Diesel-electric liner speed and QE2's conversion

What speed could a four-screw diesel-electric ship the size of Lusitania reach?

It depends on the installed engines and the period assumed. A modern design is suggested as capable of more than 40 knots, while QE2's 1987 diesel-electric conversion is cited with a speed of 34 knots.

A Lusitania-sized hull and four propeller shafts do not establish speed by themselves. The installed engines and the period assumed determine what power is available. More than 40 knots is suggested for a modern design, without specifying a complete ship or machinery arrangement. QE2 provides the liner comparison through its diesel-electric conversion in 1987 and a stated speed of 34 knots. The modern speed estimate therefore remains separate from the figures cited for an existing ship.