That's probably a later Potter vintage 20' SeaCraft SF, maybe a '76 or later. The vents are there to ventilate the bilge, regardless of whether it's an I/O or OB. I/O models typically have additional vents in the transom cowling aft of the engine box. Some ignorant folks often eliminate the vents when they restore a boat, and then wonder why they end up with lots of mold and mildew in the boat!
Carl Moesly never foamed in the fuel tanks in the original 1960-1970 models, and some early brochures mentioned that ventilation of the bilge was a USCG requirement for that configuration. It added cost but they did it anyway because it was the right thing to do. Potter apparently made the mistake of using foam around the tanks sometime around 1976 or so, although he kept the vents. The inevitable expansion & contraction of the tank will create a small gap between the foam and tank that holds water against the tank, leading to crevice corrosion. Leaking fuel tanks are relatively common on the later models, but my '72 does not have a foamed in tank. I"m still running the original tank.
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