A diesel Scharnhorst: power, speed and the whole machinery plant

What power and top speed could a Scharnhorst hull achieve if Germany had concentrated on diesel propulsion?

The expectation is broadly historical performance, perhaps about a knot either way. The comparison must include boilers and steam systems as well as the turbines, with merchant diesel development offered as evidence of available German capability.

A diesel Scharnhorst is expected to achieve roughly historical power and speed, with about a knot of variation in either direction depending on the engines chosen. German merchant-marine diesel installations provide a guide to the size and power available. Comparing only a diesel engine's weight with a steam turbine leaves out the boilers, gearing and steam pipes of the complete plant. Those pipes also impose maintenance demands and hazards from live steam. Larger diesel engines could use space otherwise occupied by boiler rooms, potentially allowing a four-shaft arrangement. German effort spent on high-pressure steam machinery provides a comparison for the diesel development that could have been pursued. Gas turbines' high power density differs from that of steam turbines with associated boilers, so the modern gas-turbine comparison does not answer the historical question.