One of the best shapes for a Marine Impeller is that of the 3-blade marine propeller. This Matine Impeller is quite sophisticated. It incorporates a complex blade shape that can only be readily manufactured as a casting. There lies its downfall. Cast marine propellers are heavy. They create a mechanically limited design, because of the large shafts and gear reducers necessary to support their weight. Fabricated impellers were developed for just this reason. Today the only place we see the Marine Propeller used on mixing equipment is the smallest Portable Mixers, where propeller diameters are in the 3" - 6" range.

Marine type propellers are the same as those used on ships. Usually they are driven at speeds above 190 RPM. The flow is primarily axial (discharge flow parallel to the agitator shaft) and are most effective in low viscosity fluids.

The leading face can be flat or concave while the back side is convex.

The pitch is on the basis of its being a section of a helix. Pitch is described as the advance per revolution. Almost all propellers today are square pitch where the pitch is equal to 1.0 times the diameter, or the impeller would advance a distance equal to it's diameter in one revolution. Propellers having a pitch ratio of 0.7 are becoming more popular, due to the higher efficiency of the low blade angle.

Propellers are characterized by high discharge capacity with low head. Another characteristic (although seldom mentioned) is the sensitivity to almost any change in viscosity.

The Marine Propeller is an efficient pumping device when comparing propeller flow to horsepower, however, they are very costly in sizes over 12" diameter.