Recently had boat out for slow cruise w/family. Was running along just fine and it seemed like it came out of gear. Motor revved up and was going nowhere. This happened last year but i just dropped her back into neutral and then back into drive and she took right off. This time it just revs up and goes nowhere. Although it did get me back to ramp but only at an idle. Is my outdrive junk or is it something simple, maybe driveshaft sheared keyway? Not to familiar with alpha one any help would be appreciated.