While in the cavitation observation test the cavitation behaviour in one particular propeller operating condition is described, recorded and judged, the inception test gives information about occurrence of all different kinds of cavitation phenomena in dependence of the propeller loading. The result is the so-called cavitation inception diagram showing cavitation inception curves for tip vortex, sheet and root cavitation on face and back of the propeller in a σn-KT-diagram. The ship operating curve (normally obtained from the towing tank propulsion test) is also included in this diagram so that ship speeds of first cavitation occurrence can be red off at the intersection points of this latter curve with the respective inception curves. The area above all the inception curves indicates the potential of the propeller for cavitation-free operation.
In case of vortex cavitation scale effects are considered by McCormick’s scaling law so that all test results are valid for full scale.
Performance of cavitation inception tests at highest possible Reynolds Number with the complete ship model for wake generation ensures highest reliability of the test results. HSVA’s scaling procedure has been tuned over more than 20 years and is approved by various correlation studies where full scale cavitation inception investigations have been replicated in HYKAT.
This kind of test is a must whenever complete cavitation freeness has to be ensured up to a certain ship speed, e.g. for matters of high comfort or for military reasons.