1) Have a group "move" waypoint with a boolean condition, eg tx_Chasenow
when you want the chase to start, have the boolean = true and setpos the waypoint to the boat you want chasing
loop the setWPpos command in a script every couple of seconds or so
eg
#START
~2
? (tx_Chasenow): goto "SKIP"
goto "START"
#SKIP
[Groupname,0] setWPpos (getpos escapee_vehicle_name)
~2
goto "SKIP"
setpos a group waypoint to the boat you want them to chase, loop this every second or so