This paper discusses cutting performance of water jets for coral rock excavation at high jet energy.
　The jet energy employed in this experiment was 441 to 968 PS under the conditions that the jet pressure was 290 to 500 kgf/cm2 and the flow rate was up to 900l/min.
　Values of physical properties of the coral rccks showed a great scatter band, since these specimens were porous and heterogeneous from their outward appearance.
　The Schmidt hammer test revealed that these specimens locally have higher compressice strength which is close to that of marble. The brittle indices were 14.
　The specimens were fractured into some pieces during cutting. Therefore, it can be said that the coral rocks are very sensitive to the Water Wedge Effect induce
d by water jets because of their characteristics.
　The empirical equation proposed by Hamada and others can be applicable for predictions of the mean depth of cut only by modifying the empirical constants in the equation.
　This study concludes that water jet cutting is considerably promising to coral rock excavation in practical dredging.