The subtle weight brag. As scuba instructors here in Omega Divers we hear it all the time, and it goes something like this: Guide: “How much weight do you need?” Diver: “Oh, I don’t need any. I just use my lungs.” While sometimes the diver is correct (usually in the case of a waif-like female, or an extremely muscle-bound man), more often than not, these people end up being the divers finning downwards at during their safety stops duck diving to start the dive, or sneaking weight from the dive guide. Somehow, these divers have translated the concept of not being overweighted to the mistaken belief that the less weight you use, the better diver you are; that adding air to your BCD during descent is undesirable. Nothing could be further from the truth. In fact, underweighting can be just as dangerous as severe overweighting. Here are some tips on getting your weight just right.
1. Understand That Equipment and the Environment Will Both Affect Your Buoyancy
Wetsuits, tanks, and even accessories and tools (like cameras) will affect your buoyancy. Whenever you change one of these items, it is necessary to complete a buoyancy check to determine the effect of the new item on your buoyancy. The last thing you want is to don your nice new wetsuit, and then have a miserable dive because the neoprene is very buoyant (as it is when it is new). The salinity of the water will also affect a divers buoyancy. The obvious example is buoyancy in fresh water vs salt water, but keep in mind that the salinity of the ocean may also vary in different regions of the world, and you may need slightly more or less weight depending upon your dive location.
2. Conduct a Buoyancy Check Before Diving
Don’t guess! Test your buoyancy in a new location or whenever diving with a new piece of gear. Most of the time, diver’s have a limited number of dives on vacation, and it is worth the effort to make every dive comfortable and safe. In fact, most dive operators will be thrilled if you ask to wade into the ocean or hop of the pier before your first dive to double check your weighting. The general rule of thumb for proper weighting is that with all of his gear in place (including tools and accessories), with a nearly empty tank, a diver who completely empties his BCD and holds a normal breath should float at eye level. When he exhales he should sink. As a professional, I have observed that many divers seem to forget the “nearly empty tank” portion of this procedure, and conduct the test with a full tank. Guess what? As the tank empties, it will become positively buoyant. If you can empty your BCD, hold a normal breath, and float at eye level at the beginning of the dive, you will not have enough weight to comfortably maintain neutral buoyancy at the end of the dive. The problem here is that most dive shops are not in the practice of providing nearly empty tanks for buoyancy tests. There are two solutions to this:
Conduct the buoyancy test with a full tank as outlined above, and then add the appropriate amount of weight to offset the buoyancy swing of your tank as it empties. Of course, this will depend upon the type of tank you use and the type of water you dive in. Time for some research.
Conduct the buoyancy test as outlined above with a full tank, but instead of checking that you float at eye level, check to see that you sink slowly while holding a normal breath.
3. Double Check Your Buoyancy at the End of a Dive
Once you have successfully completed a dive with enough weight to keep you comfortably below water the entire time, it is a good idea to double check your weighting at the end of the dive. To do this, purge your regulator gently until you are down to about 500 psi or 30 bar. Then, on the surface, conduct a buoyancy check before exiting the water. Do you float at eye level and sink when you exhale? Bingo! Perfect? Do you have to swim to get down? Float like a balloon on the surface? Add a little weight on your next dive. Do you still sink while holding your breath? Remove a few pounds and try again on the next dive.
4. Adding a Small Amount of Air to Your BCD During Descent Is Good
Many divers seem pleased that they can descend and arrive at the planned depth without adding air to the BCD. Again, this is not a desirable situation. Because most tanks become more positively buoyant throughout a dive, divers who do not need to add air to their BCDs during descent to establish neutral buoyancy are likely to be underweighted. Confused? Click here to understand more about the proper steps for a controlled descent.
5. But I Don’t Need to Add Air During Descent. I Am Fine at the End of the Dive!
We know that these people exist, we dive with them all the time. These are the people who have exceptionally low air consumption rates, and surface with at least half (sometimes more) of their air remaining. Yes, they can be perfectly neutral during their safety stops, and they don’t go flying to the surface like awkward buoys at the end of the dive. The reason? Their tanks have not become positively buoyant because they haven’t breathed enough gas to cause a buoyancy swing*. The problem with this habit is that it does not prepare divers for an emergency situation, when they are low on gas because they over-breathed a tank due to a stressful situation, surface with less gas than normal due to an unforeseen occurrence, or are forced to share air with another diver. In these situations, such a diver will have trouble staying down, and of course, these are the situations when having enough weight can make a big difference between an annoying situation and an uncontrolled ascent to the surface. Do you really want to be fighting buoyancy at an emergency decompression stop after accidentally exceeding a no-decompression limit and blowing through more air than you normally do? Do you want to be fighting to stay down while sharing air with a buddy? No. Plan for the worst case scenario: a low tank and increased breathing rates due to stress. * Of course there are exceptions to every rule. In this case they are rare.
6. The More Tanks You Carry the More Weight You May Need
Technical divers, who use doubles and stage tanks, may need to carry a little more weight than they normally would with a single tank. The reason for this is that they must offset the buoyancy swing of all the tanks they carry. In this case, conducting a proper buoyancy test with nearly empty tank can be indispensable. Remember, that even tec divers following the rule of thirds may find themselves in a emergency situation in which the tanks are much lower than planned, and blowing a decompression stop can be deadly.
The Take- Home Message About Proper Weighting for Scuba Diving
Diving with less weight does not make you a better diver. Diving with the correct amount of weight does. We will take a slightly overweighted diver over a slightly underweighted diver any day. Slight overweighting is correctable: just add a little air to the BCD. Underweighting is not. To be safe on dives, proper weighting is key. Overweighting can cause a diver to plummet to the floor, risking panic, ear damage, and the inability to float on the surface. Underweighting can cause uncontrolled ascent, skipped safety stops, and exertion underwater. Take the time to get your weighting right and you can avoid many potentially dangerous situations and dive more comfortably. Finally, please don’t brag about using less weight than other divers. This can create the impression that using less weight is better, and as discussed above, this is not always the case.