As a general rule of thumb: you pay for (installed) power. Dividing the power over two or three drivetrains make no difference. In the range from 65 tons to 80 tons of bollard pull you can achieve a competitive advantage due to smaller sized thrusters and engines.

Comparing the Z-drive to Voith-Schneider propulsion types, the Z-drives generally has a much better bollard pull to power ratio. This can save up to 20% in capital investments and fuel consumption for equally powerful tugboats.