Cycloidal drive propulsion commissioned to power local tugboats

Drive components and systems company Voith’s cycloidal drive marine propulsion system, the Voith Schneider propeller, was chosen to power State-owned freight logistics company Transnet National Ports Authority’s (TPNA’s) new fleet of tugboats currently under construction as part of the 9 Tug project.

The first locally manufactured tugboat, the Mvezo, was launched on November 12, 2015, at the Durban premises of shipbuilding contractor Southern African Shipyards.

The tugboat renewal project is valued at R1.4-billion and is planned to introduce nine new tug boats, which will be allocated to the ports of Durban, Richards Bay, Port Elizabeth and Saldanha. Additional tugboats will be handed over every three months until early 2018, when the last tugboat is expected to be launched.

Each new tugboat is equipped with two forward-mounted Voith Schneider propellers.

Boksburg-based marine technology solutions company Integrated Ship Handling (ISH) – the sole sales and service partner for Voith Turbo Marine in Southern Africa – is executing the project on behalf of Voith.

ISH is also supplying the complementary firefighting equipment required for the new tugboats, which is manufactured by firefighting equipment company CounterFire, and includes auxiliary gearboxes built by Norway-based gearbox company Kumera.

ISH director Graham Russell tells Engineering News that the TNPA 9 Tug project is the largest single marine order received by Voith and CounterFire and it is, therefore, “essential that local project management is strong enough to maintain the duration of the project, which is where ISH plays a strong role”.

Strongly supporting Southern African Shipyards, Russell mentions that ISH’s scope of work includes local project management on behalf of Voith and CounterFire, thereby tasking ISH with resolving any technical or commercial issues before they become more urgent.

Moreover, ISH is also responsible for implementing the skills and enterprise development commitments of its partners.

In terms of key deliverables relating to the Voith Schneider propellers, Russell indicates that the project is on time and within budget. This was evident during the successful naming ceremony and launch of Mvezo, which served as affirmation that Southern African Shipyards can execute complex engineered projects.

“A key challenge for ISH in the 9 Tug project was meeting tight deadlines for the delivery of the Voith Schneider propellers. Considering the strong order book of Voith, the German company pulled out all the stops and reorganised internal schedules to meet the requirements of Southern African Shipyards and its client, TNPA,” notes Russell.

Propeller Advantages
Russell states that Voith Schneider propellers were chosen for the 9 Tug project mainly because they are easy to operate and safe, and cost of ownership is low.

Older-generation (up to 40 years old) tug- boats currently used by TNPA – some of which use azimuth thrusters or smaller cycloidal drives – have bollard pulls of about 42 t. The larger, size 32 Voith Schneider propellers used for the project produce bollard pulls in excess of 70 t, thereby enabling greater harbour assistance capability.

TNPA manages and operates 21 Voith Water Tractors in six of the eight South African commercial ports, in addition to two Voith-equipped floating cranes, he says.

Russell adds that 43% of these vessels were built prior to 1980 and have thus been deployed in increasingly demanding operations by having to assist and handle larger ships calling at local ports.

“Improvements in engineering practices, better materials and the full adoption of simulation tolls, such as computational fluid dynamics, have resulted in an almost doubling of the power density through the complete drivetrain of the Voith Schneider propeller.

“Because the propeller combines propulsion and steering in a single unit, it is very simple to operate,” he says, adding that it offers an intuitive driving experience. “Less training is thus required . . . and it is easier for tug operators to adapt to the Voith system,” he adds.

The Voith Schneider propellers assist in increasing the safe operability in harbour assistance operations, as they allow for the execution of complex manoeuvres in challenging circumstances, such as under the bow of a ship, where negative pressure fields can produce disastrous results such as the capsizing of a tugboat.

“A further consideration of TNPA is that a Voith tugboat can operate under blackout conditions, for example, during a total electrical failure,” says Russell.

Further, because the propeller uses a cycloidal drive principle, the direction of thrust can be changed instantaneously. According to Voith, shifting from full-ahead to full-astern produces no unwanted steering forces and can be undertaken in as little as five seconds, making it five to ten times faster than any other propeller when changing direction. It can also do a complete 360° turn on its own axis.

The Voith Schneider propeller also offers redundancy because the system can be operated under the complete failure of one propeller.

Russell points out that TNPA’s full visibility of vessel operating costs and Voith Schneider propellers’ having “categorically and statis- tically proven themselves in terms of low operating costs over their lifetime” when used on older-generation TNPA tugboats are evidence of the propellers’ low cost of ownership.

He concludes that Voith can still reliably deliver spare parts for a number of TNPA tugboats built more than 40 years ago, some of which have clocked more than 70 000 operating hours.