Had a really bad day yesterday

Left the RIB on a pontoon overnight. Conditions were awful - very very windy and wet, and consequently quite a bit of water got onto the deck of the boat. Not a massive problem; got down there, let the trunk down, and took it for a spin. All the water drained out, ideal. The plan was to put the boat back on the trailer, so was heading for the slipway at medium revs when I hit something in the water. Must have been a rock or similar, as there was a clunk. I immediatly switched the engine off and lifted it out of the water - there was a chip out of the prop. Not a particularly large chunk, but it had certainly hit something. Anyway, trimmed it back down, fired it up, but alas no forwards or reverse. You can hear the gearbox going into forward and reverse but the prop just doesn't spin.
It didn't hit whatever it hit at great speed, so I suspect there was already some weakness there from a possible previous incident - only had the boat/engine a week