You know you aren't taking on any water at the dock, under normal
circumstances.

I suspect a cracked stem that is not visible when the hull is not being
stressed, or a failing htd joint.

To test for the latter, rig up a hose and spray water on the hull near the htd
joint in suspected areas. It would help to have somebody in the bilge observing
for water ingress. When you move the hose to a point and water begins appearing
in the bilge, you have found the problem area.

In addition, if you are taking on that much water through failing htd joint or
a breach well above the static water line, there could easily be visual
evidence on the interior of the hull. The water has to be running down the hull
to get to the bilge. Look for a small area that is super clean, or discolored,
still wet, or any of the other typical signs of a stream of water.