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With all the talk of light ranges and alternates I made the mistake of looking 
back in COLREGS and found some things to wonder over. I put it to the list 
for comment and note as usual I am not licensed to practive mathematics, 
don't accept any numbers I present as being correct.

COLREGS gives examples of lamp brightness as:
1nm     0.9cp
2       4.3
3       12
4       27
5       52
6nm     94cp

and for vessels under 12m requires a sidelight range of only 1 nm (0.9cp)
and all other lights 2nm (4.3cp)

for 12-50 meters,
masthead 5nm (52cp) (20-50m oal)
masthead 3nm (12cp) (12-20m oal)
all others 2nm (4.3cp) including all-around lights.

I note this because it would mean a sailboat 12-50m, using red/over/green all 
around lights would need a total of 8.6cp with that lighting scheme--but 12cp 
with a masthead tricolor light. So here the alternate lighting saves 25% on 
power needs.

For a boat under 12m it would mean 8.6cp instead of 4.3cp, actually doubling 
power consumption on the mast.

Pros and cons, it would seem. And I have no idea how the lamp manufacturers 
match bulbs for this criteria, I'd expect them to use "stock" bulbs so 
perhaps with tungsten bulbs it is simply 10W vs 20W and devil take the 
details.

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