Crack at joint?
If it is the crack that develops between the f/g keel stub and an external keel, what worked for me was:
1. Clean up any loose material and let it dry comletely.
2. Fill gap with 5200 and let dry
3. Put a 3" piece of f/g tape over the the gap with epoxy resin (I used West epoxy and tape)
4. Fair and paint.
In South Africa doing lots of boat stuff. Departure north from Cape Town around December 15th. Arrival in the Caribbean around the beginning of February, after 5300 miles or so.