Usually means rainwater is coming in thru a deck or cabinside opening and running through some wood core and finding its way into the bilge. Windows are prime suspects... the water doesn't come into the cabin so that you can see but rather gets between the outside shell and inside liner .. Any part on the deck that has a hole into the shell could be doing that.. Mast step, winch mounts, handrails, deck tracks.. Sometimes you can find the trail where this ran into the bilge and that trail will help ya locate the real source. Happy Hunting !