http://www.nationalmarineregister.com.au/NEWS/tabid/199/categoryid/6/Default.aspx
Have look at this link that shows some of the boats stolen recently especially the side bar showing monthly uploads of stolen boats. Clubmarine states that they process more than 2 claims a week for stolen watercraft
if you have an alarm fitted most insurers will give you a premium discount so the GPS tracker will have you ahead by the second year.