Possibly to remove the keel???
The only reason I can think of to cut a 9 X 9 hole there would be if there had been a problem in the past removing the keel bolt. The bolt can sometimes seize into place, making it a bit harder to remove to either work on the keel or replace the bolt and seals. It's possible that someone cut the area out, maybe so they could get a hammer in there and really work at the bolt. I don't know if there is any difference in the model years, but in my 1985 M25, the area you describe as being cut is simply the liner anyhow, and nothing structural. If it's glassed over, you will need to at least cut out a hole to access the keel bolt as it will need to be changed at some point. The lock bolt is a matter of preference. I don't use it, mainly because I have to raise my keel to get back to my slip and the water I sail isn't always deep. On my boat, I'd guess there is a 1+1/2 inch hole centered over the bolts so you can get a wrench in there. There are plastic caps that snap in to close the hole for asthetic reasons. You could easily replicate these with a hole saw and new plugs. -John
