http://www.marinebeam.com/44felednaliw.html
This is the bulb I am using to replace the incandescents on Levitation( which are FESTOON style bulbs) - the mast light and the running lights, and also the bathroom light...... It is markedly brighter than the incandescent bulb and draws one third of the current...Yes it is the price of 3 incandescent bulbs - but will outlast a hundred of them...
After having to cancel our 4th of July fireworks cruise because the shiny, spanking new, just installed, mast light bulb lasted all of 90 seconds (lessee, $10 per 90 seconds is how much an hour?) I immediately said I am not going through that again...
If you buy from another source be sure that the Festoon bulb you get is the "dimpled" end variety, not the one with spikes...
A FESTOON style bulb looks like a small Buss fuse...
For the running lights, I recommend that you line the backside of the light housing with aluminum foil (contact cement), which increases light output tremendously...
Use silicone grease from the auto store (for spark plug boots) to generously coat the bulb contacts and the brass fingers in the lamp housing to prevent corrosion as it will be a long, long, time before you have to open the housing again... Lacking that, I would at least use petroleum jelly...
I haven't gotten to sourcing an LED bulb for the interior cabin and chart lights yet, but I will...