Understanding How a Boat’s Propeller Works

As your boat’s propulsion device, the propeller is obviously very important—but do you know how propellers work? Do you know what kind of propeller is the most effective choice for your boat? Understanding how a boat’s propeller works will allow you to make an informed decision when selecting the necessary parts for your boat.

The “Lift” Concept

Propellers are either “right-handed” or “left-handed” depending on which way the blades are angled. They achieve propulsion as the angled blades generate lift, not unlike the lift generated by an airplane’s wings. In addition, water must fill in the space made by the propellers as they push water aside. This creates a pressure differential between the two sides of the blade and forms a negative pressure on the forward side of the blade and a positive pressure on the aft side of the blade. 

Thrust

The pressure differential caused by this concept draws water into the propeller from the front and accelerates it out the back. Think of a household fan. It sucks air in from one side and propels it out the opposite side to create a breeze. By drawing in this water, the propeller creates a “cylinder” of water that exits the propeller and propels the boat in the opposite direction of the thrust. Fewer blades on your propeller equate to greater efficiency, while more blades can handle greater power input and loading. 

Materials

More than just the process of propulsion, understanding how a boat propeller works is understanding the materials that are used to manufacture custom boat propellers. Propellers for commercial boats are typically made from either a stainless steel alloy, a nickel-aluminum-bronze alloy, or a manganese bronze alloy. The costliest material, stainless steel, is very easily repaired and stands up to quite a bit of abuse. The hardest alloy is nickel-aluminum-bronze. This material is typically used in clean, deep water with minimal chance of grounding or fowling. Manganese bronze propellers are the least expensive in terms of materials, and when they do impact a hard object, they can often be bent back into shape when being repaired.