The most often used definition of "TIT" is Turbine Inlet Temperature for a jet/turbofan/turboprop engine: It is the temperature aft of the combustion chambers and immediately prior to the gas entering the turbines. Horsepower required to turn any propeller is proportional to RPM cubed, i. e., to turn a propeller twice as fast takes eight times the horsepower. For example: if we have a 230 HP diesel @ 2200 RPM and burns 11.5 GPH (yes, one gallon per 20 Horsepower, but this should really be a manufacturer's number), but because of the way the boat has been mis-propped the engine will only turn 2000 RPM when we look at the Horsepower vs RPM curve we find the engine is only developing 200 HP. Further, we have decided to cruise the boat at 1800 RPM. What is the rought estimate of the expected fuel burn? We have (1800/2000) = 0.9 and 0.9 x 0.9 x 0.9 = 0.729 and 0.729 x 200 = 143.8 HP in cruise. Fuel burn would be approximately 143.8HP/230HP x 11.5GPH = 7.19 GPH @ 1800 RPM. Hope this clarifies it. John