Jul 25, 2016

Mercury Racing has announce the release of their new Propeller Slip Calculator App. Available for both Apple or Android devices, the app provides all of the functionality of the calculator featured on their website at . The app enhances the versatility of the tool – making prop testing much easier and a ton more accurate. Download it for free from Google Play Store or Apple iTunes.
Scott Reichow, Mercury’s Prop Guru says “I use the slip calculator daily when assisting customers with propeller questions. It is a great tool that provides much more information than just slip. Results for each of the five fields can be derived by populating the other four.”
Scott walked through an outboard example on the Mercury Racing blog.  “Let’s look at a single engine OptiMax 250 ProXS outboard powered hull.  When communicating with customers, I always first ask for baseline information such as the pitch of prop they are running, gear ratio and engine RPM at wide open throttle. Using the app, I can plug information they provide (pitch, gear ratio, engine rpm and speed) to first determine slip.
Decreasing the pitch by two inches results with an improved hole shot and acceleration while sacrificing 2 mph off top end speed.
Now – after getting some additional information, the customer informs me the rig is under a heavy load and thus he is looking to increase RPM for enhanced hole shot and mid-range acceleration to carry the load. Let’s see what happens when we drop the propeller pitch by two inches. Typically, one inch change in pitch affects engine speed by 150 RPM. In this case – dropping two inches of pitch will increase engine speed by 300 RPM. I plug in the new RPM and pitch size into the app – leaving everything else the same.  The engine is running at the upper end of it operating range. This will provide the added thrust needed for the enhanced hole shot and mid-range performance the customer desires. The App tell us that the top end speed will drop by 2 mph.
We are getting close to what the custom-er needs for his application. The customer sometimes runs under lighter loads and he is concerned with it being so close to the rev limit using the smaller wheel. Let’s see what happens when we go back up one inch in pitch. I go to the app and change the pitch to 24 and decrease the engine speed by 150 RPM. I again select Actual Speed and find a gain of one mph in top end speed. With help with the app – the 23.5 pitch is perfect size for what the customer expects from his application.
Let’s see what happens when we go down one-half inch in pitch. Knowing the engine speed will increase 75 RPM, I change the RPM  to 5925 and pitch to 23.5 and select the Actual Speed button.
Top speed is comparable to what is achieved with using the 24 pitch prop. The higher engine RPM will enhance the hole shot and mid-range performance. There is enough of a gap between the actual engine speed to the upper engine operating range to allow for occasional light load applications without worrying about hitting the rev limit. This is the prop I would recommend for this application.”