Published in Public Safety Diving Monthly, November 2010
Written by Jessica Harned
Public Safety Technical Advisor
Diving Unlimited International, Inc.
Often times the question arises as to how much weight a diver should wear when using a drysuit. This can certainly be an important factor in having an enjoyable dive. If the diver is weighted too little, he/she could be fighting to stay submerged especially during the safety stop. If the diver is over-weighted, he/she could have trouble maintaining neutral buoyancy throughout the dive. Either way, the diver could become frustrated and exhausted. Additionally, being improperly weighted could result in a potentially unsafe condition.
When determining how much weight to wear with a drysuit, there are many factors to consider. The diver can start with a weighting equal to 10% of their body weight. Adjustments will need to be made as there are a few things that will affect buoyancy including water type, insulation thickness, and tank material. After compensating for these differences, it is important for a diver to perform a neutral buoyancy weight check. If the appropriate amount of weight is added and the diver is still having trouble descending, he/she can troubleshoot to avoid being over-weighted.
The first thing the diver needs to determine is if they are diving in freshwater or saltwater. Because saltwater is more dense than freshwater, the diver will need approximately 2-4 lbs more when diving in saltwater than in freshwater. Secondly, the thickness of insulation the diver is wearing underneath the drysuit will affect buoyancy. The diver will be more buoyant with an increase in the thickness of undergarment. For example, if the diver is going from a 150 wt undergarment to a 300 wt undergarment, they would want to add approximately 2 lbs to their weight system. Finally, the use of aluminum versus steel tank will influence the diver’s buoyancy. Aluminum tanks become positively buoyant once the air is used. Therefore, a diver diving with an aluminum tank who is neutrally buoyant with a full tank would need to add approximately 5lbs to compensate for the end of the dive.
Once the above mentioned adjustments are made, it is important for the diver to perform a neutral buoyancy weight check. To do a proper weight check, the diver should enter the water where it is too deep to stand, fully geared with regulator in mouth. Once the diver is in position, he/she should fully deflate the BCD and drysuit and breathe normally. The diver is correctly weighted for neutral buoyancy if he/she floats at eye level vertically and sinks slowly when he/she fully exhales. If the diver sinks very quickly right away, he/she is over-weighted and needs to remove weight. However, if the diver floats at the surface he/she is under-weighted and may need to add weight. It is recommended to make weight adjustments in small increments. For example, add or remove 2-3 lbs at a time and repeat weight check. Remember, once the diver has established proper weighting and is floating at eye level, if diving with an Aluminum tank, add 5lbs to compensate for the end of the dive when he/she will have less air in the tank.
If the diver has added weight and continues to have difficulty descending, he/she can try a couple of things before adding even more weight. The most common problem is the diver not getting all of the air out of the drysuit when trying to descend, so he/she is fighting against the air to try to get down and compensates for that by adding more weight. This causes the diver to be over-weighted throughout the entire dive. The diver should be sure to fully deflate the drysuit. In order to properly vent excess air from the drysuit prior to entering the water, the diver should open drysuit valve fully, place a finger under the neck seal and squat down. While still squatting, remove his/her finger from the neck seal. Then, stand up. The diver should remember, after he/she vents the drysuit, any manipulation of the seals will put air back in the drysuit.
In addition to excess air, another possible factor in being unable to descend is that some new drysuit divers have a tendency to kick their feet on the surface. If the diver is kicking his/her feet while trying to descend, he/she will continue to kick themselves up to the surface. The diver should be sure to keep their legs still if he/she is performing a feet first descent.
Finally, it is also possible the diver is not exhaling completing. A person’s lungs hold 8lbs of lift. Therefore, if a diver is not exhaling, his/her lungs could be buoying him/her up.
If the above mentioned techniques are followed, the diver should be properly weighted for diving in a drysuit. Once the weighting has been established, the diver should record what weight they wore. The diver recording his/her weight will allow for use with future dives and the neutral buoyancy weight check may not need to be repeated as long as all the factors remain the same. If there is a change in conditions (insulation change, water type, and/or tank), it is recommended to repeat the weight check.
Now that you know how to properly weight a diver for diving in a drysuit, where do you put that weight? There are a variety of options for weight systems. For the most part, it comes down to personal preference and comfort.
Below is a list of weight systems most commonly used:
Traditional Weight Belt – Weight belts are worn around the waist. They do a good job of holding weights, but could be uncomfortable and may need adjustment at depth. Depending on the person, the weight belt could have a tendency to slip. For the most part, the weight belt can only sit at the waist and does not have placement adjustability.
Weight-Integrated BC – The weights in a weight-integrated BC are worn in the BCs quick release system. Adjustability is limited to BC adjustability. Some find that this system holds the weight too high on the body.
Weight and Trim System – The weight and trim system is worn as a harness system with full adjustability. This system can be adapted for a person’s individual buoyancy characteristics.
Ankle Weights – This weight system is worn on ankles. Only minimum weight should be used. This system is used in addition to a main weight system to get weight lower down. Divers should be aware that wearing ankle weights may make it harder to kick.
Tank Weights – These weights added to the tank. There are a few methods to attach tank weights. Some are integrated into the tank boot. Others are attached to the tank band. Some folks even attach the weights to the neck at the base of the valve. Only minimum weight should be used. This system is used in addition to a main weight system