Weight: Your boat may have a lot of heavy gear inside, or you may sometimes use it to tow skiers or wakeboarders, in which case the original-equipment prop may have too much pitch, causing your engine’s rpm to be on the low side. You can partially compensate for this decrease in performance by carrying a second prop with reduced pitch, making it easier for the engine to achieve the correct rpm at WOT. Reduced concentrations of oxygen at high altitude cause engines to produce less power (about 20 percent less at 7000'). If your engine is over revving, consider a propeller with more pitch.Įlevation: Many small, trailered boats are used at vastly different elevations, such as high mountain lakes and bays at sea level. Going back to the question of performance at WOT, if your engine is under revving, consider a propeller with less pitch. Conversely, a two-inch decrease in pitch will result in an increase of 300 to 400 rpm. As a general rule, a two-inch increase in pitch will result in a reduction of 300 to 400 rpm. Increasing the pitch will decrease engine rpms and decreasing the pitch will increase engine rpms. Should you "pitch up" or "pitch down"?Įngine rpms and pitch are inversely related. Over revving or under revving can be corrected by selecting a prop with a different pitch. Allowing your engine to under rev or over rev at WOT can result in engine damage.
#Boat inboard propeller calculator manual
Your owner’s manual should include this spec-usually 5000–5500rpm for an outboard or 4200-5000rpm for a sterndrive-or your mechanic or dealer may know. Selecting the correct prop should result in your engine running within the designed rpm range at Wide Open Throttle (WOT). Is your boat sluggish coming out of the hole and slow to get on a plane? Are you not hitting the top speed you think you should? Do you want an improvement in fuel economy? Hoping for better all-around performance? Is your current prop blowing out or ventilating excessively in turns or when you accelerate? Are you looking to improve your boat’s watersports performance for tubing, skiing or wakeboarding? Once you have defined your goals, you can move on in the selection process. What Problems Are You Looking to Solve?.Or maybe it is in good shape but you're looking to improve your boat's performance. Your prop might be damaged and need replacement. Depending on how you use your boat and its current performance, you might be wondering if you should “pitch up”, “pitch down”, switch from aluminum to stainless steel or move from three blades to four. Apart from keeping your boat’s hull clean and your outboard or engine tuned, selecting the right propeller is one of the easiest actions you can take to optimize boat performance.
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