It's a Beckson PB525 series, with optional inside rain louver. Some Becksons have the knobs, while most have the cams. I just installed a pair of small opening Beckson ports which came with the knobs. I've also installed the inside louver on a boat I no longer own, which replaces the screen but has its own bug screen.Does anybody know the manufacturer of this combination fixed and opening port on a 1987 Pearson 27?