Sailboat Propeller Calculator
The sailboat propeller calculator uses standard marine engineering formulas to estimate the optimal propeller diameter and pitch for your vessel. By taking into account your engine horsepower, gear reduction, and hull speed, it calculates the thrust required to efficiently push your displacement hull.
Understanding Propeller Dynamics
Propellers are categorized by two main numbers: Diameter and Pitch. For instance, a 16 x 11 propeller has a 16-inch diameter and an 11-inch pitch. Propellers on sailboats require entirely different geometry than speedboats, focusing on massive low-end thrust rather than high top-end speed.
Diameter vs. Pitch
- Diameter: The total width of the circle created by the spinning blades. Sailboats require large-diameter props to push heavy displacement hulls against headwinds and tides. The required diameter is heavily dictated by your gearbox ratio.
- Pitch: The theoretical forward distance (in inches) the propeller moves in one complete revolution (assuming zero slip). A higher pitch means more theoretical speed, but if the pitch is too high, your engine will be overloaded and fail to reach max RPM.
2-Blade vs. 3-Blade
Because sailboats spend the majority of their time under sail, propeller drag is a major concern. 2-Blade propellers can be aligned vertically behind the keel to minimize drag, but they suffer from vibration and reduced thrust in reverse. 3-Blade propellers offer drastically smoother motoring, better control in marinas, and stronger headwind performance, at the cost of a slight loss in sailing speed (unless you opt for a feathering or folding propeller). To compensate for missing blade area, a 2-blade prop usually requires a slightly larger diameter than a 3-blade.