DPVs – The Myth of Swimming Out – Part 2 of 4

The most dangerous misconception in DPV cave diving is also the most common: that carrying twice the gas required to swim out makes you safe. It sounds reasonable but it’s not. It is a rule that works in a narrow set of conditions and fails badly everywhere else.

Where the rule comes from

The logic is straightforward. Scooters fail. When yours does, at maximum penetration, you need to swim out. So carry enough gas to do it twice — once for you, once for your buddy. Build your dive plan around that number and you're covered.

For a short, shallow dive this is workable. A diver swimming out of a high-flow spring from 2,200 feet at an average depth of 90 feet, moving at 50 feet per minute, will take roughly 44 minutes and consume approximately 125 cubic feet of gas. Double that for your reserve: 250 cubic feet. Manageable.

That is where the rule's usefulness ends.

Where it breaks down at depth

Take the same logic to a deep system. A dive to an average depth of 240 feet with a 2,200-foot penetration changes every variable. The swim out now takes 60 to 70 minutes. At that depth, a technical diver's depth-adjusted RMV not surface SAC, actual consumption at pressure — burns through roughly 400 cubic feet during that exit. Twice that is 800 cubic feet of reserve gas. That requires a full set of double 104s and six stage bottles. Just for the emergency reserve.

And that's before you account for what that 60-to-70-minute swim at 240 feet does to your decompression obligation. You have now added four to five hours of mandatory decompression to your dive — decompression you did not plan for and do not have gas to cover.

Where it breaks down on long penetrations

Depth isn't the only problem. Modern DPVs are capable of taking a diver 8,000, 9,000, 10,000 feet into a cave. At 10,000 feet in a shallow system with good flow — optimistic conditions — sustaining a maximal swim effort of 70 feet per minute still takes over two and a half hours to exit. That is two and a half hours of continuous, maximum-effort swimming in an overhead environment.

Be honest with yourself: if you are not doing cardio sessions regularly exceeding two hours, that swim is not survivable. The gas requirement for it — over 400 cubic feet — requires a set of doubles plus five stage bottles. And that assumes you physically make it, which most divers will not.

A buddy tow from 10,000 feet is not a realistic alternative. In a straight, flat, low-restriction cave with no vertical change it is marginal. In anything more complex, it is not really a good plan.

The correct framework

Swimming out should not be your contingency. It is a last resort at short, shallow penetrations only. For everything beyond that, the contingency is a spare scooter — and knowing the actual, tested capabilities of every scooter on the dive.

That means knowing your battery's real capacity, not the manufacturer's rating. Batteries degrade. A pack rated at 1,000 watts new may hold 860 watts two years later. Plan to 70% of real tested capacity, not 100% of the spec sheet. Know your scooter's load under actual dive conditions. Test it. The math only works if the inputs are accurate.

Beyond 120 feet or 3,000 feet of penetration, a spare scooter is not optional equipment — it is part of the dive plan. How many spares depends on the depth, the distance, the restrictions, and the honest capability of every diver on the team.

What this means for your planning

Every variable in a DPV cave dive is an estimate: dive time, travel time, gas consumption, task time, battery performance. The margin for error shrinks as penetration and depth increase. The rule of thumb that carried you through your first scooter dives does not scale. Building a dive plan on a simplified rule in conditions where that rule no longer applies is not conservative, it is the mechanism by which experienced divers get into serious trouble.

Plan your dive to what it actually requires.

In our next article we’ll talk about proper gas planning for DPV dives.