The Classical Problem Of Predicting The Hydrodynamic Forces On A Ship As It Travels Through A Seaway Has Been A Challenging And Active Area For Over More Than Hundred Years. It Was William Froude Who First Studied The Unsteady Oscillations Of A Ship In Waves In As Early As 1861. Since Then, The Problem Of Determining The Behaviour Of A Ship In Waves Has Remained As One Of The Most Interesting Topics In Marine Hydrodynamics. The Ship- Motion Problem Or The Seakeeping Problem As It Is Known, Has Its Own Importance Because Oceangoing Ships Are Designed To Operate In A Wave Environment That Is Frequently Uncomfortable, And Sometimes Hostile. Unsteady Motion And Structural Loading Of The Ship Hull, Are Two Of The Principal Engineering Problems Which Result When A Vessel Travels Through Ocean Waves. From The Point Of View Of The Underlying Basic Hydrodynamic Principle, Prediction Of Ship Motions Can Be Regarded As A Problem Under The General Class Of Free Surface Flow Problems In Ship Hydrodynamics. One Of The Unique Features Of These Classes Of Problems, In Comparison To Problems In Other Branches Of Fluid Mechanics, Is The Presence Of The Free Surface: The Interface Between Water And Air. Free Surface Flow Problems In Marine Hydrodynamics Are In General Those Where The Concern Is To Determine The Fluid Forces Exerted On A Stationary Or An Advancing Rigid Body In The