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.