The forstner bit is correct tool to use because the brad point pilot allows exact placement of the bit without wandering.

The strip thickness of the hatch cover cut-out alone is too thin to prevent blow through of your fostner bit. The margin of error is too fine, even with a drill press, with a depth stop and work clamped to your drill press table.

Adding a 3/16" spacer ring of wood, solves this problem, and solves others.

In the illustration below, the spacer ring allows magnet to magnet contact (strongest) and compression of the gasket for the best seal when the gasket is placed inside of the hatch cover spacer ring. Finally a bead shaped ring is installed on the deck lip to press into the gasket for an air tight seal.

Most hatch cover systems using only a wide flat gasket will leak because it is difficult to compress the gasket evenly over the entire hatch cover circumference.

With the gasket placed inboard of the spacer ring on the hatch cover, the bead on the deck lip has room to press into the gasket without bottoming out on the hatch cover bottom, for a uniform airtight seal. Only a very small amount of gasket is compressed and the bead presses deeply into the gasket for a positive seal around the whole hatch cover circumference.

Another spacer ring must be added before the deck lip is installed, to compensate for the hatch cover spacer ring thickness, to allow a flush hatch cover fit to the deck. A drain slot should be cut in the deck at the sides of the hatch opening to drain water, before the deck spacer is installed.

With the powerful magnet to magnet contact this system allows, a webbing loop is needed to pull the hatch cover open.

I've just given you the result of twenty years of experience of building kayak hatches.

Too much work? Success or failure is in the details.

All the best,
Rob