CD Model Ice - Preliminary Observations on the Effect of Density on Tank Testing

A brief description of the apparatus for producing controllable density (CD) model ice is given. Ice density is shown to affect nearly all aspects of ice tank testing. Some preliminary results are given for ice-propeller interaction, presawn ice resistance, rubble ice resistance and level ice resistance. The level of ice-propeller interaction is reduced using low density level ice primarily by increasing the minimum model speed before ice in ingested in to the propellers. This leads to a significant reduction in propeller milling at low speed. Rubble ice resistance is shown to be dominated by the ice buoyancy with an approximate 400% increase in resistance as ice density was reduced from 930 kg/m3 to 750 kg/m3. Presawn ice resistance has a buoyancy dependent component which is important at low speed. Ice buoyancy is seen to significantly increase this component. The effect of ice density on level ice resistance is quite insidious in that it can alter the icebreaking process significantly increasing the resistance of certain bow forms. The increased buoyancy of the broken ice cusps causes them to float higher as they are rotated by the advancing bow. These pieces may then have a higher incidence of jamming between the hull and the unbroken ice sheet leading to crushing events and large loads in the shoulder region.