For what its worth, I was talking with a marine patrol officer once about the 150' rule and people's disregard for it or inability to know how far it really is. He told me as a rule of thumb, to someone with average eyesight 3" block boat numbers are distinguishable up to 150'. If you can read the numbers, you are inside 150'.
Good to know, we had another wild weekdend on Squam with the Yahoos, getting bad. They dont like slower boats like mine and pass no matter where or how close.