Breathing for Buoyancy: Fine-Tune With Your Lungs, Not Your BCD

At a steady depth, a well-balanced diver can often hover without repeated inflator adjustments. They're making small adjustments all the time, but they're making them with their lungs.

That only works once the rest of the system is right. Get it right, and breathing becomes your most precise buoyancy control.

Why do your lungs control buoyancy?

Your lungs change volume with every breath. Each liter of air in them displaces about a liter of water, roughly a kilogram, or about 2 pounds, of lift. A full breath can easily shift your buoyancy by several pounds.

That's enough to rise or sink gently, which is exactly what you need for fine control.

What does the wing do, then?

The wing balances the system. It carries the weight of the gas in your cylinder that you haven't breathed yet, and it makes up for your exposure suit compressing at depth. It sets your starting point, close to neutral.

Your lungs make the small corrections around that point. If you're constantly adding and dumping air to hold depth, either your weighting or trim is off, or you're using the wing to do your lungs' job.

How do you breathe for buoyancy?

Think in terms of your average lung volume: where your breathing sits between empty and full.

• To rise slightly, breathe a little higher in your range, with slightly fuller lungs on average.
• To sink slightly, breathe a little lower in your range.
• To hold depth, find the range where you neither rise nor sink, and stay in it.

Keep breathing the whole time: slow, relaxed and continuous. Buoyancy changes lag a few seconds behind your breathing, so make small changes and wait to see what they do before making another.

What should you avoid?

• Holding your breath. Never hold your breath on scuba. It's dangerous during ascents, and it doesn't help you hover anyway.
• Skip breathing. Pausing between breaths to "save gas" builds up carbon dioxide, which makes you breathe harder later.
• Short, shallow breaths. They make you bob and don't clear carbon dioxide well.
• Chasing every movement. Overcorrecting with your lungs is as unstable as overcorrecting with the inflator. Small changes, then wait.

Drills for your next dive

1. Hover on a reference. Stop over sand or beside a line at a comfortable depth. Get neutral with the wing, then put your hands together in front of you and hold your depth only by adjusting your breathing. Start with 30 seconds; build to two minutes.

2. Rise and sink on purpose. From the hover, breathe higher in your range until you rise a foot or two, then lower until you sink back. You're learning how big a change produces how much movement.

3. Breathe while you work. Hold your depth with your breathing while you read your gauge, check a teammate or deploy an SMB. Fine control while doing something else is the real skill.

4. Use it at your stops. Rebalance and vent the wing and suit as needed, then use relaxed breathing for small corrections. Never delay a necessary vent or inflation adjustment just to complete a drill.

UTD's training uses the same idea. In confined water, students practice buoyancy and trim with their lungs only, without using the wing for buoyancy underwater, while holding position on a fixed line.

When should you use the inflator?

When the change is too big for your lungs: descending, ascending, or changing depth enough that your suit compresses or expands noticeably. Make those adjustments in small amounts, then return to breathing for the fine work.

If you find yourself reaching for the inflator every few seconds while you're at a constant depth, check your weighting first. See How Much Weight Do I Need?

Get feedback on it

It's hard to tell whether you're holding depth with your lungs or just drifting slowly. Video and a coach show you. Our Scuba Coaching program includes a training plan and video review, and breathing for buoyancy is one of the foundations taught in Essentials of Recreational Diving. For the full picture, read How to Master Scuba Buoyancy and How to Hover Without Using Your Hands.