Sorry for the delay in answering your question.
The Strider Club has an interior tray moulding which is bonded all round the gunwales. The space between it and the hull is a large watertight compartment with several bulkheads and stringers.
The keel is part of the hull moulding and not blocked off.
Thus this inner tray moulding forms a double bottom and provides buoyancy. If a hull is holed then the Strider should stay afloat, floating on its inner tray moulding.
Thus it is important not to make holes (even for echosounder or log transducers) in this inner moulding.
The drawback to all this is of course that you don't know what is under the inner moulding. Clearly in your case someone decided to fit inspection hatches in the soles so that they could check for any leaks.
There should be no problem opening them. However first check that the boat is floating with the transoms out of, or just touching, the water when the boat is empty. If they are immersed then you already have a leaking boat and will need to get the boat ashore before opening the hatches.
I hope that isn't the case. However, if there IS a leak then it will be those hatches that are keeping your boat afloat.
You may want to remove them and glass patches over the holes, but definitely you want to make sure they are really watertight. You can buy hatches specifically designed for use as buoyancy compartment inspection hatches, but they are quite expensive.
I hope this helps answer your question.