A boat propeller is an important part for your boat and performance. We explain on this page what a propeller is, how it works and how to choose the right propeller for your outboard motor. Need help choosing the right propeller? Please contact us.
What is a boat propeller?
A boat propeller is an important part of the boat’s engine. It is also called a boat propeller. A propeller and a screw are therefore exactly the same product. A propeller drives the boat underwater. It is the final link that actually transfers the engine’s horsepower to the water. Each motor has a recommended maximum number of revolutions per minute that it can run at full speed. That is why it is important that you choose the right propeller for your boat. One that will give the right revs to get your outboard motor to the right power.
To find the right boat propeller, we look at the pitch.
What is a pitch?
The pitch is the most important feature of the boat propeller. The pitch is the curvature of the propeller blades. It represents the forward distance (inches) a boat propeller would travel in one complete rotation. A greater pitch creates more curvature and therefore a higher top speed. If your outboard motor revs too much at full throttle, you can increase your speed. A smaller pitch ensures less curvature and therefore more acceleration. If your outboard motor does not rev enough at full throttle, you can reduce your pitch.
Example of how the pitch works
You can best think of a small pitch and a large pitch as the gears of a car. Driving away in first gear (small pitch) is fastest, but you will not get up to speed. Driving away in a higher gear (greater speed) is more difficult, but eventually you will get up to speed more quickly. However, if you select too high a gear (greater pitch), the engine will no longer rev up. So it will no longer reach high speed. If the gear is too small (pitch), the engine will overspeed, which can be harmful.
This is how you choose the right pitch
Does your engine rev too much or too little at full throttle? Or do you want to use your boat’s propeller for another purpose, where you need more or fewer revolutions? Then it is important to choose the right speed.
A good indicator for choosing the right pitch is the number of revolutions per minute that your engine makes at full throttle. The optimal speed of an engine is on average between 4500 and 6000 revolutions per minute. Should the speed of your engine block be increased or decreased? Then remember the following rule of thumb: for every 2 inches of a propeller, the revolutions per minute change by 400 revolutions. If you choose a smaller pitch, the number of turns increases. If you choose a higher pitch, the number of turns decreases.
Does your current propeller need to be replaced, but does it work properly? Then it is best to maintain the current pitch of your boat propeller.
How do I find my current boat propeller size?
Your current propeller and pitch size can be found on the outside of the propeller hub. Below is an example of the indication:
- 11 ¼ X 13 or 11.25 X 13
The first number is the diameter (11 ¼ & 11.25) of the screw, the second number is the pitch (13). Some brands have a different indication for the pitch size.
- Yamaha: 11 1/4 X 13 – G. Here ‘G’ is the blade type.
- Mercury Mercruiser: 48-832832A45 21P. The last number 21 is the pitch size.
- Solas: 5111-093-10. The last four numbers are the dimensions (9.3 is the diameter and 10 is the pitch size).
- Volvo Penta: 814629. This brand uses its own numbering system.
Aluminum, stainless steel or plastic
Most propellers are made of stainless steel, aluminum or, in some cases, plastic. Stainless steel is stainless steel and is made of chromium and iron. Stainless steel propellers are stronger than the other materials and therefore less vulnerable to influences. This makes stainless steel durable. However, a propeller made of this material is more expensive.
For smaller engines up to 40 hp, an aluminum propeller is used as standard. Even when sailing over a rocky bottom, an aluminum boat propeller is better than a stainless steel propeller. This is because aluminum bends more, which limits damage. Plastic propellers are only used for very small outboard motors of 2 and 2.5 hp.
3 blades vs. 4 sheets
Most boat propellers have 3 blades, because this improves speed the most. A propeller with 4 blades is usually used in boats with two engines where a lot of grip is needed at low speeds, such as water sports. A 4-blade propeller provides better acceleration, but a lower top speed.
Do you have additional questions about the propeller or pitch of your boat? Please feel free to contact us.
