Backpack Construction
Designing for Total Size or Capacity
Travel Packs
A 65 litre Backpack in a Medium Harness Length
Daypack Capacity
If we determine that the daypack size is to be 20 litres - White
Mountain™ do not include the compressed portion of the daypack when
zipped to the main body of the travel pack in stating the total pack
capacity. This would constitute approximately 33% to 50% of the
daypack capacity, or 5 to 10 litres depending on the travel pack series
or design choice. If we allow the compressed portion to be 10 litres or
half the daypack capacity, this would leave a balance of 10 litres.
Please note, that some manufacturers do include the compressed portion
of the daypack to represent the total pack capacity.
Main Body Capacity
We would then need to construct the main body of the travel pack to
be 55 litres (daypack 10 litres plus the main body of the pack at 55
litres, for a total travel pack capacity of 65 litres). The total
length of the Internal staves would be a Medium Size Stave length of
60cm. We would then include 5cm of backpack outside the Stave Length,
for total backpack length of 65cm. With a total travel backpack
length of 65cm and an acceptable approximate width of 35cm (keeping
within the average body width), we would need a depth of approximately
24cm to ensure the main body of the travel pack was 55 litres.
The total Travel Pack size and capacity would then be;
Pack Length 65cm x Width 35cm x Depth 24cm = 54,600 cubic cm or 54.60
litres.
= Approximate total Travel Pack Capacity is 55 litres plus daypack of
20.00 litres
= Net Total Travel Pack Capacity of approximately 75 litres, or 70
litres when excluding the compressed portion of daypack when zip to the
main pack body..
Hike Packs
A 65 litre Backpack in a Medium Harness Length
Considerations
Hike packs do not have the extra capacity of a removal daypack as in
the travel packs and would compensate for this loss of capacity, by
having a top pocket in the lid and extra loading capacity above shoulder
height. With hike packs we are not restricted in the length of the back
pack, as hike packs are top loading and can extend past shoulder height.
On some hike packs as in the White Mountain™ Main Peak series, the lid
of these backpacks can be extended to sit on top of the storm collar
giving an extra 15 or more litres which is not stated in the hike pack
capacity. It is important when designing hike packs to allow for head
room in the design when proceeding past shoulder height, or as you would
imagine the hike pack would be very uncomfortable to wear.
Top Lid Capacity
If we determine that the top lid is to be 5 litres and the hike pack
75cm in length, we would then proceed to construct a hike pack with a
capacity of 60 litres.
Main Body Capacity
To construct a hike pack of 65 litres in a Medium Back Size, we would
proceed as follows. The total length of the hike pack staves would be
Medium Size Stave of 60cm, plus 5cm of backpack above the harness, or
backpack length of 65cm. With a backpack length of 65cm plus the 10cm
extension and an acceptable width of 35cm, we would need a depth of 23cm
to establish a backpack capacity of approximately 60 litres.
The total Hike Pack size and capacity would then be
(Pack Length 65cm + Extended Length 10cm) x Width 35cm x Depth 23cm
= Gross Total Hike Pack Capacity of 60,375 cubic cm
= 60 litres plus Top Lid of 5.00 litres
= Net Total Hike Pack Capacity of 65.00 litres.
Further Considerations
It would not be wise to construct a 90 litre travel pack to fit an
extra small back. The greater the backpack depth, the further the
backpack is from the body, the further it is from the body, the more
pressure is exerted on the lower back and chest through leverage. We
would always endeavor to keep the backpack close to the body by limiting
depth and construct all White Mountain™ backpacks in a width no wider
than the average body size. With Hike Packs, overall capacity can be
increased by providing an extendable top lid, as in the Main Peak
bushwalking pack, and the Antarctica hybrid travel pack. This feature
allows the manufacturer to increase volume without affecting the rules
applying to individual body size. This feature is not possible with the
average travel pack.
Conclusion
Obviously these dimensions are variable, by determining a different
depth or width to the above examples and the beginning or ending
position of the internal staves the backpack shape can change
dramatically. The above information is given as a broad example of the
process in developing a backpack of a particular size to suit an
individual back length. The above samples are an example of the
calculations implemented in determining backpack capacity and vary
greatly when backpacks are of a teardrop or tapered design. Some
wholesalers and/or manufacturers also allow for expansion in their
backpacks to determine the final backpack capacity. White Mountain™ do
not allow for expansion when calculating backpack capacity and it should
be noted that many methods are implemented for calculating backpack
capacity.
There is an existing standard for calculating backpack capacity
documented at
http://www.astm.org/Standards/F2153.htm however these standards are
not enforced and this allows for a great variation between brands.
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