I am a sailor with 70 years of sailing experience–Started when I was 14 and am currently scheduled to be 84 in Oct. My last boat was a 38 ft Offshore Cheoy Lee. I sailed in Hong Kong waters for a year then shipped it back Seattle.
In a race in Hong Kong I was on a Yamaha 33 and we had water over the floor boards after launching off a wave with a big bang. Bailed like the dickens for 4 hours, Checked the head to see if it was overflowing – and it was OK, and finished the race. (did not win) At the dock pumped the boat dry and took out all the floor boards so I could see the surface of the hull. Checked all sea cocks. None had leaks. But I found a crack in what I thought was the inner liner of the boat and informed the Skipper. The Skipper informed me it had no liner. So we had cracked the hull. Your head may be overflowing on the side of the boat it is mounted on when you are on a Beat. (head on port side on Starboard tack and head on Starboard on a Port tack sometimes will overflow the head.) If it is not any seacocks, not the hole where your speed log is set, not the engine cooling water supply while the motor is running, not the shaft log while sailing—–sometimes the shaft log will leak if your prop is free wheeling while you are sailing, Not the head joint between the hull and the base of the head and not the head overflowing, and if you have a hull liner you may have to haul the boat and after the hull dries put a few buckets of water with bright colored die, into the cavity between the hull and the liner. You may have to make a hole here and there to get the colored water in all the various cavities that may otherwise prevent the water from getting to all the places a leak might exist. After you haul the boat wait until the hull is dry and try to use a die that has contrast to your bottom paint.
By the time you do all this I believe you will find the leak.