I had a very nasty experience a few year back with a 50 Mercury on a 4m Searider . It had a manual start and also manual tilt .To tilt the engine the throttle lever had to be in FWd position to disengage the tilt lock .On this occasion I had anchored a few yards off the beach at Calshot and my young son was swimming in the water near the beach . I swam out to the RIB got in and lowered the engine into the water and pulled the start cord , the 50 Merc was a 4 cylinder engine and started so easily that even my small son coukd do it . This must have been the first occasion I had tried to start it with the lever in FWD and I discovered the hard way that the previous owner had disabled the in gear start interlock . As usual the engine started first pull I went out the back without even knowing what had happened the boat shot forwards about 10 yards complete with anchor and missed my son by inches it went straight up the beach engine still running at about 3/4 throttle .The prop was throwing an arc of gravel into the air and chewing itself to pieces ,I swam in checked James was ok and stopped the engine , sat down and was sick! It still makes me cold writing this 10 years later .We were very luck that day . Whilst all tghis was going on some kind soul stole our kneeboard !!
Moral of the story check that you cannot start in gear when hand starting as it may be possible as the interlock may not work when manual starting.