# How to choose the right propeller?

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- www.seamanpropeller.com

- Issue Time
- 2018-03-07

Summary

1. Find out which propeller size (diameter and pitch) you have now (written on your prop)

2. Select your engine type on our site and automatically find the propellers that fit!

3. Select your current pitch propeller, or optionally choose a different pitch to change the performance

**Find the right propeller in 3 easy steps!**

*1.Find out which propeller size (diameter and pitch) you have now (written onyour prop)2. Select your engine type on our site and automatically find thepropellers that fit!3. Select your current pitch propeller, or optionally choose a different pitchto change the performance (read below)*

If you are currently satisfied with the performance of yourengine, we recommend to choose the same pitch. However, if you wish to changeperformance you can consider a different pitch.

**How do I find my current propellerpitch?**

The pitch is usually indicated on the in- or outside of thepropeller hub. It is usually written like this (example):

*111/4 x 13 or 11.25 x 13*

The first number is the diameter (11.25) and the second numberis the pitch (13).

Note for Yamaha outboards: sometimes a letter is added at theend (like the G in this picture), this is a brand indication, but is notrelated to the size.

Note for Mercury/Mercruiser engines: the number on your propmay look like: 48-832832A45 21P. This last number (21P) indicates a 21 pitch.You can now choose a propeller in our shop with the same pitch. The most common48-numbers are also mentioned at the product page.

**What is pitch?**

The pitch is the most important property of a propeller thatyou can select from. It is in fact the “curvature” of the propeller blades. Thepitch (e.g. 13) represents the forward distance (number of inches) which apropeller would make in a complete rotation

*A larger pitch means more curvature and potentially a highertop speed. A smaller pitch means less curvature and thus moreacceleration.*

Think ofpitch as the gear of your car. Starting in the first gear (small pitch) you canaccelerate quickly, but your top speed is limited. Driving away in a highergear (larger pitch) is slower, but your top speed will be higher. But, ifyou choose a too large gear (pitch) the engine will not be able to reachenough RPM (rotations per minute) and will thus also not be able to comeup to speed. With a too small gear (small pitch) the engine will make too muchRPM which may also damage your engine.

Readbelow how you can get a good indication of the pitch you should choose.

**Choosing the right pitch**

If youare currently satisfied with the performance of your engine, we recommend tochoose the same pitch. However, if you wish to change performance you canconsider a different pitch. For example if you want to use your boat for aspecific purpose (eg. waterskiing). Also, if your engine currently makes toomuch or too few RPM at full throttle.

A good indicator for selecting the optimal pitch is the RPM yourengine makes at ´wide open throttle´ (WOT). Each engine has a prescribed´optimal´ RPM that it should be making at wide open throttle. This differs perengine but often it is between 4500 and 6000. You can check your manual, orcheck this RPM Range Chart for the most common engines.

If yourcurrent RPM is too high, you may consider a larger pitch that will improveyour top speed. If the current RPM is too low, the engine is not reachingits full potential because of a too high pitch. In this case choosing a lowerpitch can result in better acceleration (smaller pitch) and higher top speed(now it can reach full RPM).

If you’rechanging pitch on a recreational boat, remember that each inch of pitch isworth about 200 rpm. Lowering the pitch will increase rpm and choosing a higherpitch will make it less. For example, going from a 23 pitch to a 21 pitch willincrease engine rpm by about 400 to 600 revolutions. For smaller horsepowerengines (up to 30 hp) this difference is usually bigger: one pitch can alreadymake a difference of 500 rpm.

**Other aspects of a propeller**

**3-blade vs 4-blade**

Mostpropellers have 3 blades. For speed this is the most efficient design. For extrathrust at low speeds (for example needed for waterkiing or wakeboarding) youmay consider a 4 blade design. This will give more acceleration but will go atthe cost of top speed.

**Aluminum vs Stainless Steel**

Stainlesssteel propellers are stronger than aluminum propellers. This makes them lessvulnerable to scratches by sand. Because of the stronger metal the blades areusually also thinner which improves the efficiency of the propeller. Stainlesssteel is relatively more expensive though than aluminum propellers.

**Diameter**

Thediamter is the length of your propeller from left to right (seepicture). The diameters that you can choose are determined by theshape of your engine. If you select your engine on our website you willautomatically find propellers that have a diameter that fits on your engine.Please note that choosing a 1 inch larger diameter has approximately the sameeffect as a 2 inch larger pitch.

The hubsystem is the connection between the propeller and the propeller shaft of yourengine. All propellers that we deliver are standard including hubkit. Most ofthem have a rubber pressed-in hub kit. Some of them have an exchangeable hubkit(especially models with higher horsepower).

**What are tooth splines?**

A newpropeller will only fit if the number of ´tooth splines´ on your propellershaft is the same as the

number of tooth splines on the inside of your propeller hub. When selectingyour engine in our shop, it will automatically select the propellers with theright number of tooth splines.