The art of buoyancy control stems from proper weighting when diving. During your open-water course, you learn the basics of proper weighting when diving in confined water or a swimming pool. Moving to open water during those training dives, your instructor may have helped you find a starting point for your weight so that you could comfortably leave the surface without being severely over-weighted.
As you progress, dialing in your ideal weighting when diving is a constant process of trial, experimentation and recording what works best for you. Here are a few tips to help you find the right weight for you.
Why is proper weighting when diving important?
Proper weighting when diving is the foundation of good buoyancy. The correct weight helps you make smooth descents and ascents. It allows you to comfortably hold position during safety stops. Carrying less weight, and therefore having less drag, also means your gas consumption (or SAC rate) should go down. And, as your overall scuba technique improves, correct weighting helps you achieve better trim in the water. This in turn helps you fin and maneuver smoothly.
The science behind correct weighting
To understand correct weighting and achieve neutral buoyancy, you must understand the underlying science: Archimedes’ Principle.
Archimedes stated that “An object placed in a liquid will be buoyed up by a force equal to the weight of the liquid it displaces.”
Buoyancy characteristics depend on the object’s density, i.e., its weight divided by its volume. For example, an object is extremely dense if it weighs a (relatively) great deal without displacing a lot of water, such as a pebble or coin.
This principle applies directly to you as the diver, in combination with your diving equipment. For example, a very slim diver with low body fat in just a rash vest and board shorts will require less weight to dive than a larger person wearing a more buoyant drysuit. However, change the weight/volume ratio by, for example, giving the drysuit diver twin tanks, and they will need to carry less weight on their belt. Because of the tanks, the weight has increased proportionately greater than the volume.
Where do I start?
Check your logbook. If you were diligent during your initial training, you should have noted the style and thickness of your exposure suit and how much weight you were carrying. This information will give you a starting point as to how much lead to carry.
If you’re not sure what you were carrying during your training, or if you’ve changed your diving environment, your exposure suit, or your body weight, some basic weighting guidelines may help. These are very much guidelines on how much weight to add based on your exposure protection. You may find that, when tested in-water, you are either slightly over (or under) weighted.
- Swimsuit or dive skin: 1-4 pounds (1 to 2 kg)
- 3mm wetsuits: 5 percent of your body weight
- 5mm wetsuits: 10 percent of your body weight
- 7mm wetsuits: 10 percent of your body weight plus 3 to 5 pounds (1 to 3 kg)
- Crushed neoprene drysuit*: 10 percent of your body weight plus 3 to 5 pounds (1 to 3 kg)
- Trilaminate drysuit*: 10 percent of your body weight plus 3 to 5 pounds (1 to 3 kg)
*Based on thin/lightweight undersuit base-layers. Thicker base-layers will require more weight.
For example, a 165-pound (75 kg) man wearing a 3mm full-length wetsuit may find a good starting weight as follows:
165 pounds (75 kg) x 5% = 7 to 8 pounds (3 to 4 kg)
Where possible, distribute your starting weight evenly for best trim. If you’re using a belt, position your weight on your hips and slightly forward on your body. Many BCDs have weight-integrated pockets where you can evenly distribute the weight. Taking a Peak Buoyancy course will help you understand correct trim and buoyancy as well.
Do a buoyancy check
Having made your best estimate of the correct weighting, it’s time to get in the water. To make a buoyancy check at the surface, follow a few steps:
- Ensure your mask is on and your primary regulator is in your mouth.
- Take a normal inhalation — not a maximum inhalation but a normal, deep breath.
- Completely deflate your BCD, keeping the low-pressure inflator hose in your hand to see if you are over-weighted and you begin to sink unexpectedly fast. If wearing a drysuit, vent your suit completely at the surface before beginning this procedure. When checking, keep the exhaust valve at the highest point and the opposing arm pointing down.
- If you’re properly weighted, you should hover with the water’s surface at or slightly above eye level, with your forehead brushing the surface.
- Demonstrate negative buoyancy by sinking past eye level as you exhale.
- If you can easily descend when exhaling, fin back to the surface and establish positive buoyancy. Reduce your weight and repeat the exercise until you’re just able to leave the surface gently when exhaling.
- If you remain positively buoyant, add a small amount of weight and repeat the exercise.
Ideally, you would do your weight check with a cylinder at ending pressure of 700 psi (50 bar). If you’re conducting your weight check with a full cylinder of 3000 psi (200 bar), add approximately 5 pounds (2 kg) for the air you’ll consume during the dive.
Consider your cylinder
Consider the size and construction of your cylinder before calculating your weight. An aluminum cylinder is more buoyant than the equivalent steel cylinder by approximately 3 to 5 pounds (2 to 4 kg). Remember to make this adjustment before entering the water.
Finally, once you’ve found your ideal weight with the equipment and exposure suit you’re wearing, write it down. Record each combination as you change gear and environments. While you should always check your buoyancy when moving to a new environment or you’ve not dived in a while, you’ll know what works as a reasonable starting weighting.
Dialing in your proper weighting when diving is a foundational skill. Test and record your weight in each new diving environment — you’ll have safer, happier and more comfortable dives.