So, we can say D H P or p d is equal to 2 pi n q; q you are measuring on the shaft. So, we can get the D H P. Thrust power, what is thrust power? T into V A, and effective power - R T into V V S. It is the V S ship speed. Please recall we had defined this before. So, now the drop in speed a power from P B, that is, B H P to D H P is defined by an efficiency called shafting efficiency is equal to B H P by D H P which we have seen can vary from 2 to 8 percent depending on gear drive or non gear drive aft engine or slightly mid-ship engine or whatever.