Silicon Bronze is a fantastic material for boat fasteners. It will outlast even stainless steel in many conditions.
Why do we offer Frearson head screws rather than square-drive (Robertson), slotted or Phillips? Well we think they're the best, the point on the driver bit is sharp and the recess in the head of the screw matches perfectly, giving you the ability to apply more torque without stripping out. We can't say that for Phillips. We've all mangled the heads on slotted screws, they may look very traditional, but they can be difficult to drive. And square drive just doesn't have that traditional look you want in your bronze fasteners. So we choose to use and sell these screws.
They're equally good above or below the waterline and they look great exposed too.