The weight of a keel

[amolitor]

You could write down a potentially useful rule of thumb for righting moment per square foot of sail, but that doesn't translate directly into keel weight. It depends on the hull form (for the form-stability part of things) the vessel size (again, form stability) and where the center of gravity is (this is the only part where keel weight figures).

The keel weight contribution to the center of gravity depends on the weight of the keel, and the configuration.