Buoyed Weight: Suspended Drillstring. Consider a drillstring made up two pipe configurations: (i) an upper 10,000-ft-long drillpipe (steel; 19.5lbm/ft length) and (ii) a lower 600-ft-long drill-collar (a thick-walled joint of steel pipe; 147lbm/ft-length). This drillstring is to be suspended (completely immersed) in an underground vertical borehole filled with a 15-ppg ( lbm per gallon) drilling mud (clay slurry; "weighted" drilling fluid). The density of steel is 490lbm/ft3 (for both drillpipe and drillcollar). Calculate the "hookload" (force) that must be supported by the hoisting system. [1 gallon = 77/576ft3;1 slug =32.174lbm;g=32.174ft/s2.] Ans. 218,348lbf. Remarks. The "heavy" drill-collar keeps the drillstring in tension (avoiding pipe buckling) and provides downward force/weight on the attached drill-bit (to break up the rock; not shown here)