W60 Propellers

For the W60 we have fitted high skew propellers.

In the past we have always designed and fitted low skew type propellers. These are designed in accordance with findings of the towing tank research facility MARIN, based in the Netherlands who over the decades have published extensive information on propeller development.

Typically we design a four blade propeller which is better for vibration. There is however diminishing returns with the number of blades; a greater number of blades results in lowering propeller efficiency.

The use of high skew has been shown to be effective in reducing both shaft vibratory forces and hull pressure induced vibration; in most cases by at least 50%.

They are a proprietary design with no published design information. Any propeller manufacturer offering high skew options has completed its own development work. They will generally offer a price for the standard propeller and a high skew alternative. The price difference can be as much as double.

Along with vibration considerations high skew propellers have been shown to have benefits as regards propeller cavitations.

Along with the propeller casting we also have the propeller nut cast. This enables a streamline shape rather than a crude hexagonal “two nut” arrangement.

The hole in the flange of the nut is for the locking screw. Once the propeller has been “flogged” up onto the propeller shaft taper the propeller boss is drilled and tapped to take the locking stud.

The popularity of this type of propeller for ships has grown exponentially. I don’t have more recent figures, but one percent of ships classed by Lloyds in the period 1980-84 were fitted with high skew propellers. By 1985-89 this had grown to 15%. In the competitive and conservative world of shipping where operational costs are refined to the minute degree this would indicate their efficiency and acceptance.

There are two types of high speed propellers; a balanced and a biased. Without going into a great deal of technical terminology these are “a balanced”. 

In the photo above the camera is held approx. 18 inches above the keel shoe; the skeg giving the propellers more than adequate protection in the event of grounding.

So why have we gone to this expense?

It forms part of our overall response to mariner’s ever increasing demand for quiet vessel while underway.

I will report back on these after sea trials are completed.

Last Updated (Wednesday, 28 December 2011 02:20)

 

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