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Swimmer Delivery Vehicle / Diver Propulsion Vehicle / Diver Delivery Vehicle

Covert military operations use swimmer delivery vehicles (SDV) to deliver and retrieve operators into harbors and near-shore undetected. As Diver Propulsion Vehicle [DPV] get bigger, they gradually merge into submarines. A wet submarine is a small submarine where the pilot's seat is naturally flooded and he must wear diving gear.

In general, divers use diving suits and fins for propulsion in the water. One disadvantage is that the diving suit is generally manufactured only from a relatively thin, synthetic material which closely follows the human body in order to offer as little water drag as possible. Consequently, the human body surrounded by the synthetic skin is subjected virtually directly to external influences underwater, such as cold or attacks by fauna. Furthermore, in the case of conventional diving suits, an oxygen cylinder also has to be carried, in order to make it possible to remain underwater for a lengthy time. Since this oxygen cylinder is generally of a relatively cumbersome design and has to be carried on the diver's back, it results in additional drag in the water, which makes it necessary to use more force for propulsion in the water. Furthermore, in this type of diving, it is scarcely feasible to remain underwater for a lengthy time, for example for several days, since it is extremely tedious and tiring to carry items essential for life, such as oxygen or drinking water.

Providing supplemental propulsion for divers, in particular scuba divers, is desirable for a variety of reasons. For example, supplemental propulsion enables a scuba diver to direct to other tasks energy that normally would be expended in swimming or maneuvering through water. One kind of well known propulsion unit is a "scooter" that is positioned in front of a scuba diver. The scooter includes handles at the rear of the scooter. A diver grasps the handles and the scooter pulls the diver through the water. While scooters are useful, the size of a scooter limits the mobility in the water of a diver and makes transport and storage of the scooter cumbersome. Scooters allow no "hands-free" operations, if necessary.

The frogmen's individual means of movement in the assigned area are of great importance for the success of their actions. They use towing devices and guided torpedoes, which are delivered along with the frogmen to the action areas of the underwater sabotage forces in various types of submarines, including midget ones, surface combat ships, motorboats, merchant ships, self-propelled landing boats, andalso in aircraft and helicopters.

For a towing device, the a propeller (the motor is powered by a 24-volt battery) enables it to move at a speed of two to five knots (three to nine kilometers per hour) for a distance of 10 to 15 kilometers. Recently, in anumber of NATO countries, especially in the US, experimental workhas been conducted on the production of improved models of underwater towing devices. They are researching the possibilities of getting electric power by means of various chemical reactions, which will make it possible to increase the independent movement of the devices and improve their other tactical and technical components.

Another type of movement means for frogmen is the guided torpedo, an underwater self-propelled guidable device in several versions that resembles an ordinary ship torpedo in dimensions and a miniature submarine in external appearance.

The diver delivery vehicle is used to carry divers to enemy coastlines for covert surveillance operations. Diver Delivery Vehicle (DDV) are specially designed for independent transport of a combat diver unit to, within, and out of an area of operation where there is a need for covert infiltration. In short time, transfer from high speed surface mode to swimmer mode, to underwater mode and back to surface and to be able to travel several nautical miles under water in order to avoid detection from sensors on the surface and on a depth that makes it invisible from the surface.

There has long been a requirement to protect naval facilities and vessels from underwater attack. However, underwater security poses unique considerations because physical barriers to stop intruders are often not practical or possible. The use of hydrophones and various types of anti-submarine sonars in harbors have provided limited deterrence from underwater attack by swimmers and divers since the 1960s. Except for very limited deployment of an expensive US Navy system dedicated to detecting and tracking divers in 1990, solutions through the 1980s and beyond did not offer the coverage, resolution, or ability to track divers that provided the necessary probability of detection.

Since the mid-1990s, high frequency multibeam sonars have provided the potential technology to develop dedicated swimmer detection systems. These systems are able to meet the detection and tracking requirements posed by ever-increasing threats to both naval and commercial port facilities, and the vessels that use them. No simple solution to the underwater detection problems exists to date. Waterside security issues are receiving much greater emphasis than in the past, and as a resultmany manufacturers have provided their versions of active high frequency sonars tocounter the perceived threat.

