My Boat has an inboard engine, it runs Good but The propeller does not spin?

If it is an inboard engine then the shaft should have a keyway, commonly caled a woodruffe key. Check to see if that has sheared into bits

jmcx20
June 2013

jeff beat me to it. remove the nut that holds the prop, remove the prop (some bits (of the old shear pin) may drop out) there will be a pin through the shaft which you will probably have to punch out with a drift.
get a new shear pin from chandlers, these vary in hardness/softness (as well as size) get a selection, use the softest that will allow the engine to run normal operation without breaking.

vic
October 2012

you've probably sorted it by now but there is usually a shear pin in the shaft at the prop end. It is designed to stop excess damage if the prop catches on something

Jeff
December 2011