The most common problems involve how and where the lights are mounted. Take a careful look at each fixture; depending on the size of your vessel and its configuration of sail and power, your boat may have as many as six navigation lights: port, starboard, stern, masthead tricolor, steaming, and anchor. Make sure that no light is obstructed in any way. The usual suspects include davit-hung tenders and other stern-mounted gear as well as mast-mounted radar domes. In some cases, I’ve seen the transom itself block a portion of a stern light’s required arc of visibility.