Assuming is going to be tough without looking at more picutres. you have an iron keel. Once out you need to check for several things. There is a protruding stub from the hull where the keel is bolted up to inside. See if any leaks there first. If none, that means the sealant which is 5200 between the keel and stub is sound. Second you will need to see if any rust and deal with that by wire brushing to the metal, clean off, apply protective barrier so the keel will not rust but make sure it contains zinc chromate, the fair with two part epoxy, and finally apply barrier coats. If you have any blisters on the hull, then you will need to address that just like the keel except no paint in the first part to protect the metal from rusting.
If you want to apply barrier coats, the boat will need to dry out for two months in warm temps so you will not apply barrier coat to a hull that is wet. As for anti fouling paint, check with your local yard as to what they would recommend what is the best for your area.
Former Hunter dealer who painted the 25.5 Hunter
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