The world's largest, most fuel-efficient, diesel powered high speed catamaran ferries - Natchan Rera and Natchan World – have recently entered service, plying the Tsugaru Straight between Honshu and Hokkaido islands, in Japan. Built half a world away, by Incat, in Hobart, Tasmania, these two aluminium vessels are affectionately known as 'hull 64' and 'hull 65'.

The luxuriously appointed Natchan Rera and Natchan World have been custom-designed to carry up to 800 passengers per voyage, although the standard Incat 112m catamaran design can accommodate up to 1500 people and 355 cars, or 193 cars and 450 lane-metres of trucks. A 3000 tonne fast ferry of this type has the same passenger and car carrying capacity as a 10,000 tonne conventional steel vessel. The Natchan sisters' passage takes two hours - about half the time of a conventional vessel - allowing twice the number of voyages, daily.

These 'Made in Australia', 112.6m long, 30.5m "Panamax" wide, 3.9m draft vessels, are capable of weathering full sea state conditions and must, justly, be called ships. They are also amongst the largest welded aluminium constructions ever built.

Incat Australia
A visit to Incat's shipyard, today, might find them busily building 'hull 66' after earlier last year making rush delivery of Natchan World, to meet Higashi Nihon Ferry's urgent operational service requirements. That rush delivery left Incat's three-ships-long final assembly building empty for the first time since being built. Incat's first 74 metre, all-aluminium high speed 'wave piercing' catamarans, accommodated 198 dead weight tonnes. The 112 metre vessels accommodate more than 7 times that amount. From 74m to 78m, then 86m, 91m, 96m, 98m and now 112m designs, Incat now has 29 such vessels in service around the world, capturing an estimated 40% global market share.

Incat anticipates increasing global demand for such vessels, not only from Europe and the Atlantic but, in future also from Asia and the Pacific. A joint venture partnership exists with Bollinger Shipyards, USA, with whom Incat are presenting their specially designed vessels for possible future military logistics service.

Since its founding, in 1975, by Robert Clifford, A.O., the company has taken an interesting voyage to arrive at its current position.

• The first ferry was built to operate in the Derwent River, in Hobart, filling an urgent river crossing need after a section of the Tasman Bridge was destroyed in a shipping accident, in 1975 - virtually cutting Hobart in half. When the bridge reopened, two years later, the direction of Mr. Clifford's business changed from operating to building ferries.
• The catamaran type vessel was chosen from the outset but demands for operation on longer, open water crossings, challenged Incat to develop their wave piercing hulls.
• Incat was one of the earliest builders in the high speed ferry business to design and build all-aluminium vessels. Aluminium provides light weight without sacrificing strength. The exceptional dent resistance and toughness of aluminium contributed to seaworthiness and safety, while its high corrosion resistance reduced maintenance and overhaul expenses. Incat's avant-garde ship design and building methods evolved, in-house, through repetition, monitoring, maintenance and adoption of accumulated improvements from vessel to vessel. Additionally, Incat has built symbiotic partner relationships with many of its key vendors including Pacific Industrial Supplies, ESAB and AlcoTec for supply of aluminium welding wire.

Originally, the principal material used to build Incat wave piercing vessels was aluminium base alloy 5083, which is traditionally welded with its companion welding filler material 5183. A few years ago, Incat evaluated and then adopted 5383 alloy as a replacement base material to 5083. The improved strength of this material allowed further design enhancements but placed additional weld quality, strength, and porosity control demands on the filler metal to be used. AlcoTec worked with Incat to provide a 5183 type welding wire with tighter controlled porosity limits, chemistry, and diameter than described by nominal Standards Australia or American Welding Society specifications.

In 100% radiographed welds, joints are typically designed to avoid fillets, by milling radii on heavy corner sections and butt welding. Techniques such as material tapering to match butt weld thickness and using run-off tabs, are commonly employed.

Uniform welding techniques assure uniform weld appearance and quality throughout the yard. As the business was developing, Incat worked with the state of Tasmania to establish a Technical and Further Education campus adjacent to site. Here, welders were taught the principles of aluminium welding - alongside Incat's own company welding techniques - before being allowed to weld in the yard. Interestingly, carpenters were often the preferred choice of candidate for training as they were considered to be easier to train, correctly, rather than undertake retraining of steel welders!

Welders are the first-in-line for quality assurance control. If any operator experiences a problem or observes a possible discontinuity, they are expected to stop welding and involve yard supervision in evaluating the situation. Such methods and policies ensure Incat's cost-effective quality control and productivity.

Design features
Generally, as each vessel has slightly different topside requirements from a base vessel design, Incat produces a standard sea-frame for the main hull. This sea-frame has strength stiffness and integrity separate from the superstructure. Since it is desirable to separate passenger spaces and bridge from the machinery and dynamics of a vessel transiting the open ocean at 75km/hr, the superstructures are separate structures mounted on rubber brackets on the sea-frame.

Along with the centre forward bow, the wave piercing bows are important elements in the ship's design. The hydrodynamics and aerodynamics of these bows demand that they be particularly rigid elements. There are areas in these bows where the skin thickness is up to 25mm.

The ship's propulsion jet room assemblies are welded aluminium, as are the propulsion nozzle connecting flanges. To avoid distortion, the flanges are welded first and then milled in place.

The Holy Grail of Passenger Transportation
As with other forms of passenger transportation, the Holy Grail all are seeking is the right combination of safety, speed, comfort and efficiency. It seems clear that for high speed ferry design and construction, Incat may have their Holy Grail in sight. As partners, Pacific Industrial Supplies, ESAB Australia and AlcoTec Wire Corporation, are pleased to have been able to contribute to Incat's quest.

By Jerry Mirgain, ESAB Global Aluminium Product Line & Alcotec International Sales

Acknowledgement
Thanks are extended to Mr. Robert Clifford, AO, Chairman of Incat Board, and also Mr. Maurice Harvey, R&D, Shipyard and Welding Manager for permission to take and use photographs and write this article. The photographs were taken by the author over several visits to Incat's shipyard and ships over several years. Other photographs of completed vessels in service were made available for use in this article by Incat.