Below is some important information to help you chose the right propeller for you.
A wide variety of propellers, (varying in diameter & pitch) have been made available to ensure engines operate within the Honda recommended operating range. When mounting Outboard Motors, some factors must be considered prior to installation. All of these are important to boat handling, engine performance and to maximise engine fuel efficiency.
1/ Horizontal Postioning
In most boat applications, engine location is normally at centre line of the transom. However, some boats do require a slight offset to starboard side. The boat manufacturer should provide details on the necessity of this if required. For twin motor applications, both outboards must be mounted at the same distance from the centre point on the transom of the boat.
2/ Vertical Positioning
The vertical positioning of the engine is also very important and this will directly affect cavitation/ventilation characteristics, top speed and fuel efficiency. The chosen height position will be different on boat types and dependant on boat hull shape, weight and usage, such as high performance, fi shing, commercial, cruising etc. The position for optimum performance may need to be decided upon, only after on water testing with different height settings and propeller types. Always allow for passengers, fuel and equipment on board when determining propeller type.
Is the distance between propeller blade tips through the centre line of the propeller. Large diameter propellersare commonly found on larger slower moving boats and smaller diameter propellers on faster moving craft.
Is the theoretical distance the propeller travels forward upon completion of a full 360° of rotation. This is defined as the propeller pitch. However, as water is not a solid, this figure will not be achieved due to “slip” in the water.
Tip: 1″(25MM) change of pitch will vary engine rpm by approximately 300 / 400 rpm
The propeller rake is given by the angle between the vertical line on the prop axis and a line following the edge of the blade. If viewed from the side, the blades will be seen to slope forward or rearward, positive or negative rake. High rake propellers provide better results on higher mounted or trimmed outboards. In general, if the negative rake angle is large, cavitation and ventilation toughness is improved as the rake can help strengthen the blade sections.
Propeller Slip (Slip Factor)
Propeller slip is most commonly expressed as a percentage, this being the difference between the theoretical distance travelled forward (propeller pitch) and the actual distance measured as a result of a full 360° rotation of the propeller. If a propeller with a pitch of 10″ only moves the boat forward a distance of 9″, the slip factor can be judged to be 10%.
When the trailing edge of a propeller blade has a “curl” away from the boat, it is normally described as being cupped. Cupping the propeller blade is an easy way to increase the pitch or rake without bending the entire blade.
Counter Rotating Propellers
On selected higher HP outboards, counter rotating propellers are available. The port side propeller is a mirror image (of the std type) and rotates in the opposite direction to the starboard propeller. The opposite turning effect of the propellers reduces the necessity for constant adjustment of steering by the customer, (a neutral steering control) and ensures easier manoeuvrability by balancing out the turning forces created by the propeller rotation. This becomes a more important requirement, especially with motors in excess of 75Hp.
3 Blade Propeller
This is the most common type used and provides excellent levels of performance throughout the outboard operating range. Selected counter rotating versions are also available. A good general purpose type, available in Stainless Steel and Aluminium. (Click on the links to order.)
4 Blade Propeller
Less common than 3 blade types, 4 blade propellers provide increased acceleration and mid range performance over similar 3 blade types (although a slightly lower top speed will be achieved). The additional blade also adds to a smoother running application. Ideal for ski-ing/wakeboarding where acceleration and trust is an important operating factor. Available in Stainless Steel and Aluminium. (Click on the links to order.)
High Thrust Propeller (BF8D / BF10D / BF15D / BF20D)
Although the BF8D ~ BF20D are supplied with 4 blade propellers as standard equipment, a high thrust 4 blade propeller is also available for use with these motors to enable better matching to heavier, slower moving watercraft. This type of propeller provides higher levels of thrust over the standard type, both in forward and reverse.
High Thrust Propeller (BFP60A)
The BFP60A (High Thrust Model) features a gearcasing based upon that of the BF75D / BF90D. By use of this gearcasing and a different gear ratio to the std BF60A, high thrust performance is achieved by the slower turning of the propeller and increased grip in the water. Selected propellers from the BF75D / BF90D are listed for use with BFP60A along with newly added versions, unique for use with this model.
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