We have some very busy shipping lanes nearby. So I was contemplating to have a navlight on the mast top. But then, considering all the hassle with cabling and having to drill holes into the boat, the light on the mainmast top always being partly obscured by the gaff yard or mainsail, and finally a fixed mast top light not being well protected when the mast is lowered,  I started to look for a more practical -and less expensive- alternative.
I think I found an optimum solution with these portable battery operated LED navlights by Aqua Signal: http://www.aquasignal.info/ecat/htdocs/index.php?category_id=1&subcategory_id=1&product_id=43

I tested one for duration with a fresh set of 4 AA size Alkaline batteries (price 90 cents for the set). It\\\'s been switched on in continuous use for more than 13 hours and was not looking tired even then, that\\\'s really plenty of mileage on the water at night.
Each of these lights costs just EURO 33.00 at a chandlery nearby. With just one dual light and one stern/360 degree white light one can emulate all the different navlights for a vessel of less than 7 mtrs. under sail, under motor and under oars, plus of a vessel lying at anchor. BTW, the white light doubles as a very powerful waterproof handheld light for general use around the boat.

Highly recommended.

Bill,
these lights are mounted lying horizontally, so they fit below the clubboom.
BTW, the light is now in use for 21 hours with the initial first set of 4 AA batteries, still shining bright. I would have been happy enough with 8 hours, but 21 so far, I am really surprised. With such usage time of a AA battery powered LED navlight, who would really need fixed cabled navlights any more?

Hi, Claus.
I admire your nav. lights. They look just the thing for a small boat with no battery charging facilities. Given the choice, I  very rarely sail after dark and always keep well clear of shipping lanes so my original set (tungsten bulbs and D cell batteries) have died the death of neglect before ever being used....and thank goodness I\\\'ve never needed them as they were pathetically dim.
For emergencies I now have a small LED lantern with a strobe setting which I fix to the mast head. (Blurred picture with coffee cup, below!) This is, of course, totally illegal and so cannot be recommended.  It gives other  ships no idea of your heading but I know it can be seen for miles on a clear night and, flashing white at about 200 times a minute, is unlikely to be mistaken for anything else, except a North Cardinal buoy. An added bonus is that it can be seen easily against a background of shore lights.
In view of the number of fatalities caused by the mixing of small craft and commercial shipping recently, I am surprised that the rules of the road cannot be altered to allow small boats to employ the superior visibility of rapidly flashing lights. Correct me if I\\\'m wrong but is it also illegal in the UK for cyclists to show flashing lights? I think they, too, would rather be seen by other road users on a dark, wet night against a confusing background and take their chances with the possibility of court action!

Hi, Claus.
You are, of course, perfectly correct but you must admit that flashing lights are much more noticable than steady ones, especially at low wattages. ( Hovercraft are allowed a flashing amber light ....and I have seen trawlers use them, too. Presumably illegally.)
To judge by recent press reports it would seem that ANY lights we are capable of showing on a small boat are in danger of being overlooked by officers of the watch on some vessels. It appears that unless you set off a proximity alarm on their radar or AIS sets  you are quite likely to be missed by even the most diligent of look-outs.  If I had to mix it in the shipping lanes I think minimum requirement would be an active radar pinger – the sort that re-transmits a received radar signal.  (A friend of mine was asked by Humber Coastguard to turn his off as it was making such a big squawk on their radar, so they DO work!) The developing AIS transmitter/receiver market is worth watching, too. A hand held version is surely not too far off – although the screens might get a bit cluttered on Cowes Week! Meantime I will keep well clear of anything bigger and faster than the Four Sisters...Err....Thats most things, actually... and never assume that the other guy knows what he is doing!

Agreed. Especially when you remember that we cant get the two sides of the Atlantic to have the same colour port hand buoy! 
Cheers!
Tony