Always Windsurf With a Buddy - This is a good idea no matter what time of year it is, but it is a must in the extreme winter conditions most of us sail in. Self-Rescues can be difficult in any conditions but add in temps 40 degrees or below, then they can become deadly really quick. As you can see from the hypothermia chart below you don't have a much time to spend in cold water before you start to shut down. Sailing with a friend can save yours or their life. Besides it's more fun to sail with friends anyway!
Rig Small and Use A Bigger Board - By using a slightly smaller sail and bigger board you won't get fatigued as quickly and you will have the added volume of a bigger board in case something happens - the wind dies or you break something. While you may not be as fast or be able to plane quite as early if you rigged a bigger sail, you will be able to sail longer. The "arm pump" or forearm burn you get from sailing with gloves won't be quite as bad with a less powerful sail. With all your rubber on you are also much heavier than you are sailing in trunks so the extra volume in a bigger board helps to offset this weight difference. Your reaction time in cold conditions is slower and the bigger board gives you more margin for error in your maneuver.
Bring A Jug Of Hot Water - If you have ever sailed in 40 degree or less conditions for more than an hour you'll know just how difficult in can be to de-rig. The hot water will probably be just warm water by then but it is a great way to thaw your hands where you can actually move them enough to be able to break down your equipment. It can also be used to help squeeze an extra couple runs out of a session as well. If you hands or feet start getting cold come in a warm them back up with the hot water and go back out for a few more runs. Once you are finished it feels great to have a "hot shower" as well. If you want to step up your game there are gravity and even pressure portable showers that are around $99 and store about 2-3 gallons of water.
Layer with Fleece Under Your Wetsuit or Drysuit - Layering is a most for winter time sessions. It will create a bigger boundary layer between your body and the elements and allow you to sail much longer. A good piece of polar fleece can turn a 4mm wetsuit into an 5mm and a 5mm into a 6mm. The fleece also wicks moisture away from your skin keeping it dry which allows you to stay much warmer than if you were just wearing a suit. The fleece makes a huge difference especially when you are on the beach in between runs. Standing around in a wetsuit you become clammy and cold pretty fast and it really discourages you from wanting to get back out on the water. By wicking the moisture away from your skin you don't get that clammy cold sensation and you are much more likely to be motivated to get back out there for another couple runs. And after all isn't the whole idea to spend more time on the water?
Change Into Your Suit Before You Get to the Beach- It's much warmer and easier to change in the warmth of your house rather than trying to fumble around inside your car or worse stand out in the elements wrapped only in a towel. Rigging in your suit can be a little challenging but I've found that if you have a Jacket you can put over your suit to keep the wind off it really helps. It's also can be a good place to store rigging tools in the pockets so you don't lose them. Right when you are ready to downhaul you reach in your pocket and there's your tool. There are a variety of neoprene jackets that work great and can be put on after sailing over your suit as well. They can be a bit pricing though so I recommend just and older jacket than you don't mind getting a little wet.
The Best Thing to Make a Winter Session Better is Your Mind - The right mental attitude can make or break any session especially in the winter. If you go into it thinking about how cold it is and how cold you are going to be you probably aren't going to enjoy the session. A positive mental approach will make even the coldest days better. Don't think about how cold it is or how you wish you could get this much wind in the summer. Think about how good the wind is right now and how good it feels to hook in, put your feet in the straps, sheet in, and start blazing across the water. Even a 15 -20 minute session is well worth it. We all know there's nothing like that feeling so don't let a little cold get in the way of you and a great day of WINDSURFING!