A few culprits immediately sprung to mind and we thought we'd nailed it when we identified leaking seals on the cabin portlights. I sealed these up with adhesive tape to tackle at a later stage and drained and dried the bilges.
Imagine my surprise after an unusually dry spell when I discovered the bilge on the port side of the keel box was wet again. It never seemed to dry out fully and I was baffled as to the source of the water.
I let it drain, emptied the bilge and watched it fill up again! Bear in mind that the boat is sitting high and dry on a trailer about 15 miles from the coast! Eventually, after a day the water stopped draining but my curiosity was not satisfied. After all, where on earth was the water coming from?
The hole needed to be repaired, so I used a Dremel to cut back the uneven edge and this exposed more of a hole. Water was visible pooling in a crevice. I sucked approximately 20 litres of water out of the hole using this (originally designed for oil changes but damn useful where you need to suck anything out of a tight space):
Here is a photo after I cut back the uneven edge with the Dremel.
What's clear from this is that the bottom of the boat and the lower part of the keel box is double skinned. Water had leaked into this space over a period of years filling it up. When we repeatedly drained the bilge on that side, the water within the double skinned section found itself at a higher level than the bilge, and water drained into the bilge.
I suspect the perforation was made when the keel bolt nuts were secured. The clearance is a little tight on the port side, and there was evidence of GRP being cut away to accommodate the washer & nut. You can see this in one or two od the photos above. I think that whoever did this, realised they'd penetrated the GRP and there was evidence of some sort of sealing compound being used.
I re-glassed the area with a laminate of chopped strand mat and woven glass mat. It was a little fiddly to get behind the innermost keel bolts.
Now all I need to do is put the nuts and new washers back without undoing my hard work!