The average boater could easily assume marine propellers come in a single form. However, marine propellers come in a vast assortment of construction types, materials and sizes, and are specialised for specific applications. Additionally, the cost for propellers varies greatly depending on these factors and their size.
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Marine propellers are typically made of corrosion-resistant metals since the saltwater environment can quickly degrade a general steel propeller. Though a painted or powder-coated steel propeller may be used for some applications, the most common materials for marine propellers are aluminium and stainless steel. The biggest benefit of stainless over aluminium is the much greater durability of stainless, though the cost is greater as well.
The construction of marine propellers includes the number of blades and the method of attachment. Marine propellers come in either three- or four-blade configurations, though aluminium propellers only come in three-blade forms. The benefits of three-blade propellers are the lower cost and good top speed performance, but four-blade propellers have improved handling in exchange for a generally higher cost. Blades can either be attached to the hub by welding or forged in one piece. Welded blades are much less expensive, typically less durable and offer less performance compared to forged blades.
In addition to materials and construction, marine propellers have other features that can produce subtle, and sometimes dramatic, effects on the performance of the boat. Pitch, or the distance the propeller moves as it revolves around the hub, determines the thrust of the propeller. In addition to fixed pitch propellers, which have a static geometry, there are variable pitch and adjustable pitch propellers for specific applications. The rake is the angle of the blade in relation to the hub; this affects the performance of the propeller. These and other variables determine the overall performance of the propeller. Consult a professional marine supply shop or marine engine store to ensure the proper blade is matched to the boat and engine.
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