Impeller vs. Propeller

Boat on the water

Both an impeller and a propeller are vital for a boat’s operation. However, their purpose and function are very different.  

A propeller is a fan which propels a fluid by pushing against it: it converts rotational motion into linear motion. An impeller is a rotor that produces a sucking force and is part of a pump. A propeller is always open, and an impeller is always closed, as it draws fluid. Let’s take a closer look at an impeller and a propeller to identify similarities and differences. 

What Are They? 

Impeller 

A boat impeller is a series of rubber vanes molded around a hub. The hub rotates the flexible vanes on an eccentric within a stainless-steel liner in the pump housing.  An impeller pumps cold water into the boat’s engine to keep it cool while the engine is running. Marine engines contain an impeller in the water pump. The pump draws water from outside the boat through the plumbing system.  

The impeller has an inlet that allows water inside and vanes that push the fluid forward. As a rotating component of a centrifugal pump, the impeller accelerates fluid outward from the center of rotation. This action transfers energy from the pump motor to the water being pumped. The sudden velocity in the water creates pressure within the pump casing and causes outward movement.  

Propeller 

A boat propeller is a fan that generates boat power by converting rotational motion into thrust. Propellers typically consist of three to four rotating blades that spin around a shaft to create the needed dynamic for forward movement. When the blades rotate, they accelerate water pressure behind each blade, causing the vessel to move in the water. 

The blades extend outward from the prop hub at an angle. This allows water to pass through the prop from front to rear instead of pushing the water from side to side. The more blades attached to the prop, the more power the prop can create. More blades also reduce drag that occurs simply because the prop is in the water. Manufacturers design props to run closer to the water surface, giving them additional bite and stability at higher speeds. 

How Are Impellers and Propellers Similar? 

There are several ways that impellers and propellers are similar. 

  • Both use water to create energy (pressure or propulsion). 
  • Both use rotation to move water. 
  • Both rely on a motor to operate. 
  • Both require ongoing care to maintain peak performance. 
  • Both require lubrication to keep all parts from wearing out quickly. 

And, of course, both impellers and propellers are necessary for a boat to operate. Without an impeller, the boat engine cannot stay cool. Without propellers, the boat will not move.  

How Are Impellers and Propellers Different? 

The primary difference between an impeller and a propeller is their function or purpose. The impeller is the main component in the boat’s cooling system. It feeds water into the engine to keep it at optimal operating temperature. The propeller is the main component in the boat’s movement. When the blades turn, the boat accelerates to the desired speed. 

Despite this primary difference, there are other ways that impellers and propellers are different. 

 Impellers Propellers 
Motion Forward rotation Clockwise rotation 
Primary function Create water pressure Create water propulsion 
Containment Pump housing No containment 
Primary part Vanes Blades 

Professional Impeller/Propeller Maintenance in Pensacola 

Pensacola Shipyard offers propeller and impeller maintenance services for all types of larger vessels. Our divers clean the bottoms of your vessel and inspect the props for any underwater appendages. Contact us today to schedule. Whether you need ongoing boat maintenance, resources or facilities, we have everything you need for a complete boating experience.

To find out more about our marina and boating services, call 850.780.8441.