There are three specific pieces of data that can be used to classify a shaft;

• Diameter (in inches)
• Bearing spacing (in feet)
• Shaft Material

The shaft diameter should as a rule of thumb be about one fourteenth (1/14) of the propeller diameter. Any thinner than this and the shaft will be liable to bend or break, and any thicker is a waste of power and material. The spreadsheet will specify the correct shaft diameter based upon all the appropriate factors, but it is important to compare this to your fitted shaft before launch.

Bearing spacing is important, too great a spacing and the shaft will whip or twist and eventually fail, too small a spacing and you lose too much power to bearing friction.

Shaft Material has taken a back seat in recent years, with everyone and his dog specifying Stainless Steel shaft material. Why? possibly because it’s nice and shiny, it certainly is not the best all round prop shaft material because it is far too brittle and is also a source of galvanic corrosion when fitted with a bronze propeller.