Figure 3. The two graphs compare ship heave motion (top) and drill pipe motion (bottom) with the AHC in use during Leg 189. Ship heave motion was substantially reduced for the drill pipe when the AHC was used. Typical ship heave in this diagram is ~4 ft, except for the two excursions marked in the top diagram at 200 and 280 s. Drill pipe deviation is defined as drill string motion. It is referenced to sea bottom, but measured at the rig floor. Typical deviation in this diagram is 4.8 in., except for the two excursions indicated where maximum ship velocity was exceeded. Historical data indicate that the maximum drill pipe deviation is 4.8 in. The range is the same in both graphs (12 ft).