Understood that it is not legal, and I imagine that it could get the offender in trouble if it was brought to the attention of authorities. I think the confusion was part of my reason for asking ... confusion could get the watch paying closer attention until they realize it is just one boat. What difference would it make if the watch thought there might be 2 boats in the same direction if it got them to pay closer attention. What difference would it make when they realize it is just 1 boat. It shouldn't make any difference in their decision making process. The one set of signals would only mimic the other set of signals and be in very close proximity, so there would be no distinction in how boats around them should react. The lights wouldn't indicate conflicting positions. It would look like one small boat with waterline lights and another small boat with masthead lights right next to each other going in the same direction and at the same speed. Why would that make any difference when it is discovered that it is just one boat? It may be misleading, but I don't see how it could lead to a dangerous crossing. Just give me one good example where it would be dangerous ...
(that's a challenge)
I know it is a silly question. I rarely see lights that are that distinguished, especially when they are head on. The red and green bow lights usually bleed together, as would a masthead tri-color.
Scott, in the open ocean where there are not a lot of distractions, showing 2 light patterns would probably not make much of a difference. The bigger concern is in more congested waters when we want the skippers to be able to quickly and accurately identify other boats and navigation aids. While I can't say with certainty that these rules were based on any scientific data, there is good science based reasoning behind them.
Human perception is pretty good at recognizing patterns and seeing movement. The well trained mariner's eye will quickly recognize a light pattern and know the type of boat, direction, and and any special circumstances (such as towing or dredging). When the light pattern does not conform to the agreed upon standard the skipper must divert attention from the bigger task of piloting the ship to figuring out what the noncompliant light pattern means; it becomes a distraction. Navigating at night near shore is challenging enough, without boats with noncompliant lights running around.
Navigation lights are not the only area that this pattern recognition is used. Traffic lights are almost uniformly designed with green at the bottom, red at the top (See exception
here). We respond to traffic lights more because of the light placement than the color. While I can't quote a source, I'm sure some psychologist studying human perception has studied reaction times based on compliant traffic lights, color less traffic lights, and noncompliant traffic lights. We are well trained to stop for the light at the top and go at the light on the bottom. We also use pattern to speed recognition on other traffic signs, stop signs are always octagonal, directional signs on Interstates are always green and rectangular, caution signs are triangles, etc. All of this is designed to speed recognition to allow the driver's attention to be focused on other potential hazards.
A long answer to a short but important question.
BTW, did you hear about the Waimea Valley Botanical Gardens? A few weeks ago there were extremely heavy rains and the valley flooded. The stream rose to 12 ft. Lots of destruction to a beautiful spot.