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Shipbuilder Austal first came to Gizmag’s attention in 2005 with the launch of the world’s largest aluminum vessel, the 127 meter Benchijigua Express. The company then started building Littoral Combat Ships (LCS) for the US Navy, based on the same trimaran design. And, now, Austal is launching an even more refined version that improves sea-keeping, passenger comfort and fuel efficiency. This week, Tony Armstrong, Austal’s head of R&D, spoke exclusively to Gizmag about potentially building 20% of the US Navy fleet, how they reduced fuel consumption by a quarter, what sick bags can tell you, and much more.
The Benchijigua Express was the world’s first high-speed trimaran, capable of moving 1350 passengers, 340 cars and over 400 freight lane meters at a rate of 40 knots. Constructed for Spanish ferry operator, Fred. Olsen, S.A., the Benchijigua operates long, arduous routes around the Canary Islands.
Austal are now approaching completion of their next generation trimaran, the Auto Express 102. Now in week 18 of construction, the 102 meter boat is due to launch in October. The bald facts are interesting – it will carry 1165 passengers, 245 cars and 190 lane meters for trucks, travel at 39 knots, and has a 630 nautical mile range – but the story behind the ship is fascinating. Our first question was, why trimarans?
Monohull v catamaran v trimaran. A primer
To achieve real speed and comfort in a ship, the aim is, as Tony Armstrong puts it, “long and thin. But the problem with long and thin is they tend to fall over. They lack what naval architects call stability, which is the ability to come upright. Catamarans get around that beautifully, of course, by putting two long thin hulls side-by-side. And even though there are two, they still have less drag than the equivalent monohull.”
The inherent stability of a catamaran is, however, also its biggest drawback – it rolls very quickly and uncomfortably. “If you’re not careful with the design of the catamaran, the roll period becomes very similar to the pitch period and then the boat tends to operate like a corkscrew as it goes along, which is most uncomfortable.”
“The trimaran is a slightly different approach in that it’s long and thin but to stop it from falling over we’ve put two training wheels on the side like a kid’s bicycle. You’re very slippy in the water with low drag, but you don’t have the high roll accelerations that a catamaran would have. It combines the wave cutting ability of a mono-hull with the stability of a multi-hull.”
The unexpected pleasures of the trimaran
In developing the trimaran, Austal discovered a number of unexpected pluses along the way. “It’s got greater speed for the same cargo weight and the same power compared to a monohull and a catamaran. It’s got better passenger comfort, by which I mean less sea-sickness. It’s got a better sea-keeping ability – able to operate in higher sea states without something breaking.”
Austal also found the trimaran could operate at high speed in much higher wave heights. ”When you go out in waves as opposed to a flat, calm water it’s better than a catamaran, “ says Tony. “And, of course, that’s a practical application because, in reality, most boats are operating in waves.”
There also proved to be less slamming – water hitting the hull – which causes huge loads on a catamaran’s structure and leads to a very noticeable ‘bang’ and the whole structure vibrating. “It’s just not an issue on a trimaran because we don’t have that cross-structure.”
Curiously, the trimaran turned out to produce very little wash. “The waves that it makes – which, of course, impacts on the environment when they come into shore – were fractions of those made by a catamaran. Maybe one-third, one-quarter, something like that. So it’s got that big environmental advantage.”
Tony can think of only one disadvantage to the trimaran: “It’s a little more complex shape to build which, of course, reflects in an increased cost. We’re talking five percent more to build it.”
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