Client: KEWATEC | Kokkola, Finland

Hybrid fireboat RESCUE 1500

A turning point in sea rescue – hybrid waterjet lifeboat

Kewatec AluBoat Ab shipyard from Finland has built a ground-breaking firefighting and rescue boat on behalf of the Kiel Fire Brigade, equipped with an advanced hybrid waterjet propulsion system developed by DOEN Waterjets, utilising MOLABO’s Aries i50 electric motors. The boat, which is designed for the Kiel Canal, Kiel Fjord and up to 10 nautical miles offshore, is based on Kewatec’s e-FiFi 1470 design and is suitable for fire protection, rescue services, disaster relief and civil defence.

Further information on the ARIES electric inboard system

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Boat

Total length	16,05 m
Maximum width	4,79 m
Displacement	23,9 t (light), 25,5 t (full load)

Motor

Motors

2 x Doen DJ172-HE Waterjets
2 x Volvo D13-700 Motors
2 x MOLABO Aries i50-Electric motors

Structure of the drive system

Final installation (port side nozzle, looking outwards). The MOLABO electric motor (right) drives the power take-in system (PTI) via the Neugart planetary gearbox (centre) and via a flexible pin-bush coupling (van Doen, left). Both the electric motor and the planetary gearbox are cooled with fresh water via a heat exchanger.

This powerful hybrid drive system has three different operating modes

Diesel mode: Utilises the diesel engines exclusively for high-speed travel.

Electric mode: Utilises electric motors for quiet, emission-free propulsion and reaches up to 6.8 knots for two hours.

Boost mode: Combines diesel and electric drive, increasing performance to up to 33.5 knots.

Innovative waterjet and motor design

The DJ172, the largest waterjet in the compact series, has a 432 mm diameter impeller designed for high bollard pull and moderate input power. DOEN’s unique Power Take-In (PTI) system increases reliability and allows for project-specific customisation by driving the jet shaft in parallel with the diesel engine. This design avoids the complexity and cost of gearbox modifications or in-line hybrid systems. In addition, MOLABO’s Aries i50 electric motors utilise a safe 48-volt system that simplifies installation and allows freewheeling when not in use.

Mastering design challenges

The development of the hybrid system required the harmonisation of power and torque between the diesel engines, the electric motors and the waterjets. Optimised belt ratios and engine speed configurations ensure robust performance in both boost and electric modes. To maintain the functionality of the hydraulic system in electric mode, the team implemented a DC power pack to ensure reliable operation independent of the main engine.

Performance tests

The ship’s performance tests produced impressive results.

Diesel operation: Reached a speed of 31.3 knots.
Electrical operation: Reached a speed of 6.8 knots, exactly matching the predicted performance.
Boost mode: Reached a speed of up to 33.5 knots.

These results emphasise the efficiency of the hybrid system and confirm the decisions made during development.

Operational advantages

The hybrid propulsion system offers significant operational benefits, including improved manoeuvrability, which is crucial for firefighting and rescue operations, as well as a significant reduction in emissions and fuel consumption, which promotes sustainable vessel operations. The ability to switch between the different operating modes provides operational flexibility and optimises performance for different scenarios. This hybrid propulsion system represents a successful integration of MOLABO’s electric propulsion technology with DOEN’s advanced waterjet systems, setting a new standard for efficiency, performance and environmental sustainability in marine rescue operations.

Further applications