The equation for steady, free floating ice is derived and analysed for a shallow sea. The analysis treats how accurate the free ice drift can be computed when variations in the ingoing parameters are introduced. Besides errors due to unperfect winds, areas with large currents cause bad accuracy. If further more the bottom depth is neglected in these areas the accuracy become worse. Variable ice roughness and variable friction velocity introduce errors which are less important but still noticable in the computed ice drift.