The success of that early vessel led to the subsequent use of Voith propellers in ferries, and many other types of inland waterways and seagoing craft.

It was also 50 years ago that the first Voith Water Tractor was put into service, a landmark event that was to have a dramatic effect on the towage industry around the world. Again it started with a relatively simple demonstration vessel. Named the Bien (Bee), this first tractor tug of only 116hp was introduced in 1952 and had a bollard pull of just 1.7 tonnes. This tiny vessel was followed by an order for a series of small tractor tugs for the Belgian Navy in the same year and the first true shiphandling tractor Stier in 1954.

Development of the Voith Schneider propulsion unit has continued relentlessly throughout it's 75 year lifespan. A number of intricate mechanisms have been used to produce the 'cycloidal' blade motion all of which have now been superseded by the present robust 'kinematic' linkage. In very recent years several new innovations have been introduced that have enormously increased the efficiency of the propeller, and much of that research and development has gone 'hand in hand' with that of the water tractor concept. Propellers are now available for tugs with a blade orbit of up to 3.6m in diameter. A new blade design with end plates has done much to improve power and lessen cavitation and in some cases longer blades are now available.

A new tractor tug recently constructed in Singapore by ASL Shipyard Pte for use in Port Napier, New Zealand , marks another milestone for Voith.

Named Ahuriri, the new vessel is the first to be fitted with a new type of propulsion unit incorporating six blades for the first time. This extremely compact tractor is only 23.80m in length overall but has a beam of 11.00m and draft of 5.00m.

Two Wartsila 8L 36A main engines produce a total of 4800kW (6522bhp) at 1000rev/ minute to power a pair of Voith propulsion units designated 32R6/210-2.

On trials Ahuriri produced a bollard pull of 65 tonnes at MCR and 68 tonnes on overload settings, and a free running speed of 13 knots. With this performance this vessel is undoubtedly the most compact and powerful Voith water tractor ever produced for shiphandling.

Ahuriri is designed to be operated with a crew of two, with onboard accommodation suitable for day work and short voyages.

The tug is fitted with a single drum Plimsoll towing winch with a 180 tonnes brake load and capacity for 130m of 60mm manmade HMPE fibre towline.

This small, extremely agile, tug when compared with the Cape Pasley mentioned later in this report, illustrates perfectly the wide range of technology available to an operator looking for a shiphandling vessels capable of being operated by a very small crew.