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Underwater Scooter

Diver using a underwater scooter for underwater propulsion

An underwater scooter (also known as diver propulsion vehicle DPV or underwater propulsion vehicle) is an item of diving equipment used by scuba and rebreather divers to increase range underwater. Range is restricted by the amount of breathing gas that can be carried, the rate at which that breathing gas is consumed under exertion, and the time limits imposed by the dive tables to avoid decompression sickness.

An underwater scooter usually consists of a battery-powered electric motor, which drives a propeller. The design must ensure that: the propeller is caged so that it cannot harm the diver, diving equipment or marine life; the underwater scooter vehicle cannot be accidentally started or run away from the diver; and it remains neutrally buoyant under all conditions.

Underwater scooter are useful for long journeys at constant depth where navigation is easy. Typical uses include cave diving and technical diving where the underwater scooter vehicles help move bulky equipment and make better use of the limited underwater time imposed by the decompression requirements of deep diving.

For many recreational divers underwater scooter are not useful. Buoyancy control is vital for diver safety: The underwater scooter has the potential to make buoyancy control difficult and cause barotrauma if the diver ascends or descends under power. Visibility of less than 5 metres makes navigating a underwater scooter difficult. Also, many forms of smaller marine life are very well camouflaged or hide well and are only seen by divers who move very slowly and are very vigilant.

Types of underwater scooter

Diver-tugs underwater scooter, tow-behind underwater scooter

The most common sort of underwater scooter is where a diver is towed behind it holding onto one of its two handles on its stern or bow. These types of underwater scooters are efficient because the divers ride in the slipstream of the underwater scooter as opposed to a "ride-on-top" which must be ridden and increases drag, which affects underwater scooters battery burn time. Even more efficient are the tow-behind underwater scooter where the diver wears a harness and backplate or BC with a front crotch-strap D-ring and the underwater scooter is clipped by a bolt snap and tow leash with proper length. This way the diver rides above the slipstream of the underwater scooter while remaining horizontal, thereby minimizing the energy used to move water (bollard pull).

Manned torpedoes and similar underwater scooter

These are roughly torpedo-shaped or fish-shaped underwater scooter vehicles that one or more divers (often two) ride. Sometimes they sit astride it. Sometimes underwater scooter has hollows in its top and the divers sit inside them. One well-known type is the manned torpedo or "chariot" which commando frogmen used in World War II. Similar underwater scooter vehicles have been made for work divers or sport divers; as these do not have a warhead, their bow tends to be pointed for better streamlining. One example is the Dolphin which was made on the Isle of Wight (UK) in the 1970s.

Torpedo-shaped with handles near its front end underwater scooter

Some Farallon and Aquazepp underwater scooter have this arrangement and have a raised arm at the rear to support the diver's crotch against the water current.

Miscellaneous of underwater scooter

Wet subs

As underwater scooter get bigger, they gradually merge into submarines. A wet sub can be classed as a small submarine where the pilot's seat is naturally flooded and they must wear diving gear. Covert military operations use swimmer delivery vehicles (SDVs) to deliver and retrieve operators into harbors and near-shore undetected.

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