See link for photo of screws: 4-bladed centerline, threes outboard.

Following from link:

.As most us know, the triple-screw steamer Titanic, and her sister ship Olympic, were propelled by a combined machinery arrangement consisting of two reciprocating engines and a single Parsons’ turbine. The reciprocating engines were of the triple-expansion type with one high-pressure cylinder, one intermediate-pressure cylinder, and two low-pressure cylinders. The Parsons’ turbine, which was fed by exhaust steam from the reciprocating engines, was a low-pressure reaction type. Each reciprocating engine drove one 3-bladed wing propeller of 23½ feet diameter, one on the port side of the vessel, and the other on the starboard side of the vessel. The turbine engine drove a four-bladed propeller of 17 feet diameter located on the ship’s centerline directly ahead of the rudder. The reciprocating engines were designed for 15,000 indicated horsepower (IHP) each when running at 75 revolutions per minute. The turbine was designed to develop about 16,000 shaft horsepower (SHP) when running at 165 revolutions per minute. At those numbers of revolutions, the ship was expected to make 21 knots.1 Titanic'’s propelling machinery was registered at 50,000 horsepower. Standard “normal full revolutions” in service was considered to be 78 revolutions per minute for a speed a little over 22½ knots. When running ahead at 83 revolutions per minute on her reciprocating engines, the entire power plant would develop about 59,000 horsepower, of which 18,000 horsepower would be contributed by the turbine.2 When carrying those number of revolutions, the ship would have made close to 24 knots through the water.