Most divers will need to use weights to compensate for a wide range of factors, such as the diver's natural buoyancy characteristics, lung volume, the type of cylinder used and its capacity, exposure suit, accessories weight and displacement, the salinity of the water in which you're diving, and altitude. Many of these factors are variable.
The natural buoyancy of people varies quite a lot between individuals. Two people of identical build may have very different weight requirements. Factors such as bone weight, amount of fat and lung volume, even intestinal gas, can come into the equation. Lung volume has a considerable influence - to which advanced divers who use lung volume as part of their routine buoyancy control will testify. New divers, people making a dive after a lay-off, or apprehensive divers, tend to take deeper than normal breaths, filling their lungs and displacing more water, which increases their buoyancy. As they relax they take smaller breaths and should reduce the amount of weight they carry. Even experienced divers can find it hard to get down if they've just made a tiring surface swim.
The tank has quite an influence too. Many tanks are naturally negative - a diver using one of these with a shortie or dive skin may not need weights at all. Others my be quite buoyant. The air in a full cylinder may weigh in at 3-4 kg and as the tank goes from full to empty, the diver has to compensate for the increasing buoyancy.
Some exposure suits, like skins, have virtually no effect on buoyancy. Neoprene wet and dry suits have a lot of natural buoyancy which is affected by depth, which is reduced the deeper you dive. Over time, neoprene loses its buoyancy and so a diver needs to keep track of this and alter his weights accordingly. With membrane drysuits, the type and amount of underwear worn will be the principal influence on buoyancy.
Accessories can make quite a difference to a diver's weight. Many camera systems, lights and reels are quite negative. Divers need to be especially careful with heavy equipment they might put down or drop!
Salt water provides more lift than fresh. So ocean divers need more weight than inland divers. But, because the salinity of the ocean varies, so too do the weight requirements.
Altitude can also have an effect. Neoprene suits contain gas which will expand at the lower pressures encountered at altitude, and this will increase the natural buoyancy of the suit.
So we therefore use a combination of breath control, buoyancy control devices - and the unsung weight belt to control this multiplicity of factors, so that we can dive safely and easily.
At its most basic, a weight belt is just a strap and buckle on to which you slot lead bricks. The buckle is the most important feature.
Dropping a weight belt is an extremely effective self-rescue technique. You may ascend so fast you embolise, burst a lung, get a bend or head-butt the boat - but at least you'll be on the surface - most dead divers are found on the bottom with their weight belts on. Most diving injuries are treatable. Drowning is not. Better on the surface bent up like a pretzel with a chance of survival, than dead on the bottom. So it is vital that you can drop your weight belt quickly. That's why weight belt buckles have quick releases that should allow you to jettison them instantly with one hand.
A problem with most buckles is that in trying to fulfill the role of being instantly ditchable, they can release accidentally if you brush up against them or a weight shifts.
Because a self-releasing belt would be a great hazard in overhead diving activities (you'd just end up pinned to the ceiling), cave and cavern divers may not use quick releases. Wreck divers sometimes use a compromise - two cam buckles through which they thread the belt before penetrating. It is very unlikely that they will trip both buckles, especially if the buckles open in opposite directions. If you use this technique, ensure your buddy knows you will do it. On my belt, I pass the webbing over the first buckle so only the working buckle is visible to my buddy in normal open water use.
I like my weight belt to be clearly identifiable. In an emergency I don't want there to be any confusion. So I changed the cam buckle on my BCD to a Fastex so it would contrast. Alternative coloured webbing and releases and notched buckles can aid quick and positive identification.
The length of your belt should be adjusted to fit you. With cam buckles you don't have more than a couple of inches of spare webbing through the buckle - passing that extra length through the belt will slow down an emergency jettison. You don't normally need to cut the belt. Get rid of the excess by pulling the webbing attached to the buckle through the slots and feeding it through your weights. This will keep it out of the way and means the extra length is available if you need it (because you added more weights, a thicker suit or got fat). If you must cut the belt, do it with the weights in place or your belt will end up short.
Some weight belts use pouches to contain the weights. Block weights or packets of shot can be used. A big advantage is that weights can be removed or added in seconds. I like these belts for trainees because I can keep removing weights as they relax, without having to leave the pool. They can be an excellent choice for traveling divers as they allow you to use the belt you are familiar with. A disadvantage is that you may have to place some weights in the small of your back, which can be uncomfortable and cause the belt to spin around your waist.
Shot weight belts are very comfortable. They mould around your body like a bean bag. A Dacor rep. once invited me to drop a fully-loaded belt on to my foot. Calculating that the ensuing lawsuit would have paid for my trip to the Las Vegas dive show, I did it. No pain, no lawsuit, and definitely no gain.
Shot belts work best once you know how much weight you will need. They are tricky to adjust. Some divers weight them for fresh water and attach small block weights for sea diving, rather than adjust the shot itself. If you choose a shot belt with mesh drainers, make sure the shot isn't so small it falls out - it has happened!
To account for suit compression during descents and ascents, some belts use spring-loaded buckles, bungees in the webbing, or are elasticated to automatically compensate for these changes.
Some alternatives to conventional weight belts are weight systems built into BCDs. These use breakaway pockets as a rule, into which block weights or packets of shot are placed. Some divers place all their weight in here, others distribute the weight between these and conventional belts. They can then drop part of their weight system, which means they will surface in an emergency, but at a slower rate than if they ditch everything. Be aware that integrated systems can be very heavy to manhandle, and care must be taken to ensure a clean jettison.
Weights are not just for getting you down. They also form part of your trim control, allowing you to be not just neutrally buoyant, but to hang at an angle that suits you. That might be horizontal, but it could also be feet-up to avoid disturbing silt or kicking coral; or feet-down while working under a boat. The waist is not, therefore, always the best place for all of your lead. Harnesses are available that allow you to move your weights - and centre of balance - during the dive to suit your needs of the moment. Ankle weights can also be helpful. Some divers attach weights to their tanks.
When it comes to choosing your lead, coated weights are more environmentally friendly and won't leave deposits on your suit. Also, think through how your weighting requirements may alter. I like to use a pair of 6 lb hip weights to begin with. These are the absolute minimum I need with a cold water wetsuit or with my drysuit. I then use 2 lb weights to adjust for all the other factors. This allows me to dive with the absolute minimum of weight possible. It is amazing how just a little extra weight can completely throw your buoyancy and trim control.
With conventional block weights, use retainers. Sliding weights can jam or can open releases. I once used a borrowed belt that did this: the belt fell off and I made a very fast ascent from 15 m that scared the bejesus out of me. I like to have the weights near the front of my body, so I usually stack the smaller weights on top of my hips. This helps keep me on an even keel, and stops the belt rotating.
If you want, you can choose shaped weights. Hearts are bad enough, but grenades... I have visions of beaches being cleared and the bomb squad abseiling from helicopters because some nitwit left his belt behind.
I'm happy to put D-rings on to my belt for carrying accessories. I use piston clips on the accessory, not the belt. Snap hooks can snag and lock on to shotlines, cables and other debris found in wrecks. I don't hang gear off my belt if I'm going into a tight wreck; it can be difficult or impossible to untangle.
Weight belts may lack the glamour of shiny titanium regulators and
military-black ballistic BCs (for some!), but spare a thought when you choose
them. They can contribute a surprising amount to a comfortable and safe dive.
