Re: How much water is normal?
90% chance that if there's nothing else obvious, on a Pearson the keel bolts are corroded and started to leak. The keel bolts are vertical out of the top of the keel and IIRC the 3rd or 4th one back on the starboard side has the boat's grounding system attached to it. You'll probably find significant corrosion on that bolt. Can't be fixed in the water. The boat has to be hauled out and drop the keel out.
If you pull the cabin sole plate and see that the nuts and washers are badly corroded, squirt them right away with WD-40 or equivalent, and keep them soaked up for a week or two, to hopefully make it easier to get the nuts off to drop it out. Otherwise they'll be seized solid and an impact wrench will probably just twist them off.