Divers wear
weighting systems,
weight belts or
weights, generally made of
leadLead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metals. Lead has a bluish-white color when freshly cut, but tarnishes to a dull grayish color when exposed to air...
, to counteract the
buoyancyIn physics, buoyancy is the upward force that keeps things afloat. The net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body. This force enables the object to float or at least seem lighter....
of other
diving equipmentThe fundamental item of diving equipment used by divers is the SCUBA equipment, such as the Aqualung or Rebreather. There are other important pieces of equipment that make diving safer, more convenient or more efficient.-Scuba life support:...
, such as
diving suitA diving suit is a garment or device designed to protect a diver from the underwater environment. Modern diving suits can be divided into two kinds:* "soft" or ambient pressure diving suits - examples are wetsuits, dry suits, semi-dry suits and dive skins...
s and aluminium
diving cylinderA diving cylinder, scuba tank or diving tank is used to store and transport high pressure breathing gas as a component of SCUBA . It provides gas to the SCUBA diver through the demand valve of a diving regulator.Diving cylinders typically have an internal volume of between and a maximum pressure...
s.
Providing the weights have a method of quick release, they provide a useful rescue mechanism: they can be dropped in an emergency to provide instant buoyancy which may return the diver to the surface. Dropping weights increases the risk of
barotraumaBarotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding fluid....
and
decompression sicknessDecompression sickness describes a condition arising from the precipitation of dissolved gasses into bubbles inside the body on depressurisation...
due to uncontrollable ascent to the surface.
Divers wear
weighting systems,
weight belts or
weights, generally made of
leadLead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metals. Lead has a bluish-white color when freshly cut, but tarnishes to a dull grayish color when exposed to air...
, to counteract the
buoyancyIn physics, buoyancy is the upward force that keeps things afloat. The net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body. This force enables the object to float or at least seem lighter....
of other
diving equipmentThe fundamental item of diving equipment used by divers is the SCUBA equipment, such as the Aqualung or Rebreather. There are other important pieces of equipment that make diving safer, more convenient or more efficient.-Scuba life support:...
, such as
diving suitA diving suit is a garment or device designed to protect a diver from the underwater environment. Modern diving suits can be divided into two kinds:* "soft" or ambient pressure diving suits - examples are wetsuits, dry suits, semi-dry suits and dive skins...
s and aluminium
diving cylinderA diving cylinder, scuba tank or diving tank is used to store and transport high pressure breathing gas as a component of SCUBA . It provides gas to the SCUBA diver through the demand valve of a diving regulator.Diving cylinders typically have an internal volume of between and a maximum pressure...
s.
Providing the weights have a method of quick release, they provide a useful rescue mechanism: they can be dropped in an emergency to provide instant buoyancy which may return the diver to the surface. Dropping weights increases the risk of
barotraumaBarotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding fluid....
and
decompression sicknessDecompression sickness describes a condition arising from the precipitation of dissolved gasses into bubbles inside the body on depressurisation...
due to uncontrollable ascent to the surface. This risk can only be justified when the emergency is life threatening. Very often divers take great care to ensure the weights are not dropped accidentally, and many heavily-weighted divers arrange their weights so subsets of the total weight can be dropped individually, allowing for a somewhat more controlled emergency ascent.
The quantity of lead weight required is determined by the overall positive buoyancy of the diver, which depends on the diver's body composition, buoyancy of other diving gear worn (especially the
diving suitA diving suit is a garment or device designed to protect a diver from the underwater environment. Modern diving suits can be divided into two kinds:* "soft" or ambient pressure diving suits - examples are wetsuits, dry suits, semi-dry suits and dive skins...
), water
salinitySalinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
, and water temperature. It normally is in the range of 2 kg / 4 pounds to 15 kg / 33 pounds.
The weights are generally made of
leadLead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metals. Lead has a bluish-white color when freshly cut, but tarnishes to a dull grayish color when exposed to air...
because of its high
densityThe density of a material is defined as its mass per unit volume. The symbol of density is ρ .- Formula :Mathematically:where: is the density, is the mass, is the volume....
, low cost, and resistance to
corrosionCorrosion is the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a...
. The lead can be cast in blocks, cast block with gaps for straps or shaped as pellets often named "shot".
Weight belt
Weight belts are the most common weighting system currently in use of recreational diving. Weight belts are often made of tough
nylonNylon is a generic designation for a family of synthetic polymers known generically as polyamides and first produced on February 28, 1935 by Wallace Carothers at DuPont...
, but other materials such as
rubberNatural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene, which can also be produced synthetically...
can be used. Weight belts are generally fitted with a quick release buckle to allow the dumping of weight rapidly in an emergency.
