Paulr and several others have already made some excellent recommendations here, I'll try not to be too redundant /ubbthreads/images/graemlins/smile.gif.
It's been a few years since I've participated in any organized sailing, and I didn't have access to any of these lights back then. I still get out on the water when I can though, and based on my experience I'd recommend the following:
PT Aurora Headlamp - It's a great low intensity, long burntime task light. If you're reading charts, walking on deck or trail by night, it keeps your hands free, it's relatively cheap, and robust. It's rated as waterproof, though probably not below 3-10ft., it's definitely sealed against splashes and heavy rain.
Inova 24/7 - If you buy the headstrap for it, or have a place to clip it on (like a PDF or vest), this makes a great substitute for the PT Aurora. Rated as waterproof (though only water-resistant when tested), you get several modes in one light, High White, Low White, and Red being the most useful. It also has several flasher and SOS functions, in addition to a "find me" setting that helps to keep track of it at night.
UK 2AAA LED - Your CMG is probably fine, but the UK is cheap, and designed to be around water. It's completely waterproof, handy, and solid enough that you can drop it and accidently whack it without feeling bad. You can also buy a Red LED module for it. If you decide to go with the PT Aurora or Inova 24/7, this becomes more of a neck lanyard/pocket backup.
Eternalight - EliteMax, X-Ray Elite, or Marine. Though with all of their functions they might seem more like a toys than a serious flashlights, they are completely waterproof, float with the included lithium batteries, and are quite solid. Like the Inova 24/7, its variable light output is very useful, and you shouldn't have to replace the batteries, at least very often. As Roy already mentioned, this one really shines when attached to a PFD or vest. When I take my EliteMax, it rides in a Compass/Strobe pouch on my vest.
UK 4AA or UK 2L - I really love these lights. With the new LED modules, and the 4W bulbs (which I'm excited to try out). They work like a system. Choose your battery type, (4AA/Q40 vs. 2L) then whichever head is appropriate for the task. I actually bought a pair of UK 4AA LEDs, then a pair of UK 2Ls, and so I have an LED and an Incan head for each body type. Aside from my EDC, the 4AAs (both Incan and LED) see the heaviest use of the lights I own. The 2Ls are more expensive and harder to use one handed, but are more compact and far lighter.
For a heavier light, I'd recommend either the Pelican SuperSabrelite or PT Surge. I've used both, and the Pelican definitely seems more robust. The tradeoff is C cells, and it's nearly impossible to use it one handed. I think the decision comes down to battery type, operation, and personal preference.
The one thing I haven't heard mentioned, and I'm hoping that's because you already have one, is a dedicated strobe. I always have my ACR MS-2000 attached to my PFD, riding in a Tactical Tailor Strobe/Compass pouch. As great as LEDs are, they don't match the intensity of a search and rescue strobe. Any of the standard ACR strobes work well, I prefer the models that use AAs rather than the hard to find and extremely expensive lithium types. You can buy an adapter to use 123As, but they're aftermarket and don't guarantee the depth rating while you're using it.
I enjoyed Sub_Umbra's post, and I though he made some excellent points.
As a personal preference, I tend to shy away from SFs, or any Incandescent without some kind of water-resitant rating in general, especially the more expensive models like the A2. Salt water is about as harsh an environment as it gets for electronics, and SF doesn't give a definitive "waterproof or water-resistant to x" rating. In my experience any equipment you take on deck with you is bound to get kocked around... aluminum or any other metal isn't very kind to the bulb or whatever it hits on deck. Again, this is just my opinion, I'm sure the A2, and a variety of other lights, work fine on a day to day basis for most people.
I hope some of this helps, if you have any questions feel free to drop me a line. Oh, and though the X5 isn't my first choice when sailing or camping, it's a fantastic EDC. Hasn't died on me either, like my Arc AAA /ubbthreads/images/graemlins/frown.gif. Have a safe trip!
Sail fast, live slow,
- Corliss