Is this the world’s best ship design? The Austal 102 trimaran
August 6, 2009
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.”
Learning from the Benchijigua Express
When Austal delivered the world’s fastest and largest aluminum boat to the Canary Islands in 2005, the work didn’t stop there. Benchijigua operated for over a year with a lot of instrumentation on board, gathering data. And, fortunately, the same operator runs two catamarans in the same area, so Austal could make direct comparisons.
“Now, you’ve got to appreciate that Austal sell both, but we found that power consumption is reduced about 20% when operating in a seaway compared to a catamaran in that area. And reduced by as much as 50% when compared with a monohull operating in waves. Which is substantial, because all those power reductions equate directly to fuel consumption reductions.
“We found the vertical accelerations, which are related to motion sickness, reduced about 30% over a monohull. And this one is a sort of non-scientific comparison but one that I’m sure the general public can identify with – the general store of the ship operator issues only one tenth of the sick-bags to the trimaran that it does to the catamaran.”
A perfect platform for going to war
According to Tony, the attack on the USS Cole in the Yemeni port of Aden in 2000 led the US Navy to seriously rethink their priorities. Eschewing traditional warships, which are sitting ducks in foreign ports, they decided to pursue the idea of Littoral Combat Ships (LCS) – fast, maneuvrable and relatively small craft that can operate close to shore. Austal’s trimaran platform was an obvious choice.
“It’s about a three meter draft and you’re talking ten meters plus for a military warship usually, so it’s a huge advantage there,” Tony explains, but that’s just the start. “On the LCS, although it’s only 120 meter in length, quite small compared to other vessels in the US Navy, it nevertheless has the largest helicopter deck of any US warship. It also has the highest helicopter deck above the waterline of any US warship and that’s important because you don’t want to ingest spray in to the helicopter engines.”
In the long term, the US Navy wants 55 of these vessels. On top of that, Austal has an order for two JHSV catamaran troop carriers. “If they build all of the boats that they’re promising to build, by 2014 we will have built 20% of the US Navy’s fleet,” says Tony, “Which is quite astonishing for a West Australian company.”
Coming soon - the new, improved Auto Express 102
A number of refinements will make the 102 an even better ride. Chief among these is the radical use of T-foil stabilizers – horizontal wings on struts that help control pitching – on each “corner “ of the boat. “In effect, we’ve got three underwater wings at the apexes of the boat to give us the greatest control over the ship’s motion. We have sensors on board that sense that one corner’s coming up, so it sends a signal to the wing to provide a force down. All the numbers suggest that that will give a much superior ride compared to even Benchijigua Express, which was good enough.”
Tony and his team also rethought their approach to power. “We’ve got three engines, whereas Benchijigua Express had four, and we’ve done that for reasons of fuel economy. Benchijigua could carry 750 tons with 36mW. The 102 meter can carry a weight of 700 tons and has only three-quarters of the power of Benchijigua, 27mW. So its fuel consumption is less, even though it’s only carrying 50 tons less and it performs in the same area of speed, about 39 knots.”
We’ll soon be able to see the results ourselves, with the 102 due to launch in October. According to marketing, the vessel is already attracting international attention, particularly in China and Taiwan where the trimaran would be well-suited to the challenging sea conditions of the Taiwan Strait.
In the meantime, Tony Armstrong is philosophical about Austal’s relative invisibility. “I get a little frustrated that we do some pretty amazing engineering things here and most of the world doesn’t know about it. But we go on and design the next one and don’t worry about it.”