It is a common occurrence that water that was previously trapped in the stringers below the sole would become dislodged with boat motion releasing some of it into the bilge. The sources of this water could be rain leaks, leaks in water tank or plumbing, lake water spray when under sail, wash downs, etc. The points of entry could be deck fixtures, hatches, portholes, plumbing and drain hoses, keel bolts, packing gland etc. The reality is that there are likely to be a good number of gallons trapped down there and will continue to release slowly and could be ever present as long as there might be leaks. Check the packing gland or shaft seal as it is designed to drip a few times a minute but sometimes may drip more often and this water usually goes directly into the bilge.