I'm still stumped. went for a sail again on Sunday. One tack pretty much each way. Nice 20kts of breeze. On the starboard tack, no water ingress. dry bilge. On the return trip, port tack all the way, healing at about 10-15%. Nice comfortable sail. Not much in terms of waves so the bow was not getting any action and no water on deck. I really don't see where the water can be coming from. The rail was not in the water so it could not be the joint.
Its clean salt water which ends up under the floorboards in several sections as far forwards as the one section just forward of the bilge (a little water), with the bulk of the water coming in further aft specifically the sections of the bilge and the two other sections further aft right up to and in front of the engine. The only thru hull would be the engine exhaust (which is on the starboard side near the transom) but then the space between the stringers where the engine is only takes in water from the prop shaft which is a little water a day, quite manageable and the thru hull for the engine water intake, which does not leak. These would take in water even when the boat is docked, which is very little. It is clearly when and only when the boat is on a port tack.
I routinely close the thru hulls for the head and sink while underway so its not that either.
I really want to solve this as I unscrewed the floorboards to rinse off the salt water after each sail. Annoying. Salt water also damages if left so I pump it out and then rinse it with fresh water.
Sherlock Holmes, where are you?