don't try this experiment at home. Take my word for it. I
have verified it several times.] The answer is because the body gains weight
all over so the body's center of gravity changes very little. 

If you look at a person walking, you'll see the obvious place to carry extra
weight is a hump over the shoulders and behind the head. For most people
this location is roughly on the centerline of the body. Weight carried on
the centerline doesn't ask the body to reconfigure its balence. Weight
carried behind the centerline requires the body to stoop forward even more
to regain its balance. This unnatural position adds to fatigue and physical
problems.

Old external frame packs that were designed to carry very heavy loads, 100
pounds or more, were specifically designed to place the bulk of the weight
high across the shoulders as close to the natural centerline of the body as
possible. The old Kelty packs had curved frames. The old Jansport actually
had a 20 degree angle in the frame. In both cases the goal was for the upper
portion of the pack bag to reside in the area above the shoulders and behind
the head. 

When the external was in vogue the rule was pack high and tight, in the
upper quadrent nearest the back. The other goal was to carry high. The Kelty
Tioga pack bag did NOT extend all the way down to the hip belt. There was a
5-8" gap between the hip belt and where the pack bag ended. Reason? No, that
was NOT the place to carry the bedroll. The bedroll was to be carried on top
under the flap. Just put the light insolite pad there. [I know, NOW you tell
me!] The pack was designed to carry the load high across the shoulders. The
Jansport went one better. The pack bag was suspended from the frame above
the shoulders and was divided into two compartments, a higher and a lower
compartment. Heavy items were carried in the top compartment or above the
pack bag on the frame that supported the pack bag. This frame member created
a shelf about 4-5 in width that was ideal for carrying the heaviest items,
in those days the tent.

Ok, now that you understand the theory, lets look at the modern minipack.
You will notice very quickly that pack with hip belts rarely extend high
enough to carry anything above the shoulders behind the head. The centerline
of the load is well behind the person. Although I have not talked to him, I
believe that the reason why Golite dropped the hipbelt for packs designed to
carry very light loads is because a shoulder-only pack will, at least, keep
the load closer to the centerline. You will also notice that the VanPeski
GV4 pack uses a relatively unstuffed sleeping bag in its bottom. This means
that the heavier items [food and water] will ride higher than if the
sleeping bag was fully stuffed. If you see a properly loaded, properly
fitted Dana pack, you will see it extend well above the hikers head in order
to place the load over the body's centerline. Unfortunately most expensive
internal frame packs are designed for heavy loads. With an ultra-light or
even light load there won't be enough bulk to get the load high.

My personal experiences;

Both with my Kelty Cloud and my custom made pack I suspended the heavy items
[either the water bag or bear canister/food bag] from the top of the
internal frame. This kept the load much higher and closer to the centerline
then simply piling everything on top of each other. People who tested my
pack during the 2001 ADZPCTKO were amazed to find out how much weight was in
it. The perception was that it was much lighter than it actually was.
Unfortunately, the opening of the Kelty Cloud made carrying a bear canister
in the proper horizonal position difficult, a condition I rectifed with my
custom pack. With an internal, one solution is to keep the water bag in the
top flap's compartment. Another possibility is to suspend the food bag from
the top of the pack frame. Naturally, for this to work the internal frame
must extend 4-5 inches or MORE, ABOVE the shoulders. In short, prefer a
tall, skinny internal frame pack to a short fat one. [To most people this
doesn't seem logical.....Until you understand the theory.]

Still, all in all I cannot say that stripping the heavy pack bag from a
Jansport swing arm pack is inferior. True it is heavier by a pound and a
half BUT the load is higher.

Tom