Nav lights
 

A question that has come to mind as I have recently done the shore based study for the RYA Day Skipper.
Why in aviation do we divide the red/green/white nav lights into 120 degree sectors while our maritime brethren use 112.5/112.5/135?
Given that the maritime standard was probably devised before the Wright brothers were born why have we chosen to be different or was there no maritime standard until much more recently?

The red and green lights on board ships go back till before The Rule of the Road written in 1867 by Thomas Gray. 1846 or so. Still searching when the precise sectors were defined.

I agree that the colours would have been standardised long ago but I'm just wondering if there were different sectors in different parts of the world until more recently than one might think.

As a recently retired Licensed Engineer, and RAF technician before that, I was always under the impression that we followed the maritime precedent regarding angles; certainly something I remember from basic training in the 70's (like ".... and half a degree? Are you serious?").

I don't think I ever took a protractor to it, but every nav lamp fitting I've seen had a much wider aperture at the tail than at the wingtips.

How long ago did you take the air law exam?

My understanding is that the port and starboard lights have an arc of 110 degrees each and the tail light 140 degrees.

1864
US law

light sectors 10 compass points (8 points is 90 degrees)

https://cimg2.ibsrv.net/gimg/pprune....90a2fcc31.jpeg

1984. I did look at the ANO last week but couldn’t find any angles mentioned.

(90/8)x10=112.5 so that confirms that angle in the USA.

I’ve now found FAA and EASA documents that mention 110 degrees for port and starboard so I’ll admit to poor memory on that but we still have a difference of 2.5 degrees to account for.

Presumably you did pass the lights exam... :8

110 port / stbd and 70 degrees either side of dead astern for aircraft.

This US law was based on British/French law and also signed/ adopted by 30 other countries.
So I assume they all have used same lights description.

When ships lights were regularised bearings and course were given in compass points and and parts there off, Degrees only came in with improvements in the numeracy of helmsmen, The old style continued in part use in my time, starting 60 years ago, for example Norwest. 10 north, Rarely heard nowadays.


https://cimg7.ibsrv.net/gimg/pprune....768bcebdb6.jpg

Here's a thought. A compass is traditionally divided into 32 points (and once I could box the compass, though I have no idea why I learned: NNW, North by NW and so on). 360 over 32 gives 11.25, and 112.5 neatly equals 10 points of the compass. But I have never heard of aviation directions being given in terms of "Turn left to S by SE -- no, not SE by S, silly pilot"; so I suppose a decimal-friendly number of degrees were chosen

I see reefrat posted while I was posting.

So why has nobody objected to that stupid Elton John song where he claims he can 'see the RED tail lights going to Spain'?

Actually the port wingtip light. It was a strong crosswind that day. :ok:

Mid 1976, during the 3rd Cod War. Low level off Iceland in a Nimrod, being directed onto something by a trawler. First instruction, in a strong Northern accent was " Coom two points to port, lad."
Port no problem, had to think about "two points". Got it right - the next instruction was "Steady as tha goes, lad".
Perhaps, as Reefrat put it, he had concerns about the numeracy of the helmsman.

You would have to blame Bernie Taupin for that. Give him some points on his Artistic Licence...

This thread reminds me that about 55 years ago, maybe more, we changed from degrees to mils (milliradians) for the purposes of surveying in and aiming (HM's Royal) artillery. 6400 to a circle (for practical purposes) and no more nnn degrees, nnn minutes, nnndecimalnnn seconds and all that blether. And we used metres for all distance measurements.

I know that degrees are dearly beloved and have been used for centuries, and all that, but surely to Himself-Up-There it would save a lot of time and bother if ship and aircraft navigators, chart producers and so on caught up? Maybe we could ditch the Nautical Mile as well. I know. I know, nnn degrees of latitude equals yyy nautical miles, and so you can use the degrees on the side of the chart to measure distance. So what? It's just a scale, and a mils scale would serve equally well. And of course, we could then lose the Knot as a measurement of speed. Happy Daze!

I let my membership of the Institute of Navigation lapse some time ago; pity, really, I could have launched this battle there.

Maybe something was lost in the conversion from Imperial to Metric degrees.

With the invention of the metric system, based on powers of ten, there was an attempt to replace degrees by decimal "degrees"[note 3] called grad or gon, where the number in a right angle is equal to 100 gon with 400 gon in a full circle (1° = ​10⁄9 gon). Although that idea was abandoned by Napoleon, grades continued to be used in several fields and many scientific calculators support them. Decigrades (​1⁄4,000) were used with French artillery sights in World War I.

I recall the tale of one of our "older" captains being asked by a lady visitor to the Flt Deck one night, how he know which way to "steer" the aircraft ? " Well madam, can you see the glow from that red light on the end of the wing ? " Yes, "and can you see the glow from the green light on the other wing ?" Yes. "Well, I just steer between them " I can't recall the response from the lady !