Get a grip!
Have you ever found yourself playing in rough water and your hands slip all over the paddle shaft, sometimes losing your paddle altogether? This is nothing new and many manufacturers now supply heat-shrink rubber-type grips that are simple and easy to apply. However, if you find that these give you 'hot spots' on your hands, eventually turning to large blisters if ignored, then another solution is needed.
Sex wax! Yes, that's right, sex wax! The surfer's old partner used for producing a grippable surface for their composite surfboards. So get yourself a block of the blue (hard) board wax and just rub it on before launching and problem solved. The heat of your hands will eventually soften the wax and it will rub off so take a block with you and apply as necessary. I find that one application in the morning and a second application in the afternoon is all that is needed.