DPVs – Gas Planning – Part 3 of 4
Gas planning for a DPV cave dive is not an extension of standard cave diving gas planning. It is a different problem. The variables multiply, the margins shrink, and the simplified rules that work on a swim dive become actively dangerous when a scooter is involved. Here is what the planning actually requires.
Start with your real RMV, not your SAC
Surface air consumption rate is a surface number. The moment you apply it to a dive at depth without adjustment, your planning is already wrong. The formula is straightforward:
RMV = SAC × ATA
ATA = (Depth ÷ 33) + 1
An experienced technical diver with a SAC rate of 0.75 cubic feet per minute at 90 feet is actually consuming 2.8 cubic feet per minute. At 240 feet that same diver is consuming approximately 6.2 cubic feet per minute. These are not the same dives. Planning them with the same surface number produces a plan that runs out of gas.
Know your actual SAC rate from logged dives. Apply the depth conversion. Use the real number.
Siphon versus spring changes everything
Flow direction fundamentally changes your gas and time planning, and it does so asymmetrically. In a spring — water flowing toward the exit — you have flow assistance on the way out. Your swim speed on exit is higher, your time in the water is lower, your gas consumption is lower. In a siphon — water flowing away from the exit — every one of those variables reverses. You are working against flow on the exit, which is exactly when you can least afford it.
On a DPV dive in a siphon, your exit gas requirement is higher than your penetration gas requirement. Plan accordingly. A turn pressure calculated on spring assumptions applied to a siphon dive is not conservative — it is a miscalculation.
Battery capacity: test it, don't trust it
Manufacturer specifications are marketing numbers. They are generated under controlled conditions that do not reflect actual dive conditions — your drag, your load, your depth, your water temperature. A battery rated at 1,000 watts new may hold 860 watts after two years of use. The number on the spec sheet does not degrade with the battery. Your planning has to use the real number.
Test your battery capacity using a WattsUp meter and resistor pack. Know your scooter's load under actual conditions. The formula:
HOURS = WATTS ÷ LOAD
Multiply by 60 for minutes. A battery holding 860 watts in a scooter drawing 300 watts under load gives you 172 minutes of real burn time. That is your planning baseline — not the manufacturer's 200-minute claim.
Burn-test annually at minimum. If you are regularly pushing your scooter near its limits, test more frequently.
The 70% rule
Never plan a DPV cave dive to 100% of battery capacity. Planning to full capacity leaves zero margin for towing equipment, assisting a teammate, navigating against unexpected flow, or any other unplanned demand on the battery. It also risks damaging the battery itself if you run it to depletion.
Plan to 70% of real tested capacity. Using the example above: 172 minutes real burn time × 70% = 120 minutes maximum trigger time for the entire dive. That is your budget. In and out.
For a spring dive with no significant flow differential, split that time evenly — 60 minutes in, 60 minutes out. For a siphon, weight the exit more heavily. For a deep dive with significant vertical change, account for the increased load on the motor during ascent and descent.
Planning for scooter failure
Scooter failure is not a theoretical scenario. It is a when, not an if, over a career of DPV cave diving. The question is not whether to plan for it, it’s what that plan realistically looks like given your penetration and depth.
For shallow, short penetrations of under 120 feet, under 3,000 feet a buddy tow is a viable contingency if your team practices it regularly. Beyond either of those thresholds, it is not. The gas required to swim out, the physical demands of that swim, and the decompression implications of the additional bottom time make swimming out an increasingly theoretical option the further and deeper you go.
Beyond 120 feet or 3,000 feet: plan a spare scooter into the dive. Not as a luxury, as a requirement. The spare does not need to match the primary, but it must have sufficient tested range to exit from your maximum penetration point.
The full planning picture
A complete DPV cave dive plan accounts for all of the following:
Dive time, DPV travel time, depth-adjusted gas consumption, task time and task gas, penetration totals, battery capacity at 70%, siphon or spring flow differential, and the full failure scenario: scooter failure, gas failure, navigation, silt, stress, and decompression implications of an extended exit.
Every one of those variables is an estimate. The accuracy of your estimates improves with experience and with honest logging of actual consumption rates, actual swim speeds, and actual battery performance on real dives. The planning is only as good as the data behind it.
A DPV gets you further into a cave than you can swim. Your gas plan has to account for every foot of that distance on the way back out under the worst conditions you might reasonably encounter, not the best.
