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

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

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 speedboats and which propellers are best for boats carrying cargo, what characteristics they have and how will it depend on propeller's type and size.

One of the main components of outboard engine is lower unit. Engine's lower unit can not upshift or downshift the same way as car which 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 (depends on designated tasks),
  • Fuel optimization,
  • Increase of engine life cycle.

How to make the right choice?

Selection of propeller for outboard engine begins with task designation (for example, carrying cargo, speed riding with little or no cargo, etc.). Once task is designated, you can start choosing propeller, but keep the following moments in mind:

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

 Propeller for boats carrying cargo - propeller with lower pitch than standard. 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 the first thing to pay attention to because it influences load on outboard engine. Speed and RPM depend directly on pitch. At average one pitch is one inch (25,4 mm) and it changes RPM by 200-250 units. Please use tachometer to make correct choice and note that engine should work within RPM range indicated in the engine passport/documents. Otherwise (if you choose incorrect propeller pitch) engine RPM will be either too high or too low, which may cause damage to engine and propeller.

Propeller diameter is not so important, but manufacturers nowadays 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 rather small, efficiency is high and vice versa. Commonly if engine can not reach maximum RPM, sliding is to blame. Such engines fail to achieve maximum efficiency.

Acceptable sliding rate is up to 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 choosing propeller, please kindly refer to our highly skilled and experienced technical specialists.