The tracker device is meant to have a range of about 10 miles or so. All i can say is that if the boat is used in local waters it may be detected but i would not count on it. Dont pay attention to the sales person i know from experience in my work that you would be lucky if a police car picked the tracker up at a couple of miles. There are other devices that use satelitte tracking systems such as trackback these are more expensive but offer a better coverage
There is a system available for boats. I read an article about a wandering charter yacht being recovered in anither country using a security tracking system. I have no details but someone may remember the article.