Editing Propeller (section)

===Variable-pitch propeller===
[[Image:Controllable pitch propeller schematic.svg|thumb|right|A controllable-pitch propeller]]
[[File:Rudder and propeller Beached fishing vessel Nørre Vorupør Denmark 2017-04-14.jpg|thumb|right|A variable-pitch propeller on a fishing vessel]]
Variable-pitch propellers may be either controllable ([[Variable-pitch propeller (marine)|controllable-pitch propeller]]s) or automatically feathering ([[folding propeller]]s). Variable-pitch propellers have significant advantages over the fixed-pitch variety, namely:
* the ability to select the most effective blade angle for any given speed;
* when [[motorsailer|motorsailing]], the ability to coarsen the blade angle to attain the optimum drive from wind and engines;
* the ability to move astern (in reverse) much more efficiently (fixed props perform very poorly in astern);
* the ability to "feather" the blades to give the least resistance when not in use (for example,  when sailing). For large airplanes, if the engine is uncontrollable, the ability to feather the propeller is necessary to prevent the propeller from spinning so fast it breaks apart.