Propping Correctly and how to test props

[Bushwacker]

Due to popular requests for a sticky post on this subject, I decided to start a new thread with the link to the post from the Verado site which contains a ton of useful info. There are a couple other items also required for a good prop test:

1. Make sure your tach is accurate! If you're running a factory digital tach that gets it's signal from the engine computer you're good, but if you're running an analog tach, you should know that they are notoriously inaccurate! Even factory analog tachs can be off by several hundred rpm! I bought a new OMC tach when I bought my new 115 Evinrude in 1975, and it turned out to read high by about 200 rpm, which led me to buy the wrong prop! Fortunately my dealer checked it, discovered the problem and exchanged it for an accurate tach. Based on comments from the techs on the E-TEC forum, this situation is still true today!

2. Make sure you test with at least as heavy a load as you ever expect to run, if not the maximum possible load! When I first got my new motor, I found a prop that gave great gas mileage and ran almost 50 mph, but one day I had 6 divers on the boat and discovered that it would only turn 4600 rpm @ WOT and took forever to get on plane! Ever since then I always test with full fuel, and live well, plus a couple coolers filled with sea water for ballast!

3. Check your min-planing speed! This is often neglected but it's especially important on an 18 or 20, because although they're great riding hulls for their size, they are relatively light and will start going airborne at about 20 kts when seas get up to about 3'! In heavy traffic or rough sea conditions, it's really nice to be able to hang on plane at 12-15 kts and not lose your fillings!

If you have an E-TEC, you should know that BRP has published the specific narrow OPTIMUM WOT rpm range for each motor, such as 5300-5500 as opposed to a 5000-6000 rpm "Recommended Operating Range". Propping to the OPTIMUM range will give you the best overall performance. BRP discontinued model year designations starting in 2013, but uses the last 3 letters in the model number to indicate any significant changes. For 2013 and later motors designated by letters in the model number, you can find the Optimum RPM charts in the General Information section of the Owners Group forum. In general, ALL engines will perform better, last longer, and build up fewer carbon deposits if they rev up the correct/Optimum rpm @ WOT. Although 2 strokes won't have the risk of crankshaft failure mentioned on the Verado if over-propped, they will build up more carbon on the pistons, rings and exhaust ports. And just like your car or truck engine doesn't like to be lugged by running in too high a gear, ALL marine engines are more likely to encounter damaging detonation or pre-ignition (pinging) if over loaded with a prop that has with too much pitch!