Diving weighting system
Encyclopedia
Divers wear weighting systems, weight belts or weights, generally made of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

, to counteract the buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

 of other diving equipment
Diving equipment
Diving equipment is equipment used by underwater divers for the purpose of facilitating diving activities. This may be equipment primarily intended for this purpose, or equipment intended for other puprposes which is found to be suitable for diving use....

, such as diving suit
Diving suit
A diving suit is a garment or device designed to protect a diver from the underwater environment. A diving suit typically also incorporates an air-supply .-History:...

s and aluminium diving cylinder
Diving cylinder
A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport high pressure breathing gas as a component of a scuba set. It provides gas to the scuba diver through the demand valve of a diving regulator....

s. The diver must be weighted so that he is negatively buoyant by default, and then adjust the amount of air in his Buoyancy Compensation Device (BCD) in order to achieve neutral or positive buoyancy as needed.

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 barotrauma
Barotrauma
Barotrauma 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 sickness
Decompression sickness
Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization...

 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 suit
Diving suit
A diving suit is a garment or device designed to protect a diver from the underwater environment. A diving suit typically also incorporates an air-supply .-History:...

), water salinity
Salinity
Salinity 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 lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

 because of its high density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

, low cost, and resistance to corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

. 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 nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...

, but other materials such as rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...

 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 suit
Diving suit
A diving suit is a garment or device designed to protect a diver from the underwater environment. A diving suit typically also incorporates an air-supply .-History:...

 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 lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

 blocks with two slits in them threaded onto the belt. These blocks can be coated in plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

, 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 shot
Lead shot
Lead shot is a collective term for small balls of lead. These were the original projectiles for muskets and early rifles, but today lead shot is fired primarily from shotguns. It 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
Lead chloride
Lead chloride may refer to:* Lead chloride , mineral name: cotunnite.* Lead chloride...

.

BCD integrated weights

These are stored in pockets built-in to the buoyancy control device. Often a velcro
Velcro
Velcro is the brand name of the first commercially marketed fabric hook-and-loop fastener, invented in 1948 by the Swiss electrical engineer George de Mestral...

 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 kg) 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 rebreather
Rebreather
A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...

s (e.g. the Siebe Gorman CDBA
Siebe Gorman CDBA
The 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
    Diving suit
    A diving suit is a garment or device designed to protect a diver from the underwater environment. A diving suit typically also incorporates an air-supply .-History:...

     leggings, made worse in drysuits by the migration of the internal bubble of air to the feet, and positively buoyant fins
    Swimfin
    Swimfins, 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
    Backplate and wing
    thumb|right|A stainless steel backplate, wing and manifolded twinsetA backplate and wing , is a type of Scuba harness with buoyancy compensation device worn by scuba divers. Unlike most other BCDs, the backplate and wing is a modular system, in that it consists of separable components...

    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.
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