Hi Sandra,
 
I have an M15 and my routine on launching is:
 
Rudder mounted on transom and in the UP position.  This is the keep the rudder from hitting things during launching.
 
Once the M15 is floating, then I lower the rudder, fire up my O/B and take off..............
 
Steering with an O/B is possible as long as the engine is running
 
Shut off the O/B and you have no way of steering.  Been there done that!  Not to be recommended, if you are trying to maneuver in tight quarters.  You totally loose control of the boat.
 
Also, make sure that your C/B is in the UP position prior to launching, otherwise it will hang up on your trailer aft cross member and you won't get the boat off the trailer.
 
Connie
 
M15  #400