

Why Dive a Computer? – Increased Dive Time!
SKubaSteve - 11/15/2013 3:00 PM
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Editor’s note 2: None of the figures were transferred from the original blog post - not sure why. The full article is here!

Now… why dive a computer?



And here’s why…
Increased dive time Safety The tables seem like they were designed to sell dive computers Gas mixture programming Dive logging Convenience

Increased Dive Time

Who wouldn’t want more time on each dive? We spend time and money training and traveling to exotic locations so we can immerse ourselves in another world!

The dive plans that you will calculate when you use the recreational dive tables will provide a depth and time combination that will keep you within the recreational limits and will assume your descent goes directly to your deepest depth and that you stay there for the full bottom time of your dive then make your direct ascent to the surface. So what does all that mean to me as a diver? Let’s look at an example.

SKuba Steve is going to dive to 60 feet and expects the dive to last 30 minutes. The purpose of the dive is to see a frogfish like this guy shot by Mika Hiltunen (photo used with permission – thanks Mika!) …that the dive master says lives on a coral formation at 58 feet (oops I think I just made a word problem). The dive profile is shown below.

SCUBA dive profile to 60 feet for 30 minutes.

The dive tables will assume that SKuba Steve is going to be at 60 feet for the full 30 minutes. Bottom time, surface intervals/desaturation and repetitive dive constraints are being calculated assuming he is absorbing N2 at the rate for the maximum depth and full duration of the dive as shown below in green.

SCUBA diving profile showing N2 absorption assumed by using dive tables.

The truth, of course, is vastly different and when we add the actual dive profile we find it looks something more like the figure here.

SCUBA diving profile of a typical example dive.

Now it is clear that SKuba Steve was not absorbing N2 at a rate consistent with a 60 foot depth during the entire 30 minute dive. The actual N2 absorption occurs as shown in green below.

SCUBA diving profile with N2 absorption for a typical example dive.

Now we see the visual difference between what a computer calculates in green and the extra absorption assumed by the tables shown by the white space under the curve.

Compare the two graphs side by side below and you’ll easily see the difference in the time/depth related to nitrogen absorption for the dive with the table calculation on the left and the computer on the right.

SCUBA diving profile with N2 absorption for a typical example dive.

SCUBA diving profile N2 absorption based on tables.

When using a dive computer, your actual depth and time is used to regularly update your remaining bottom time based on calculated nitrogen absorption.

Practically speaking this means that time spent shallower than your maximum depth will allow you a longer dive as you absorb N2 at a lower rate at these shallower depths.

So to break it down to the core value added: Imagine the dive tables think you absorbed the quantity of N2 shown in green by the left graph and the computer (using better data) calculates that you absorbed only what is shown in green on the right graph.

More accurate data = Less calculated N2 absorption = More SCUBA Diving!

This, more accurate representation of your nitrogen absorption, is also used to plan consecutive dives throughout your dive day on your computer ultimately resulting in more allowable time exploring the underwater world and my #1 reason for diving with a computer (if you don’t count the gear-o-phile one).

Okay, I just noticed that I put Safety as my second reason for owning a dive computer and that seems like I’m setting a bad example. I’m sticking with my decision and I’ll explain why next week.

The surface interval’s over … get out there and dive!

SKuba Steve

© 2013 Stephen Krausse – All rights reserved.