What’s a bilge?
The bilge is the lowest compartment on a sailboat, below the waterline, where the two sides meet at the keel. Water that doesn’t drain off the side of the deck will drain down through the boat into the bilge. Water can creep into the boat through (for example) cracks in deck fittings (cleats, traveller) and the hull-deck joint.
Bilges on yachts are basically our last line of defense against sinking. Given their vital importance it’s surprising how little love and attention we give them. Checking them regularly is highly recommended.