Marine Vessel Turbines
At the same time, Parsons was developing steam turbines to power marine vessels. The Turbinia was 100 feet long and 9 feet wide with a displacement of 44.5 tons. The first turbine was a single radial flow model driving a single shaft at 2,400 rpm. Parsons had calculated a speed of 34.5 knots, but the Turbinia wouldn’t even do 20 knots. Parsons figured out that the high rotational speeds of the propellers, 18,000 rpm, caused water pressure to decrease, forming bubbles. So most of the power was making bubbles rather than pushing the boat.
He overcame this problem ingeniously, by changing the radial flow turbine with three parallel flow turbines. One had high pressure, one medium, and one low pressure, and each reused the same steam in turn. Each of these turbines drove a separate shaft attached to three triple-bladed screws (for a total of nine propellers). When the steam pressure was 157 psi, the central shaft turned at 2,000 rpm, and the side shafts rotated at 2,230 rpm. With this configuration, the Turbinia did indeed reach 34.5 knots.