Possiblyt he starter got stuck. I just started my boat today after it had been sitting since september. The starter made a spiining noise as if it was disconnected at first, after a few more tries it finally kicked in and cranked and the boat fired right up. Gotta love that sound of that boat engine when its out of the water. So Mean and a nice growl to it.
I would suspect your starter may have frozena bit. When that happens, some tap it with a hammer or mallet of some sort, to help knock it loose. Then its usually good for a while before it freezes again and needs to be tapped again. at some point it just wont spin over anymore.
I am going to see about maybe replacing my boat starter with a new one if it happens again. Well it is 18 years old.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.