Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
I don't mean to be rude but if you don't already have an opinion based on your training, then you shouldn't be considering either of the options.
I have never seen standard agency tables that goes to 120mins at 21m. Even the table you supplied only goes to 75mins at 21m. So I'm still curious what deco time you intended to use for 120mins. For this you will have to use one of the planning softwares mentioned in various threads on this board.
In all the examples you gave of a 36m dive you forgot the ascent time of 3min (36m at 12m/min by your table) when calculating total dive duration.
Jean eve:Off course you never seen a standard agency tables that go to 120 min at 21m.The table I'm using is speacially invent for pearl farm diver and it's only used it here.You can't find it in the table I supplied is because it is very rare that a diver will stay for so long at 21m!So it is no point to put it in the table.(You can only can find it from the book of the author)
Also if they put it in the table,can you imagine that how big is the table if they put all the max. limit on each depth!!
The time I given was already included the ascent time of 3min.(40min+3min)
Originally posted by padiscubapro
2 hours at 21m is nothing difficult (I do 90-120 min levels at the end of many of my Deep multilevel dives).. in fact I can run 3hours at 21m on my CCR without ANY deco requirements.. This puts me just over the recommended exposure limit of 100% using a setpoint of 1.3bar
Jean eve:If using ccr of course there is nothing difficult!But I'm using normal air, open circuit.With this,I'd dove for 180 min at 21m and Deco for 120min(using my dive table).
Because of this kind of dive profile(open circuit,normal air),that is why I'm asking which one is better.One long dive or seperate it to two dives. :06:
Originally posted by padiscubapro
My whole point is that AIR is stupid... For dives at shallow working depths (21m qualifies as shallow) using a rich nitrox mixture is the proper way to conduct the dive..