Another Tables vs. Computers Thread

[Thalassamania]

But you always wind up with moderate or fast tissue problem (e.g., 20 min data being lost when you go to a rep group in the USN tables).

 

[Thalassamania]

It can be explained at an appropriate level. I just went over decompression with my 9 year old, who is good at math but far from calculus.

 

[The Chairman]

You can demonstrate nitrogen loading with a couple of 2 litre coke bottles. In fact, I had this method published by NAUI as an excellent way to show this.

You don't need either tables or computers to understand the process.

You definitely don't need to quantify the values to understand the process.

 

[TheRedHead]

You can demonstrate nitrogen loading with a couple of 2 litre coke bottles. In fact, I had this method published by NAUI as an excellent way to show this.

Everyone learns that in OW. I was talking about tissue compartments and deco theory in depth and why deep stops are a good idea.

 

[Charlie99]

Ugh. Just run it through a deco planner instead and cut your own tables.

I don't bring a computer along to run a deco planner on charter boats. The technique is pretty straightforward, providing that you can add numbers.

Take as an example the profile I mentioned a few posts back: 10@100', 10@70', 20@50', 20@40'.

If one doesn't bring a computer or palmtop onboard, what sort of methods are available to do a sanity check if someone proposes that profile to you?

One crude but effective method is to look at average depths. 10@100' + 10@70' is 20@85', so we are OK so far. Add in 20@50' and we are roughly 40 minutes at 70'. Probably OK, but pushing it a bit. Add in another 20 minutes at 40' and we are at ...... hmmmm. OK, I'll let someone else do the math.

Using a square profile table to approximate a multilevel dive is another potential method of doing a rough sanity check of a proposed dive profile. While the explaination using just the Internet makes it sound difficult, if you grab a PADI RDP and follow along, you might very well find it easy. Use the backside of the RDP since the numbers are bigger (the data on front and back are actually the same!) If you don't have an RDP handy, just use the rdp-like spreadsheet I've attached.

10@100' is column E. Go up to 70'. The entry there is 14. This simply means that, as far as the 60 minute halftime compartment is concerned, 10@100' is equivalent to 14@70'. Add your 10 minutes at 70' to that 14 minutes, and find that you are now in column K. Move up to 50' to find that the dive is so far equivalent to 36 minutes at 50'. Add your 20 minutes at 50' to get 56@50'. Move up to 40' to get the total dive equivalency so far of 79 minutes at 40'. Add the 20 minutes at 40' to get an equivalent of 100 minutes at 40'.

Of course, that dive profile doesn't make much sense if I won't have the air to do it. The little gas planning table on my spreadsheet turns gas planning into some simple addition. Looking in the table I see that the segments use 40+31+50+44=165 surface equivalent minutes. In other words, the dive takes the same air as breathing at 1ata for 165 minutes. That happens to be my budget for an AL80 at my standard 0.4cfm.

After doing these rough calculation on the boat, I splash in and let my dive computer keep track while I watch the fishies swim about.

Anybody else willing to post how they plan multilevel dives ?????

 

[The Chairman]

Everyone learns that in OW. I was talking about tissue compartments and deco theory in depth and why deep stops are a good idea.

Again, there is no need to "prove these" empirically. My simple demonstration helps them to understand all of that. Unless we are teaching them how to derive the algorithms, there is no need to use a mathematical model at all for either OW, AOW or NitrOx.

 

[TheRedHead]

Of course, that dive profile doesn't make much sense if I won't have the air to do it. The little gas planning table on my spreadsheet turns

I thought you didn't bring your computer on the dive boat?

Anybody else willing to post how they plan multilevel dives ?????

I can do it on either one of my dive computers or on my Palm Pilot.

 

[Blackwood]

Take as an example the profile I mentioned a few posts back: 10@100', 10@70', 20@50', 20@40'.


One crude but effective method is to look at average depths. 10@100' + 10@70' is 20@85', so we are OK so far. Add in 20@50' and we are roughly 40 minutes at 70'. Probably OK, but pushing it a bit. Add in another 20 minutes at 40' and we are at ...... hmmmm. OK, I'll let someone else do the math.

I'd say

(100+70+50+50+40+40)/6

Which is (100+100+80+70), or (200+150).

350/6, or (35/6)*10. 36/6=6, so I'll round up to 60'

Wouldn't be that easy without the nice even 10 minute intervals, but it can be done in your head and hey, we're planning, so why not make it easy?




Regardless, I too use the method of estimating multilevel dives as individual square dives with no SI.

I thought you didn't bring your computer on the dive boat?

One doesn't need a computer to read a spreadsheet. One only needs a hard copy

 

[Charlie99]

I thought you didn't bring your computer on the dive boat?

The only computer I bring is my heavily waterproofed Oceanic Data Plus 2 that I take with me on the dive.

I just have a 8-1/2 x 11" sheet of paper with everything I need on it.

Gas planning is a little table that has 40/50/60/70/80/100/120' columns, with rows of 10-30 minutes in 5 minute increments. The entries in this 7x5 table are the equivalent surface minutes. So I can just look at the table and see that 10@100' is going to use the same amount of air as 40 minutes on the surface (of course 100', being 4ata, is an easy case. The table helps more in converting 20@50' to 50 surface equivalent minutes).

 

[Blackwood]

The only computer I bring is my heavily waterproofed Oceanic Data Plus 2 that I take with me on the dive.

I just have a 8-1/2 x 11" sheet of paper with everything I need on it.

Gas planning is a little table that has 40/50/60/70/80/100/120' columns, with rows of 10-30 minutes in 5 minute increments. The entries in this 7x5 table are the equivalent surface minutes. So I can just look at the table and see that 10@100' is going to use the same amount of air as 40 minutes on the surface (of course 100', being 4ata, is an easy case. The table helps more in converting 20@50' to 50 surface equivalent minutes).

That's pretty cool. I may pirate your idea.

I bring with me a table listing how long (in surface minutes) from various fill pressures to 500PSI. I'll check various conditions before leaving, update the spreadsheet based on my expected (estimated) SAC (if I know it's going to be a strenuous dive, for example, I may throw in 0.8), and print it out.



If I'm expecting a SAC rate of 0.55cfm, my table tells me that I've got 155 minutes of surface breathing from a full HP100. If the boat only manages to fill my tank to 2700PSI, a quick consult tells me I've only got 115 minutes of surface air.