The boundary between distinct limestone layers are what cave divers call bedding planes. Bedding planes provide an excellent place for underwater passageways to form. Unfortunately, such passageways, while wide, are often not tall enough to permit divers with back-mounted cylinders to pass. Cave divers responded to this challenge by developing the technique of sidemounting.

Additionally, some divers who suffer from back problems or disabilities that affect use of their legs find that sidemounting provides a welcome alternative to the use of heavy, back-mounted doubles.

For many years, it was impossible to purchase off-the-shelf equipment for sidemounting. For a long time, the terms best used to describe sidemount equipment included words such as home made and jury rigged. Fortunately, these days are over.

When designing the Transpac II, Lamar Hires also developed a system for modifying the Transpac harness and Trek Wings air cell so that the same harness can be used for sidemounting, as well as for backmounted singles and doubles. Switching back and forth between these configurations takes only a matter of minutes.

In the Spring of 2000, Lamar introduced two new items that further enhance the Transpac II's ability to convert to a ready-to-use sidemounting system. These are:

• Special attachment rings designed specifically for sidemounting (item number 2765).
• A new Limiting Strap (item number 2770), designed to be used in conjunction with Dive Rite's 2778 Sidemount Bungee.

Together, these items help solve two problems common to older sidemount rig configurations. These are:

• The tendency for the shoulders of sidemounted cylinders to put uncomfortable pressure on the user's rib cage.
• The tendency for the bottoms of sidemount cylinders to splay outward, away from the diver.