ARE YOU CALLING YOUR DIVES TOO EARLY… OR TOO LATE?
According to a couple of website searches and the RAID cave-diving manual, we learn that a cave diver typically travels about 15 meters (50 feet) per minute under normal, low-flow swimming conditions.
But how true is it… How accurate… Is it a real number for you and your team to use?
For most open water divers, the question is more or less moot. Something nice to know, but really a secondary concern. However, in the overhead… a cave or a mine… it’s way more important to know how far you swim in a set time. The reason is simple: we all need to follow safety guidelines.
Most agency standards dictate how far from the surface or the cave entrance a graduate of their programs can penetrate. For example, for a RAID Cave 1 diver, it’s 300 metres… that’s about 1000 feet.
At 15 metres per minute, that’s a 20-minute swim. But is it? Since most main lines have no distance markers, you could be calling your dives on distance before you need to, or pushing standards too far and over the edge.
With all that in mind, when was the last time you measured how far you and your buddy do swim in a minute?
You might be surprised. You might not be. But at least, you’ll know.
Consider three factors that influence that 15 metre default and why measuring is worth the effort.
Being laid back. In clear, relaxed conditions where we’re relaxed and in a familiar spot, we move slowly to look around and enjoy the sights, or to conserve air; the distance covered in a minute can drop to 10 or 12 metres.
Water is not always still. Currents are another factor to consider: Strong currents, or even a mild one, will change the effort of swimming and the distance you can cover in a minute. The difference can be dramatic for swimming in and drifting out. (N.B. no sumps.)
Most important of all. Understanding the connection between time and distance is a crucial reality check for overhead environments. Many divers rely blindly on textbook metrics like 50 feet per minute without realizing how much personal physiology and fitness, equipment, the drag extra gear exerts, even the stress of being on a “mission” skew those numbers.
Measuring Your True Swim Rate Matters Because…
First, it helps you avoid turning a dive before we have to. If you and your team swim slower than the standard 15 meters per minute because of bulky gear like cameras and big video lights or strobs, or just plain caution, calling a dive based purely on elapsed time could mean you’ve covered significantly less distance than you think. That’s okay but you do need to be aware of it.
And the opposite is important too. We should also be aware of “Scope Creep. When you glide effortlessly or catch a slight tail flow, a relaxed 20-minute swim can push you past your certification depth or distance boundaries (like RAID’s Cave 1, 300-meter limit) before your brain registers the passage of time.
And, most importantly, taking the trouble to check your normal swimming speed is going to make your job of converting Gas-to-Distance on the fly… during the dive… easier or possible. While gas management via the Rule of Thirds or Rock Bottom is your hard safety boundary, time-distance metrics help bridge the gap between where you are and how long it will take to exit under a stress scenario.