If you'll pardon this Yank sticking his nose in...
The 1:24 scale SC&H models run in the 5 foot on deck range and run about 100 pounds (7+ stone) sailing weight. Half of that, or nearly so, is in the form of a removable ballast keel attached to the very bottom of the model, adding 3 or 4 inches to the model's draft of 6 to 8 inches.
This lead bar is attached to the model by a pair of threaded rods that pass through the hull from keel to deck in tubes for water-tightness, and bolted on deck.
The nice thing about this set up is it allows you to detach half or more of the model's weight making it easier to handle out of the water. The mounting for the ballast can also double as a sturdy "invisible" display stand mount. It also get a lot of the weight as low as possible making your model stiffer in the wind. The lower the ballast, the less you need beyond just getting the hull down to the waterline.
There are, of course, variations on the theme. For my 1:36
Constellation I'm using a 2 inch I.D. PVC pipe filled with lead bird shot. It weighs in at 42 pounds (3 stone). Using iron pipe instead of PVC would gain some extra weight without a gain in size. There was no casting involved; lead or resin - just PVC glue and some hand-sawing. I'll still have 10 or so pounds internal to bring the model to proper trim.
My set-up in cross-section:
HMS Killingsworth uses basically, the same idea: