On Sat, 13 Jun 2020 15:24:42 +0100, The Natural Philosopher
wrote:

On 13/06/2020 14:06, Lee Nowell wrote:
The joists are 8 X 2 in the ceiling of this room. They are the floor joists for the room above.

Well ignore all the advice about strengthening them then

Way more than you need. Bolt through or *serious* screw in hook

When we installed the king size waterbed in the bedroom above the room
the baby bouncing chair loop in the ceiling, we hung a plumb bob from
the loop and over a metal plate laid on the floor, so that the tip of
the bob was just shy of the plate. We filled the waterbed then checked
the gap under the bob weight and it had hardly moved. ;-)

Cheers, T i m