Prediction ofshipmotionsis an importancestep intheshipdesignphasesandconsiderableresearchesarerelatedtothissubject.Itplaysauniqueroleinmainseakeepingcharacteristicssuchasmaximumshipspeedinseawaves,voluntaryandinvoluntaryspeedreductionduetowaveforcesandaddedresistanceaswellasshipsafetyandshiprouting,whichaffecttransportationtime,fuelconsumptionandtotalcost.Thispaperdescribeslinearstriptheorytopredictquicklywithsufficientaccuracyshipmotioncharacteristicsinheadwave,includingaddedshipresistance,pitchandheavemotion.Theeffectsofenvironmentalconditiononcalculationresultsis analyzed by performingsome calculationwithdifferent wave parameter of JONSWAPspectra.ThecalculationresultsfortheDTMBareexaminedbythecomparisonswithexperimentaldatacarriedoutatShipDesignandResearchCentre'stowingtankinPoland,andshowgoodagreement,whichdemonstratestheabilityofthepresentmethodtoassessseakeepingcharacteristicsattheinitialshipdesignphases.ThecalculationisperformedbyusingthecommercialsoftwareMAXSURF.