I bought this 12 ft fishing boat with a 5 hp briggs and Stratton and worked great the first time I had it out then when I had it out last night for some reason the lower unit wouldn't go into gear or at least the prop wasn't spinning. It has neutral and forward only.. If I put it in gear when its on dry land it seems like its going in gear but the prop doesn't spin. There is a wing nut up under the powerhead that was loose so I tightened that but still nothing..... any advice? Thanks!