By incorporating lessons learnt from the Austal’s inaugural 2005 trimaran “Benchijigua Express” and the Austal designed and built Littoral Combat Ship “USS Independence”, the company’s latest trimaran delivers innovation without risk. Austal undertook a detailed market study on the commercial ferry industry looking at the size and capacity of existing fleets. Based on the data collected from this study, it was determined that 102 metres, 1165 passengers, 254 cars were the approximate specifications most applicable to the existing market.
The vessel’s unique trimaran hull form combines the softer roll of monohulls with the low resistance, stability and carrying capacity of catamarans to deliver proven advantages over conventional designs. These advantages include greater speed for the same installed power, an ability to operate in higher wave heights and maintain higher speeds in waves, greater resistance to damage and reduced wake which reduces impact on the environment.
Most importantly, the trimaran’s lower roll speed means lower accelerations experienced by passengers, significantly reducing passenger sea sickness. Studies show that motion sickness on the trimaran will be approximately 56 per cent lower than on a 100 metre catamaran operating in head seas. Because the vessel was being built on speculation, the design of the vessel’s interior and vehicle deck has been pitched at a level that permits the eventual owner to easily modify the vessel to suit their particular market.
The most immediately noticeable change to its predecessor is the existence of a straight-stem bow - designed to maximise the vessel’s waterline length and deliver greater speed and efficiency. Another significant improvement is the adoption of a three-engine propulsion train which combines with the trimaran’s unique hydrodynamic hull form to deliver fuel efficiency across a range of operating conditions. The three engine arrangement also means lower fuel consumption, less emissions and reduced maintenance compared to fast ferries of a similar size which have four engines.
Powering the vessel are three class-leading MTU 20V 8000 Series diesel engines, which offer high power-to weight ratio and are established as a low risk propulsion engine option for many leading high speed ferry operators. Propulsion consists of three new-series Wartsila LJX 1300 water jets chosen for their improved cavitation margin (greater efficiency), each driven through a ZF 53800 reduction gearbox.
A speed of 39 knots (at 90% MCR) with 340 tonnes deadweight was achieved during sea trials, as well as a maximum speed of 45 knots, and a 760 nautical mile range (at 90% MCR) with fuel consumption of only 4.90 tonnes per hour.
Austal’s focus on maximising redundancy is evident throughout the vessel’s machinery spaces, with two separate main fuel and day tanks and each of the vessel’s three engines located in separate engine rooms. The vessel’s four MTU S60 generators are split between the engine room and the starboard side of the main deck, again for redundancy.
The vessel’s double retractable bow thruster arrangement delivers improved manoeuvrability in harbour along with redundancy in the event that one is damaged.
A new and simplified ride control arrangement and operating system delivers improved control over the vessel’s motions and handling characteristics in all sea conditions. Along with a central T-foil on the main hull forward, the new ride control system includes T-foil roll control fins on each of the vessel’s amahs. All foils have been designed to permit removal and servicing without the need to dry-dock the vessel, reducing maintenance cost and down time.
