Over the past year waterjet makers have advanced designs to take complexity out of their products
Australian family-owned specialist Doen WaterJets is seeing the results of long-term investments to simplify its range of jets. According to director of engineering Tim Udvary, the developments tackle one of the perennial challenges to waterjet uptake: the price premium compared to installing propellers.
For the past decade or more the company has focused on two technologies that cut both complexity and cost. The result of both projects combined is a 20-30% reduction in the cost of the waterjet, as well as maintenance and durability benefits.
The first development eliminates the need for a thrust bearing that is traditionally packaged with waterjets, explains Mr Udvary. “Waterjets are usually attached to a thrust bearing while propellers are not. But gearboxes are always made with a thrust bearing inside. We do not need to add our own as long as we can position the jet in proximity to the gearbox.”
No thrust bearing means no lubrication, cooling or maintenance requirements as well as removing parts and cost. The company has had prototypes in operation for 12 years and started to tell customers about the product five or six years ago. The technology is now available on all its models – but it is not suitable for every application, says Mr Udvary.
“The engine needs to be in a certain position. It is possible to get the engine close to the aft and in some cases, especially in high-speed craft, this is desirable. Depending on the application, having the engine near to the jets also means that you can carry more crew, cargo or passengers.”
The second technology addresses one of the most expensive parts of the waterjet: the intake. These are often made of cast or plate metal, but Doen investigated whether moulded, fibreglass hulls could have intakes moulded with the hull. The moulding process means the bottom half of the intake cannot be moulded – a limitation that has led some companies to offer a moulded intake tube for retrofitting after the hull itself is moulded. Doen decided to mould the top half of the intake as part of the hull, bolting the bottom part to the transom afterwards.
According to Mr Udvary the integrated waterjet (IWJ) design is particularly suited to series production. Although there is some upfront cost for moulding, the return comes quickly when more vessels are made.
IWJ and direct-thrust technologies have now been installed on more than 100 units. Most recently, two fibreglass catamarans built by Abu Dhabi-based Jalboot Marine have been launched for passenger service in the Maldives. They and their imminent three sister crafts feature twin DJ170HP-IWJ jets. In the governmental sector, which represents around 60% of Doen’s current business, Indonesia has ordered direct-thrust variants of the supplier’s DJ200, DJ200-DT jets for eight combat boats.
A novel impeller design boosts the efficiency of Wärtsilä's new WJX series
In March, Wärtsilä launched a new series of modular waterjets. The WXJ series will eventually replace the well-established LJX series. A new axial pump design has boosted performance, with an increased thrust of as much as 3%, while the improved cavitation margins help reduce the environmental impact by lowering noise.
Unlike a non-axial design, the Wärtsilä waterjet does not expand in a radial direction downstream. As the water flow is directed through the pump along the most efficient path, it is easier to fit the jet to the available transom space. The reduced transom size also decreases the weight of the installation significantly. These weight optimisations and savings can be as high as 20% compared to non-axial jet designs.
Thanks to the increased pump cavitation margin of 35% and the lower impeller tip speed, more power can be introduced to the pump during manoeuvring. This results in a 15% higher manoeuvring thrust and faster response to acceleration. Operating flexibility is improved thanks to the reduced number of shaft lines and the higher loads of the remaining engines.
The first installation of the new jets will be on a 100-m wave-piercing catamaran ferry being built for Trinidad and Tobago by Incat in Tasmania. The vessel will be powered by four Wärtsilä WXJ1200 waterjets. The ferry will be capable of a service speed of 36 knots and will be able to carry up to 1,000 passengers and 239 cars.
Swedish company Marine Jet Power (MJP) is also rolling out a new portfolio of waterjets that aims to simplify installation for smaller to mid-sized applications. Last July it introduced its X-series mixed-flow waterjets with the 700-kW 310 X model. Borrowing technology from MJP’s bigger waterjets, the X-series feature an aluminium skin to make maintenance simpler. To ease installations, the jet comes preassembled on a skid, with hydraulics and an integrated intake.
“It’s almost like a jet-in-a-box,” says MJP chief executive Magnus Sörenson.
The 310 X and future X-series models feature cast aluminium reversing buckets designed to decrease stopping distance and increased manoeuvrability. A new narrow design minimises the installation while a mechanical tie bar synchronises steering with the helm pump.
The first vessel with the new X Series waterjets has recently been on sea trials, Mr Sörenson reports. The 12-m fire and rescue vessel built by Italian builder Stem Marine has dual MJP 310 X waterjets. It reached speeds in excess of 40 knots.
The company has already sold two batches of the new X-series waterjets and will serve a wider range of applications when it unveils further sizes – 280 mm and 350 mm – later this year.
Durability is a point of focus for MJP, which delivered its first ever waterjet package in 1987 to the operator of Stockholm archipelago ferry Cinderella II. Thirty-two years later, the company has recently upgraded the waterjets on the ferry after 60,000 running hours. Updates to the vessels include new steering units, hydraulics and updated control systems. The vessel and its sister vessel still have their original pumps.
New Zealand-based HamiltonJet is in the process of renewing its entire waterjet portfolio after developing a new design that, according to chief executive Ben Reed, delivers three benefits: between 3% and 7% improvement in thrust; up to 40% more bollard pull; and several knots improvement in minimum speed.
“Achieving an improvement in all three of these together has been a goal of ours for some time as they usually trade off against each other,” he says.
The first new jet to be launched was the HTX30. HamiltonJet, which sells between 1,200 and 2,000 waterjets each year, reports good early sales of the new HTX30 jet. The company will eventually replace all 17 models in its portfolio, with the next new model to be launched this year.
The company spent two years capturing corrosion data from a test vessel in the Hawkesbury river, Australia. Using this data HamiltonJet developed advanced corrosion simulations which it now uses in jet design to optimise material selection, coatings, anode position and size. The result, says Mr Reed, is a 10-fold improvement in brackish water corrosion resistance for its latest products.