Pony Bottle Buoyancy Specifications

A diver who chooses to scuba dive must take his air with him. For longer, deeper dives, a scuba diver will take two full size tanks on his back. But while a diver may take only one tank on a shorter dive, he should also have a backup air supply in case the tank runs out of air or fails in some way. This backup air supply can be carried in a smaller tank called a pony bottle.

  1. Pony Bottle Use

    • A pony bottle is used for short dives where weight out of the water is a concern. It provides an emergency source of air should the air in your tank run out for a short dive. Longer dives require more backup air, so a pony bottle is not terribly useful. The pony bottle attaches to your regular tank using a bracket or harness so that it is readily available in an emergency.

    Pony Bottle Specifications

    • Pony bottles are most often made out of steel or aluminum. Steel bottles offer a slight boost in buoyancy, but are often much more expensive than aluminum bottles. They range in size from about 13 cubic feet to more than 40 and can weigh from around six pounds to more than 20 pounds when full. They are generally about 4 to 5 inches in diameter and 12 to 25 inches tall.

    Buoyancy Empty

    • The empty buoyancy of a pony bottle is important because you will need to weight yourself to this amount so you can stop ascending at about 20 feet. The empty buoyancy of most pony bottles is between negative 1.5 and 1.9. A pony bottle with negative buoyancy is heavier than the water, so it will sink. Bottles with positive buoyancy are lighter than the water and will therefore float.

    Buoyancy Full

    • The full buoyancy of a pony bottle is important to know because you must set your buoyancy compensator so it will keep you from plunging down quickly. A buoyancy compensator, or BC, is a bladder that is filled with air that allows you to control how buoyant you are while in the water. Full pony bottles all have negative buoyancy between negative 4 and negative 1.