Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 40Get this manual
OUTBOARD MOTOR INSTALLATION
Fastening Security Line
security line being used is long enough to allow the outboard to dis engage the boat transom but is too short to not allow the outboard to submerge behind the boat and stop running, the outboard could continue running and propel itself back into the boat with the propeller rotating under powerThis exposes the to serious or deathThe primary purpose for installing security line is to prevent loss of the outboard if the outboard becomes detached from the boat transomAn effective security line should be of working strength of at least five times the weight of the outboardThe security line should be attached between th boat and outboard following one of these stepsStep 1The length of the secu rity line should be short enough and affixed in manner to prevent the outboard from rising up and disengaging off the boat transomStep 2The length of the security line should be long enough and affixed in manner to permit detached outboard to submerge completely behind the boat and stop running but not too short that could allow the outboard to continue running and propel itself back into the boat