Over the years, numerous devices for electric underwater propulsion for scuba divers have been developed. Some of these involve the scuba diver holding the device in his hands, whereas other solutions involve the attaching of the propulsion system to the scuba diver's equipment.

A problem with hand held devices is that they fatigue the scuba diver's arms inasmuch as he has to "hang on" as he is pulled through the water. Another problem with prior art components is that they restrict the scuba diver's ability to function "hands free" since he must carry the device. Yet another problem is that it restricts a scuba diver's mobility since he must be able to let go of the device in order to use his hands. In this instance, the diver must be able to, in some fashion, secure the device by resting it in some suitable place, or tethering it to something.

Problems also exist with propulsion devices that attach to a scuba diver's equipment, for in order for these mounted devices to function properly, the scuba diver must face a number of sacrifices and restrictions. For example, it is known that a properly weighted scuba diver is almost neutrally buoyant when he is at the surface of the water. Any additional equipment that he carries such as a propulsion device, must also be approximately neutrally buoyant, so as not to upset this balance. For the propulsion device to be near neutrally buoyant it must displace, when submerged, an amount of water almost equal to its weight. Hence, the volume and weight are directly proportional.

The art of underwater diver propulsion vehicles can be divided into three fields of work.

One field can be identified as "battery propulsion vehicles". These inventions use electric motors connected to a propeller providing thrust. Batteries within a watertight housing supply stored electric energy required to operate the motor. Disadvantages of these battery propulsion vehicles include a heavy weight of the batteries and the ferrous electric motor. These vehicles are heavy and cumbersome to carry and transport to and from the dive site, especially through airports, and within taxis. A large bulky housing is required to contain the batteries and to provide buoyancy offsetting the vehicle weight. This large vessel is difficult for the diver to manipulate, and practically precludes the opportunity of attachment to the scuba tank for hands free operation.

Batteries are selected by the manufacturer of the battery propulsion vehicles to provide an amount of energy required (when charged) for about one scuba tank dive (around 45 minutes). After a dive, the diver has to return to the surface, and open the housing to install a second battery if a recharging system is unavailable on the dive boat. If the boat has a charging system, the diver must wait a long recharging time (one or two hours) before the battery is again ready. There would be significant advantages to having a smaller, lighter, diver propulsion vehicle which operated without use of electric batteries.

A second art field of work can be identified as "air/propeller propulsion vehicles". These vehicles attempted to make efficient use of the stored compressed air energy available in the scuba tank by operating an air motor connected to a propeller. Designers attempted to have air motors consume less air (while operating at practical diver thrust) than a diver's breathing rate of air consumption. For with such a condition, no scuba tank air would be wasted when providing practical diver transport. If this condition was not met, and if the motor (while providing practical thrust) consumed more air than a diver's breathing rate, than the diver "bottom time" or "dive time" would be curtailed.

All these air/propeller propulsion vehicle inventions shared a common impracticality: The rotary air motors used were not efficient enough to provide adequate diver thrust and at the same time consume scuba tank air at a rate less than the diver breathing rate. Because of this shortcoming, all prior air/propeller propulsion vehicle inventions wasted significant scuba tank air while the motor was operating at a practical thrust. This wasted air (beyond the diver's breathing rate consumption) was exhausted into the water, and cut the dive time or down time to much less than what it would be without the vehicle. There would be a major advantage in making a propulsion vehicle for scuba divers which used a air motor that provided both practical diver thrust and an air consumption less than the diver's breathing air consumption so dive time available from a scuba tank is not curtailed.

A third art field of work can be identified as "single water disk propulsion vehicles". These air powered propulsion vehicles do not use a propeller or rotary air motor to provide diver thrust. Instead, they use a single reciprocating water disk attached to a single piston motor for the thrust/power stroke. The water disk of these inventions has attached one or more flexible flaps and a series of corresponding openings/holes through the water disk. The flaps and openings/holes cooperate so the water disk experiences nearly zero water resistance on the return stroke and maximum water resistance on the power stroke. All these designs share a same operational deficiency. The propulsion vehicle moves forward with intermittent forward thrusts each followed by a time period of zero thrust (as the water disk returns). As a result the diver propulsion is jerky and un-constant.