60 hp Merc prop spins slowly

My son just came up for his vacation. We have a NITRO bassboat with a 2005 60HP Merc. The last time we used the boat was July 4th weekend. Motor ran fine. The boat has sat until today in the water. We wanted to go fishing but the but the boat didn't move. We raised the motor out of the water and checked to see if the prop nut was tight. It was fine. We started the motor and shifted to forward and the prop moved real slow. We put it in reverse and the prop spins in the same direction as Forward, slowly. We didn't do anything to the motor. It worked fine last time out.?????

Try this...Shut engine off, place in fwd gear. Manually turn the prop counterclockwise until you feel it lock into the clutch. Now see if you can keep turning the prop counterclockwise without the flywheel (engine) spinning.

If you can, the prob might have spun the hub. Most props are designed to break the rubber seal between the prop body and where the prop shaft comes thru when you strike an object in the water.
If you take the prop off and look at the forward end where the prop shaft goes thru, you may find a bit of mangled rubber.

We took it in. Looks like a linkage problem occured for no reason. Thanks I'll keep you posted.