Figure F9. Penetration rates in Holes U1301A and U1301B while drilling with a 143/4 inch tricone bit in preparation for casing. Information was derived from recordings of bit depth made at 1 s intervals by the shipboard rig instrumentation system (RIS). Because motion of the drill string is not monotonically downward (intervals are drilled, reamed, and cleaned, and ship heave and tides also contribute to bit motion), RIS data required hand filtering and editing determination penetration rates. Gaps in the data occur near pipe joints and as a result of incorrect recordings of bit depth. msb = meters subbasement.
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