Got the cover off today. 60º. Drained the bilge. At least the (rain) water wasn't over the floorboards.
Sounds like no bilge plug of one sort or another and some cover leak, around the mast or adjacent slot? Helpful that it was not a bilge of ice. I recently had a 2" diam pine branch fall on top of my two-bit cover, making a ragged tear that I patched up with wrong kinds (all that was available) of tape. Today is a test. Got so I didn't want any water on deck until the season for it. It is pretty dry & cozy underneath in inclement wx.