What to use to seal below water screws?

Jan 11, 2014
11,478
Sabre 362 113 Fair Haven, NY
Here's an image of an O'Day centerboard trunk. Not mine but as you can see the screws are already countersunk to accomodate the flat head screw. Any other type of screw introduces more drag
If the steel plates come off, the place to counter sink is on the hull at the gelcoat. The purpose of the countersink to allow the sealant to be thicker around the hold and get a better seal. The counter sink in the photo is as you suggest to reduce drag by making the screw heads flush with the bottom.