Did you know that according to the laws of physics the propeller is nothing more than a screw (and that’s why its colloquial name is actually screw)?
This small element is a very important source of propulsion, along with the engine. It is made of composite materials or steel or aluminum and has varying characteristics.
In fact, all boats except those with waterjet engines are equipped with a propeller. Its constituent parts are the hub (the central component) and the blades, the rotation of which generates the thrust and thus the forward motion of the boat.
Propeller types
1) Propeller foot
In this case, the foot of the engine also acts as a rudder, and mounted on it is the propeller, which is able to rotate around its own axis. This is a type of propeller that we find in outboard (FB) and inboard (EFB) engines, in the latter case the foot is called the sterndrive assembly.
2) Fixed propeller
In this case, the propeller rotates solely around its own hub, which makes the rudder essential in order to steer the unit.
In this chapter we will discuss two of the four main characteristics of the ‘propeller, namely the number of blades and the diameter.
Number of blades
The most common propeller is three-bladed, but there are also 2-bladed and 6-bladed propellers. The rotational motion of the multi-bladed propeller tends to give greater uniformity in navigation and be less prone to vibration.
Diameter
As it rotates, the propeller describes a circle. The diameter of this circle is the diameter of the propeller.
In the next article we will look at two other basic components of the propeller: the direction of rotation and the pitch.