How to log a dive: what to write down, and what you can skip

Why a log is worth keeping

A dive log is your own record: proof of experience for a course or a dive centre, a reminder of where the water was clear, and a way to see your gas use and depth change as you get more experienced. Dive centres and instructors often ask how many dives you have and when you last dived, and a log answers that in a few seconds.

It also only works if you actually write the dives down. The logbook that works is the one you fill in on the boat, not the perfect one you mean to catch up on at the end of the trip.

The four things to write down at once

If you do nothing else, record these before you leave the beach or the boat, while you still remember them exactly:

• The date. Add the time of day if you like; it helps to tell two dives on one day apart.
• The site. The name people actually use, and the country or region.
• The maximum depth.
• The dive time, from leaving the surface to returning to it.

Those four give you a dive count, total time underwater and your deepest dive. Everything else is an extra, and you can add it that evening.

What is worth adding next

• Buddy, and the guide or divemaster if there was one. In a few years you will want the name.
• Gas. The mix (air or a nitrox percentage), the cylinder size and your start and end pressures. With those, your air consumption can be worked out afterwards, and our SAC guide shows how.
• Conditions. Water temperature, visibility and current. They explain a dive better than any later memory, and they show you how a site changes over the year.
• Average depth, if your dive computer shows it. It makes the air consumption figure more honest than the maximum depth alone.
• Type of dive. Night, wreck, drysuit, deco, training. Courses and specialities ask for counts of these.
• Notes and sightings. One line about what made the dive special, and what you saw.

Log it right away

A short entry is better than none: a dive logged with only the four basics still counts in every total. Memory fades faster than you think. Write the four basics straight after surfacing, or on the way back to shore, and fill in the rest while you have your coffee. If you wait a week, the depth and the time are the first things you will guess.

Loggerfish has a quick log for exactly this: date, site, depth and time, with the rest added later by opening the dive. Where the browser offers speech recognition you can also say or type a sentence such as "twelve metres, forty minutes at the Blue Hole" and the fields fill in for you to check. The full dive form has fields for the buddy, the guide, gas, up to several cylinders, conditions, a rating from one to five stars, photos, your own tags and notes.

Your computer is the better source for numbers

If you dive with a computer, let it supply depth, time and temperature rather than your memory. Loggerfish reads Garmin .fit files, Subsurface logs and UDDF files, so a dive can arrive with its profile and the computer's own figures, and you only add the people and the story. See the guides on Garmin Descent files and Shearwater Cloud export.

A minimal habit

1. Quick log straight after the dive.
2. Add buddy, gas and conditions that evening.
3. Once a trip, check the dive numbers and the totals against your computer.
4. Keep a backup, or an export, somewhere that is not your phone.

Logging, importing and every export are free in Loggerfish. The analysis views, such as air consumption over time, are part of Pro, the optional paid plan.