Notch in pontoons 2007

About 2 feet from the front of both pontoons I have a notch on the bottom of each pontoon. When I put boat on lift water drains from this notch for 1-2 days depending on how long the boat was in the water. I assume this notch is not a 1 way drain but it is by design and is allowing water to enter the pontoon. Before I seal this area I wanted to ask about this notch and why it is there.  Thank you