We're all quite used to seeing wings on aircraft, but surely not on a passenger ferry? What about a ferry that really is just one giant wing filled with people? That's exactly what Tasmanian shipbuilders, Incat have in mind. Their vision involves a trimaran carrying 200 passengers and riding almost completely out of the water as it blasts along at 100 knots.
The company has built a succession of scale models to test their concept. The last and biggest of the prototypes was written off in an over-exuberant test run last November, but not before it had reached a speed in excess of 60 knots. Despite the setback, the company chairman Robert Clifford (who was at the helm during the ill-fated test) imagines that full-scale commercial versions of his revolutionary watercraft will be carrying passengers within 3 –5 years.
The basic structure of the vessel is a horizontal wing supported by three, sleek hulls. At speed the wing provides enough lift to pull the hulls about 90 percent out of the water, leaving just their stern sections submerged. That's enough water contact to allow the ship's advanced gas turbine water jet engines to thrust it forward whilst minimising drag. Combined, the wing's streamlining and lifting effect offer an unparalleled power to speed ratio. In speaking about the test run, Mr Clifford reported: "Never before has a heavy displacement, high-speed craft traveled so fast with so little power."
In fact the outboard motors that powered the prototype had previously been attached to a conventional catamaran fishing boat. On that vessel the engines were only capable of driving it at 40 knots, demonstrating that the wing design offers an advantage of roughly 33 percent efficiency; a promising result for a first attempt. Clifford says that his next scale model will be a few factors larger and capable of carrying 20 – 30 people.
In designing any type of rapid transport, scaling-up is the biggest problem. Principles that work very well in miniature can turn out to be impractical for a variety of reasons when applied to full-size models. Clifford cites the example of hovercraft, where increasing the size of the vehicle necessitates an exponential increase in engine power, to the point where the engines become so big the craft can't move. He doesn't see that problem with his wing concept.