Two new JIPs launch


Report provides an update on two of the latest Joint Industry Projects, one investigating the mysteries of the moonpool and the other looking into the efficiency gains of two and three bladed propellers on slow-steamers. Both JIPs are about to start.


Moonpools Oscillating moonpools can dissipate a lot of energy when ships are sailing and this is simply lost to the detriment of speed and at the cost of the required power. For vessels in stationary conditions in waves, moonpools are used to launch and retrieve equipment, divers or diving bells, or lay cables and risers.


This use is valid as long as the column of water does not enter in resonant condition. If it does, oscillations can reach as much as three to four times the wave height and sometimes the water of the moonpool ends up on the working deck.


A very critical case of oscillation is observed in transit when the moonpool bottoms are left open, even with perfectly calm sea. When oscillations happen there is a huge


increase in calm water resistance and ves- sels are usually not able to reach their ex- pected transit speed. The additional power needed, and the fuel lost, can be dramatic.


The project aims to provide more insight into the excitation mechanism and prove the feasibility of using unsteady CFD calcu- lations to investigate potential problems with a view to finding solutions early in the design stage.


This JIP will use a combination of model tests and calculations. PIV measurements will be conducted at model scale and the results will be used to validate unsteady CFD computations.


For more information please contact Guil- hem Gaillarde at g.gaillarde@marin.nl.


Two and three bladed propellers The main aim of this new JIP is to deter- mine the feasibility and efficiency gain (claimed to be 20-30%) of the application of two and/or three-bladed, large diameter, propellers for slow steaming tankers and bulk carriers.


Several tasks will be undertaken in the project. The aft ship design will be adjusted through the application of viscous flow calculations and the basic hull design will be optimised with a view to resistance and allowing high block coefficients. Propellers


and wakes will also be optimised to improve efficiency and excitation. The engine, gearbox and propeller configu- ration will be studied and any added resist- ance in waves will be identified and the bow will be optimised. Manoeuvring (including stopping) capabilities in calm water and high seas will be assessed and the structural aspects and vibrations of the propeller, shaft, thrust block and shaft bearings will be examined.


For more information please contact Johan de Jong at j.h.de.jong@marin.nl.


22 report


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