The innovation of podded propulsors has developed fast both technically and in commercial acceptance in the shipping industry. The concept of an azimuthing submerged electrically driven pull propeller provides various economic, safety and comfort advantages. Vessel layout, assembly, propulsion efficiency increase, safer navigation in restricted waters and a significant increase in comfort on board due to vibration and noise reduction have all contributed to a swift acceptance of the podded propulsors by the maritime industry.
Developments in this field so far, are concentrated at European propulsion system manufacturers and European yards, which are the market leaders in the design, construction and operation of large cruise liners and ferries. Podded propulsors are considered as key technology for these ship types as well as various others.
Starting with cruise liners and ferries operating in fairly mild conditions, it is expected that podded propellers will be applied on various other ship types such as sea-river ships, coastal vessels and navy ships in the near future. To realize such applications and to incorporate this key technology in a competitive industry, the improvement of structural integrity and reliability of podded propulsor and ship hull is essential.
PODS IN SERVICE has been aiming to:
- Assess and evaluate the reliability and integrity of podded propulsors under operational conditions, comprising extreme loads during harsh conditions such as imposed by severe waves and manoeuvres, cumulative fatigue loads and 'incident loads and responses', such as originating from emergency manoeuvres and crash stops; and
- provide computational methods for determining these loads in the design and engineering stage.
To achieve the above objectives the following tasks were identified:
- Concurrent measurement campaign on-board four pod-driven ships, namely two cruise liners, a ropax ferry and a supply vessel;
- data analysis;
- computational methods; and
PODS IN SERVICE ran a full scale monitoring campaign, using extensive measuring equipment on-board the following four vessels:
- The supply vessel Botnica, equipped with ABB Azipods, and operating in the North Sea;
- the new, 300m long cruise ship GTV Radiance of the Seas, equipped with ABB Azipods, and operating on the American west coast including Alaska;
- the new, 300m long cruise ship GTS Summit, equipped with Rolls-Royce Mermaid pods, and operating in the Mediterranean, Caribbean and Baltic Seas; and
- the new-built Ropax ferry Nils Holgersson, equipped with Siemens Schottel SSP pods, and operating the TT-line Travemünde-Trelleborg service.
The Joint Industry Project (JIP) has:
- Determined loads of podded drives from strain gauge measurements during dedicated sea trials, and by computational methods;
- developed a pod load calculation model that allows for assessing force components and overall loads;
- found loads during crash stops and during extreme manoeuvres in transit (under full engine power) to be the most extreme; and
- observed a higher than anticipated impact of slamming and whipping of the ship hull in severe weather conditions on pod body dynamics.
Podded drives are a new type of propulsor but drawing on proven components, hence will be suitable for adaptation to other vessels, e.g. in offshore operations and inland navigation. However, no specific recommendations to this respect have been made as part of PODS IN SERVICE.
Sea trials with pod driven ships are currently conducted according to the IMO requirements for conventional propellers and rudders and in particular the steering trials such as hardover/hardover tests induce severe loads on pods whereas they are not considered as realistic or necessary for this type of ship. Therefore tailored requirements for sea trials of ships using podded propulsors are proposed to IMO for implementation in future regulations.
No results directly relevant to this theme. However, please note that some findings relevant to the project's key theme (Safety and Security) are generically applicable.
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