dralyagmas said..
Any other tips for relaxing the grip? I get too pumped up in a race that at about the 2/3rd mark can't even grip the paddle with my left hand (when it's on the bottom). Left is worst but still feel it in the right
Practice! Focus on relaxing your hands all the time when training, the more you do it, the better the body will remember to do it automatically.
Most people will tense up more in a race than when training, that's only natural when your focus is getting to the finish line as fast as possible rather than thinking about the most efficient way to get there. But if you
over exaggerate with different drills in training (eg. letting go of the bottom hand on the recovery phase, thumbs up as Pete said, keeping fingers straight/uncurled on top hand so weight is transferred through your palm alone etc.) then what currently feels relaxed will gradually become habit, what's currently 'normal' will be your 'pumped up' race technique, and you'll stop reaching that point that's unbearable.
It may not come naturally at first, but learning to relax (hands, feet, hips, shoulders etc) will be one of the most, if not
the most, beneficial things you can do to improve your paddling.
Also...
When you say the pain is in your bottom hand... are you pulling the blade towards you with your bottom hand? Try leaning your weight onto your top hand ie. pushing the blade down (vertical movement) rather than pulling it backwards (horizontal movement). Even though you're putting the force vertically through the paddle, as the paddle moves downward it will propel the board forwards towards the paddle rather than pulling the paddle back towards the board. This should ease the pressure on your bottom hand (it can then be used to stabilise the paddle and stop it sliding from side to side) and make your paddling both easier and more efficient.
Hope this helps