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.
Finished the circumnavigation in early February in Grenada. Have to work on a book project for the next several months so the boat will be waiting for next year.