Monthly Archives: May 2013

Pros & Cons

Advantages

Pump jets have some advantages over bare propellers for certain applications, usually related to requirements for high-speed or shallow-draft operations. These include:

Higher speed before the onset of cavitation, because of the raised internal dynamic pressure
High power density (with respect to volume) of both the propulsor and the prime mover (because a smaller, higher-speed unit can be used)
Protection of the rotating element, making operation safer around swimmers and aquatic life
Improved shallow-water operations, because only the inlet needs to be submerged
Increased maneuverability, by adding a steerable nozzle to create vectored thrust
Noise reduction, resulting in a low sonar signature; this particular system has little in common with other pump-jet propulsors and is also known as “shrouded propeller configuration”;[2] applications:
submarines, for example the Royal Navy Trafalgar-class and Astute-class, the US Navy Seawolf-class, Virginia-class, the French Navy Triomphant class, and the Russian Navy Borei class.
modern torpedoes, such as the Spearfish, the Mk 48 and Mk 50 weapons.

Disadvantages

Can be less efficient than a propeller at low speed
More expensive
The intake grill can become clogged with debris; e.g., seaweed. The effects of this can be mitigated by having a reversing gearbox between the engine and the water jet.

Workings

A pump-jet works by having an intake (usually at the bottom of the hull) that allows water to pass underneath the vessel into the engines. Water enters the pump through this inlet. The pump can be of a centrifugal design for high speeds, an inducer for low speeds, or an axial flow pump for medium speeds. The water pressure inside the inlet is increased by the pump and forced backwards through a nozzle. With the use of a reversing bucket, reverse thrust can also be achieved for faring backwards, quickly and without the need to change gear or adjust engine thrust. The reversing bucket can also be used to help slow the ship down when braking. This feature is the main reason pump jets are so maneuverable.

The nozzle also provides the steering of the pump-jets. Plates, similar to rudders, can be attached to the nozzle in order to redirect the water flow port and starboard. In a way, this is similar to the principles of air thrust vectoring, a technique which has long been used in military jet-powered aircraft. This provides pumpjet-powered ships with superior agility at sea. Another advantage is that when faring backwards by using the reversing bucket, steering is not inverted, as opposed to propeller-powered ships.

Pump-jet powered watercraft do suffer from the Coandă effect, which must be taken into account when making changes in heading. The heading needs to be adjusted two degrees further than what would normally be required because of this effect.

Pump-jets

A pump-jet, hydrojet, or water jet is a marine system that creates a jet of water for propulsion.

The mechanical arrangement may be a ducted propeller with nozzle, or a centrifugal pump and nozzle.

The Italian inventor Secondo Campini showed the first functioning man-made pump-jet engine in Venice in 1931. However, he never applied for a patent, and since the device suffered from material problems resulting in a short life-span, it never became a commercial product.

The first person to achieve that was New Zealand inventor Sir William Hamilton in 1954.

Pump-jets were once limited to high-speed pleasure ships (such as jet skis and jet boats) and other small craft, but since 2000–2010 the desire for high-speed vessels has increased[citation needed] and thus the pump-jet is gaining popularity on larger craft, military vessels and ferries in particular. On these larger craft, they can be powered by diesel engines or gas turbines. Speeds of up to 40 knots can be achieved with this configuration, even with a conventional hull.[1]

Pump-jet powered ships are well known to be very maneuverable. Examples of ships using pumpjets are the fast patrol boat Dvora Mk-III craft, the Hamina class missile boats, all Virginia Class submarines, the Stena HSS High-speed Sea Service ferries, and the United States Littoral Combat Ships (LCS).

In the Ordovician geological period, the first known cephalopods swam by a natural built-in reciprocating hydrojet.

Recent developments

The British Ice Challenger exploration team used a screw drive in their Snowbird 6 vehicle (a modified Bombardier tracked craft) to traverse the ice floes in the Bering Strait. The rotating cylinders allowed Snowbird 6 to move over ice and to propel itself through water, but the screw system was not considered suitable for long distances, and the cylinders could be raised so that the vehicle could also run on conventional caterpillar tracks. The Ice Challenger website says that the design was inspired by a Russian vehicle used to pick up cosmonauts who landed in Siberia (perhaps the ZIL-2906).

Russian inventor Alexey Burdin has come up with a screw-propulsion system “TESH-drive Transformable worms”.

