March 3, 2010

Estimating the Right Amount of Weights for Scuba Diving

perfect divers weight

Being properly weighted is one of the key elements in scuba diving. Through a few simple steps you can make your dive easier, longer and safer. Let’s run though the benefits of being properly weighted and how it’s done.

Being Underweight:

If you’ve underestimated the weights you need to carry, you may not know it at the beginning of the dive. As we dive, our tank becomes lighter due to our air consumption by as many as 2kg. An Aluminum Tank will be more buoyant throughout the dive and you may find it hard to stay underwater with an empty BCD. That means kicking downwards to stay underwater, and risking popping up to the surface in shallow water.

Being overweighted:

Over estimating the amount of weights you need is a much more common mistake. most divers prefer to or unknowingly carry more weights than needed. That creates a few problems and hazards:

1. Heavy weights (on a belt) drug the lower part of the buddy down, while an inflated BCD pulls the upper body up

A. You’re more likely to brush you fins or legs against the reef, or stir up the sand, thus risking yourself and damaging the environment.

B. Being less Hydrodynamic you increase drug and effort, wasting air which eventually leads to a shorter dive.

2. Having to inflate your BCD at depth means that you have to constantly adjust your BCD’s volume when changing depth, making buoyancy control harder. Air volume changes in the BCD pretty dramatically in the shallows, so you better not relay on a full BCD to support you in shallow water.

Bad Buoyancy- Not Using Your BCD Can Couse a Lot of Damage to the Environment

Example of Bad Buoyancy

How do we estimate the weights we need for our dive?

There are a few factors that contribute to our buoyancy when scuba diving:

1.Estimating weights needed with different exposure suits ( Salt Water):

Weight estimation lbs Weight Estimation kg Exposure Suit Type
  Add 0.5-2kg Add 4lbs Swimsuit or skin
About 5% Buddy Weight About 5% Buddy Weight 3mm one piece or shorty
About 10% Buddy Weight About 10 % Buddy Weight 5mm one or two piece
About 10% Buddy Weight + 4 to 5 lbs About 10% Buddy Weight  + 2kg  7mm two piece
About 10% Buddy Weight + 3 to 5 lbs About 10% Buddy Weight  + 1.5 to 2 kg Shell dry suit with light undergarment
About 10% Buddy Weight + 7 to 14 lbs About 10% Buddy Weight  +3 to 6 kg Shell dry Suit with heavy undergarment
Additional 2 lbs Additional 1 kg Add hood and boots

2. Estimating weights differences due to changes in water salinity:

Salt water is denser than fresh water. It simply has more particles in it. When moving from fresh water to salt water, with the same equipment, we tend to float and need to add weights according to this estimation:

Body weight Weights to add ( salt water)
100-125lbs/45-56kg 4lbs/2kg
126-155lbs/57-70kg 5lbs/2.3kg
156-186lbs/71-85kg 6lbs/3kg
187-217lbs/86-99kg 7lbs/3.2kg

3. Estimating weights changes due to tank/cylinder type:

We can choose to dive with tanks made of Aluminum (AL) OR Steel (ST), and in various volumes. Different tank types float differently. We want to be able to stay neutrally buoyant especially at the end of the dive, when our tanks are emptied and lighter.

Cylinder type and volume Weight change
AL80 + 4.4lbs/ 2kg
AL100 +3.0lbs/1.4kg
St HP80 -2.5lbs/1.1kg
St HP100 -1.0lbs/0.5kg
St HP120 0

Steel cylinders are heavier than Aluminum ones and don’t tent to float and contribute to your buoyancy when diving.

Once you’ve estimated the weights needed, its time to perform buoyancy check:

Remember, it’s recommended to perform a quick buoyancy check prior to diving after one of the followings:

1. You haven’t been diving for a while (gained a beer belly lately?)

2. Wearing new items or different equipment than those used before

3. Moving from fresh to salt water

5 step buoyancy check:

1. Enter the water fully equipped

2. At water to deep to stand in, empty your BCD fully.

3. Hold a normal breath, stay vertical and motionless

4. Add/subtract weight till you float at eye level following steps 1-3

5. Exhale and you should be able to slowly sink

Remember. Due to our air consumption our cylinders weigh 5lbs/2kgs less at the end of the dive. Add those extra weights prior to diving in order to be able to complete a safe and comfortable safety stop at the end of your dive.

PADI Advenaced Open Water Course- PPB

PADI Advanced Open Water Course- PPB. Improve your buoyancy

Weights estimation prior to scuba diving is an important step towards becoming a better, safer scuba diver. Estimating the right amount of weights for scuba is often neglected and both the diver and the environment are left to deal wit the consequences.

Once you’ve estimated and checked the weights you need for diving you’ll find it a lot easier to move about, saving air and getting closer to the reef without messing it all up. If you’re still struggling with your buoyancy, or use air way faster than you dive buddies, consider a pick performance buoyancy class to fine tune your buoyancy skills.

Category: Safety