Double 7L/8.5L Tanks vs. Single 12L/15L: Why the "Hogarthian Configuration" is the Ultimate Safety Upgrade

Double 7L scuba tanks with Hogarthian configuration.   The ideal setup for recreational diving: D7/8,5L cylinders offering ultimate safety and perfect trim.

In recreational diving, a single 12L or 15L cylinder with a standard "octopus" is considered the norm. However, if you are looking for maximum safety, streamlined hydrodynamics, and peace of mind underwater, the comparison clearly favors Double 7L / 8.5L (D7/8.5) cylinders.

This isn't just about carrying more gas—it's about a complete system: the Hogarthian Configuration.

1. Single 15L vs. D7/8.5: The "Single Valve" Fallacy

Many divers believe that a single 15L tank with a "Y" or "H" valve (two outlets) offers the same safety. It doesn’t.

• The Single Tank Issue: Typically, you have one first stage and two second stages. If the first stage fails or the tank's O-ring bursts, you lose your entire gas supply in seconds. Even with two independent regulators on a "Y" valve, it is nearly impossible for a diver to reach and close the valves behind their head in time. Most importantly: if you do manage to close one valve, you are left with only one regulator, meaning you cannot share gas with your buddy if needed.

• The D7/8.5 Advantage: Here, you have two completely independent systems (two first stages and two second stages). With the Manifold (isolator bridge), you have total control. If a failure occurs on one side, you isolate the bridge and retain all the gas from the other cylinder, always keeping a functional regulator for yourself or your buddy.

2. The History of the Hogarthian System & DIR

The system is named after William (Bill) Hogarth Main. In the 80s and 90s, cave explorers in Florida (such as Bill Gavin and Jarrod Jablonski) realized that equipment complexity leads to accidents.

Hogarth proposed a philosophy of Minimalism:

• Remove everything unnecessary (extra D-rings, dangling gear, redundant pockets).

• Every piece of equipment has a specific place and a vital reason for being there.

• This philosophy gave birth to DIR (Doing It Right), transforming diving from a casual hobby into a system of absolute discipline and safety.

3. Gas Sharing with Purpose: The Long Hose

Forget the traditional "octopus" that forces you to stay face-to-face with your buddy, making swimming impossible. In a Hogarthian setup, we use a Long Hose (ranging from 1.80m to 2.10m).

• Real-World Rescue: In an emergency, you donate the regulator you are currently breathing from (ensuring your buddy receives a working gas source immediately).

• Share Air comfortably: With a 2-meter hose, you can swim comfortably in a "single file" (one behind the other). This allows you to navigate through tight spots or swim back to the boat or the shore for a controlled exit, rather than performing a risky direct ascent in the middle of the "blue."

4. Hydrodynamics, Trim, and Low Profile

D7/8.5 tanks offer:

• Low Profile: They are slimmer than a bulky 15L tank, significantly reducing water resistance.

• Perfect Weight Distribution: The weight is distributed on either side of the spine against the backplate. This provides the ideal Trim (horizontal position) effortlessly, improving gas consumption and overall comfort.

5. Training: The SSI Foundation Course

Equipment alone doesn't make a better diver. Transitioning to this configuration requires the right culture and training. The SSI Training Techniques / Foundation course is the perfect gateway.

Through the Foundation course, a diver learns:

• Perfect trim & buoyancy control and "Hogarthian" gear rigging.

• Critical problem-solving skills (V-drills, S-drills).

• Propulsion Techniques: Master the Frog kick, Back kick, Heli kick, and Modified Flutter kick.

• How to operate as part of a cohesive, high-level team.

Conclusion: Less is More

If the Hogarthian setup is the gold standard for technical diving, caves, and mines to maximize safety, imagine how much more protected you are during a recreational dive.

It is important to note that the D7/8.5L configurations we advocate for are specifically recommended for recreational diving. They provide the perfect balance of weight, volume, and redundancy for "no-decompression" limits. While technical divers might opt for larger cylinders for extended bottom times, these smaller doubles offer the recreational diver the ultimate safety of a technical rig without the unnecessary bulk.

Less is More.

References & Sources

• SSI (Scuba Schools International): SSI Training Techniques / Foundation Course Details

• GUE (Global Underwater Explorers): The DIR Philosophy and Hogarthian Configuration

• Hogarthian Background: Historical data from the Woodville Karst Plain Project (WKPP) expeditions.