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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