Posted by MHK on March 05, 2001 at 18:14:36:
These type of dicussions we're having lately are the real reason to stay on this list, and events such as this weekend help bring the dive community together. I've noticed that Ken has started putting out the Chamber Day info and I hope the spirit of cooperation will continue through Chamber day...
But it seems that we spend an inordinate amount of time discussing ways to increase bottome time, and while we always don't agree on the means to the end, it seems to me that we all want more bottom time.
In that regard it still puzzles me why, since we all want to be under water longer, that Nitrox has yet to gain in popularity out here.
The shops tell me that no one buys it;
The boats tell me it's a break even/ money loser
but yet, many diver's tell me that if they could get it more easily they would use it more often. It's the cart before the wagon.
It is a often misunderstood gas so I thought I'd bring the issue to it's lowest common denominator. According to the DSAT tables
If you were on air you could do 100' for 19 minutes ( NDL )
If you were on Nitrox 36% you could do 100' for 34 minutes
If you were on Nitrox 32% you could do 100' for 29 minutes
At 100' some diver's experience Nitrogen narcosis but with a Nitrox 36% you would have the equivalent narcotic depth of 75' or with a 32% you would have the equivalent narcotic depth of 81'.
If you sat out 45 minutes you could do the next 80' as follows:
On air you would have an RNT of 14 minutes and would be limited to 15 minutes for your next dive. I used 45 minutes since that's about the average time for the boat to move and drop anchor.
On 36% you would have an RNT of 26 minutes and could do a 27 minute dive at 80'
On 32% you would have an RNT of 21 minutes and could do a 24 minute dive at 80.
So by diving air you would be limited to 34 minutes of bottom time
by using 36% you would get 61 minutes of bottom time
by using 32% you would get 53 minutes of bottom time
So you can see that in two dives the added increase in bottom time, now average that over 4 dives ( a usual one day trip) or a multi day trip and you'll see the added BT's add up dramatically, the SIT's become shorter and the ancillary benefits of a clearer head are noteworthy..
I always felt that this discussion was to abstract so I thought I'd provide what is exactly at stake given that we are focusing on increasing BT's.
Later