Mercury Racing has released a new propeller-slip calculator app for Apple or Android smartphones. The app has all the functionality of the calculator at mercuryracing.com, which makes propeller testing easier and much more accurate. It can be downloaded for free from Google Play or Apple iTunes.
Mercury Racing’s propeller guru, Scott Reichow, posted some real-world examples using the app in a recent blog post.
Looking at a boat powered by a single Mercury OptiMax 250 Pro XS, Reichow worked with a customer who was looking to increase rpm for enhanced hole shot and midrange acceleration. Reichow suggested to drop the propeller pitch by 2 inches, working off the knowledge that every inch of pitch affects rpm by 150 rpm. When he plugged the new pitch into the app, it showed that the outboard should be at the top of the operating range, which would provide the thrust needed for the improved hole shot. It also showed that top-end speed would be lowered by 2 mph.
The customer was concerned about the engine hitting the rev limiter when under a light load, so Reichow went back to only 1 inch, which decreased engine speed by 150 rpm, but provided a 1 mph increase in top boat speed. The app let Reichow arrive at the best prop when he plugged in a half-inch drop in pitch. The engine speed increased by 75 rpm, the boat delivered a better hole shot, and the motor would not over-rev in a light-load situation. In a matter of minutes, Reichow arrived at an answer that previously would have taken at least one half-day of testing.