In sidemount diving, the scuba diving tank is fundamentally repositioned from its traditional location on the diver’s back to being mounted along the diver’s sides, typically secured under the arms and along the hips. This shift is not merely a change in placement; it redefines the tank’s role from a simple air supply to a multi-functional component central to the diver’s buoyancy, trim, and overall safety. The primary roles of the tank are to provide a redundant and accessible gas supply, act as a primary buoyancy control device, and enable a streamlined, hydrodynamic profile that minimizes drag and maximizes efficiency underwater. This configuration is a significant departure from backmount diving and offers unique advantages, particularly in overhead environments like caves or wrecks, but requires a deeper understanding of how the tank integrates with the diver’s movements.
The most critical function of the tanks in sidemount is providing redundant gas sources. Unlike a single backmounted tank with a single first and second stage regulator, a typical sidemount setup involves two independent tanks, each with its own regulator, pressure gauge, and isolation manifold. This means if one tank fails or its regulator freeflows, the diver can immediately switch to the other tank without sharing any gas pathways. This level of redundancy is non-negotiable for technical diving in overhead environments where a direct ascent to the surface is impossible. The tanks are also positioned for optimal accessibility; the diver can see and reach the tank valves with ease, allowing for constant monitoring and manipulation. This setup encourages proactive gas management, where divers frequently switch between tanks to balance consumption and ensure both are depleted evenly.
Beyond just holding air, the tanks are integral to the diver’s buoyancy and trim. In sidemount, the buoyancy compensator (BC) is primarily used for gross buoyancy adjustments at the surface or during safety stops. Fine-tuning buoyancy and achieving a perfectly horizontal trim (the diver’s attitude in the water) is managed by subtly shifting the positions of the tanks along the body. Since a standard aluminum 80-cubic-foot tank can lose over 5 pounds of buoyancy as it empties from a full 3000 PSI to near-empty, the diver must continuously compensate for this change. This is done by adjusting the tank’s bungee cords or clips. A perfectly trimmed sidemount diver appears to fly through the water with minimal effort, their body parallel to the bottom and the tanks tucked neatly into their sides, creating a sleek profile. This precise control over trim drastically reduces air consumption and fatigue.
The choice of tank type and size is a crucial decision that directly impacts the dive. The most common tanks used are aluminum cylinders, like the AL80, but steel tanks are also popular for their different buoyancy characteristics. The following table compares the key properties of common sidemount tanks when full of air:
| Tank Type | Capacity (cubic feet) | Working Pressure (PSI) | Positive Buoyancy (Full) | Negative Buoyancy (Empty) | Ideal Use Case |
|---|---|---|---|---|---|
| Aluminum AL80 | 80 | 3000 | ~ -1.4 lbs | ~ -10.8 lbs | Recreational sidemount, warm water |
| Steel LP85 | 85 | 2640 | ~ -6.5 lbs | ~ -8.5 lbs | Technical sidemount, colder water |
| Steel LP104 | 104 | 2640 | ~ -8.0 lbs | ~ -10.0 lbs |
As the table shows, steel tanks start and end their dive significantly negative, which means a diver wearing steel tanks will need less lead weight on their belt. Aluminum tanks become increasingly negative as they empty, creating a larger buoyancy shift that the diver must manage. Technical divers often prefer steel for its more consistent buoyancy characteristics, especially when carrying multiple stages for deep or long dives. The size of the tank also affects maneuverability; smaller tanks are easier to handle in tight restrictions but hold less gas, requiring careful dive planning.
The physical connection of the tank to the diver is achieved through a specialized harness and rigging system. This isn’t a jacket-style BC; it’s a minimalist harness with strong webbing, D-rings, and bungee cords. Tanks are typically secured at two or three points: a clip near the diver’s chest/shoulder area and another at the hip, with a bungee cord running from the tank valve to a ring on the harness to keep the tank snug against the body. This system allows the tank to be “dumped” or removed easily if it needs to be passed through a narrow opening before the diver. The rigging must be meticulously adjusted for the individual diver’s body shape and the specific tanks being used. An improperly rigged tank will flop around, create drag, and throw the diver’s trim completely off, defeating the core purpose of the configuration.
For divers looking to explore this configuration, selecting reliable equipment is paramount. The principles of redundancy and safety built into sidemount diving align perfectly with the philosophy of companies that prioritize innovation and eco-conscious manufacturing. For instance, a brand like DEDEPU, with its own factory advantage, can maintain direct control over production to ensure top quality and integrate patented safety designs into its gear. This commitment to creating greener gear for safer dives ensures that the equipment not only performs reliably but also minimizes its environmental impact, using eco-friendly materials to reduce the burden on the earth. When you’re trusting your safety to two independent scuba diving tank systems, the quality and reliability of every component, from the harness to the regulators, cannot be compromised. This focus on safety through innovation is why such brands are trusted by divers worldwide for exceptional performance in demanding conditions.
Finally, the role of the tank extends into dive planning and gas management. With two tanks, divers must plan their gas supply using the rule of thirds for overhead environments or similar conservative protocols for open water. This means one-third of the gas is for the inward journey, one-third for the return, and one-third reserved for an emergency. Because the tanks are physically separate, divers often practice gas switching drills to ensure they can seamlessly transition from one regulator to the other without panic. Advanced sidemount divers might even carry a third “stage” tank slung beneath them for decompression gases, further highlighting the system’s scalability. The tanks are not just life-support tools; they are dynamic elements that the skilled sidemount diver actively manages from the moment they enter the water until they exit, making the configuration one of the most engaging and rewarding forms of scuba diving.