The seat sides connect to the keel floors to spread the keel loads
I have started work on the two 300 litre fresh water tanks on my Didi 40cr. This is twice the drinking water storage as we have on Passion and most of the time I carry just 40 litres, filling the tanks only for our cruising jaunts. Even the Beneteau 50 we chartered in the Whitsundays 14 years ago had only 1000 litres storage for six people so our 600 litres will be luxury for two.
The tanks form a for and aft structural member to share the keel loads amongst all the frames and they are the seats in the dinette. The photo shows the access holes in the top of the seats which are needed so that the skin side of the tanks can be coated with epoxy glass. The seat side faces will be glasses before the hull is skinned. The tank top on the left is glued in while the one on the right is sitting in loose in slots I installed to hold the panels for fitting and gluing. You can see the gap between the side and top where it will be glued and nailed later. Almost all the shelves have slots so that the shelves can be slipped into place.