Marine propellers

The propeller was first used for ship propulsion in the first half of the 19th century, when alternative steam engines had reached an acceptable level of reliability and efficiency to compete with sail-powered ships, for which wind power was free. It was only in the second half of the 19th century that the propeller definitively prevailed over sails and paddlewheels, the latter nowadays being used only in a few cases for inland navigation for tourism purposes.

Several countries claim to have invented the propeller in the 1830s. In France, the inventor of the propeller is Frédéric Sauvage, whose patent was registered in 1832.

The first propellers were nothing more or less than a two-threaded Archimedean screw whose length was equal to the geometric pitch. The captain of a ship who had seen his propeller accidentally reduced to half its length noted, not without surprise, that his ship's speed had increased as a result. Thus, through successive modifications to the shape and number of blades, resulting from tests on models and on real boats, the propeller evolved into its present form. With the exception of special applications, the propeller is the propulsion unit of almost all boats, from small motorized pleasure craft to huge oil tankers weighing several hundred thousand tonnes.

Numerous tests of model propellers have made it possible to define their hydrodynamic characteristics (thrust, efficiency) as a function of blade number and geometry. These results, published in the form of curves, can be used to quickly define the propeller geometry that best meets a given specification.

Two major problems are still the focus of a great deal of research aimed at improving propeller performance: cavitation and ship vibrations induced by propeller operation. The development of hydrodynamics applied to propellers, and of increasingly powerful computers, means that these two problems can now be tackled more rationally, and propeller layouts can be defined that offer the best compromise between various constraints (efficiency, cavitation, vibration, mechanical strength, etc.). This is what we will focus on in this article.