Engine will not shift into gear

[Boston-boater]

I went down the boat today,family and friends in tow for a a day of boating. Was all set to cast off, engines running and the starboard engine would not shift forward or reverse. The shift lever will not move. Port engine shifts smooth and normal. Last time I used the boat two weeks ago, I had no issues. Thoughts?

 

[Bt Doctur]

open the hatch and inspect the shift cable, remove the detent lock and see if the cable moves or if you can shift it manually.
someone stepped on the shift cable connection at the transmission and damaged the cable?
trans cooler has failed and trans is filled with water ?