Entry-level dive courses always teach students to log their dives. A typical entry will consist of the dive site, day and time of the dive, duration of the dive, depth, and perhaps things like water temperature, equipment used and sights seen.
Based on the depth and duration of the dive, divers used to calculate their saturation profiles to make sure they stayed within decompression limits. But as dive computers become nearly universal that need has decreased. Old-fashioned dive-table calculations treat every dive as if it had a box profile: you descend to your maximum depth, spend the entire dive there, and surface, ending the dive. But this isn’t how most of us dive; it’s far more common to descend to your maximum depth and then slowly ascend as the dive goes on, to extend your dive time. While there have attempts at tables and logs that allowed users to log of this profile, they were never really successful. And since a typical dive computer will remember hours of dives, why bother with the log?
First, you may need to document your number of logged dives. A number of dive locations around the world are considered advanced enough that dive guides will require you to have a certain number of dives total, or a certain number of a specific type of dive, before they’ll allow you to dive there. And in most organizations, a minimum number of dives is required before you can achieve certification levels such as Divemaster or Instructor. The same rule applies if you want to take certain purpose-specific dive certifications, such as some technical certificates. A log, including verifications from a certified buddy, is your documentation.
Provided you record your equipment for each dive, your log quickly becomes a handy reference to see how much weight you’ll need to descend in a given wetsuit. If you dive in various locations around the world, and in various climates, a dive log takes the guesstimation out of the equation. Of course, things change, and perhaps you need less weight now than the last time you dove tropical waters in a 3 mm shorty, but at least you’ll know if your starting point should be five pounds or 15 pounds. And if you note whether a given amount of exposure protection was adequate or not, you’ll also know if you need a 3 mm or 5 mm suit in 70-degree water.
A dive log also serves as your own memory, detailing every dive you’ve done, and noting the most spectacular things you’ve seen while diving. You’ll remember when you did your first wreck dive, and when you saw your first manta, right down to the date and time of the dive. We dive for pleasure, for fun, and we dive to create memories. A dive log helps you maintain those memories.
Logging your dives forces you to take out your dive computer and go over the parameters of the dive, making you consciously aware of your actual depth, and how long you were actually there. While this should be a no-brainer, I’ve seen too many divers who seem to just jump in the water, and as long as their depth or dive time alert isn’t sounding, they assume everything is probably fine. Unless of course, it isn’t. These are the kinds of divers that give dive computers a bad name, because diving obliviously like that can be hazardous. An alarm may not sound, or you may not hear it, so if you’re not monitoring your depth yourself, you could easily exceed your maximum depth. Logging your dives makes you aware of the need to check your computer, and of your dive history for the past few days, which is particularly useful if you’re doing a multi-day dive vacation.
Whether you log with good old paper and pen or you use an app on your computer, tablet, or smartphone is up to you. Pen and paper never runs out of battery, and there’s less risk of your data being lost if you switch phones. Digital logs are easier to carry around, and often have backup functions should your phone get stolen or lost. Regardless of which you choose, don’t stop logging those dives once you’ve graduated far beyond a beginner.