What kind of system might constitute the ‘holy grail’ of waterjet technology? Presumably, a jet system with a minimal number of components, which is light and easy to maintain, would fit the bill – particularly if it also happens to be cost-efficient. Other highly desirable features would include the ability to meet the most stringent environmental regulations for coastal and freshwater areas, as well as the ability to maintain the high speeds and manoeuvrability that waterjet users have come to expect of these solutions.
The aforementioned features are just a few of the considerations that Colorado-headquartered manufacturer NAMJet believes it has addressed with the launch of its new, patent pending RAPTORJet range, which provides users with a choice between hydraulic and electric actuation. However, as NAMJet engineering manager Tim Curtis notes, there are a few industry sceptics who believe that the notion of such a system remains as unlikely and elusive as the legendary Grail itself.
The RAPTORJet debuted at this year’s Seawork show in Southampton, UK, the jet type having been installed aboard the 10m demonstrator craft RAPTOR. NAMJet, though, was giving little away; visitors to the group’s quayside slot were denied the sight of the actual internal workings of the jet and instead shown the installation aboard a typical vessel, and silent operation of the system without the engines running.
No leaks, less parts
The first question is, why bother with electric actuation at all? Hydraulic actuation certainly has its advantages, including the ability to deliver high power-to-weight ratios, but these benefits come with the risk of potential oil leaks. Curtis explains: “Oil leaks can be very common – these often occur as the result of a burst hose or loose fittings. Hoses can become brittle, be struck by an object, or just be subjected to the type of abuse you get in a high-speed, marine environment, leading to cracks and then leaks.” The nature of these leaks themselves are also troublesome, Curtis adds; few will envy the crew members forced to react to a hose spraying oil into the environment or bilges.
Similarly, hydraulic actuator-based systems typically require an investment in multiple companion parts, which can also be time-consuming and costly to maintain and repair. The key advantage to electric actuation, then, is the ability to do away with the presence of hydraulic pumps, oil tanks, filters and plumbing – leading to savings in weight, time and cost.
Eliminating the need for these components can result in genuine lightship gains. For instance, Curtis comments, the stainless steel or aluminium manifold blocks required by hydraulic actuators can weigh between 18-22kg alone, and an electric actuator can also eliminate the need for a raw water system to cool hydraulics. Similarly, and importantly for marine users operating in zones subject to strict noise level control, electric actuation can also negate the need to purchase and install noise-reduction equipment.
In terms of time savings, he adds: “Many in the industry claim that hydraulic actuation-based systems should be serviced every 100 hours, and each service job will typically take a couple of hours to complete. In contrast, the mean time between failures [MTBF] for the electric actuation model is estimated at 20,000 hours.” Such an advantage could result in reduced manpower overheads and lesser risk of vessel downtime and/or damage during operations.
Swapping from hydraulic to electric actuation is a relatively straightforward process, Curtis says, necessitating the switching of a control box. The electric actuation is enabled by NAMJet’s Intelligent Navigation & Control (iNAV) system, which can be configured either as the iNAV-iN1, a basic set-up that provides control over the RAPTORJet’s throttles, transmission, jet buckets and steering, all the way up to the iNAV-iN5, which comprises a touch-screen interface, joystick control and positioning.
Features of the iNAV include the ability to oversee station-keeping and dynamic positioning (DP), as well as to exert multi-vessel positioning control from a single vessel – a capability that could prove highly useful to vessels engaged in undertaking personnel transfers, survey work and/or oil spill response operations, for example. In this way, personnel located in one of the vessels in the fleet, or in a mothership – or even seated within a shore-based station – can control the positioning of other vessels in the fleet from a single operator console. “There is a limit to the number of boats that could be used, as with any system, but we haven’t found that limit yet – it’s probably in the range of several dozen,” Curtis says.
Although this remote control feature is primarily intended for localised operations, should the control vessel / shore station and target vessel be equipped with satcomms terminals, there would be no limits on vessel distance and range.
Initial trials of the RAPTORJet were conducted aboard RAPTOR – which was built specifically for this purpose by NAMJet’s parent company, Birdon America – in Pueblo, Colorado, earlier this year. For these tests, the vessel utilised a propulsive set-up comprising twin 358kW Cummins 6.7litre QSB engines, ZF 301-1c transmissions and the RJ431e model of the RAPTORJet.
“The trials took place in freshwater conditions, at high altitude; hardly an environment with optimal conditions for thrust,” Curtis recalls. “Even so, we were able to achieve a comfortable speed of 39knots. You can add a few knots to that in saltwater or coastal conditions, so we’re looking at the ‘low 40s’ when using this system.”
Another reported achievement was a silent and smooth system – certainly in comparison to hydraulic actuator-based jets. Curtis even describes the initial trial runs as an “eerie” experience, with the ‘usual’ waterjet noise reduced to inaudible levels, accompanied by a notable reduction in abrupt stops/starts, feedback and shuddering. “The boat was moving exactly as it was supposed to,” says Curtis, “but the jet wasn’t producing the noise that typically indicates this. The lack of sudden ‘stop/start’ jolts was also encouraging, and could extend the lifespan of the active system.”
Following Seawork, NAMJet is now looking to clinch its first RAPTORJet sales, and will continue to tweak the product for various future configurations. For example, Curtis reveals that there are plans to roll out the electric actuation tech to cover the group’s entire range of waterjets. “We don’t envisage an upper power limit,” says Curtis. “We want to develop an electrical actuation version of our largest jet.”