You might be asking why? Why should a diver be “properly” weighted and neutrally buoyant? An over-weighted diver will typically rationalize the weight they are using by adding air to their Buoyancy Compensator Device (BCD). What most over-weighted divers do not realize is they are exerting additional effort throughout the dive by dragging around the unnecessary amount of weight they are wearing; which in turn increases the diver’s rate of air consumption, shortening the dive, and adding post dive fatigue. An over-weighted diver might find it troubling to stay off the bottom and accidentally damage the bottom contour of the environment they are in whether it’s a beautiful reef, wreck, or even disturb a critters home in the sand. So what does it mean to be “properly” weighted? When properly weighted, the diver should be able to comfortably hover at a safety stop (at the shallow depth of three to six metres or 10 to 20 feet) without popping to the surface, without exerting any effort to stay down, and without struggling to kick to maintain neutral buoyancy at the end of a dive. With the cylinder now near-empty, the diver should need little to no air in the BCD to hover motionless at the safety stop depth.
Now you might be asking, how do I get properly weighted? Simply put, most often proper weighting is determined through a process of trial-and-error experimentation. To start, you should complete a weight check by completing the following steps:
- Enter the water wearing all gear and an estimated amount of starting weight. This amount can be the weight you think you will need or the estimated number advised by a dive professional.
- With the regulator in your mouth, take and hold a normal to full breath.
- Deflate your BCD – If you are “properly” weighted you should float at eye level and when you exhale you should descend.
Tip: remember to keep your legs still and do not kick! Any kicking motions will move you upward in the water obstructing your ability to determine the true amount of weight required.
- Add or subtract weight as necessary until you float eye level in the water; vertically at the surface.
It’s worthwhile for a diver to complete or repeat the steps above upon surfacing after a dive. The reason why it’s a good idea to complete a weight check after a dive is to make up for the buoyancy shift your cylinder may have during the dive. When a cylinder is full at the start of the dive, it may be heavier versus a near-empty cylinder at the end of a dive.
For example; see the chart below for a commonly used cylinder in salt water (Luxfer AL80)
|Service Pressure||Capacity||Weight||Full||½ Full||500 psi||Empty|
|3000 psi||77.4 cf||31.5 lb||-1.7 lb||+1.3 lb||+3.2 lb||+4.2 lb|
The data above shows when a cylinder is full it is 1.7lbs negatively buoyant. When it’s near-empty with 500PSI remaining; it will be positively buoyant by 3.2lbs.
It’s important to conduct a weight check at the end of the dive to compensate for any buoyancy shift your cylinder may take during your dive to avoid becoming positively buoyant towards the end of the dive.
Once the proper amount of weight is determined, the diver should make note of this number and apply it for future dives in the same exposure protection, gear configuration and environment. In the event any of these factors change; like going from fresh water to salt water (increased buoyancy in salt water) weight requirements will change. Finding your proper weight requirements and completing weight checks more often will reduce additional drag in the water, increase your air consumption rate and in turn increase your dive times. More time in the water often leads to more things to see and more fun to be had! Diving properly weighted will also allow you to glide effortlessly through the water and avoid damaging the underwater world.
Take the next step of fine tuning your buoyancy by taking the SDI Advanced Buoyancy course!
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