Yanmar Powers ‘Spirit of Freedom’


The dive business is booming worldwide and nowhere in Australia is it more pronounced than on the Great Barrier Reef. Back in May 2015, the dive vessel Spirit of Freedom was repowered with a pair of Yanmar 6HYM-WET engines and 6,000 hours later the owners could not be more pleased.

Originally built in Gladstone in 1992 as a high-end charter fishing boat, Spirit of Freedom is an unusual construction. The hull is steel, but the superstructure is alloy. With an overall length of 37m and beam of 7.4m, this displacement hull displaces a very hefty 250 tonnes.

In the early 2000’s the Spirit of Freedom was acquired and brought into the Tusa Dive fleet to operate from Cairns as a liveaboard boat. A variety of trips of 3, 4 and 7-day duration are on offer, taking a complement of 26 divers to the Great Barrier Reef and also remote Coral Sea reefs.

It is little wonder why Spirit of Freedom is so popular amongst divers. Spread across the three decks of living space are generous cabins with private bathrooms. All the amenities of a hotel are supported by first class meals and outstanding service. Typical of a vessel of this era, there is also an impressive amount of timberwork through the cabins and lounges.

Naturally, when customers have high expectations with their live aboard dive trip, the pressure is on the operator to deliver. At the heart of the Spirit of Freedom experience are two Yanmar 6HYM-WET engines which are relied on to perform faultlessly every day of the year.

The Yanmar 6HYM-WET is a purpose built commercial marine engine. The engine is a 6 cylinder in-line block which has a displacement of 13.733 litres and an all up weight of 1,386 kgs. This model engine is continuously rated to develop 500 mhp (368 kW) at 1950 rpm. A key feature is the high torque developed, together with industry leading durability.

This model includes Yanmar’s latest combustion chamber design, named ASSIGN, a system originally pioneered by Yanmar on their large bore, low speed propulsion engines. These engines are IMO Tier 2 compliant, ensuring emissions are exceptionally low, an important consideration when operating on the Great Barrier Reef.

The ASSIGN technology combined with Yanmar’s mechanical fuel system provides commercial operators with excellent fuel economy. The cylinder head is a quad valve design. In this configuration, the Yanmar 6HYM-WET excels in conditions demanding continuous commercial use.

The upgrade to Yanmar 6HYM-WET represented more than a change in brand. The new Yanmar engines represented an increase in power from 410 mhp (306 kW) to 500 mhp (368kW). The Yanmar engines are much lighter and more fuel efficient than the original British origin engines. In addition, the engine is specifically designed for ease of maintenance, minimising downtime and speeding up all routine maintenance.

The winning formula of smaller, lighter, less fuel and more power is exactly the winning formula that any charter boat operator is seeking. According to skipper Ross Thompson, the Yanmar repower has proven to be a great initiative.

“We work these engines continuously on a rigid 7-day schedule with virtually no opportunity for anything but routine maintenance,” Ross Thompson said.

“Typically, we log up 52 engine hours every week. Every 400 hours we change the oil and replace filters. We’re in port for 6 hours each week so it is a very tight schedule that we work to.”

“On our 7-day dive trip Spirit of Freedom travels 577 nautical miles and the Yanmar’s fuel consumption is 5,700 litres for both engines. It works out to about 50 litres per engine per hour which is exceptionally good.”

An optimum cruise speed of 11.5 knots is achieved at 1500 rpm, but at the wide open throttle of 1900 rpm, Spirit of Freedom is good for 14.5 knots.

“The Yanmar repower has been an unqualified success,” said Ross Thompson.

“The Yanmar engines have proven to be much stronger with more power and torque. They give us an increase in hull speed using less fuel.”

On the strength of the Yanmar repower with Spirit of Freedom, Tusa Dive in Cairns then repowered their day boat, Tusa 6 with a pair of Yanmar 6HY marine diesel engines. This is the strongest possible endorsement of Yanmar by a commercial operator.