This research started with the aim of improving the prediction of tool consumption for rock dredging contracts (Verhoef 1988). The approach taken was to view the problem this time from the perspective of the rock mass to be excavated. Earlier, most attention was given to the improvement of the cutting machines and cutting tools. Two aspects can be distinguished: The proper geological and geotechnical description of the rock mass and determination of rock parameters (to be done at the site investigation) and the prediction of the tool consumption and production of the rock cutting dredger.