Waterjet manufacturers are streamlining their propulsion systems in response to demand for products that are simpler to install and maintain
The pace of product development across the waterjet sector belies the relatively mature technologies that dominate the market. As suppliers find innovative ways to reduce cost, weight and complexity, operators of fast craft are benefiting.
Australian family-owned specialist Doen WaterJets is seeing the results of long-term investments in simplifying its products. 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 been focusing 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 don’t need to add our own as long as we can position the jet in proximity to the gearbox,” he says.
Doen's direct power take-in recognises the increasing importance of hybrid power configurations for waterjets
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 about 12 years and started to tell customers about the product five or six years ago. The technology has now been made available to all its models – but it is not suitable to 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 that 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.
“The impeller has a fixed relationship between power and rpm, so the trick is configuring it to work efficiently with both the electric motor and the diesel engine”
The company is also exploring opportunities around hybrid propulsion, driven by interest from customers for both low-speed electric manoeuvring as well as boosting top speeds with an electric motor. Here, the challenge for waterjets is in the design of impellers, which are tailored to a specific power output at a specific speed.
“The impeller has a fixed relationship between power and rpm, so the trick is configuring it to work efficiently with both the electric motor and the diesel engine,” says Mr Udvary. “Making this work for both is about having a relationship with the diesel engine and electric motor companies and understanding the design limitations.”
Doen’s tailored approach to impeller design, casting specific products for each application, means that it can tackle that challenge. What remained was to find a cost-effective way to connect the waterjet to the electric motor. Gearboxes with power take in (PTI) are presently only available on some of the larger size gearbox models. Clutchable PTIs that would be sandwiched between the diesel and transmission are available, but can cost more than the gearbox itself.
The solution was to build a PTI directly into the waterjet. This is more cost effective than a large device between the gearbox and waterjet and means that the PTI only has to be rated to the power of the electric motor, rather than the motor and the diesel engine. Another advantage is that the captain has only one set of controls whether the waterjet is being powered by the electric motor, the diesel engine or both.
Mr Udvary reports that the company has developed a PTI-enabled DJ170HP waterjet that connects with a BAE Systems 150 kW electric motor as part of their Hybrid Assist solution. The company can also make a PTI available on its DJ200 jet.
A trend for hybrids
New Zealand-based HamiltonJet also notes a trend for hybrid and electric drive solutions on waterjet-equipped vessels.
“This is still a small trend, but it is definitely here to stay,” says HamiltonJet CEO Ben Reed.
The company is in the process of renewing its entire waterjet portfolio after developing a new design that, according to Mr 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.
HamiltonJet's HTX30 is the first of its waterjets to be subject to a portfolio-wide redesign
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 be replacing all 17 models in its portfolio, with the next new model to be launched this year.
HamiltonJet has also investigated the perennial issue of corrosion in brackish water – something that affects vessels which spend a long time in estuarine waters, where lower salinities cause anodes to become less effective.
The company spent two years capturing corrosion data from a test vessel in Hawkesbury river in 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.
Last year HamiltonJet launched a new vessel control system, AVX, which offers a fully dual redundant class-approved primary control system and improved user interface. The system is designed specifically to make the addition of new features and functions easy. One current function is a low-cost, open-water station-keeping system called JETanchor. Mr Reed explains that the company is working on a precise GP-based manoeuvring control that can allow safe use both around moorings and closer in to obstacles.
One key consideration for HamiltonJet as it developed its control system is that it should not be open to the internet, due to the risk of hacking or corruption. The company is working on a new architecture to allow its jets to connect to the Internet-of-Things without breaking this rule. The system will be trialled on multiple vessels this year.
“Ultimately it will allow us to provide our customers with connected services such as remote support and upgrades, predictive maintenance, vessel data logging and analysis, without any risk to the control of the vessel,” says Mr Reed.
Given HamiltonJet’s exposure in the military and patrol sector – representing more than 40% of sales – it is not surprising that vessel autonomy has emerged as a trend that the company is looking into. The supplier has completed more than 80 installations on vessels with autonomous or remote-control systems. One publicly known example is a minesweeping platform built by Atlas Elektronik and operated by the UK Ministry of Defence.
“The waterjet control system should not be open to the internet, due to the risk of hacking or corruption”
Mr Reed notes that autonomy does not just mean unmanned operation. “We believe ‘skipper assistance’ tools will play a bigger part in the short term, particularly in the commercial space where we are working on products to improve safety and productivity,” he says.
One current example of ‘crew assistance’ is the partial automation of firefighting functions on two new vessels for the Singapore Civil Defence Force. The vessels deploy HM721 jets and Hamilton’s new firefighting control system. The fire pumps are driven off the front of the main propulsion engines and the waterjet control system manages the complicated clutch engagement, priming process and speed control. This leaves the captain free to steer the vessel and operate fire monitors.
Swedish company Marine Jet Power (MJP) is also in the process of 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 (the 310 references the diameter, in millimetres, of the pump intake nozzle). 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 – 280mm and 350mm – 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 include new steering units, hydraulics and updated control systems. The vessel and its sister vessel still have their original pumps.
Marine Jet Power's original reference Cinderella II will host a prototype of the supplier's remote monitoring system
Cinderella I and Cinderella II will also be the first two vessels to receive a newly developed remote monitoring option for MJP’s JetMaster 3 Electronic controls. This allows the supplier to receive real-time data from the vessel to push software updates and run diagnostics remotely, reducing the time operators will have to wait for service.
Italian waterjet specialist Castoldi has also upgraded its portfolio with the introduction of a 1,324 kW, 490 mm diameter unit. The major components have been completely redesigned, with a hydrodynamically optimised steering nozzle and reversing bucket offering higher precision. The new design aims to minimise performance loss while turning as well as improving crash stop capability. Meanwhile, improved pump efficiency leads to a better cavitation resistance, higher bollard pull and thrust compared to its predecessor.
The new model is equipped with an integrated heavy-duty gearbox with 20 gear ratios, as well as a hydraulic clutch and unclogging system. The jet can be controlled by Castoldi’s ACES electronic control system, which manages the engines and all waterjet functions It can also be configured to include dynamic positioning and autopilot features.
Propulsion generalists are also moving in on new waterjet technologies. 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 levels.
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 a combination of 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 new, 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.
Kamewa has also improved on one of its established models after more than three years of research and development. The A5 Series builds on the FF range with greater thrust and a more compact inboard footprint. Aimed at smaller boats of up to 25 m in length, the series is manufactured from aluminium and is available in seven sizes with power outputs between 100-1,230 kW. It will eventually replace the FF range.
The central technology improvement of the A5 is a new single-stage axial-flow impeller. The cavitation margin has been improved significantly which, combined with improved pump efficiency, offers a high bollard pull which improves vessel acceleration as well as station keeping. Other hydrodynamic improvements include a more streamlined steering nozzle and reversing bucket.
According to Kongsberg Maritime general manager sales, Americas, Shival Sapre, the short delivery times and simplicity of installation compared to other waterjets of this size offers advantages for shipbuilders. “For vessels operating at speeds between 25 and 40 knots, it is a very cost-effective solution,” he says.