More recently, commensurate with the ever increasing demand for commodities whilst refinery operational footprints remain within set boundaries, mud farming with the larger machines with deep profile penetration capacity (termed MudMasters by their manufacturer) has proven to be an efficient method for high intensity tailings management.

Popular culture

A screw driven vehicle has been produced as a toy by Mattel.
In the video game Metal Gear Solid 3: Snake Eater, a screw drive powers the fictional vehicle Shagohod.
In the intro of the video game Command & Conquer: Red Alert 2, the (fictional) soviet amphibious transports are using screw drives for movement.
The first DLC for the videogame Fallout 3, Operation: Anchorage, features Chimera Tanks that uses screw drives as a means of movement.

Amphibians

The threaded cylinders are necessarily large to ensure a substantial area of contact and buoyancy. Being lightweight, the cylinders may conveniently serve as floats and the arrangement may be used in the design of an amphibious vehicle.

During the Vietnam War, the American Waterways Experiment Station (WES) tested the Marsh Screw Amphibian, designed by the Chrysler Corporation. The counter rotating screws “…propelled the vehicle through water and marsh terrain adequately, but failed miserably on soil surfaces, especially sand. The average maximum speed attained on test lanes was a meagre 1.6 miles per hour (2.6 km/h; 1.4 kn).” Despite such disappointing results, Chrysler produced a much larger vehicle, the Riverine Utility Craft (RUC) for the Navy in 1969. The RUC travelled on two aluminium rotors, 39 inches (991 mm) in diameter. The RUC achieved impressive speeds of 15.7 knots (29.1 km/h) on water and nearly 25 knots (46 km/h) on marsh. Again, however, speeds on firm soils proved disappointing, reaching only 3.6 knots (6.7 km/h) and crossing dykes proved difficult – the vehicle would get stuck.

The Soviets built a screw-propelled vehicle, the ZIL-2906, specifically for the challenging task of recovering cosmonauts who landed in inaccessible areas.

In the 1960s, Joseph Jean de Bakker was the busy owner of the De Bakker machine factory in Hulst in the southwest of the Netherlands. He was also a keen fisherman, but he did not want his fishing time to be constrained by the vagaries of the tide. His solution was the Amphirol, a screw-propelled vehicle superficially similar to the Marsh Screw Amphibian. The Amphirol was able to convey him over the sticky clay revealed by the outgoing tide and to swim in water at high tide.

De Bakker’s Amphirol had a top speed of 12 km/h (6.5 knots) on mud and 10 km/h (5.4 knots) in water. It was powered by two modified DAF 44/55 variomatic transmission units; this made possible the significant innovation that the flanged cylinders could be deliberately driven in the same direction so that the vehicle could crab sideways on dry land at the alarming speed of 30 km/h (16 knots). Also, when moving sideways, steering is effected by shifting the front of the cylinders so that they are no longer parallel – giving a large minimum turning radius.

Amphirols are used for ground surveying, for grooving the surface of newly drained polders to assist drying, and to carry soil-drilling teams.

Today, modern vehicles widely known as amphirols, perform specialised tasks such as compacting tailings from industrial processes. The advantage of these machines to tailings densification is by way of providing a means to allow water or process liquor to run off without repulping the profile. This approach subsequently largely negates the impact of rainfall on densification and dewatering. However, the lighter, faster machines are better suited to marginal terrain access, but not densification due to repulping and their limited penetration depth. The process of using these machines specifically for tailings and dredge spoil densification is commonly termed “mud farming” in the mining industry.

Second World War period

The Second World War period

With the occupation of Norway by Nazi Germany in World War II, the quixotic Geoffrey Pyke considered the problem of transporting soldiers rapidly over snow. He proposed the development of a screw-propelled vehicle based on the Armstead snow motor. Pyke envisaged that the vehicles would be used by a small force of highly mobile soldiers. The damage and casualties that a small force could inflict might be slight, but they would oblige the enemy to keep many men stationed in Norway in order to guard against every possible point of attack. Pyke’s ideas were initially rejected, but in October 1941, Louis Mountbatten became Chief of Combined Operations and Pyke’s ideas received a more sympathetic hearing. Mountbatten became convinced that Pyke’s plan was worthwhile and adopted it. The scheme became Project Plough and many high-level conferences were dedicated to it.

