How to Judge Your Diving Ascent Rate Without A Dive Computer
Novice divers often express frustration about how to best conduct safe and controlled ascents from their scuba dives. Learning how to judge your diving ascent rate is part calculation and part experience.
I see many new divers questioning the best technique for judging their ascent speed. The common use of dive computers has automated this skill: providing divers with a graphical illustration of their ascent speed – and warnings if they exceed a safe ascent rate.
However, many novice divers don’t have a dive computer and dive computers occasionally do fail during dives. Therefore, every diver should be familiar with analogue methods for judging their ascent rate. Proper ascent control is one of the most critical scuba diving skills – as this plays an important role in preventing the occurrence of decompression illness.
Without a dive computer (all have ascent rate monitors/displays), it can be more tricky to monitor the speed of your ascent. During training, the instructor will have demonstrated an appropriate rate as part of scuba diving skills development, but I do understand that it can be hard to replicate this initially.
It will become an instinctive/unconscious skill as you practice it more and more.
Diving ascent rate: the bubble method
The old scuba adage of “never ascend faster than your smallest bubbles” is practicable in emergencies, but for general diving, it is imprecise and far from foolproof. It should not be viewed as a routine technique – especially for deep and/or repetitive diving.
You should always bear in mind that the recommended ascent rate is the maximum speed. Ascending at a rate below this can be viewed as a prudent and conservative diving practice.
Diving ascent rate: appropriate speed
PADI recommend 18m/60ft per minute. Other training agencies recommend a much slower rate, typically around 8-10m/25-30ft per minute (in line with the ascent speeds used by modern dive computers).
The techniques taught to you on your Open Water course should go a long way towards ensuring that you can ascend safely – and also enable you to track and assess your ascents.
You should have a depth gauge and timing device for your dives.
Read more about the best ascent speed for scuba diving
Diving ascent rate: simple math
When you decide to end your dive and make a direct ascent to the surface, it is helpful if you check the time and depth. This ensures that you know your dive’s bottom time (for dive logging and repetitive dive calculation) and also allows you to gauge your ascent through a simple speed-distance-time calculation. Simply divide the depth by the time (i.e. 40ft divided by 40 seconds = 1ft per second = 60ft per minute)
As you ascend from a dive, you can monitor your depth and time to ensure that your ascent speed is not excessive. To ensure a uniform and constant rate, break the ascent into smaller ‘levels’ and apply the speed-distance-time calculation to that.
The time taken to ascend each level allows you to determine your rate as you go. A 30ft per minute rate is ideal (half of the maximum speed recommended by PADI). For ease of monitoring, this means you are ascending 1ft every 2 seconds / 10ft every 20 seconds.
For instance, for a 60ft/18m ascent, you can subdivide the ascent into six 10ft levels, each of which should take you 20 seconds. Your entire ascent to the surface would take 2 minutes.
To add a safety stop, simply pause at 20ft depth and hover for 3 minutes – meaning your total ascent time is 5 minutes. After the stop, recommence your ascent – allowing 40 seconds for the final two 10ft levels.
If you know how long your ascent should take, even a casual glance at your dive watch will inform you of whether you are on track or not.
Diving ascent rate: buoyancy control helps
Direct ascents to the surface, especially without a visual/tactile reference (shot line/reef wall/slope) can be very taxing for novice divers. Buoyancy control is essential to maintain a slow ascent speed – which, of course, is reliant upon proper weighting.
If over-weighted, the diver will suffer excessive and regular positive buoyancy from the expansion of a greater volume of air in their BCD. Proper weighting ensures that a minimal amount of air is needed in the BCD. The smaller the amount of air, the smaller the proportional expansion of air…and the less likely you are to lose control.
Where possible, utilise a line for ascents. When boat diving, a shot (buoyed) or anchor line is often present. Ascend on a line hand-over-hand – that will give you a slow, regular ascent rate. If that isn’t available, then you could consider getting a Delayed Surface Marker Buoy (DSMB) and a spool.
Whilst this takes some practice to deploy safely, it is invaluable in providing a ready reference from which to gauge an ascent. If you are winding in a reel/spool, it is hard to ascend too quickly (I’ve found that winding in a finger spool tends to keep my ascent rate well below 12ft per minute).
The benefits of improving scuba buoyancy control & how it can be developed in training & practice.
What are the buoyancy control benefits for scuba divers? The reasons why it is worth devoting time & effort to developing core diving skillset
This is how you achieve great buoyancy control when scuba diving. There are a few key things to know, then you will find it easy
How to perfect your scuba weighting. Get this right & your buoyancy control will be much easier. Advice not taught in Open Water courses
Stable diver trim is the foundation for good buoyancy control and efficient propulsion. It also helps conserve the marine environment.
How to control your breathing & scuba buoyancy for more comfort, confidence and competency as a scuba diver.
How to improve your diving ascents & descents for safer and more comfortable scuba dives. This article can change your diving.
The balanced rig principle for diving describes a calculated approach to the amount of weight which can be jettisoned in an emergency
The benefits of streamlined dive gear and how to achieve it with your own scuba diving equipment. Small kit changes can have big effects.
About the Author
Andy Davis is a RAID, PADI TecRec, ANDI, BSAC and SSI-qualified independent technical diving instructor who specializes in teaching sidemount, trimix and advanced wreck diving courses.
Currently residing in Subic Bay, Philippines; he has amassed more than 10,000 open circuit and CCR dives over 27 years of diving across the globe.
He has published numerous diving magazine articles, designed courses for dive training agencies and tests/reviews dive gear for scuba equipment manufacturers. He is currently writing a series of advanced diving books and creating a range of tech diving clothing and accessories.
Prior to becoming a professional technical diving educator in 2006, Andy was a commissioned officer in the Royal Air Force and has served in Iraq, Afghanistan, Belize and Cyprus.
Originally posted 2018-11-05 06:10:26.