The particulars of this new tug are as follows:
- Length overall: 24.40 m
- Beam, moulded: 11.25 m
- Depth, moulded: 4.38 m
- Draft Extreme: 5.42 m
The vessel is classed by ABS with the notation:
✠ A1, TOWING VESSEL, ✠ AMS, ✠ ABCU, UWILD, QR, UNRESTRICTED SERVICE,
BP (70 tonnes)
Tank capacities are:
- Fuel oil: 72.4 m3
- Fresh water: 10.8 m3
- Fi-Fi foam: 6.6 m3
The CAT AVD TM system consists of a pair of dual input, continuously variable transmissions, located in the shaftlines between the main engines and the Z-drives. The AVDs can accept power from the CAT 3512 main engines, rated 1765 kW at 1800 rpm and/or from two 435 kW hydraulic motors powered by a single CAT C32 auxiliary engine rated 1081 kW at 2100 rpm. The power is delivered to two CAT MTA 627 FP Z-drive units with 2.7 metre diameter fixed pitch propellers.
A primary advantage of the CAT AVD TM system is the continuously variable transmission which can modulate propeller speed down to 0 rpm like a slipping clutch. It can also spin the propeller up faster than would be possible if the engine was directly coupled to the drive, allowing the engines to operate in their peak efficiency zone instead of operating along the propeller demand curve at higher specific fuel oil consumption, thus resulting in significant fuel savings. With a FP propeller pitched for bollard condition at 0 knots, this feature enables full power to be taken from the engine when free running, much like a CP or DEP system.
In the words of Nathan Kelly, Caterpillar Marine Product Definition Engineer:
“This (AVD system) allows propeller speed independent of engine speed so optimal engine efficiency can be achieved leading to fuel savings of fifteen to twenty percent. Basically, all the benefits of a variable speed Diesel Electric Propulsion (DEP) system at a fraction of the cost and size.”
Other advantages include improved response and acceleration as well as lower overall maintenance costs due to significantly reduced operating hours on the main engines.
It is noteworthy that with this system the engines are smaller than would normally be the case in a tug of this power (3512 vs. 3516 engines). The additional power to achieve maximum bollard pull comes from the C32 engine that also drives the Fi-Fi pump. The machinery configuration and power flow scenarios for the four operating modes are illustrated below: