View Full Version : It's time for some SCUBA questions

Okay, I know that alot of the SF guys here aren't scuba qual'ed, but I do know that there are some here that are certified and seeing that Scuba is an SF fieldcraft, I thought I'd post this here.

Okay, here goes....

----How is it possible to do two seperate recreational dives, where your 2nd dive is your deeper dive and not run the risk of DCS (Decomperssion Sickness)?

***For those of you that aren't certified, It's ALWAYS taught that you do your DEEPER dive first, then move in progressivly shallower.***

Here's what you have to work with.....

1st Dive is at 80 feet

2nd dive is at 70 feet

***Remember, your 2nd dive is the deeper one.***

Both dives are for 30 minutes.

You have a 1 hour and 30 minute (1:30) serface interval.

You are diving on AIR only. No NITROX or mixed gases.

No computers can be used.

No protable chambers.

You must SHOW YOUR WORK !!!! I want to see dive profiles.

Roguish Lawyer

05-09-2004, 00:32

Originally posted by Sdiver

Here's what you have to work with.....

1st Dive is at 80 feet

2nd dive is at 70 feet

***Remember, your 2nd dive is the deeper one.***

Both dives are for 30 minutes.

You have a 1 hour and 30 minute (1:30) serface interval.

You are diving on AIR only. No NITROX or mixed gases.

No computers can be used.

No protable chambers.

You must SHOW YOUR WORK !!!! I want to see dive profiles.

It's been a while, but I'll try.

I assume you mean that the 1st dive is at 70 and the second is at 80; otherwise the second would not be deeper!

Pressure interval after first dive (70 feet, 30 minutes) is O.

1:30 surface interval takes you down to pressure group C.

Residual nitrogen time after surface interval at 80 feet is 10 minutes, and total permitted time for next dive is 20 minutes. So, we're proposing to dive for 20 minutes longer than we should (i.e. 30 Dive 2 + 10 RNT).

I take it that we can't increase the surface interval, right?

I don't recall how to address this problem. Decompression stops? Seems to me this is not a recreational dive!

I am the acorn that becomes the oak. Teach me, oh divemaster.

Originally posted by Roguish Lawyer

It's been a while, but I'll try.

I assume you mean that the 1st dive is at 70 and the second is at 80; otherwise the second would not be deeper!

I take it that we can't increase the surface interval, right?

Seems to me this is not a recreational dive!

First...NEVER ASSUME !!!!Assumtion is the mother of all F**k ups.

Again Dive Profile is as follows.....

1st dive .... 80 feet

1:30 surface interval

2nd dive .... 70 feet

2nd dive is the deeper dive.

This is/can be a recreational dive.

Roguish Lawyer

05-09-2004, 01:35

Originally posted by Sdiver

First...NEVER ASSUME !!!!Assumtion is the mother of all F**k ups.

Again Dive Profile is as follows.....

1st dive .... 80 feet

1:30 surface interval

2nd dive .... 70 feet

2nd dive is the deeper dive.

70 feet is deeper than 80 feet? What am I missing here? :confused:

Originally posted by Roguish Lawyer

70 feet is deeper than 80 feet? What am I missing here? :confused:

I don't know....You Tell Me !!

Work the problem.

Roguish Lawyer

05-09-2004, 01:58

Originally posted by Sdiver

I don't know....You Tell Me !!

Work the problem.

I think this is above my pay grade. Matchanu!

What are the ATMs for each dive?

Thank you,

Solid

Desert Fox

05-09-2004, 09:19

Simple: dive tables

30 min for the first dive.Secure round-up in dive table is 35min with a decompression schedule of 10 min at 10 feet.

RDG for 80 feet 35 min is: G.

Surface interval:

RDG = G and surface interval is 1:30. The result is class V.

Nitrogen penalty times:

second dive at 70 feet and class V:

nitro penalty time = 18

no decompression limit = 17

return to table 1:

30 min + 18 min = 48 => 50

70 feet at 50 min => 10 min decompression stop at 10 feets.

The second dive is not necesarely deeper, it's just 'longer', in the point of view of nitrogen penalty.

RMK: I'm running a canadian table from ACUC.

froglegz

05-09-2004, 09:50

what is the altitude at each dive site???

Originally posted by Desert Fox

Simple: dive tables

30 min for the first dive.Secure round-up in dive table is 35min with a decompression schedule of 10 min at 10 feet.

RDG for 80 feet 35 min is: G.

Surface interval:

RDG = G and surface interval is 1:30. The result is class V.

Nitrogen penalty times:

second dive at 70 feet and class V:

nitro penalty time = 18

no decompression limit = 17

return to table 1:

30 min + 18 min = 48 => 50

70 feet at 50 min => 10 min decompression stop at 10 feets.

The second dive is not necesarely deeper, it's just 'longer', in the point of view of nitrogen penalty.

RMK: I'm running a canadian table from ACUC.

Sorry bud, Waaaay off.

Originally posted by froglegz

what is the altitude at each dive site???

You're getting warm.

If I told ya, you'd get it easy.

This is a no BS, dive profile. I've done this dive several times and is a sample question I give my students.

Desert Fox

05-09-2004, 12:24

Originally posted by Sdiver

You're getting warm.

If I told ya, you'd get it easy.

This is a no BS, dive profile. I've done this dive several times and is a sample question I give my students.

You are diving in caves!

Originally posted by Desert Fox

You are diving in caves!

NO !!!!

