| The second limitation of the extruded aluminum arm is the material. With aluminum, the clock starts ticking on it from the first load cycle. Every aluminum part loaded structurally will fail at some point. Yes, that goes for you saltwater boaters with your aluminum trailers, too! Many of us are familiar with how shaft mounted aluminum rockers tend to fail near the first thread of the adjuster screw. The aluminum here fatigues and cracks. Steel, on the other hand, doesn’t have this limitation. In fact, structural parts made of steel can be designed to have infinite life, as long at the stress is low enough. The good news is, this can be done even in offshore powerboat applications. Besides fatigue and cracking, aluminum has the perception of being a lightweight option. This is not necessarily the case. Steel has nearly the same stiffness to mass ratio as aluminum, so a steel arm can be made the same stiffness as an aluminum arm at around the same mass, potentially with an infinite fatigue life. For offshore powerboats, steel is the right material choice. Click here to read about the first failure mode in offshore powerboat valve train. |
