How to Pick the Best Prop for your Boat
If you’re not satisfied with the way your fiberglass boat performs, a different prop might be the key to significant improvement.
Before shopping for a prop, think about what disappoints you with your current setup. Do you want a better hole shot? Do you want to go faster for long runs in a tournament? Do you just want better handling?
Use the following information to guide your search for the prop that will provide the performance you desire.
Prop for optimum performance
In the owner’s manual, find your outboard’s recommended operating range, expressed in engine RPM. This is a key number because propping to get top speed at the top end of the RPM range translates into the most efficient setup you can get. You’ll get the best fuel economy this way, as well. It’s also important to know the range in order to keep from selecting a prop that will take your engine outside the recommended RPM range.
Diameter and Pitch
All props include diameter and pitch specifications. Imagine a circle that a prop will fit inside snugly. Prop diameter is the diameter of that circle – the distance across the prop from edge to edge, with the line running through the center of the hub.
The pitch number represents the theoretical distance your boat will move for each revolution of the prop without any slippage. Both specs are given in inches. So, a 15×21 prop has a 15-inch diameter, and it is designed to move a boat 21 inches per revolution without any slippage. Some slippage always occurs, so the actual pitch will vary slightly.
How many blades?
Many OEM props – especially those on lower-horsepower outboards – are aluminum. They are less expensive than stainless steel props, and are generally 3-blade units. In many cases – especially when optimum performance is a concern – a stainless steel prop is the way to go. They are available as 3- and 4-blade models, which provide more options.
In general, 3-blade props offer the highest speed. However, there are situations when a 4-blade prop will deliver higher speeds because you can trim them higher and, as a result, get better bow lift. The less bow contact your boat has with the water at full plane, the less drag – and less drag translates to higher speeds.
Consider a 4-blade prop if your goal is a better hole shot because that’s one of its advantages. A 4-blade prop also has less slippage, so it will stay on plane at lower RPM.
It’s best to comparison-test props whenever possible. When you test, have your boat set up the way you routinely use it. Testing with unusually low fuel levels and/or with most of your gear removed to save weight isn’t going to provide real-world results. If you fish, test your props with a full load of fuel, all your tackle or gear and if possible with a buddy along for the ride. If you’re looking to improve hole-shot performance in you ski boat, test with the fuel load and gear you usually carry, and try to bring a few friends along to recreate your routine passenger load.