vinsanity
Contributor
My background is PADI, but I recently took the TDI Nitrox class and in the process noticed that the PADI tables and TDI/Navy tables are pretty different and wanted to understand why. I searched the forum and found some very interesting old discussions summarized as roughly:
- Navy Tables were designed for Navy work, which is typically 1 dive to do as much of a job as time permits, and then come up for the rest of the day. So the tables reflect a maximum first dive followed by very long surface intervals for repeat dives. There is probably also some limit pushing because everyone is fit and there is a medic on the boat.
- PADI wanted to support for multi-recreation dive charter boat trip, so they made their own tables with tweaks to reduce surface intervals, which also included reduced the NDL. With multiple dives, you'll recoup the lost NDL time from the first dive in the form of sooner or longer repeat dives.