Another Tables vs. Computers Thread

[TheRedHead]

I just dive until I feel the nitrogen pressure gradient get too high, then I ascend a bit.

Duuuuddde, you're gonna die.

 

[The Chairman]

Personally Kev,

I just go to the aquarium store and get me some "NitroZorb" to eliminate that pesky Nitrogen.

 

[Charlie99]

I would do it similarly but a bit more simply, and during the dive, not on the boat. <snip realtime 5 min snapshot, depth avg, and compare to NDL>

.........which brings up another question -- honestly who ever says "do you want to do 10 @ 100, 10 @ 70 .... and so on.

.....

This is a profile that's (probably intentionally hard to average since the two portions of the dive are done at pretty different depths.

More normal would be "Let's average 60 feet for 40 mins or 50 mins, and then stay between 80 and 40-50 for the dive. The 80 feet depth on the way out, converging up more to the 40 on the way back and then a slow ascent). One exception is that we dive the oil rigs sometimes where we go down to 100 but some of the best stuff is on platforms at 55 feet. So a profile there looks like 10-15 @ 100 (on 32%) and then 30-40 mins at 55 feet.

Actually, wide variances in depth like my example profile are common in some areas. In places like Cozumel, Grand Cayman, Maui and anywhere else that you have walls and/or interesting coral formations all the way from deep to the surface. And yes, you really will hear multilevel dive plans like I described ---- very common on guided tours in those resort areas.

I wanted a way to do a quick validity check when a DM says "OK, the plan is 7 @ 130, then another 7 at around 80 or 90', then on up to 50-60' for about 10 minutes, then finish off the dive at 40' or shallower." I chose not to do it either blindly following the DM, or blindly following my computer.

For the DMs it isn't an issue, since someone in their organization has already set the typical profiles for the different dive sites, and they have repeatedly used the same profile and know which one work out well both for deco and for the gas consumption rates of their clientele.

 

[Charlie99]

I just dive until I feel the nitrogen pressure gradient get too high, then I ascend a bit.

I used to be on submarines...
now I am one.

Hey! Submarines have a nice shirtsleeve 1 ata envirionment. Why are you worrying about nitrogen pressure gradient?

With the near square profiles of dives to the 3rd reef off of Boynton, multilevel profiles are a non-issue,and I'm not even sure I'd bother buying computer. But I would be using nitrox on every dive.

The few times I've used Splashdown my dive plan was not much more than
.... use a hot mix
.... start my ascent at about 55 minutes runtime
.... hit the surface not too long after the 60 minutes max time requested by the Capt.

 

[Jason B]

I would do it similarly but a bit more simply, and during the dive, not on the boat.

(actually this is a profile that's cutting it pretty fine with air, and I'd use 32% or shorten the dive. I plugged it into deco planner and if you add even a few mins to the 50 or 70 depths, you start getting into some (very small admittedly) amounts of deco)

Since the two dive portions are at pretty different depths, you could say:
10@ 100 and 10 @ 70 = 20 @ 80 = 2/3 of my NDL

then 20 @ 50 and 20 @ 40 = 40 @ 45 or so, where my NDL is 55 mins. I have about 17 mins left on my NDL at 45 feet -- too close for my likings.

If i was actually diving, I'd say:
5 mins - avg 100 feet
10 mins - ave 100 feet
15 mins (now going up to 70) avg 90 feet
20 mins avg 80 feet
25 mins (now at 50) avg 75 feet
30 mins (now at 50) avg 75 feet
35 mins avg 70 feet
40 mins avg 70 feet
45 mins (now at 40) avg 65
50 avg 65
55 avg 60
60 avg 60

which gives me 60 mins @ 60 feet, which is over my NDL (maybe not the PADI one) of 50 mins.

So I'd cut down one of the sections, depending on the dive (maybe make the 40 portion 10 at 40 and a slow ascent).