The problem of developing a suitable vehicle was passed to the Americans, and Pyke went to the USA to oversee the development. However, Pyke, who could be very inflexible, fell out with various individuals on the project and the Americans moved on to design a more conventional tracked vehicle, the M29 Weasel.

In 1944, Johannes Raedel, a soldier of the German Army and veteran of the Eastern Front invented his schraubenantrieb schneemaschine (screw-propelled snow machine). Raedel had seen the problems of operating tracked vehicles in the deep snows of Russia where a tank would dig out the snow under the tracks leaving the tank stuck on the snow compressed under the hull.

According to Siegfried Raedel, son of Johannes:
“ The vehicle idea evolved while looking at a meat mincer, also employing a screw type of compression. He convinced the OKH in Berlin to allow him to make a prototype of his concept machine. At that time, Austria was annexed to Germany already and he was dispatched to the Austrian Alpine Vehicle Test Center at St. Johann in Tyrol.

Using whatever materials were available, he built a working prototype during the period of 10 February 1944 to 28 April 1944. It was tested extensively. It was very slow, but it could pull one ton. It also possessed good climbing capabilities. It would penetrate about 30cm into the snow, but no more. Raedel’s machine never went into production.

Armstead Snow Motor

Armstead Snow Motor
In the 1920s the Armstead Snow Motor was developed. When this was used to convert a Fordson tractor into a screw-propelled vehicle with a single pair of cylinders. A machine used in the Truckee,CA area was referred to by locals as the “Snow Devil” and that name has been erroneously attached to these machines, although no known advertising of the time referred to them as such. A film was made to show the capabilities of the vehicle as well as a Chevrolet car fitted with an Armstead Snow Motor. The film clearly shows that the vehicle copes well in snow. Steering was effected by having each cylinder receive power from a separate clutch which, depending on the position of the steering gear, engages and disengages; this results in a vehicle that is relatively maneuverable. The promotional film shows the Armstead snow motor hauling 20 tons of logs.

In January 1926, Time magazine reported:
“ Having used the motor car for almost every other conceivable purpose, leading Detroit automobile makers have now organized a company entitled “Snow Motors Inc.,” to put out a machine which will negotiate the deepest snowdrifts at six to eight miles an hour. The new car will consist of a Ford tractor power-plant mounted on two revolving cylinders instead of wheels—something on the order of a steam roller. The machine has already proved its usefulness in deep snow previously unnavigable. One such machine has done the work which formerly required three teams. In Oregon a stage line uses a snow motor in its two daily round trips over the Mackenzie Pass between Eugene and Bend. Orders are already in hand from Canada, Norway, Sweden, and Alaska. The Hudson Bay Co. has ordered a supply to maintain communications with its most northern fur-trading stations. The Royal Northwest Mounted Police have also gone into the market for snow motors, and may cease to be horsemen and become chauffeurs, to the deep regret of cinema people. A number of prominent motor makers have also been interested in the proposition from the angle of adapting the snow motors equipment to their ordinary models. Hudson, Dodge and Chevrolet are mentioned especially as interested in practical possibilities along this line. ”

An extant example is in the collection of the Hays Antique Truck Museum in Woodland, California. This particular vehicle is said to have been used to haul mail from Truckee to North Lake Tahoe.

Early developments

Early developments
One of the earliest examples of a screw-propelled vehicle was designed by Jacob Morath, a native of Switzerland who settled in St. Louis, Missouri in the United States in 1868. Morath’s machine was designed for agricultural work such as hauling a plough. The augers were designed with cutting edges so that they would break up roots in the ground as the machine moved.

One of the first screw-propelled vehicles that was actually built was designed by James and Ira Peavey of Maine. It was patented by Ira Peavey in 1907; the Peavey family has been famous for its contributions to the lumber industry ever since blacksmith Joseph Peavey of Stillwater, Maine, invented the tool known to this day as a Peavy. The Peavey Manufacturing Co. is still located in Maine.

