Weights and weight systems: what they are and how they differ.

Why divers carry weight

PADI explains that most people float, so divers carry weight to offset the buoyancy of their body and their exposure suit. It adds that spreading the weight well helps with fine buoyancy control. Exactly how much weight a diver needs, and how to check it, is taught and practised in training with an instructor. This page does not give amounts or methods.

The main systems

PADI names three main approaches:

PADI lists a quick-release feature as standard, so that a diver can drop enough weight to float. It also says dry-suit divers may benefit from combining an integrated system with a belt to spread the weight more evenly.

Dry-suit maker DUI says the conventional belt is still the most widely used system, especially in rental equipment. That is the maker's description.

Other systems Wikipedia describes

Wikipedia (secondary) adds several more:

• Weight harnesses: pouches carried lower on the body, held by shoulder straps.
• Clip-on weights attached to harness webbing.
• Fixed trim weights such as cylinder weights, V-weights and backplate weights.
• Ankle weights, which Wikipedia says help correct a head-down position in the water but make finning harder.
• Rubber "Marseillaise" belts, which stay snug as a suit compresses and are popular with freedivers.

Wikipedia also says the capacity of integrated BCD pockets is usually lower than a belt's, which can matter for divers in thick cold-water dry suits.

Ditchable and fixed weight

Wikipedia separates weight into two kinds. Ditchable weight can be released in an emergency to gain positive buoyancy, which carries its own risk of an uncontrolled ascent. Fixed weight is secured firmly and is typical in surface-supplied diving. When and whether to drop weight is an emergency skill taught in training and is not covered on this site.

Release mechanisms in BCD pockets

SSI says integrated weight pockets include quick-release mechanisms. Scuba Diving magazine, in a page we could see only as a search summary, describes three kinds of release used on integrated systems: mechanical clips (often made of Delrin), Velcro and ripcords. The same source says Velcro-secured pouches are being phased out because Velcro weakens over time and can let go by accident, that ditchable pouches are the most common integrated design, and that drop-down designs keep the pouch attached to the BCD after release. We could not confirm those statements on the full page.

More on BCD styles is on BCDs.

What the weights are made of

PADI describes lead weights in several sizes, either moulded for a belt, plain or vinyl-coated, or as lead shot in pouches.

Wikipedia (secondary) says lead is the standard material because it is dense, cheap and resists corrosion, but that its toxicity is a concern for users and the environment, especially lead shot in fabric bags. It names bismuth, tungsten, and iron or stainless steel as alternatives, noting that iron and steel are less dense.

Weight and the rest of the kit

The weight a diver carries is tied to the rest of the kit. PADI links it to the buoyancy of the exposure suit (see wetsuits and dry suits), retail guides, seen only as search summaries, say steel and aluminium cylinders behave differently as they empty (see cylinders), and Wikipedia says a steel backplate can replace some ballast. How a change of kit affects weighting is taught in training, not on this page.