OW Review Dive Table Question - Please help

**brianwferguson** · 04-07-2008, 10:03

Hi All,
I ran into this question during my OW review session and I do not know the answer, and more importantly HOW to get the answer. Can someone please explain it to me?

Question:
What is the minimum surface interval required between a dive to 20m/70ft for 29 minutes followed by a dive to 14m.50ft for 39 minutes?

Thanks

Brian

**fisheater** · 04-07-2008, 10:11

My best advice (as I won't do the problem for you), is for you to review the booklet that should have come with your dive tables. (If PADI, it was a separate booklet that came with the Recreational Dive Planner.) There is an explanation and example of how to compute the minimum surface interval.

After you've done that, download the FREE ScubaToys dive table tutor software. It's a really great program that will give you excellent practice and assistance.

Good luck and keep at it. With a bit of diligence, you WILL figure it all out.

***ScubaToys Larry*** · 04-07-2008, 10:31

Yea, the table tutor software will allow you to do thousands of these missing surface interval questions. Table Tutor, Education, ScubaToys, Table Tutor

But here is the answer in a nutshell... When you have that kind of problem, go to table 3. The repetitive dive one. I'll assume you're on a Padi Table.

So now look at that table you will see.. to do a 50 ft dive for 39 minutes... you would have to be a M diver. After doing the first dive... you are an O. So then that means an O diver must hang out long enough to become an M. And that would only take 7 minutes according to our surface interval table... but there is a suggested hour between dives ... so an hour might be a good answer to.

Of course, different tables will give you different answers - but hopefully that gives you an idea.

**No Misses** · 04-07-2008, 10:36

Run your Dive #1 Profile & calculate your PG (Pressure Group).
Using Table 3, find the highest PG that you can start dive #2 at and still end as a no-deco dive.
Go back to table 2 using your Dive #1 PG and Dive #2 PG find the minimum surface interval.

**brianwferguson** · 04-07-2008, 12:01

Thanks guys,
Fisheater, I was not so much concerned WITH the answer as to HOW to get the answer, thanks for the suggestion, I'm doing the e-course, so no book (but I do have access to one).

I actuall don't want you to give me the answer, but instead explain the how.

No Misses, thanks, that exactly what I was looking for.

After several questions on the Table Tutor, I finally got it. I was acutall doing it right the first time but my copy of the tables is hard to read (I have a photocopy I'm using at work to study, instead of actually work). I then started second guessing myself until I was competely confused.

Thanks again.

brian

**brianwferguson** · 04-07-2008, 12:16

Thanks again guys,
after doing several more "Missing Interval" questions, it now makes much more sense to me.

BTW, thanks for not giving me the answer (I'm serious here). I know how important knowing this stuff is even without a dive computer.

Brian

**fisheater** · 04-07-2008, 12:18

Even with the e-course, you're getting a plastic dive table with a paper booklet, right? They came with my DVD course.

If you didn't get an actual, physical, plastic-so-it'll-survive-water dive table (with booklet), you should.

The PADI booklet is entitled "Instructions for Use," and the procedure for minimum SI computation is in Section Two, starting on page 24.

**brianwferguson** · 04-07-2008, 12:40

Thanks fisheater, I'll have to look again when I get home. Thanks for your help

brian

**ertechsg** · 04-07-2008, 13:13

I know this is a bad answer but I hope my computer never lies to me

**in_cavediver** · 04-08-2008, 11:25

Originally Posted by ertechsg

I know this is a bad answer but I hope my computer never lies to me

Just remember - Garbage in = Garbage out.

It would serve all divers well to have a basic grounding in reasonable dive times. You never know when your computer is gonna 'take a dive' in a bad way.

The other item I think ought to be taught is a means for estimating how to get yourself out of a bad situation. We all have heard the when in doubt, sit at 15' until your air runs out speel. A slightly better answer is that for most situations that you can get yourself into as a rec diver, 10-15 minutes at 15' will get you out of. Even more so, understanding that 5 minutes at 15' is far better than 0 at 15' in these situations.

Get a free deco program such as GAP and play with the NDL limits and see what is called for. Its enlightening.