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What do you need to know about propeller before buying it?

Which propeller should I choose for outboard engine? This question is common for all owners of marine equipment. We will try to summarize key moments which you should pay attention firstly.

Usually owners of outboard engines want to buy propeller for high-speed riding. Let’s understand and make clear which propellers are the best choice for speed boats and which propellers are for boats carrying cargo, what parameters and how will depend on propeller type and size.

One of the main components of outboard engine is lower unit. Engine lower unit can not upshift or downshift the same as car. This means that ration is fixed. To unlock power potential of installed outboard engine you should choose correct propeller. Right choice will give you the following advantages:

  • Quickest transition onto plane,
  • Full engine speed,
  • Increase of loading capacity or speed (it depends on designated tasks),
  • Fuel optimization,
  • Increase of engine life cycle.

How to make right choice?

Selection of propeller for outboard engine begins with task designation (for example, carrying cargo, speed riding without cargo or with small cargo, etc.). Once task is designated, you can start to choose propeller, but should keep the following moments in your mind

 Propeller for speed riding – propeller with higher pitch than standard pitch. If you install such propeller, RPM will decrease.

 Propeller for boats carrying cargo - propeller with lower pitch than standard pitch. If you install such propeller, RPM will increase.

  • Diameter – it is diameter outlined by propeller blades.
  • Pitch – distance which propeller passes for one rotation (except sliding).
  • Sliding – difference between referred and real pitch for one rotation.

 One of the most important propeller characteristics is pitch. Propeller pitch is first thing to pay attention to, because it influences load on outboard engine. Speed and RPM directly depend on pitch. At average one pitch is one inch (25, 4 mm) and it changes RPM for 200-250 units. Please use tachometer to make correct choice and be noted that engine should work within RPM range indicated in the engine passport/documents. Otherwise (if you choose incorrect propeller pitch) engine RPM will be not enough or too much that may cause engine and propeller damage.

Propeller diameter is not so important, but now manufacturers can bring propellers into line with main engine characteristics (engine torque, RMP, capacity/power). That is why in most cases if pitch is high, diameter is rather small and vice versa.

Engine efficiency depends on sliding. If it is small, efficiency is high and efficiency is going down, if sliding is increasing. Commonly if engine can not reach maximal RPM, it is because of sliding. Such engines fail to achieve optimum effect.

Acceptable sliding rate is 18%.

There are a lot of other important things concerning propeller choice and characteristics and we can talk a lot about this, but not to make a mistake, when you choose propeller, please kindly refer to our highly skilled and experienced technical specialists.