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.