The better (in my opinion) option would be use nitrox 32, ignore the 40 portion and ignore most of the 50 portion (as they fall into the < 40 feet 170 minute NDL portion)

I wouldn't bother planning if I had enough gas to do the dive or not on the boat since unless its a spot I do a lot, I'm not going to know how the depths are going to go anyway (which brings up another question -- honestly who ever says "do you want to do 10 @ 100, 10 @ 70 .... and so on.)

What I *would* plan is enough reserve gas to get an OOA diver to the surface and the gas plan (all usable, out and back or 1/3ds)

This is a profile that's (probably intentionally hard to average since the two portions of the dive are done at pretty different depths. More normal would be "Let's average 60 feet for 40 mins or 50 mins, and then stay between 80 and 40-50 for the dive. The 80 feet depth on the way out, converging up more to the 40 on the way back and then a slow ascent). One exception is that we dive the oil rigs sometimes where we go down to 100 but some of the best stuff is on platforms at 55 feet. So a profile there looks like 10-15 @ 100 (on 32%) and then 30-40 mins at 55 feet.

I think getting into 1/2 times and compartments during the dive or planning on the boat is un-necessary and just makes things overly complex. Those concepts have a place in deriving the tables or data that you base your deco/NDL on, but not when you're in or about to get in the water.

Nice post...

 

[Soggy]

Yeah, what Limeyx said....there's a lot of overcomplexificationizing here going on.....

 

[TheRedHead]

Actually, wide variances in depth like my example profile are common in some areas. In places like Cozumel, Grand Cayman, Maui and anywhere else that you have walls and/or interesting coral formations all the way from deep to the surface. And yes, you really will hear multilevel dive plans like I described ---- very common on guided tours in those resort areas.

This is very true, but many of my dives in Cozumel are of the type where we drift until until gas dictates the DM blows the bag and we make our way up. I'm looking at my Suunto dive manager and see I did a dive in April with BT of 1:15 max depth of 106 ft, avg. depth of 55.8 feet on EAN32. The deepest part of the dive occured at 31 minutes into the dive and we were 53 minutes into the dive before we ascended to 49 feet. Most of the dive was spent between 50-60 feet. We gradually ascended and at 69 minutes into the dive we were at 20 feet and spent 5 minutes at 20-15 feet and a minute at 10 and ascended. We did this dive on 100s and 120s and this was the second dive after a 2.5 hour SI. I incurred no deco on this dive with my conservative Suunto and I don't see any way it could have been planned this way or dived without a computer.

 

[Soggy]

I incurred no deco on this dive with my conservative Suunto and I don't see any way it could have been planned this way or dived without a computer.

I wouldn't choose to do that profile with or without a computer. Just because your computer says it is ok, doesn't mean dropping down 50 ft during the middle of your dive is a good idea. I bet you were pretty tired at the end of that day.

"Just because you can do something doesn't mean you should."

Anyhow, you can do a profile like that without a computer...figure average depth (not "most of the time was spent around..."), and weight it towards the deep portion of the dive since the deep part was in the middle.

 

[TheRedHead]

I wouldn't choose to do that profile with or without a computer. Just because your computer says it is ok, doesn't mean dropping down 50 ft during the middle of your dive is a good idea. I bet you were pretty tired at the end of that day.

It's not an atypical dive for Cozumel. We drifted over 2 reefs and we following the terrain, not dropping down. Why shouldn't we do this dive? We all had computers (I had 2) and were expected to follow them. In fact, computers are required with this dive op because of the profiles. We had a live boat following us and we were all experienced divers with 1 DSMB per buddy pair (my buddy and I both had DSMBs and spools).

 

[Soggy]

Why shouldn't we do this dive? We all had computers (I had 2) and were expected to follow them.

Bounce diving like that is not particularly good for you from a decompression standpoint. Like I said, I bet you were pretty tired a couple hours after that dive. It's just not an optimal or even good way of doing a dive.

The fact that you are 'following' your computer illustrates the reactive nature of the problem. You don't know if your computer is feeding you BS.

Who cares if it is 'typical' in Cozumel?