The Peaveys’ machine had two pairs of cylinders with an articulation between the pairs to effect steering. At least two prototype vehicles were constructed: one was steam powered the other used a gasoline engine. The prototypes worked well on hard packed snow but failed in soft powder because the flanges had nothing to grip into. The machine was designed to haul logs, but its length and rigid construction meant that it had difficulty with the uneven winter roads for which it was intended. Peavey’s invention could not compete with the Lombard Steam Log Hauler built by Alvin Lombard and it was not produced commercially. (The Lombard vehicle was an early example of a half-track vehicle, it resembled a railway locomotive with a sled or wheels in front for steering and caterpillar tracks for traction.)

screw-propelled vehicle

A screw-propelled vehicle is a land or amphibious vehicle designed to cope with difficult snow and ice or mud and swamp. Such vehicles are distinguished by being moved by the rotation of one or more auger-like cylinders fitted with a helical flange that engages with the medium through or over which the vehicle is moving. Modern vehicles called Amphirols and other similar vehicles have specialised uses.

The weight of the vehicle is typically borne by one or more pairs of large flanged cylinders; sometimes a single flanged cylinder is used with additional stabilising skis. These cylinders each have a helical spiral flange like the thread of a screw. On each matched pair of cylinders, one will have its flange running clockwise and the other counter-clockwise. The flange engages with the surface on which the vehicle rests. Ideally this should be slightly soft material such as snow, sand or mud so that the flange can get a good purchase. An engine is used to counter-rotate the cylinders—one cylinder turns clockwise and the other counter-clockwise. The counter-rotations cancel out so that the vehicle moves forwards (or backwards) along the axis of rotation.

The principle of the operation is the inverse of the screw conveyor. A screw conveyor uses a helical screw to move semi-solid materials horizontally or at a slight incline; in a screw propelled vehicle, the semi-solid substrate remains stationary and the machine itself moves.

Type 63A

The Type 63A (also known as the ZTS63A) is an Amphibious light tank upgraded from the Type 63, designed for river-crossing operations at inland rivers and lakes. Its industrial designation is WZ213.
Development

Before the mid-1990s, Chinese ground forces relied on the Type 63 amphibious light tank developed in the early 1960s. The low swimming speed and weak firepower of the Type 63 was insufficient to the needs of modern maritime amphibious assault operations that PLA would conduct. The PLA demanded a replacement for the Type 63 in the early 1990s, which led to the development of the Type 63A in 1997. Reports indicate that over 300 examples has been delivered to the PLA by the end of 2000.
Design

The Type 63A is lightly armoured amphibious light tank with a flat, boat-like hull. Suspension is made up of 6 road wheels and lead or return rollers. A redesigned welded turret from the original Type 63 is mounted center of the hull, with the powerpack positioned in the rear. The Type 63A has 2 additional floating tanks to increase the stability of the vehicle in the water. There are 3 water inlets on both sides of the hull. In the rear of the hull there are to allow 2 large water jets for travelling in water.

Type 63A introduces an enlarged welded turret replacing the original Type 63 turret, the modernised Type 63A utilises the dual-way stabilised 105 mm rifled gun replacining the 85 mm gun. The 105 mm rifled gun, fires armour piercing fin stabilised discarding sabot (APFSDS), high explosive (HE), and high-explosive anti-tank (HEAT) ammunitions, with 45 rounds carried inside the vehicle. APFSDS round penetrates 650 mm steel armour or destroy a reinforced concrete bunker a distance of 2,000 m.

To overcome the inaccuracy of firing when swimming, the Type 63A uses laser-beam guidance ATGM which isn’t affected by the wave motions while swimming. The missile has a maximum firing range of 4–5 km with a first hit probability of +90% against stationary targets. Its secondary functions can engage low-flying helicopters.
Performance

The Type 63A enhance capability allows the vehicle to conduct amphibious operations from its host amphibious warfare ships at distances from 5–7 km to shore at a speed of 28 km/h.

Compared to the Type 63, the Type 63A featured five major improvements: The modernised Type 63 to Type 63A has given enhanced sea travelling performance, increased swimming speed, improved fire-control system, ATGM capability, and larger 105 mm rifled gun with dual stabilizers.
System

The FCS includes digital fire-control computer, integrated commander sight with laser rangefinder input, and white-light spotter or image-stabilised gunner’s sight w/ passive night vision. The Type 63A night vision is an image intensifier system. Alternatively the gunner sight can be fitted with a thermal imager night vision. It is also equipped with the satellite positioning (GPS/GLONASS) system to allow accurate landing position in harsh weather conditions and night operations. It’s also equipped with computerised fire-control to enable accurate firing both on land and at sea.

AAAV

Amphibious Vehicle