I have three different options for you. Your profile says
Dominican Republic, so that may affect availability.
And yes, you should fix it properly out of the water, but the realities sometimes trump the “proper way”.
1. Underwater epoxy as mentioned above. Semi-permanent but not always great in very narrow cracks - may require enlarging the crack to get enough of a good bonding surface.
2. There are underwater silicone-like sealants and adhesives.
Adiseal is one brand that makes a fully underwater curable sealant/adhesive. About the same cost as most caulk, applies with a caulking gun (or a finger). Works well, but availability in DR may be a question.
3. I know available in the DR -
toilet wax ring seal (used to seal
toilet to floor/pipe flange). These are a relatively soft wax. Easily applied underwater, I carry one on board exactly for this purpose. Temporary, harder to clean up when making the permanent
repair, and can wash out depending on location, shape, boat speed, etc. But,
cheap, easy to get and use.