What Are the Benefits of Stainless Steel Props?

Using stainless steel props on your outboard provides advantages over other prop materials, with most of these related to the inherent strength of the steel. Stainless steel has a high chromium content -- above 11 percent -- and is highly resistant to corrosion of the sort that often troubles most metal propellers.

  1. Damage

    • Steel propellers are less likely to sustain damage than bronze or plastic propellers. The water is full of things, from the soda can someone throws into a river to logs from a flood upstream. They all lie in wait for your boat to come by, and they can chip, bend or break a blade on the propeller. Stainless steel also resists damage from cavitation. Cavitation occurs when a prop's blades move so fast they change the water pressure. As the water pressure changes, the water boils, and when the bubbles explode, they damage the blade.

    Strength

    • The tensile strength of a stainless steel propeller is between 70,000 and 80,000 pounds per square inch. This means the stainless steel boat propeller is twice as strong as the 40,000 psi tensile strength of an aluminum propeller, and almost one and a half times as strong as the 65,000 psi tensile strength of a manganese-bronze alloy propeller. Stainless steel propellers also are significantly stronger than plastic propellers, which often are best used for trolling motors rather than main propulsion.

    Galvanic Corrosion

    • A stainless steel prop offers the fiberglass boat owner an advantage because of its superior resistance to galvanic corrosion. Galvanic corrosion occurs when two different metals are immersed in water. A weak current forms between them, and ions from the more reactive metal flow to the less reactive metal. A boat with properly installed zincs does not suffer from this, if the difference between metals is small enough that the current is less than 0.15 volts on the anodic index. The difference between aluminum and stainless steel is 0.15 volts. Zinc offers good protection for both because its anodic index is 1.25 volts.

    Cost Effectiveness

    • Stainless steel propellers can be repaired, unlike plastic propellers. Since stainless steel propellers are stronger, they are less likely to suffer casual damage. This means they do not require repairs as frequently as aluminum or manganese-bronze propellers.