In these days of over-the-top gasoline prices, reducing fuel consumption is a big deal. One of the ways to do that is to make sure your boat is outfitted with the right propeller. But reducing fuel consumption is but one of many factors that might guide your propeller selection. The right prop affects your top speed, your acceleration, your pulling power and how fast you can get on plane. The question, of course, is what is the right prop?
In order to get the best performance from your propeller, you need to know the recommended wide open throttle (WOT) operating range for your engine. You can find this information in the engine owner's manual and/or your boat owner's manual, the numbers stated as a specific horsepower at a specific number of revolutions per minutes (RPM). If you don't have a manual, any boat dealer who services your brand of engine should be able to supply you with those figures.
The WOT range is just that, a range. The difference between the lower end of that range and the upper end will most likely fall somewhere between 400 and 1,000 RPMs. If your boat has the right propeller, it should run in this range at full speed. For optimum overall performance, however, you're better off running at the upper end of the range.
To select the right prop, you need to be able to try it out, test it and return it if it isn't the right one, so choose a reputable dealer who will let you do so. You will most likely want to test several. Fortunately, many dealers have test props for just this purpose.
Prior to any test, calibrate your tachometer with one at the servicing shop. You'll also want to load your boat as it would be typically loaded for use – average number of passengers, for instance, gear and a gas tank that's at least half full. Be sure to conduct your test in different water conditions, too.
If the RPM isn't in the sweet spot of the WOT operating range, try a propeller with a different pitch. The general rule of thumb is that for every one-inch increase in pitch, the RPMs will drop by 150 to 200. Conversely, for every one-inch decrease in pitch, you should see a corresponding increase of 150 to 200 RPMs. In other words, if you're engine is operating beneath the optimum WOT range, try looking at props with less pitch. For engines that exceed the recommended RPMs, you may want to look at increasing the pitch.
Once you have identified a propeller or propellers that operate within the recommended WOT range, be sure to take into consideration your particular needs. Higher pitch props generally offer better fuel economy when cruising and a greater top speed. Lower pitch props get you on plane quicker, though you'll sacrifice some in the areas of fuel economy and top speed.
Just FYI, don't assume that your new boat has been matched with the right propeller. Test it to be sure and swap it out as needed.
- Linda Hoff