As I stated above, this is/can be a Recreational dive.

Diving in Caves/Caverns is not classified as Recreational.

By changing the position of the two dives relative to sea level, you can create the atomspheric effect of having the second dive be 'deeper'. If the first takes place at over 10ft above sea level, the second dive will be 'deeper'.

I think.

Solid

my wild-ass guess:

you are up a 5000 ft mountain, wait 12 hours so you have no starting pressure group, do a 60 ft dive that counts as an 80 ft dive, new pressure group of 'R', your 1:30 SI time is spent driving down to sea level which somehow lowers your pressure group to 'A' rather than 'C' (maybe excess off-gassing), leaving you with 5 minutes RNT and a maximum TBT of 35 for a 70 ft dive.

Originally posted by pulque

my wild-ass guess:

you are up a 5000 ft mountain, wait 12 hours so you have no starting pressure group, do a 60 ft dive that counts as an 80 ft dive, new pressure group of 'R', your 1:30 SI time is spent driving down to sea level which somehow lowers your pressure group to 'A' rather than 'C' (maybe excess off-gassing), leaving you with 5 minutes RNT and a maximum TBT of 35 for a 70 ft dive.

Okay you're kinda in the ballpark. But using words like "somehow lowers you PG to 'A' rather than 'C'." and "Waiting for 12 hours" to dive.....ahhhh NO.

Altitude is a factor.

When you've had enough torture, I might reveil the answer.:D

Originally posted by Sdiver

Okay you're kinda in the ballpark. But using words like "somehow lowers you PG to 'A' rather than 'C'." and "Waiting for 12 hours" to dive.....ahhhh NO.

I could not find anything out about altitude reverse profile. I discovered from the NOAA manual that there is a PG of 'D' upon arrival at 5000 ft, before the first dive. Thus my WAG that one might off-gas a bit by coming down the mountain.

When you've had enough torture, I might reveil the answer.

LOL. there are ways of making you talk.

Roguish Lawyer

05-12-2004, 20:38

How about an answer? Looks like Matchanu is busy elsewhere . . .

I smell chum. Have to investigate . . .

Very Well...I'll post an answer later tonite.

I'm just scanning now, before I have to blaze off to work.

still treading

signed,

AC #4

Roguish Lawyer

05-14-2004, 14:49

Yeah, let's get it together! :rolleyes:

Sorry I'm late....the short bus got a flat and no one knew how to change it.

Anyway, where were we ??? Oh that's right, you guys want to know how it's possible to do two dives with a profile like this :

1st dive 80 feet for 30 min.

1:30 S.I.

2nd dive 70 feet for 30 min.

and not run the risk of coming up/down with a DCI

and the 2nd dive is the deeper dive.....

Well here goes.

Yes altitude is going to be a factor. I'll be using three (3) dive tables for this problem.

The first table is the TDAA (Theoretical Depth At Altitude) table

Second table will be the PADI RDP (Recreational Dive Planner)

Third Table will be, the standard Navy Dive Table (Just to show the contrast between it and the RDP)

Our first dive is going to be a Mountain lake at 7859 feet. Water temp is low to mid 40's. Our actual depth is going to be 49 feet.

We are going to round up both our altitude and dive depth.

8000 feet and 50 feet.

On the TDAA a 50 foot dive at 8000 feet is like diving at 67 feet at sea level.

Round that up to 70 feet.

Now we want to add 10 feet for it being a COLD and Strenous dive (water temp in the low to mid 40's) I don't care if you are wearing a dry suit, you'll still add that 10 feet, onto your dive profile.

So on this dive it'll be like diving at 80 feet. We dive for 30 minutes. Our Pressure groups after the dive are now:

PADI : R

Navy Table : G

We have a 1 hour and 30 minute Surface Interval, driving DOWN the Mt. to our next dive spot. Which will be a Natural Spring/Sink Hole, like the Blue Hole, in Santa Rosa, New Mexico.

After our 1:30 S.I., our new Pressure Groups are:

PADI : C

Navy Table : E

The Blue Hole is also at altitude. The altitude there is 3920 feet. Water Temp. is in the mid to upper 60's. Our actual depth is going to be 58 feet. Round up....

On the TDAA a dive at 60 feet at an altitude of 4000 feet is like diving at 69 feet at sea level. Round up....

70 feet for this dive.

On the PADI RDP, as a C diver your ABT (Actual Bottom Time) would be 28 minutes.

On the Navy Tables, as an E diver, your ABT is 26 minutes.

But we overshoot our ABT and are under for 30 minutes. So in order to complete the REST of the above question ***and not run the risk of a DCI*** we would need to do an Emergancy Decompression stop at 15 feet for 8 minutes.

So.....Original question.....How is it possible to do 2 recreational dives with the following dive profile:

80 feet for 30 minutes

1:30 S.I.

70 feet for 30 minutes

and not run the risk of coming down with a DCI and your 2nd dive is your deeper dive ?

Actual depths:

1st dive......49 feet

2nd dive.....58 feet

This is how your 2nd dive, is the deeper dive.

Dozer523

10-14-2010, 17:48

Loathe to start a new thread for this but maybe we need a SCUBA thread.

(There's a HALO one -- I can just feel the envy)

This one is for the bubble-blowers . . .

An USAF guy asks an Army guy:

"Why do Scuba divers always fall backwards off their boats?"

To which the brilliant US Army soldier replies:

"If they fell forwards they'd still be in the f@ckin boat."