Some DIY info (with caveats)
Here are some DIY experiments I did which might be of interest. Note that a home-made LED bulb replacement in a navigation light, or a completely DIY navigation light, IS NOT USCG approved, obviously, so if you have any concerns at all about absolutely meeting the USCG standards, or avoiding any possible liability arising from using unapproved LEDs and fixtures, you should simply buy the complete USCG-approved LED navigation light units.
Note also that unless it expressly says so (somewhere), a commercial LED bulb replacement isn't necessarily USCG-approved for use in nav lights, either.
Due to being cheap, with a small boat that's seldom out at night, and having an electronics background, I have been trying some raw LEDs in bulk from suppliers like Digikey (small superbrights @ approx $0.50 ea. higher-power units @ $2+ ea.), local electronic surplus stores (hi-power suplus red & green @ $1.50 ea.), or even from ebay (150 assorted hi-brightness for $15), with mixed results.
My first project was re-lamping the anchor light. For this I soldered 3 inexpensive bright white LEDs in series, then carefully bent the leads to face 120 degrees apart, and added a series resistor selected to yield a current of 20 mA @ 12 V. This setup has proven to be visible to at least 1/2 mile on a clear night (adequate for the safety of our small boat), but not quite as bright as an approved fixture & bulb. My next step will probably be to double up on the LEDs (6 spaced out at 60 degrees) to improve this. Even so, the total current will be only 40 mA, which is about 1/20 the amount of current taken by a 10 watt incandescent bulb. I'm also thinking of adding circuitry to make the anchor-light momentarily blink OFF every 5 seconds, which greatly increases the attention-grabbing factor.
Based on the performance of the anchor light, I plan to also add a steaming light using 6 white LEDs.
I next tackled putting red and green LEDs into a pulpit-mounted bow nav light fixture. Again I used inexpensive bright LEDs. The red ones were less bright for a given current, but due to their lower voltage, you can drive 4 in series from 12v. Again, I selected resistors for 20 mA into each chain, for a total draw of 40 mA. Results here are also satisfactory, the only concern being that the employed LEDs have fairly narrow beams, leading to brighter and dimmer aspects as you view from different angles. Here I have to add more LEDs, choose LEDs with better diffusion, or choose a nav light fixture with a better-diffusing lens.
The stern white light is 3 LEDs as the anchor light, but this time 30 degrees apart to cover the required 120 degree spread. This one worked well.
For interior lights, it's also easy to fabricate bulb replacements or new LED fixtures, but most white LEDs available in bulk have that annoying bluey cast, whereas commercial interior LED fixtures are more likely to use 'warmer' white LEDs. Some of us are having great results with the small LED fixtures from IKEA. They're small, attractive, some are quite thin and elegant, and reasonably priced (eg 4 low-profile euro-styled "pucks" for $50, or two directional fixtures for $25) Some electronics knowledge is still required to select a suitable current-limiting resistor of the correct resistance and wattage.
Again, DIY nav lights or diy LED bulbs are not USCG approved. Don't follow my lead unless you are confident in your abilities to produce a dependable product, and you test carefully to ensure your units match approved units for brightness, colour and distance.
On the other hand, interior lights need no approval, so it's a great place to start if you want to gain experience with LED lights
), sell bulbs that don't have any RF noise protection and use orphan (read cheap) emitters that rarely have consistent color temps. 
