Navy Tables vs the RDP — Differences Explained
Will Welbourn explains the key differences between the US Navy tables and the RDP — Part 5 of the GPC decompression theory series.
The US Navy Tables
The first widely-used recreational dive tables were adapted from the US Navy tables, developed in the 1950s. They used six compartments, with a slowest half time of 120 minutes.
For the surface interval credit calculation, the Navy used the slowest compartment — 120 minutes — as the basis. This meant a diver was not considered clear of residual nitrogen until 12 hours after a dive (6 × 120 minutes). The Navy test subjects were all male, in their 20s and 30s, and physically fit. The pass/fail criterion was simple: bends or no bends.
Why the RDP Was Developed
In the mid-1980s, Dr. Raymond Rogers recognised that the Navy tables were not ideal for recreational divers. Three specific problems motivated a new approach:
- The 120-minute surface interval credit was excessively conservative for recreational no-stop diving.
- The Navy test subjects did not reflect recreational divers — who include women, older divers, and people of varying fitness levels.
- New Doppler ultrasound technology revealed that silent bubbles were forming at Navy table limits even without observable DCS symptoms — suggesting the M-values were set too high for recreational divers.
How the RDP Was Built
With the help of DSAT (Diving Science and Technology), Dr. Rogers developed the RDP. It was formally tested in 1987–88 at the Institute of Applied Physiology and Medicine, with Dr. Michael Powell as principal investigator.
| US Navy Tables | RDP | |
|---|---|---|
| Compartments | 6 | 14 |
| Slowest half time | 120 minutes | 480 minutes |
| Surface interval credit | 120-minute gas washout | 60-minute gas washout |
| Time to be “clean” | 12 hours | 6 hours |
| M-values | Higher (original Haldane) | Lower (Spencer limits — Doppler data) |
| Test subjects | Male, 20s–30s, fit | Broad range — reflects recreational divers |
| Test criteria | Bends / no bends | Doppler-detectable bubbles |
| Dive profiles tested | Single-depth | Multi-level; up to 4 dives/day for 6 days |
The Practical Effect — Shorter Surface Intervals, Longer Repetitive Dives
Because the RDP's 60-minute gas washout assumes nitrogen clears faster than the Navy's 120-minute washout, the RDP calculates that less residual nitrogen remains after a surface interval. The result:
- The RDP allows shorter surface intervals to achieve the same pressure group reduction.
- The RDP allows longer repetitive dive times for the same surface interval.
RDP Versions
The RDP was produced in multiple formats — the printed table version and the multilevel electronic planner, the eRDPML (originally the Wheel), which enables multi-level dive profile planning. DSAT also produced four nitrox tables: for EANx32, EANx36, an Equivalent Air Depth table, and an Oxygen Exposure table.