Bill,
Robs' SUNDOWNER is not a shoal draft Top Hat, unless he has not told us that he only has 5' 6" head room.
As I mention under "How much water" [in General] Shoal draft Top Hats have no water in the bilge as extra lead
was added there to keep them upright, but some have a raised floor, [only 2 known of at this stage]
which reduces the headroom, under which a water tank was constructed.
Without the raised floor and the underfloor water tank, the head room is as normal or slightly higher in shoal draft Top Hats.
Rob has mentioned before that he may have 80 to 100 litres in the keel tank!