Naval architect's cutting-edge powercat

Naval architect Stuart Ballantyne frequently challenges conventional wisdom in ship design, but when it comes to power plants he is very much a Yanmar advocate.

His own vessel, Passion, is a design which he initially developed 15 years ago as the Crusader design. Passion is an all-alloy 17m cat with a beam of 7.4m, draft of 1.0m and a Yanmar 6LPA-STP2 shaft drive engine installed in each of the hull sponsons.

While most look at a vessel like Passion and refer to it generically as a catamaran, Stuart Ballantyne is more definitive in his terminology. In Stuart’s terms this is a Small Waterplane Area Twin Hull (SWATH), developed by his naval design company, Sea Transport Corporation and refined with advanced tank testing in Hobart.

The entry of each hull has a piercing bulb mounted below the waterline, very much the same as the large seagoing commercial ships. This bulbous bow design delivers a series of benefits including better handling, less pitching and greater hull efficiencies.

Designed on the Gold Coast and built in Vietnam by Strategic Marine, Passion was shipped to the Gold Coast for fit out. The Yanmar 6LPA-STP2 engines comfortably slotted into their respective engine rooms with ample space all the way around for easy access.

In many ways, having just 315hp in each side of the hull would appear to be less power than needed in a hull of this length and weight. But the on-water performance stats apparently tell a different and impressive story.

At wide open throttle, Passion is good for 23.5 knots or 44 km/h. At a more sedate cruise speed of 18 knots (33 km/h) the Yanmar 6LPA-STP2 engines are ticking over at 2800 rpm and returning modest fuel consumption figures of 22.5 litres per engine per hour. 

With 4000 litres of fuel on board Passion has a massive 1000 nautical miles cruise range at 18 knots.

"This is a highly efficient hull with equally as efficient Yanmar engines," said Ballantyne. 

"My research proves that a mono hull of the same length and weight would need a massive boost in horsepower and associated fuel consumption to achieve the same performance. This data is absolute fact."

The strength of a Ballantyne’s design lies in its versatility. It has been built in both alloy and fibreglass, in both motor and motor sailing configurations. There have been commercial variants operating as game boats, charter vessels and as commuter ferries.

As a naval architect, Ballantyne pushes the boundaries of conventional wisdom. His absolute commitment for SWATH catamaran hulls is gaining favour in various markets. Even his design for military and commercial landing vessels that unload on a beach via a stern ramp (as opposed to the conventional drop bow design) is proving to be a commercially viable and superior operational system.

Further details on the naval architect's many other Sea Transport designs see www.seatransport.com.