Possible Safeguards for Cold Weather/Water - from this discussion on surfski.info
1. When alone, restrict your distance to 10 km or so. I am reasonably fit, but what always strikes me is the fatigue that grips me after one hour. This is particularly relevant as most of us are around 50 or older.
2. When alone, use a safe boat. This does not mean changing your Elite S for a Swordfish. No, I mean a really safe boat which is defined by a noticeable positive righting moment - which most intermediate skis still do not have. ⇒ V8 or similar. It is much more likely to be able to remount such a boat in rough conditions, and there is no less fun.
3. Clothing: …(Editor's note - I think surfski.wiki already has better ideas about what to wear in various cold conditions, so we are bypassing this suggestion)
4. Life vest: for winter I have a life vest with 100N buoyancy. It is cheap and does the job, also re ergonomics, and when floating in the water, the 40N+ make a huge difference. What these things usually are missing are pockets. So if you find a way to store your emergency stuff nevertheless, this could be something that could prolong your survival time beyond the said 2 hours.
5. Just a provocative suggestion: if your region allows for it, try to view surfski as a summer sport. Do not go out alone when water is below 20 degrees, and do not go out at all below 15 degrees. Get over your addiction and try to do something else when conditions are dangerous. I know that for the more Northern locations this advice is not practicable, but pals living there might still try the other options. (Editor - we don't follow this guideline at the suggested temperatures in Bellingham, WA, USA because it would preclude our going out on the water even in our summers, but a number of factors can and should enter into the decision about when it is okay to go on the water and when it is not for an individual and many of our locals have their own temperature limits of water and air below which they will stay on land).