Yes, please come back with enough information about the boat that we can be helpful. 3M5200 is commonly used for bedding keels when doing repairs (don't know about when building the boat) and 3M4200 is just a less adhesive version of the 5200. It would seem 5200 is the more appropriate product for the application mentioned. There are other "googes" as well that one might use....
Why is the crack there? what's the backstory? If the boat has been on the hard for a while, you might not get the full picture as it may have dried out completely, btw.
Fair winds