What is Underwater Propulsion?
Scuba and rebreather divers are using an underwater propulsion vehicle, or called diver propulsion vehicle (DPV) or underwater scooter, as one of their diving equipment items that increases their range underwater.
Range is described under three conditions, and these are the limited amount of breathing gas that can be carried, the rate at which the breathing gas is used under efforts while diving, and the limited time imposed by dive tables to prevent decompression sickness among divers.
A DPV has some basic components which are a pressure-resistant watertight casing containing an electric motor that is battery-powered, and this drives a component which is the propeller. Some factors are considered in the design of this vehicle, and these are that it cannot harm the diver, diving equipment, marine life, and that it cannot run away from the diver or accidentally started, and the vehicle is to remain neutrally buoyant while being used underwater.
The usual uses of underwater propulsion vehicle are for cave diving and technical diving, where deep diving needs the help to move big equipment and making divers use better of the limited underwater time based on the decompression requirements. To make a DPV more useful, some accessories can also be mounted to the DPV accessory board. The accessories that can be mounted on to the DPV are compasses, cameras, lobster sticks and even spear guns.
DPV also serves for military applications that include delivery of combat divers and their equipment over distances or at speeds that can be considered as not practicable.
The operation of DPV requires more than situational awareness than mere simple swimming since its operation requires simultaneous depth control, buoyancy adjustment, monitoring of breathing gas and navigation.
There are various kinds of DPV, and the most common type tows the diver who holds onto the handles on the bow or stern. This so called tow-behind scooters are most efficient with the diver placed parallel to and above the propeller wash.
The next kind of DPV is termed manned torpedoes, shaped like a fish, where the one or more divers can sit typically astride on it or in hollows inside.
The next kind of DPV is called a subskimmer which is described as a rigid-hulled inflatable boat, powered by a petrol engine when on the surface, and when being submerged, the petrol engine is sealed and the vehicle runs on battery-electric thrusters being attached on a steerable cross arm.
Note that as DPVs get bigger, they are now merged into submarines. There is a wet sub, which is a small submarine, where the seat of the pilot is flooded and thus the diver is to wear a diving gear.