Propulsion Improving Devices (PIDs)
Propulsion improving devices (PIDs) or energy saving devices (ESDs) are different ducts, pre-swirl fins, fin on hull, rudders, caps, contra-rotating propeller (CRP) or other modifications made to the hull or propeller in order to improve efficiency. Depending on the device, the main goal for these devices is to reduce the fuel consumption by improving the flow around the hull or propeller. The three main places to do modifications are in front of the propeller, behind the propeller or do modifications on the propeller or cap. Pre-swirl devices aim to improve the propeller inflow conditions, ducts may improve propulsion efficiency, e.g. by improving the propeller inflow, and post-swirl devices are used to recover parts of the rotational energy in the propeller slip stream.
Applicability and assumptions
Retrofitting measures for propeller and rudder vary in applicability for different vessel types. Wake equalizing and flow separation alleviating devices are best suited to correct known existing hydrodynamic problems and vessels operating at low to medium speeds. They are less effective when the hull geometry has been designed correctly. Pre-swirl devices can be used on all vessel types, mainly for slender and faster vessels, and has to be designed together with the propeller and other relevant post-swirl devices. Naturally, the same applies for post-swirl devices. For more details, see the table below which provides information on different PIDs.
There are some considerations to take when looking at PIDs. It is important to evaluate different devices and identify those devices with the potential to improve efficiency based on the operational profile of the vessel. Computational fluid dynamics (CFD) simulations for the full-scale ship are recommended to evaluate the effectiveness of a propulsion improving device in design. The detailed insight in CFD simulations allows also a better comprehension of why a device is effective or not.
Cost of implementation
|PID||Range of application||Estimated cost of implementation|
|Pre-swirl||Slender and faster vessels, e.g. container and RoRo||$250 000 – $300 000 (USD)|
|Ducts||Bulky and slower vessels, e.g. bulker, tanker, multi-purpose||$525 000 – $575 000 (USD)|
|Post-swirl fins – propeller boss cap fins||All segments, especially vessels with high loaded propellers (RoRo, container)||$100 000 – $150 000 (USD)|
|Wheels – Grim vane wheel||Bulky vessels with space available||$525 000 – $575 000 (USD)|
|Bulbs – Costa bulb||All segments with slow steaming, especially container||$250 000 – $300 000 (USD)|
|Twisted rudder||All segments with slow steaming, especially container||$650 000 – $700 000 (USD)|
|Propeller optimization||All segments with slow steaming, especially container||$250 000 – $300 000 (USD) + material costs of 1.5 t/MW and $7,000 USD/t unless existing propeller is recycled|
|Advanced propeller design – winglets – Kappel||All segments with slow steaming, especially container||$525 000 – $575 000 (USD)|
A likely reduction potential for various PIDs is in the range of 0.5% to 5% on main engine fuel consumption.
Mounting or exchanging appendages such as pre-swirl or ducts may count for up to 5% in fuel savings, whereas propeller boss cap fins and rudder bulbs, such as Costa bulbs, may each count for up to 2% in fuel savings.
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