A couple of suggestions before you haul your boat into the marina. With the motor off and in gear, check to see if the prop will spin, if the prop does spin, check for other irregularities of a blown lower unit. Check the oil in the gearcase for shavings, chips of metal and other junk, grab a magnet and see what sticks. Lastly, if the lower unit is blown the pinion gear will put a big dent in the housing. With decades of experience our marine exerts are a call or click away.