Getting the right propeller for your boat is one of the more important things when maintaining your boat. It’s one of the top priorities along with keeping the hull clean and tuning your engine. If you have the right propeller you will optimize the performance of your boat. However, to select the right propeller for your boat and your specific needs you have to know what is propeller pitch, propeller size, rake, cupping, should you pitch up or pitch down, or how many blades you need on the propeller.
Propeller Related Terms
The two most important numbers to learn for the propeller size are diameter and pitch. The diameter is measured by measuring the distance from the center of the hub to the tip of the blade multiplied by two. If you have a high-performing boat you would need a smaller diameter of your propeller so you can achieve a high speed.
Related: How to Remove a Boat Propeller
Why Is The Diameter Of The Propeller Important?
The length of the diameter is important so you can properly calculate the correct prop pitch you need for your boat. A larger diameter of the propeller will result in increased power but it will also mean that the RPM of the propeller will decrease. If you have a fast boat and you enjoy high speeds you will need a propeller with a smaller diameter that has more RPM.
What Is An Outboard Propeller Pitch?
An outboard propeller pitch is a distance that a propeller blade will move when doing just one revolution through soft solid material. For example, for a propeller to move 21 inches in one revolution it would have to be a 21-pitch propeller.
To better understand this we can make a comparison with a car’s axle ratio. A lower axle ratio equals more pulling power when the car is still. It’s the same with a propeller pitch. Lower propeller pitch will have more power to move the boat from a standing position but it would have a lower top speed. A propeller with a higher pitch will be able to reach a higher top speed but will have trouble moving the boat from a standing position.
Rake is related to the slanted blades. It’s the degree to which the blades are slanted in relation to the hub. This can have an impact on the way water flows and make a difference in your boat performance. If your blades are slanted to the back it will lift the bow of your boat and increase your top planning speed.
Cupping is done on the trailing edge of the blade on the propeller. If the cupping has a downward curve it will improve the holeshot of the boat. It also improves ventilation and allows for less slippage which helps the propeller be more efficient.
How To Select The Right Propeller Pitch For Your Needs
The right propeller is different for each boat and each individual because it depends on what you are looking to use your boat for. If you are looking to go fast on the open water you will need a propeller pitch with a smaller diameter that has the right RPM at wide-open throttle (WOT). If your boat is a bit slow and has some trouble coming out of the hole you will need a propeller with a larger diameter and blade surface. There are quite a few things that you should check out before you decide what propeller pitch is good for you – here are the following things to look at:
Over or under revving
Making sure your propeller pitch is not over or under revving will prevent any damage to your engine. You need to select a propeller pitch that is going to fit the range of your engine RPM. You can check the range of the engine RPM on the specs which is usually between 5,000-5,500 for outboard and between 4,200-5,000 for a sterndrive.
Pitch up or Pitch down?
The relation between the engine RPM and propeller pitch is inverted which means when the propeller pitch goes up, the RPM goes down and vice versa. If you get a propeller with a higher pitch of just 2 inches, your RPM would go down around 300-400 but if you get a propeller with a lower pitch the RPM will increase for the same amount. Increasing the pitch will increase the distance traveled in one revolution which helps with moving the boat from a standstill but it will reduce the top speed of the boat.
Learning what propeller pitch is and getting the right one for your boat will surely improve your boating experience as well as providing better performance for your boat. It will also ensure that your engine lasts longer and does not suffer any damage because of a wrong propeller.