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How are props sized?

- The prop size has two numbers; diameter and pitch. Pitch always follows the diameter when describing a propeller.

What is Diameter?

- The diameter is the distance across the circle that the prop makes measured in inches.

What is Pitch?

 - Pitch is the distance the propeller would move forward in one revolution with no slippage, measured in inches.

What is Cupping?

- Cupping is a small lip at the trailing edge of a prop that can help give the prop better bite, sometimes better holeshot, and top end speed.

What is Ventilation?

- Ventilation is the prop grabbing air from the surface or from exhaust gasses. If a motor is trimmed too high, your prop may start breaking the surface and start grabbing air, raising your rpm rapidly and possibly losing speed. If your motor is mounted too high on the transom the same effect can take place. On many props there are ventilation holes that you can plug or unplug allowing more or less exhaust gas around the prop during holeshot. If your engine can’t get high enough rpm during holeshot you can unplug holes and allow the prop to ventilate slightly to get your engine to a more powerful rpm. If you unplug to many holes, you will loose traction and holeshot will suffer.

What is Cavitation?

- Cavitation is boiling water with your propeller. It can be caused by a number of reasons; incorrect pitch, style or a damaged blade. It can result in a “burn” on the backside of the blade. It can also remove a lot of metal from the blade.

What is WOT?

-Wide Open Throttle.

What are the advantage/disadvantages in a three, four blad configuration?

A three blade prop has less surface area in the water therefore, less drag then a four or five blade prop. As a general rule it has higher top end speeds. A three blade prop “normally” gets better fuel efficiency at higher speeds. Three blade props "normally" have more “bow lift” than four or five blades.

A four blade prop has more surface area, giving it better traction over a three blade. It will normaly ventilate less then a three blade because of the added traction. This can allow for better handling in rough seas.  Normally, a four blade prop lifts the stern of a boat more than a three blade prop, which can achieve lower plain speeds. Four blade props can have better efficiency at low and midrange speeds on certain setups.

There are lots of different styles of propellers. They all have different characteristics. The above is just the general differences between the 3 and 4 blade props. Lots of situations where they may react completely different.