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Take a Look at Your Prop

If it’s looking like a curled wood saw, it’s time for a new one

While walking close to the stern of my trailered boat in the drive yesterday morning, I felt a tug. My pant leg had hung up on the outboard’s prop, and for good reason. The edge of the offending blade looked like a curled wood saw.
    Fishing shallow water has its rewards, but it can be hard on boat propellers.
    You’re sometimes navigating where your skiff’s propeller is pushing through sand, silt or worse. You are inevitably going to hit a rock or two, possibly even a boulder.
    If you have a stainless steel prop on your outboard, you must be eternally cautious or have deep pockets. Stainless is expensive and doesn’t easily bend or deflect. While superb for deep-water cruising, stainless props will fracture, or fail when encountering rocks of size.
    Aluminum props are much more forgiving, bending and deflecting from collisions with the hard stuff in the shallows. My propellers for the last few decades have been aluminum for just that reason. Though they can eventually lose their operating efficiency when the blades become too rough or misshapen, replacing them is rather simple.

Know Your Propeller
    Next to the horsepower and torque of the motor itself, the propeller is the most critical link to moving through the water. The propeller and its shape determine, among other things, your top speed, fuel economy and how promptly your craft comes up on plane.
    An outboard prop’s performance essentials are identified by the numbers inscribed on the hub of the prop (which means you have to take the propeller off to determine what they are). These numbers indicate pitch (how far the prop theoretically drives through the water in one revolution, measured in inches) and the prop’s diameter (also in inches). It should also denote the direction of rotation (usually right or clockwise).
    If you are pleased by the past performance of your propeller and merely intend to restore lost efficiency (caused by dents, gouges and misshapen blades), purchase a new one with the same pitch, diameter and rotation direction as your original.
    At propeller-changing time, you can also modify any aspect of your craft’s general on-the-water performance. Choosing less pitch, or a slightly smaller diameter for your new prop can likely generate higher RPMs (engine speed) and a greater WOT (wide open throttle) speed. Expect, though, that the change (as long as the RPM increase is within the safe range of the engine’s specs) may also result in your craft coming up on plane a bit more slowly.
    If you are a shallow-depth dervish intending to cruise the shoalwaters and wanting your skiff to jump up on plane faster, choose a greater pitch or a bit larger diameter prop, recognizing you may lose a little top-end speed.
    One caveat: It is impossible to predict exactly how a different prop will affect your boat’s performance on the water. So when you decide to try a new setup, exercise care in unpacking, installing and running the new unit. If it doesn’t perform as you wish and the parts (and packaging) are still in new condition, you can return it in exchange for another better suited to your needs.
    Don’t discard a banged-up prop. It can come in handy as a backup. If you’re handy and have a hammer and a butane torch, you might restore a dinged aluminum unit to useful condition.