Capital – and operational expenses are considered for every operation. Rotortugs initial costs are divided over smaller engines and smaller thrusters, which saves on capital expenses.
Three Rotortugs provide the same service level as four ASD or tractor tugs. Escort towage, ship handling, firefighting, pilot transfer, buoy or hose handling, can all be done with Rotortugs so no additional or specialized vessels are needed.
Three smaller thrusters, instead of two big thrusters for ASD and tractor tugs saves construction costs. Costs for thrusters scale up exponentially, fitting three smaller thrusters offer a linear scaling instead. Comparing similar outfitted tugs with winches forward and aft at shipyard price level shows lower or equal construction costs for a Rotortug.
Rotortugs feature similar key equipment compared to Z-drive tractor – and ASD tugs. Smaller engines and propeller, normally have more economical spares and because rotortugs can generally make do with fixed pitch propellers, also for fire-fighting applications (where the portside main engine drives the fire-fighting pump) there is no need for more maintenance sensitive controllable pitch propellors.
Fuel consumption ship-handling
With the thrusters fitted on both ends of the Rotortug, the Rotortug needs much lower thrust and power when manoeuvring into position when ship-handling, or standing by alongside a vessel using about 30% less fuel. ASD and tractor tugs have to clutch in their Z-drives, turning the propeller thrust into each other and burning a lot of fuel just to stay in place, and manoeuvre about.
Fuel consumption free sailing
ASD tugs have a better ahead free-sailing fuel economy compared to tractor and Rotortugs, and use about 8% less fuel. This is only applicable when mobilising or demobilizing from the work job, so no towline attached or no manoeuvring involved.