Trimarans make waves in the fast ferry sector

Austal shipyard has scooped a contract to build two trimaran ferries for Fred Olsen. Its technical manager tells Rebecca Moore about this order and explains why a trimaran model is suited to the fast ferry sector

The trimaran fast ferry passenger model has hit the headlines after Australian shipyard Austal’s announcement that it is building two more trimarans for Fred Olsen.

The €126M (US$152M) contract, announced at Interferry 2017 in Split, Croatia represents Fred Olsen SA’s largest-ever ferry order. The two new ferries will add to the Fred Olsen Express fleet of six vessels that transport more than 2.8M passengers, 750,000 cars and more than 150,000 heavy vehicles over five routes in the Canary Islands each year.

This order comes on the back of the 2005 launch of Benchijigua Express, a 127 m stabilised monohull (trimaran) vessel that Austal built for Fred Olsen.

Explaining why the trimaran model was chosen by Fred Olsen and which part of the fast ferry market that the solution is particularly aimed at, Austal technical manager James Bennett told Passenger Ship Technology that the trimaran hull had been developed specifically to offer passengers and ferry companies a high-speed platform that delivers improved seakeeping and more controlled vessel motion than a monohull when operated in sea areas with challenging conditions.

He added that “high-speed catamarans and monohulls, while effective vessels for short sea and more sheltered routes, have typically suffered from a poor reputation with regards to seakeeping and passenger comfort.”

Trimaran benefits

Unlike catamarans and monohulls, the trimaran gives the designer the ability to fine-tune or adjust the roll characteristic of the hullform. This adjustment is achieved by increasing or decreasing the volume of the side hulls, termed ‘amahs’. “More volume in the amahs will give the trimaran a stiffer or faster roll characteristic closer to a catamaran; less volume [will give] a softer roll characteristic similar to a monohull,” Mr Bennett said.

The characteristic of a catamaran is to have a fast roll period, due to its large metacentric height (termed GM). Mr Bennett said that in a typical 86 m to 120 m catamaran, the GM may be between 45 m to 60 m. This results in a roll period of around three-five seconds. The GM of a trimaran can be adjusted, however, so that a slower roll period is achieved and the GM on the Austal trimaran varies between 4.5 to 7.5 m, depending on its deadweight, giving a resulting roll period of 10-15 seconds.

“The slower roll period means that when the vessel is operating in seas ranging from bow quartering through to beam and stern quartering, passengers experience a significantly lower level of acceleration, due to the slower roll period,” Mr Bennett explained. In seas forward of the beam, the length and volume distribution of the trimaran’s centre hull provides excellent soft-pitching motions, he added.

Evidence of a trimaran’s seakeeping ability on rough seas can be seen on Benchijigua Express: Fred Olsen said that it had never cancelled a scheduled sailing due to bad weather or technical faults. Fred Olsen director Juan Ignacio Liaño confirmed that Benchijigua Express had never “missed a beat” in the company’s schedule, with no sailing cancellations due to technical faults over the past 12 years of operation.

“The reliability of the vessel is outstanding and it is a testament to Austal’s hull design and quality construction that we have never had to cancel a scheduled service due to severe weather or technical issues,” Mr Liaño said.

Austal’s proprietary Ride Control technology was used on Benchijigua Express and a newly-updated version will be used on the new vessels. Austal’s new generation Ride Control system consists of a bow-mounted T-Foil and roll control foils mounted on the amahs. Mr Bennett said that this helps reduce pitching motions while roll control is helped by using two large flaps located on the centre hull just forward of the waterjets.

Austal has conducted an R&D programme to improve the control system since the earlier generation trimarans. “This work, along with advances in the vessels’ hull design, will offer passengers an improved level of comfort compared to the earlier trimaran vessels,” Mr Bennett said.

The benefits of Ride Control are that passengers consistently report a smoother journey while the crew benefits from safer and more productive schedules where seasickness is minimal and passengers, vehicles and cargo are more secure.

Mr Bennett also elaborated on the manoeuvrability of a trimaran, saying that it was similar to a high-speed catamaran or monohull using waterjets for steering. “In harbour and for low-speed manoeuvres, the trimaran’s waterjet steering is augmented by drop-down bow thrusters that are designed to offer safe manoeuvring in wind strengths up to 40 knots, which is very high,” he said. “It is just a matter of the operator specifying the capability that they require.”

New Ships

The two new ferries, to be designed and constructed by Austal in Australia, are both 117 m long, have a beam of 28.2 m and capacity for over 1,100 passengers and 276 cars each. Featuring a draught of 4.2 m and deadweight of 750 tonnes, the new vessels are light and fast with the practicality and manoeuvrability to operate in any port.

Powered by four MTU diesel engines and propelled by four waterjets, the trimarans will achieve service speeds of 38 knots with a range of up to 711 nautical miles.

Austal said that the close commercial relationship and effective collaboration with Fred Olsen over the life of the Benchijigua Express – from design through to delivery and operations – has formed the basis for the next generation of commercial trimarans.

Construction of the vessels will commence in Henderson, Western Australia in 2018, and continue over 29 – 36 months.

Trimaran vs catamaran

“A trimaran is an excellent vessel for sea routes that are long or are rough due to the superior passenger comfort compared to a catamaran” James Bennett (Austal)

Examining the case for a trimaran hull versus a catamaran, Mr Bennett said that a trimaran is an “excellent vessel for sea routes that are long or are rough, due to the superior passenger comfort compared to a catamaran.”

But “Catamarans are still an excellent high-speed platform for short sea routes that do not experience rough seas,” so Austal would always recommend and advise customers on which hull form they believe is the most suitable, for the route(s) under consideration, he added.

 

 

Snapshot CV James Bennett, Austal

James Bennett is technical manager (commercial) at Austal. As a founding team member and experienced naval architect, he has contributed to the company’s success since 1988 and will be celebrating 30 years’ service this year. During this time, Mr Bennett has held various differing roles covering design, project management and sales and marketing support. In these roles, Mr Bennett has been involved with the design and development of several key projects, including the 127 m trimaran vehicle passenger ferry Benchijigua Express for Fred Olsen SA and other major contracts including a 106 m catamaran for Virtu Ferries, a 113 m catamaran for Faergen and the 102 m trimaran Condor Liberation. Most recently, James has played a key role in the development and securing of contracts for the two new trimaran ferries for Fred Olsen. After qualifying with a Higher National Diploma in naval architecture from Southampton College of Technology, UK, Mr Bennett worked at companies including Allday Aluminium in the UK, Seaconstruct in Singapore and Precision Marine in Western Australia.

 

 

 

Austal high-speed ferry orderbook:

• 109 m high-speed vehicle passenger ferry for Molslinjen of Denmark
• 109 m high-speed vehicle passenger ferry for Fjord Line of Norway
• 56 m high-speed passenger ferry for FRS of Germany
• 2 x 50 m high-speed passenger ferries for Brave Line of Taiwan
• 30 m high-speed passenger ferry for VS Ferries of the Philippines
• 42 m high-speed passenger ferry for Blue Sea Jet of China (Aulong joint venture with Jianglong Shipbuilding)
• 35 m high-speed passenger ferry for Blue Sea Jet of China (Aulong joint venture)
• 2 x 117 m high-speed vehicle passenger ferries for Fred Olsen SA of Spain