A belt made of rubber is called a
Marseillaise belt. These belts are popular with freedivers as the rubber contracts on descent as the
diving suitA diving suit is a garment or device designed to protect a diver from the underwater environment. Modern diving suits can be divided into two kinds:* "soft" or ambient pressure diving suits - examples are wetsuits, dry suits, semi-dry suits and dive skins...
and lungs are compressed, keeping the belt tight throughout the dive.
The most common design of weight used with a belt consists of plain, rectangular
leadLead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal, also considered to be one of the heavy metals. Lead has a bluish-white color when freshly cut, but tarnishes to a dull grayish color when exposed to air...
blocks with two slits in them threaded onto the belt. These blocks can be coated in
plasticPlastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials suitable for the manufacture of industrial products...
, which further increases corrosion resistance. These weights are often marketed as being less abrasive to wetsuits.
Some weightbelts contain pouches to contain lead weights or round
lead shotLead shot is a collective term for small balls of lead. It is used primarily as projectiles in shotguns, but is also used for a variety of other purposes...
: this system allows the diver to add or remove weight more easily than with weights threaded onto the belt. The use of shot can also be more comfortable, as the shot moulds to the diver's body. Weight belts using shot are called
shot belts. Each shot pellet should be coated to prevent corrosion by sea water, as use of uncoated shotgun shot here for sea diving would result in the lead corroding into powdery lead chloride.
BCD Integrated weights
These are stored in pockets built-in to the buoyancy compensator. Often a
velcroVelcro is a brand name of fabric hook-and-loop fasteners. It consists of two layers: a "hook" side, which is a piece of fabric covered with tiny hooks, and a "loop" side, which is covered with even smaller and "hairier" loops. When the two sides are pressed together, the hooks catch in the loops...
flap holds the weights in place. The weights may also be contained in zippered or velcroed pouches that slot into special pockets in the BCD. They have handles, which must be pulled to drop the weights in an emergency or to remove the weights when exiting the water. Some designs also have smaller "trim pouches" located higher in the BCD, which may help the diver maintain neutral attitude in the water. Trim pouches typically can not be ditched quickly, and are designed to hold only 1-2 pounds (0.5-1 Kilo) each. Many integrated systems cannot carry as much weight as a separate weight belt: a typical capacity is 6 kg per pocket, with two pockets available.
Weight harness
A weight harness consists of a belt around the waist holding pouches for the weights with shoulder straps for extra support and security. Often a velcro flap holds the weights in place. They have handles, which must be pulled to drop the weights in an emergency or to remove the weights when exiting the water.
Backpack weight pouch
Some rebreathers (e.g. the
Siebe Gorman CDBAThe Clearance Divers Breathing Apparatus is a type of rebreather made by Siebe Gorman in England.The Royal Navy used it for many years. It was for underwater work rather than for combat diving. The main oxygen cylinders are on the diver's back. The oxygen cylinders at the front of the diver are...
) have a pouch full of lead balls each a bit over an inch diameter. The diver can release them by pulling a cord.
Fixed weights
In addition to the weight that can be dropped easily ('ditched'), some divers add additional fixed weights to their gear, either to reduce the weight placed on the belt, which can cause lower back pain, or to shift the diver's center of mass to achieve the optimum position in the water.
- Tank weights are attached to the diving cylinder to shift the center of mass backward and upward or downward, depending on placement.
- Ankle weights, which are typically 1 lb./0.5 kg of shot, are used to counteract the positive buoyancy of diving suit
A diving suit is a garment or device designed to protect a diver from the underwater environment. Modern diving suits can be divided into two kinds:* "soft" or ambient pressure diving suits - examples are wetsuits, dry suits, semi-dry suits and dive skins...
leggings, made worse in drysuits by the migration of the internal bubble of air to the feet, and positively buoyant finsSwimfins, swim fins, fins or flippers are worn on the foot or leg and made from finlike rubber or plastic, to aid movement through the water in water sports activities such as swimming, bodyboarding, bodysurfing, kneeboarding, riverboarding, and various types of underwater diving.Scuba divers use...
. Some divers prefer negatively buoyant fins. The additional effort needed when finning with ankle weights increases the diver's gas consumption.
- Metal backplates
thumb|right|A stainless steel backplate, wing and manifolded twinsetA backplate and wing , is a type of buoyancy compensation device worn by scuba divers...
made from stainless steel, which may be used in some Buoyancy compensators, move the center of mass upward and backward.
- Steel dive cylinders are preferred over aluminium cylinders by some divers—particularly cold water divers who must wear a suit that increases their overall buoyancy—because of their negative buoyancy, and because they shift mass upward and backward. Most steel tanks stay negatively buoyant regardless of whether they are full or empty, aluminium tanks become positively buoyant as the gas they contain is used.