As ballast in the bilge I would have liked bags of shot, but I can’t get hold of any recycled pellets at a reasonable price. As the previous lead casting exercise was very successful, I have decided to built four containers to cast lead into. Each of the boxes will hold about 25kg when half full. The box hasn’t been cleaned up yet, but they will work out nicely. The box’s section is that of the underfloor area. The cleat on the back stops the box sliding all the way against the centre-board case. That keeps the bilge clear. The box fits just through the opening in the floor boards. It can be shifted aft to sit under the cleat for the floor boards. Given the tight fit of the box through the opening in the floor, there is little chance for it to come out of its place, even if the boat has been turtled. To make absolutely sure, I will bolt a second longer stick on top of the ‘handle’ of the box in such a way that the stick can be rotated 90 degrees to lock the box under the floor boards (last photo).
Update: A fellow Pocketship builder/owner pointed out, that it might be necessary to shift the ballast further forward (between floors 2 and 4) to balance the boat properly (thanks Craig). I will adjust the shape of the other boxes so that they will fit in any of the under-floor compartments.