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Question
The first dive is at 8o ft for 20 min. 42 min.surface interval, the 2nd dive is 50 for 37 min. sur.inter, 60 min. third dive is at 50 feet....what is the maximum allowable botton time??? We are arguing over the process and the time... i say 26 my partner says 15 are either of us correct if not what is it?

Answer
I have to make 2 assumptions since this was not specified:  this is an air problem (as opposed to Nitrox), and these are PADI dive tables (SSI, NAUI, or standard US Navy would have different results).

Dive 1
80 ft for 20 min results in pressure group K; a 42 min SI results in pressure group E

Dive 2
50 ft for 37 min in pressure group E requires an RNT of 21 minutes added to the 37 for a TBT of 58 min;  50 ft at 58 min results in pressure group S; a 60 min SI brings this down to pressure group G

Dive 3
50 ft at pressure group G has an adjusted no decompression limit of 54 min.  54 min is the maximum allowable bottom time on dive 3.

Again, if the 2 assumptions are not right then this would not be accurate.  I know this cannot be an SSI dive table problem as dive 2 exceeded the ANDL.  Not sure about NAUI or US Navy off the top of my head.

Hope his helps...Jesse