Using a fabricated compass to scribe the radius for the widest part of the deck plate that will be resting inside the floor. This width will vary by deck plate.
Screw measuring twice, measure three times and cut once when dealing with the floor of your beloved boat.
Now: 1999 Malibu Response LX Monsoon 325
Past:1994 MasterCraft Prostar 205
"Call on God, but row away from the rocks"- Dr.Hunter S. Thompson