Why not just use the mechanical output of the generator directly to drive the boat. You won't get 1800 hp of electrical power out of the generator unless you could already get at least 1800 hp of mechanical power.
The only "SCR" I know is a silicon-controlled rectifier -- basically a normally-closed switch that is opened at a theshold voltage and cannot be closed again until the current through it stops. They're commonly used for protection circuits on ICs -- if you oversupply the part, the SCR opens and conducts large currents, protecting the more sensitive circuitry for a while (until the heat dissipation blows the chip up anyway).
I don't think this is what djreidt means, though..