Originally Posted by sailingfool
The NAVREGS rules don't attempt to tell you EVERYTHING you cannot do, they tell you what you MUST or MAY do. The rules for power vessel sidellights and stern light are not compatible at all with the concept of a mast-head tricolor. A sailboat under power is simply another power vessel.
I'm not sure here whether you're telling me that it's ok to leave your masthead lights on under power, whether it's not, or whether it doesn't matter, but here's what The Book says:
Rule 20, (b) "The Rules concerning lights shall be complied with from sunset to sunrise, and during such times no other lights shall be exhibited, except such lights as cannot be mistaken for the lights specified in these Rules or do not impair their visibility or distinctive character,
or interfere with the keeping of a proper look-out"
Given that there is no boat authorized to carry a masthead tricolor light, or a masthead red - over - green light, except a sailboat proceeding under sail, if you start your motor you must turn your masthead light off. Otherwise you are showing lights that can be mistaken for sailboat lights even though you're in a power boat.