i'm building an airboat with a 16 inch proppeller........the link between the motor and propller is 1/4 inch steel rod about a foot long......so the air goes around the motor suffectlly.......but when it runs.....it breaks off the shaft at the tang.......in the motor.....i've checked for drag......can't figure it out......any ideas for a driveshaft would help........what do other people do?