Water in hull

I have a fenn xt double but I notice it is starting to get a build up of water in the hull that does not drain out through the deck drain hole
Is there a simple solution to this

Solution to fixing the leak or getting the water out after the leak has been fixed?

Just getting the water out , after the water is out I will address the leak , a few pressure dings and a rudder leak

Best solution is to drill a 2-3mm hole in the deck either in the front or the back and store it with the opposite end elevated so the water can drain out.

The problem you have is that it is full of polystyrene and the water will just be soaked up by it. You will need a few days for the water to drain out of the foam, hot and cold weather day and night)helps as the hot will evaporate the water inside and then the cold will condense it and so on.

Washing the ski out with soapy water will also help drain it better, salt water does not drain out readily, seems to remain damp.

"Best solution is to drill a 2-3mm hole in the deck either in the front or the back and store it with the opposite end elevated so the water can drain out."

Do not be shy - drill a bigger hole - you are going to be doing repairs anyway. If you have a blower (reversed vacuum cleaner) then blow air in the bung hole while you have the ski elevated. This helps dry the ski. Rinsing out with fresh water first really does help - salt draws in and holds moisture.